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A Guide For Chemists


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Awesome Guide for "Chemists".I believe that this document should be with all Chemists.

Awesome Guide for "Chemists".I believe that this document should be with all Chemists.

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  • 1. A Guide For ChemistsSandeep Badarla PDF generated using the open source mwlib toolkit. See for more information. PDF generated at: Sun, 05 Aug 2012 05:11:29 UTC
  • 2. ContentsArticles Chemistry 1 History of chemistry 15 Atom 26 Chemical element 48 Chemical compound 67 Chemical substance 70 Molecule 75 Chemical bond 78 Chemical reaction 88 Chemical equilibrium 104 Chemical law 117 Outline of chemistry 118 Common chemicals 123 International Year of Chemistry 126 List of chemists 128 List of compounds 140 List of important publications in chemistry 141 List of software for molecular mechanics modeling 149 List of unsolved problems in chemistry 157 Periodic systems of small molecules 159 Periodic table 162 Philosophy of chemistry 176References Article Sources and Contributors 179 Image Sources, Licenses and Contributors 184Article Licenses License 186
  • 3. Chemistry 1 Chemistry Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties.[1][2] Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds. Chemistry is sometimes called "the central science" because it connects physics with other natural sciences such as geology and biology.[3][4] Chemistry is a branch of physical science but distinct from physics.[5] The etymology of the word chemistry has been much disputed.[6] The genesis of chemistry can be traced to certain practices, known as Chemistry is the science of matter, its properties, alchemy, which had been practiced for several millennia in various structure, composition and its changes during parts of the world, particularly the Middle East.[7] interactions and chemical reactions. In particular, chemistry studies interactions between atoms, and chemical bonds. Theory Traditional chemistry starts with the study of elementary particles, atoms, molecules,[8] substances, metals, crystals and other aggregates of matter. in solid, liquid, and gas states, whether in isolation or combination. The interactions, reactions and transformations that are studied in chemistry are usually a result of interaction between atoms, leading to rearrangements in the chemical bonds which hold atoms together. Such behaviors are studied in a chemistry laboratory. The chemistry laboratory stereotypically uses various forms of laboratory glassware, but glassware is not Laboratory, Institute of Biochemistry, University of Cologne. central to chemistry, and a great deal of experimental (as well as applied/industrial chemistry) is done without it. A chemical reaction is a transformation of some substances into one or more other substances.[9] The basis of such a chemical transformation is the rearrangement of electrons in the chemical bonds between atoms. It can be symbolically depicted through a chemical equation, which usually involves atoms as subjects. The number of atoms on the left and the right in the equation for a chemical transformation is equal (when unequal, the transformation by definition is not chemical, but rather a nuclear reaction or radioactive decay). The nature of chemical reactions a substance may undergo and the energy changes that may accompany it are constrained by certain basic rules, known as chemical laws. Energy and entropy considerations are invariably important in almost all chemical studies. Chemical substances are classified in terms of their structure, phase as well as their chemical compositions. They can be analyzed using the tools of chemical analysis, e.g. spectroscopy and chromatography. Scientists engaged in chemical research are known as chemists.[10] Most chemists specialize in one or more sub-disciplines.
  • 4. Chemistry 2 History Ancient Egyptians pioneered the art of synthetic "wet" chemistry up to 4,000 years ago.[11] By 1000 BC ancient civilizations were using technologies that formed the basis of the various branches of chemistry such as; extracting metal from their ores, making pottery and glazes, fermenting beer and wine, making pigments for cosmetics and painting, extracting chemicals from plants for medicine and perfume, making cheese, dying cloth, tanning leather, rendering fat into soap, making glass, and making alloys like bronze. The genesis of chemistry can be traced to the widely observed phenomenon of burning that led to metallurgy—the art and science of processing ores to get metals (e.g. metallurgy in ancient India). The greed for gold led to the discovery of the process for its purification, even though the underlying principles were not well understood—it was thought to be a transformation rather than purification. Many scholars in those days thought it reasonable to believe that there exist means for transforming cheaper (base) metals into gold. This gave way to alchemy and the search for the Philosophers Stone which was believed to bring about such a transformation by mere touch.[12] Greek atomism dates back to 440 BC, as what might be indicated by the book De Rerum Natura (The Nature of Things)[13] written by the Roman Lucretius in 50 BC.[14] Much of the early development of purification methods is described by Pliny the Elder in his Naturalis Historia. Democritus atomist philosophy was later adopted by A tentative outline is as follows: Epicurus (341–270 BCE). 1. Alchemy in Greco-Roman Egypt [ – 642 CE], the earliest Western alchemists such as Mary the Jewess, Cleopatra the Alchemist, and Zosimos of Panopolis described early laboratory equipment. They are estimated to have lived between the first and third centuries. 2. Islamic alchemy [642 CE – 1200], the Muslim conquest of Egypt; development of alchemy by Jābir ibn Hayyān, al-Razi and others; Jābir modifies Aristotles theories; advances in processes and apparatus.[15] 3. European alchemy [1300 – present], Pseudo-Geber builds on Arabic chemistry. From the 12th century, major advances in the chemical arts shifted from Arab lands to western Europe.[15] 4. Chemistry [1661], Boyle writes his classic chemistry text The Sceptical Chymist. 5. Chemistry [1787], Lavoisier writes his classic Elements of Chemistry. 6. Chemistry [1803], Dalton publishes his Atomic Theory. 7. Chemistry [1869], Dmitri Mendeleev presented his Periodic table being the framework of the modern chemistry The earliest pioneers of Chemistry, and inventors of the modern scientific method,[16] were medieval Arab and Persian scholars. They introduced precise observation and controlled experimentation into the field and discovered numerous Chemical substances.[17] "Chemistry as a science was almost created by the Muslims; for in this field, where the Greeks (so far as we know) were confined to industrial experience and vague hypothesis, the Saracens introduced precise observation, controlled experiment, and careful records. They invented and named the alembic (al-anbiq), chemically analyzed innumerable substances, composed lapidaries, distinguished alkalis and acids, investigated their affinities, studied and manufactured hundreds of drugs. Alchemy, which the Muslims inherited from Egypt, contributed to chemistry by a thousand incidental discoveries, and by its method, which was the most scientific of all medieval operations."[17]
  • 5. Chemistry 3 The most influential Muslim chemists were Jābir ibn Hayyān (Geber, d. 815), al-Kindi (d. 873), al-Razi (d. 925), al-Biruni (d. 1048) and Alhazen (d. 1039).[18] Their works became more widely known in Europe in the twelfth and thirteenth centuries, beginning with the Latin translation of Jābir’s Kitab al-Kimya in 1144. The contribution of Indian alchemists and metallurgists in the development of chemistry was also quite significant.[19] For some practitioners, alchemy was an intellectual pursuit, over time, they got better at it. Paracelsus (1493–1541), for example, rejected the 4-elemental theory and with only a vague understanding of his chemicals and medicines, formed a hybrid of alchemy and science in what was to be called iatrochemistry. Similarly, the influences of philosophers such as Sir Francis Bacon (1561–1626) and René Descartes (1596–1650), who demanded more rigor in mathematics and in removing bias from scientific observations, led to a scientific revolution. In chemistry, this began with Robert Boyle (1627–1691), who came up with an equation known as Boyles Law about the characteristics of gaseous state.[21] Chemistry indeed came of age when Antoine Lavoisier (1743–1794), developed the theory of Conservation of mass in 1783; and the development of the Atomic Theory by John Dalton around 1800. The Law of Conservation of Mass resulted in the reformulation of chemistry based on this law and the oxygen theory of combustion, which was largely based on the work of Antoine-Laurent de Lavoisier is considered the "Father Lavoisier. Lavoisiers fundamental contributions to chemistry were [20] of Modern Chemistry". a result of a conscious effort to fit all experiments into the framework of a single theory. Lavoisier established the consistent use of the chemical balance, used oxygen to overthrow the phlogiston theory, and developed a new system of chemical nomenclature and made contribution to the modern metric system. Lavoisier also worked to translate the archaic and technical language of chemistry into something that could be easily understood by the largely uneducated masses, leading to an increased public interest in chemistry. All these advances in chemistry led to what is usually called the chemical revolution. The contributions of Lavoisier led to what is now called modern chemistry—the chemistry that is studied in educational institutions all over the world. It is because of these and other contributions that Antoine Lavoisier is often celebrated as the "Father of Modern Chemistry".[22] The later discovery of Friedrich Wöhler that many natural substances, organic compounds, can indeed be synthesized in a chemistry laboratory also helped the modern chemistry to mature from its infancy.[23] The discovery of the chemical elements has a long history from the days of alchemy and culminating in the discovery of the periodic table of the chemical elements by Dmitri Mendeleev (1834–1907)[24] and later discoveries of some synthetic elements. Jöns Jacob Berzelius, Joseph Priestley, Humphry Davy, Linus Pauling, Gilbert N. Lewis, Josiah Willard Gibbs, Robert Burns Woodward, and Fritz Haber also made notable contributions. The year 2011 was declared by the United Nations as the International Year of Chemistry.[25] It was an initiative of the International Union of Pure and Applied Chemistry, and of the United Nations Educational, Scientific, and Cultural Organization and involves chemical societies, academics, and institutions worldwide and relied on individual initiatives to organize local and regional activities.
  • 6. Chemistry 4 Etymology The word chemistry comes from the word alchemy, an earlier set of practices that encompassed elements of chemistry, metallurgy, philosophy, astrology, astronomy, mysticism and medicine; it is commonly thought of as the quest to turn lead or another common starting material into gold.[26] The word alchemy in turn is derived from the Arabic word al-kīmīā (‫ ,)ﺍﻟﻜﻴﻤﻴﺎء‬meaning alchemy. The Arabic term is borrowed from the Greek χημία or χημεία.[27][28] This may have Egyptian origins. Many believe that al-kīmīā is derived from χημία, which is in turn derived from the word Chemi or Kimi, which is the ancient name of Egypt in Egyptian.[27] Alternately, al-kīmīā may be derived from χημεία, meaning "cast together".[29] An alchemist was called a chemist in popular speech, and later the suffix "-ry" was added to this to describe the art of the chemist as "chemistry". Definitions In retrospect, the definition of chemistry has changed over time, as new discoveries and theories add to the functionality of the science. Shown below are some of the standard definitions used by various noted chemists: • Alchemy (330) – the study of the composition of waters, movement, growth, embodying, disembodying, drawing the spirits from bodies and bonding the spirits within bodies (Zosimos).[30] • Chymistry (1661) – the subject of the material principles of mixed bodies (Boyle).[31] • Chymistry (1663) – a scientific art, by which one learns to dissolve bodies, and draw from them the different substances on their composition, and how to unite them again, and exalt them to a higher perfection (Glaser).[32] • Chemistry (1730) – the art of resolving mixed, compound, or aggregate bodies into their principles; and of composing such bodies from those principles (Stahl).[33] • Chemistry (1837) – the science concerned with the laws and effects of molecular forces (Dumas).[34] • Chemistry (1947) – the science of substances: their structure, their properties, and the reactions that change them into other substances (Pauling).[35] • Chemistry (1998) – the study of matter and the changes it undergoes (Chang).[36] Basic concepts Several concepts are essential for the study of chemistry; some of them are:[37] Atom An atom is the basic unit of chemistry. It consists of a positively charged core (the atomic nucleus) which contains protons and neutrons, and which maintains a number of electrons to balance the positive charge in the nucleus. The atom is also the smallest entity that can be envisaged to retain the chemical properties of the element, such as electronegativity, ionization potential, preferred oxidation state(s), coordination number, and preferred types of bonds to form (e.g., metallic, ionic, covalent). Element The concept of chemical element is related to that of chemical substance. A chemical element is specifically a substance which is composed of a single type of atom. A chemical element is characterized by a particular number of protons in the nuclei of its atoms. This number is known as the atomic number of the element. For example, all atoms with 6 protons in their nuclei are atoms of the chemical element carbon, and all atoms with 92 protons in their nuclei are atoms of the element uranium. Although all the nuclei of all atoms belonging to one element will have the same number of protons, they may not necessarily have the same number of neutrons; such atoms are termed isotopes. In fact several isotopes of an element may exist. Ninety–four different chemical elements or types of atoms based on the number of protons are observed
  • 7. Chemistry 5 on earth naturally, having at least one isotope that is stable or has a very long half-life. A further 18 elements have been recognised by IUPAC after they have been made in the laboratory. The standard presentation of the chemical elements is in the periodic table, which orders elements by atomic number and groups them by electron configuration. Due to its arrangement, groups, or columns, and periods, or rows, of elements in the table either share several chemical properties, or follow a certain trend in characteristics such as atomic radius, electronegativity, etc. Lists of the elements by name, by symbol, and by atomic number are also available. Compound A compound is a substance with a particular ratio of atoms of particular chemical elements which determines its composition, and a particular organization which determines chemical properties. For example, water is a compound containing hydrogen and oxygen in the ratio of two to one, with the oxygen atom between the two hydrogen atoms, and an angle of 104.5° between them. Compounds are formed and interconverted by chemical reactions. Substance A chemical substance is a kind of matter with a definite composition and set of properties.[38] Strictly speaking, a mixture of compounds, elements or compounds and elements is not a chemical substance, but it may be called a chemical. Most of the substances we encounter in our daily life are some kind of mixture; for example: air, alloys, biomass, etc. Nomenclature of substances is a critical part of the language of chemistry. Generally it refers to a system for naming chemical compounds. Earlier in the history of chemistry substances were given name by their discoverer, which often led to some confusion and difficulty. However, today the IUPAC system of chemical nomenclature allows chemists to specify by name specific compounds amongst the vast variety of possible chemicals. The standard nomenclature of chemical substances is set by the International Union of Pure and Applied Chemistry (IUPAC). There are well-defined systems in place for naming chemical species. Organic compounds are named according to the organic nomenclature system.[39] Inorganic compounds are named according to the inorganic nomenclature system.[40] In addition the Chemical Abstracts Service has devised a method to index chemical substance. In this scheme each chemical substance is identifiable by a number known as CAS registry number. Molecule A molecule is the smallest indivisible portion of a pure chemical substance that has its unique set of chemical properties, that is, its potential to undergo a certain set of chemical reactions with other substances. However, this definition only works well for substances that are composed of molecules, which is not true of many substances (see below). Molecules are typically a set of atoms bound together by covalent bonds, such that the structure is electrically neutral and all valence electrons are paired with other electrons either in bonds or in lone pairs. Thus, molecules exist as electrically neutral units, unlike ions. When this rule is broken, giving the "molecule" a charge, the result is sometimes named a molecular ion or a polyatomic ion. However, the discrete and separate nature of the molecular concept usually requires that molecular ions be present only in well-separated form, such as a directed beam in a vacuum in a mass spectrograph. Charged polyatomic collections residing in solids (for example, common sulfate or nitrate ions) are generally not considered "molecules" in chemistry.
  • 8. Chemistry 6 The "inert" or noble chemical elements (helium, neon, argon, krypton, xenon and radon) are composed of lone atoms as their smallest discrete unit, but the other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. Identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals. However, not all substances or chemical compounds consist of A molecular structure depicts the bonds and relative positions of atoms in a molecule discrete molecules, and indeed most of such as that in Paclitaxel shown here the solid substances that makes up the solid crust, mantle, and core of the Earth are chemical compounds without molecules. These other types of substances, such as ionic compounds and network solids, are organized in such a way as to lack the existence of identifiable molecules per se. Instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. Examples of such substances are mineral salts (such as table salt), solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite. One of the main characteristic of a molecule is its geometry often called its structure. While the structure of diatomic, triatomic or tetra atomic molecules may be trivial, (linear, angular pyramidal etc.) the structure of polyatomic molecules, that are constituted of more than six atoms (of several elements) can be crucial for its chemical nature. Mole and amount of substance Mole is a unit to measure amount of substance (also called chemical amount). A mole is the amount of a substance that contains as many elementary entities (atoms, molecules or ions) as there are atoms in 0.012 kilogram (or 12 grams) of carbon-12, where the carbon-12 atoms are unbound, at rest and in their ground state.[41] The number of entities per mole is known as the Avogadro constant, and is determined empirically. The currently accepted value is 6.02214179(30)×1023 mol−1 (2007 CODATA). One way to understand the meaning of the term "mole" is to compare and contrast it to terms such as dozen. Just as one dozen eggs contains 12 individual eggs, one mole contains 6.02214179(30)×1023 atoms, molecules or other particles. The term is used because it is much easier to say, for example, 1 mole of carbon, than it is to say 6.02214179(30)×1023 carbon atoms, and because moles of chemicals represent a scale that is easy to experience. The amount of substance of a solute per volume of solution is known as amount of substance concentration, or molarity for short. Molarity is the quantity most commonly used to express the concentration of a solution in the chemical laboratory. The most commonly used units for molarity are mol/L (the official SI units are mol/m3).
  • 9. Chemistry 7 Ions and salts An ion is a charged species, an atom or a molecule, that has lost or gained one or more electrons. Positively charged cations (e.g. sodium cation Na+) and negatively charged anions (e.g. chloride Cl−) can form a crystalline lattice of neutral salts (e.g. sodium chloride NaCl). Examples of polyatomic ions that do not split up during acid-base reactions are hydroxide (OH−) and phosphate (PO43−). Ions in the gaseous phase are often known as plasma. Acidity and basicity A substance can often be classified as an acid or a base. There are several different theories which explain acid-base behavior. The simplest is Arrhenius theory, which states than an acid is a substance that produces hydronium ions when it is dissolved in water, and a base is one that produces hydroxide ions when dissolved in water. According to Brønsted–Lowry acid-base theory, acids are substances that donate a positive hydrogen ion to another substance in a chemical reaction; by extension, a base is the substance which receives that hydrogen ion. A third common theory is Lewis acid-base theory, which is based on the formation of new chemical bonds. Lewis theory explains that an acid is a substance which is capable of accepting a pair of electrons from another substance during the process of bond formation, while a base is a substance which can provide a pair of electrons to form a new bond. According to concept as per Lewis, the crucial things being exchanged are charges.[42] There are several other ways in which a substance may be classified as an acid or a base, as is evident in the history of this concept [43] Acid strength is commonly measured by two methods. One measurement, based on the Arrhenius definition of acidity, is pH, which is a measurement of the hydronium ion concentration in a solution, as expressed on a negative logarithmic scale. Thus, solutions that have a low pH have a high hydronium ion concentration, and can be said to be more acidic. The other measurement, based on the Brønsted–Lowry definition, is the acid dissociation constant (Ka), which measure the relative ability of a substance to act as an acid under the Brønsted–Lowry definition of an acid. That is, substances with a higher Ka are more likely to donate hydrogen ions in chemical reactions than those with lower Ka values. Phase In addition to the specific chemical properties that distinguish different chemical classifications chemicals can exist in several phases. For the most part, the chemical classifications are independent of these bulk phase classifications; however, some more exotic phases are incompatible with certain chemical properties. A phase is a set of states of a chemical system that have similar bulk structural properties, over a range of conditions, such as pressure or temperature. Physical properties, such as density and refractive index tend to fall within values characteristic of the phase. The phase of matter is defined by the phase transition, which is when energy put into or taken out of the system goes into rearranging the structure of the system, instead of changing the bulk conditions. Sometimes the distinction between phases can be continuous instead of having a discrete boundary, in this case the matter is considered to be in a supercritical state. When three states meet based on the conditions, it is known as a triple point and since this is invariant, it is a convenient way to define a set of conditions. The most familiar examples of phases are solids, liquids, and gases. Many substances exhibit multiple solid phases. For example, there are three phases of solid iron (alpha, gamma, and delta) that vary based on temperature and pressure. A principal difference between solid phases is the crystal structure, or arrangement, of the atoms. Another phase commonly encountered in the study of chemistry is the aqueous phase, which is the state of substances dissolved in aqueous solution (that is, in water). Less familiar phases include plasmas, Bose-Einstein condensates and fermionic condensates and the paramagnetic and ferromagnetic phases of magnetic materials. While most familiar phases deal with three-dimensional systems, it
  • 10. Chemistry 8 is also possible to define analogs in two-dimensional systems, which has received attention for its relevance to systems in biology. Redox It is a concept related to the ability of atoms of various substances to lose or gain electrons. Substances that have the ability to oxidize other substances are said to be oxidative and are known as oxidizing agents, oxidants or oxidizers. An oxidant removes electrons from another substance. Similarly, substances that have the ability to reduce other substances are said to be reductive and are known as reducing agents, reductants, or reducers. A reductant transfers electrons to another substance, and is thus oxidized itself. And because it "donates" electrons it is also called an electron donor. Oxidation and reduction properly refer to a change in oxidation number—the actual transfer of electrons may never occur. Thus, oxidation is better defined as an increase in oxidation number, and reduction as a decrease in oxidation number. Bonding Atoms sticking together in molecules or crystals are said to be bonded with one another. A chemical bond may be visualized as the multipole balance between the positive charges in the nuclei and the negative charges oscillating about them.[44] More than simple attraction and repulsion, the energies and distributions characterize the availability of an electron to bond to another atom. A chemical bond can be a covalent bond, an ionic bond, a hydrogen bond or just because of Van der Waals force. Each of these kind of Electron atomic and molecular orbitals bond is ascribed to some potential. These potentials create the interactions which hold atoms together in molecules or crystals. In many simple compounds, Valence Bond Theory, the Valence Shell Electron Pair Repulsion model (VSEPR), and the concept of oxidation number can be used to explain molecular structure and composition. Similarly, theories from classical physics can be used to predict many ionic structures. With more complicated compounds, such as metal complexes, valence bond theory is less applicable and alternative approaches, such as the molecular orbital theory, are generally used. See diagram on electronic orbitals.
  • 11. Chemistry 9 Reaction When a chemical substance is transformed as a result of its interaction with another or energy, a chemical reaction is said to have occurred. Chemical reaction is therefore a concept related to the reaction of a substance when it comes in close contact with another, whether as a mixture or a solution; exposure to some form of energy, or both. It results in some energy exchange between the constituents of the reaction as well with the system environment which may be designed vessels which are often laboratory glassware. Chemical reactions can result in the formation or dissociation of During chemical reactions, bonds between atoms molecules, that is, molecules breaking apart to form two or more break and form, resulting in different substances smaller molecules, or rearrangement of atoms within or across with different properties. In a blast furnace, iron oxide, a compound, reacts with carbon monoxide molecules. Chemical reactions usually involve the making or breaking to form iron, one of the chemical elements, and of chemical bonds. Oxidation, reduction, dissociation, acid-base carbon dioxide. neutralization and molecular rearrangement are some of the commonly used kinds of chemical reactions. A chemical reaction can be symbolically depicted through a chemical equation. While in a non-nuclear chemical reaction the number and kind of atoms on both sides of the equation are equal, for a nuclear reaction this holds true only for the nuclear particles viz. protons and neutrons.[45] The sequence of steps in which the reorganization of chemical bonds may be taking place in the course of a chemical reaction is called its mechanism. A chemical reaction can be envisioned to take place in a number of steps, each of which may have a different speed. Many reaction intermediates with variable stability can thus be envisaged during the course of a reaction. Reaction mechanisms are proposed to explain the kinetics and the relative product mix of a reaction. Many physical chemists specialize in exploring and proposing the mechanisms of various chemical reactions. Several empirical rules, like the Woodward-Hoffmann rules often come handy while proposing a mechanism for a chemical reaction. According to the IUPAC gold book a chemical reaction is a process that results in the interconversion of chemical species".[46] Accordingly, a chemical reaction may be an elementary reaction or a stepwise reaction. An additional caveat is made, in that this definition includes cases where the interconversion of conformers is experimentally observable. Such detectable chemical reactions normally involve sets of molecular entities as indicated by this definition, but it is often conceptually convenient to use the term also for changes involving single molecular entities (i.e. microscopic chemical events). Equilibrium Although the concept of equilibrium is widely used across sciences, in the context of chemistry, it arises whenever a number of different states of the chemical composition are possible. For example, in a mixture of several chemical compounds that can react with one another, or when a substance can be present in more than one kind of phase. A system of chemical substances at equilibrium even though having an unchanging composition is most often not static; molecules of the substances continue to react with one another thus giving rise to a dynamic equilibrium. Thus the concept describes the state in which the parameters such as chemical composition remain unchanged over time. Chemicals present in biological systems are invariably not at equilibrium; rather they are far from equilibrium.
  • 12. Chemistry 10 Energy In the context of chemistry, energy is an attribute of a substance as a consequence of its atomic, molecular or aggregate structure. Since a chemical transformation is accompanied by a change in one or more of these kinds of structure, it is invariably accompanied by an increase or decrease of energy of the substances involved. Some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light; thus the products of a reaction may have more or less energy than the reactants. A reaction is said to be exergonic if the final state is lower on the energy scale than the initial state; in the case of endergonic reactions the situation is the reverse. A reaction is said to be exothermic if the reaction releases heat to the surroundings; in the case of endothermic reactions, the reaction absorbs heat from the surroundings. Chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. The speed of a chemical reaction (at given temperature T) is related to the activation energy E, by the Boltzmanns population factor - that is the probability of molecule to have energy greater than or equal to E at the given temperature T. This exponential dependence of a reaction rate on temperature is known as the Arrhenius equation. The activation energy necessary for a chemical reaction can be in the form of heat, light, electricity or mechanical force in the form of ultrasound.[47] A related concept free energy, which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. A reaction is feasible only if the total change in the Gibbs free energy is negative, ; if it is equal to zero the chemical reaction is said to be at equilibrium. There exist only limited possible states of energy for electrons, atoms and molecules. These are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. The atoms/molecules in a higher energy state are said to be excited. The molecules/atoms of substance in an excited energy state are often much more reactive; that is, more amenable to chemical reactions. The phase of a substance is invariably determined by its energy and the energy of its surroundings. When the intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water (H2O); a liquid at room temperature because its molecules are bound by hydrogen bonds.[48] Whereas hydrogen sulfide (H2S) is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole-dipole interactions. The transfer of energy from one chemical substance to another depends on the size of energy quanta emitted from one substance. However, heat energy is often transferred more easily from almost any substance to another because the phonons responsible for vibrational and rotational energy levels in a substance have much less energy than photons invoked for the electronic energy transfer. Thus, because vibrational and rotational energy levels are more closely spaced than electronic energy levels, heat is more easily transferred between substances relative to light or other forms of electronic energy. For example, ultraviolet electromagnetic radiation is not transferred with as much efficacy from one substance to another as thermal or electrical energy. The existence of characteristic energy levels for different chemical substances is useful for their identification by the analysis of spectral lines. Different kinds of spectra are often used in chemical spectroscopy, e.g. IR, microwave, NMR, ESR, etc. Spectroscopy is also used to identify the composition of remote objects - like stars and distant galaxies - by analyzing their radiation spectra. Emission spectrum of iron The term chemical energy is often used to indicate the potential of a chemical substance to undergo a transformation through a chemical reaction or to transform other chemical substances.
  • 13. Chemistry 11 Chemical laws Chemical reactions are governed by certain laws, which have become fundamental concepts in chemistry. Some of them are: • Avogadros law • Beer-Lambert law • Boyles law (1662, relating pressure and volume) • Charless law (1787, relating volume and temperature) • Ficks law of diffusion • Gay-Lussacs law (1809, relating pressure and temperature) • Le Chateliers Principle • Henrys law • Hesss Law • Law of conservation of energy leads to the important concepts of equilibrium, thermodynamics, and kinetics. • Law of conservation of mass continues to be conserved in isolated systems, even in modern physics. However, special relativity shows that due to mass-energy equivalence, whenever non-material "energy" (heat, light, kinetic energy) is removed from a non-isolated system, some mass will be lost with it. High energy losses result in loss of weighable amounts of mass, an important topic in nuclear chemistry. • Law of definite composition, although in many systems (notably biomacromolecules and minerals) the ratios tend to require large numbers, and are frequently represented as a fraction. • Law of multiple proportions • Raoults Law Subdisciplines Chemistry is typically divided into several major sub-disciplines. There are also several main cross-disciplinary and more specialized fields of chemistry.[49] • Analytical chemistry is the analysis of material samples to gain an understanding of their chemical composition and structure. Analytical chemistry incorporates standardized experimental methods in chemistry. These methods may be used in all subdisciplines of chemistry, excluding purely theoretical chemistry. • Biochemistry is the study of the chemicals, chemical reactions and chemical interactions that take place in living organisms. Biochemistry and organic chemistry are closely related, as in medicinal chemistry or neurochemistry. Biochemistry is also associated with molecular biology and genetics. • Inorganic chemistry is the study of the properties and reactions of inorganic compounds. The distinction between organic and inorganic disciplines is not absolute and there is much overlap, most importantly in the sub-discipline of organometallic chemistry. • Materials chemistry is the preparation, characterization, and understanding of substances with a useful function. The field is a new breadth of study in graduate programs, and it integrates elements from all classical areas of chemistry with a focus on fundamental issues that are unique to materials. Primary systems of study include the chemistry of condensed phases (solids, liquids, polymers) and interfaces between different phases. • Neurochemistry is the study of neurochemicals; including transmitters, peptides, proteins, lipids, sugars, and nucleic acids; their interactions, and the roles they play in forming, maintaining, and modifying the nervous system. • Nuclear chemistry is the study of how subatomic particles come together and make nuclei. Modern Transmutation is a large component of nuclear chemistry, and the table of nuclides is an important result and tool for this field. • Organic chemistry is the study of the structure, properties, composition, mechanisms, and reactions of organic compounds. An organic compound is defined as any compound based on a carbon skeleton.
  • 14. Chemistry 12 • Physical chemistry is the study of the physical and fundamental basis of chemical systems and processes. In particular, the energetics and dynamics of such systems and processes are of interest to physical chemists. Important areas of study include chemical thermodynamics, chemical kinetics, electrochemistry, statistical mechanics, spectroscopy, and more recently, astrochemistry.[50] Physical chemistry has large overlap with molecular physics. Physical chemistry involves the use of infinitesimal calculus in deriving equations. It is usually associated with quantum chemistry and theoretical chemistry. Physical chemistry is a distinct discipline from chemical physics, but again, there is very strong overlap. • Theoretical chemistry is the study of chemistry via fundamental theoretical reasoning (usually within mathematics or physics). In particular the application of quantum mechanics to chemistry is called quantum chemistry. Since the end of the Second World War, the development of computers has allowed a systematic development of computational chemistry, which is the art of developing and applying computer programs for solving chemical problems. Theoretical chemistry has large overlap with (theoretical and experimental) condensed matter physics and molecular physics. Other disciplines within chemistry are traditionally grouped by the type of matter being studied or the kind of study. These include inorganic chemistry, the study of inorganic matter; organic chemistry, the study of organic (carbon based) matter; biochemistry, the study of substances found in biological organisms; physical chemistry, the study of chemical processes using physical concepts such as thermodynamics and quantum mechanics; and analytical chemistry, the analysis of material samples to gain an understanding of their chemical composition and structure. Many more specialized disciplines have emerged in recent years, e.g. neurochemistry the chemical study of the nervous system (see subdisciplines). Other fields include agrochemistry, astrochemistry (and cosmochemistry), atmospheric chemistry, chemical engineering, chemical biology, chemo-informatics, electrochemistry, environmental chemistry, femtochemistry, flavor chemistry, flow chemistry, geochemistry, green chemistry, histochemistry, history of chemistry, hydrogenation chemistry, immunochemistry, marine chemistry, materials science, mathematical chemistry, mechanochemistry, medicinal chemistry, molecular biology, molecular mechanics, nanotechnology, natural product chemistry, oenology, organometallic chemistry, petrochemistry, pharmacology, photochemistry, physical organic chemistry, phytochemistry, polymer chemistry, radiochemistry, solid-state chemistry, sonochemistry, supramolecular chemistry, surface chemistry, synthetic chemistry, thermochemistry, and many others. Chemical industry The chemical industry represents an important economic activity. The global top 50 chemical producers in 2004 had sales of 587 billion US dollars with a profit margin of 8.1% and research and development spending of 2.1% of total chemical sales.[51] Professional societies • American Chemical Society • American Society for Neurochemistry • Chemical Institute of Canada • Chemical Society of Peru • International Union of Pure and Applied Chemistry • Royal Australian Chemical Institute • Royal Netherlands Chemical Society • Royal Society of Chemistry • Society of Chemical Industry • World Association of Theoretical and Computational Chemists • List of chemistry societies
  • 15. Chemistry 13 References [1] "What is Chemistry?" (http:/ / chemweb. ucc. ie/ what_is_chemistry. htm). . Retrieved 2011-06-12. [2] Chemistry (http:/ / dictionary. reference. com/ browse/ Chemistry). (n.d.). Merriam-Websters Medical Dictionary. Retrieved August 19, 2007. [3] Theodore L. Brown, H. Eugene Lemay, Bruce Edward Bursten, H. Lemay. Chemistry: The Central Science. Prentice Hall; 8 edition (1999). ISBN 0-13-010310-1. Pages 3-4. [4] Chemistry is seen as occupying an intermediate position in a hierarchy of the sciences by "reductive level" between physics and biology. See Carsten Reinhardt. Chemical Sciences in the 20th Century: Bridging Boundaries. Wiley-VCH, 2001. ISBN 3-527-30271-9. Pages 1-2. [5] Is chemistry a branch of physics? a paper by Mario Bunge (http:/ / www. springerlink. com/ content/ k97523j471763374/ ) [6] See: Chemistry (etymology) for possible origins of this word. [7] http:/ / etext. lib. virginia. edu/ cgi-local/ DHI/ dhi. cgi?id=dv1-04 [8] Matter: Atoms from Democritus to Dalton (http:/ / www. visionlearning. com/ library/ module_viewer. php?mid=49) by Anthony Carpi, Ph.D. [9] IUPAC Gold Book Definition (http:/ / www. iupac. org/ goldbook/ C01033. pdf) [10] "California Occupational Guide Number 22: Chemists" (http:/ / www. calmis. ca. gov/ file/ occguide/ CHEMIST. HTM). 1999-10-29. . Retrieved 2011-06-12. [11] First chemists (http:/ / www. newscientist. com/ article/ mg16121734. 300-first-chemists. html), February 13, 1999, New Scientist [12] Alchemy Timeline (http:/ / www. chemheritage. org/ explore/ ancients-time. html) - Chemical Heritage Society [13] Lucretius (50 BCE). "de Rerum Natura (On the Nature of Things)" (http:/ / classics. mit. edu/ Carus/ nature_things. html). The Internet Classics Archive. Massachusetts Institute of Technology. . Retrieved 2007-01-09. [14] Simpson, David (29 June 2005). "Lucretius (c. 99 - c. 55 BCE)" (http:/ / www. iep. utm. edu/ l/ lucretiu. htm). The Internet History of Philosophy. . Retrieved 2007-01-09. [15] Richard Myers (2003). " The Basics of Chemistry (http:/ / books. google. com/ books?id=oS50J3-IfZsC& pg=PA13& dq& hl=en#v=onepage& q=& f=false)". Greenwood Publishing Group. pp.13–14. ISBN 0-313-31664-3 [16] Morris Kline (1985) Mathematics for the nonmathematician (http:/ / books. google. com/ books?id=f-e0bro-0FUC& pg=PA284& dq& hl=en#v=onepage& q=& f=false). Courier Dover Publications. p. 284. ISBN 0-486-24823-2 [17] Will Durant (1980), The Age of Faith (The Story of Civilization, Volume 4), p. 162-186, Simon & Schuster, ISBN 0-671-01200-2 [18] Dr. K. Ajram (1992), Miracle of Islamic Science, Appendix B, Knowledge House Publishers, ISBN 0-911119-43-4. "Humboldt regards the Muslims as the founders of chemistry." [19] Will Durant (1935): Our Oriental Heritage: Simon & Schuster: "Something has been said about the chemical excellence of cast iron in ancient India, and about the high industrial development of the Gupta times, when India was looked to, even by Imperial Rome, as the most skilled of the nations in such chemical industries as dyeing, tanning, soap-making, glass and cement... By the sixth century the Hindus were far ahead of Europe in industrial chemistry; they were masters of calcination, distillation, sublimation, steaming, fixation, the production of light without heat, the mixing of anesthetic and soporific powders, and the preparation of metallic salts, compounds and alloys. The tempering of steel was brought in ancient India to a perfection unknown in Europe till our own times; King Porus is said to have selected, as a specially valuable gift from Alexander, not gold or silver, but thirty pounds of steel. The Moslems took much of this Hindu chemical science and industry to the Near East and Europe; the secret of manufacturing "Damascus" blades, for example, was taken by the Arabs from the Persians, and by the Persians from India."" [20] Eagle, Cassandra T.; Jennifer Sloan (1998). "Marie Anne Paulze Lavoisier: The Mother of Modern Chemistry" (http:/ / www. springerlink. com/ content/ x14v35m5n8822v42/ fulltext. pdf) (PDF). The Chemical Educator 3 (5): 1–18. doi:10.1007/s00897980249a. . Retrieved 2007-12-14. [21] "History - Robert Boyle (1627 - 1691)" (http:/ / www. bbc. co. uk/ history/ historic_figures/ boyle_robert. shtml). BBC. . Retrieved 2011-06-12. [22] Mi Gyung Kim (2003). Affinity, that Elusive Dream: A Genealogy of the Chemical Revolution. MIT Press. p. 440. ISBN 0-262-11273-6. [23] Ihde, Aaron John (1984). The Development of Modern Chemistry. Courier Dover Publications. p. 164. ISBN 0-486-64235-6. [24] Timeline of Element Discovery (http:/ / chemistry. about. com/ library/ weekly/ aa030303a. htm) - [25] "Chemistry" (http:/ / www. chemistry2011. org). . Retrieved 2012-03-10. [26] "History of Alchemy" (http:/ / www. alchemylab. com/ history_of_alchemy. htm). Alchemy Lab. . Retrieved 2011-06-12. [27] "alchemy", entry in The Oxford English Dictionary, J. A. Simpson and E. S. C. Weiner, vol. 1, 2nd ed., 1989, ISBN 0-19-861213-3. [28] p. 854, "Arabic alchemy", Georges C. Anawati, pp. 853-885 in Encyclopedia of the history of Arabic science, eds. Roshdi Rashed and Régis Morelon, London: Routledge, 1996, vol. 3, ISBN 0-415-12412-3. [29] Weekley, Ernest (1967). Etymological Dictionary of Modern English. New York: Dover Publications. ISBN 0-486-21873-2
  • 16. Chemistry 14 [30] Strathern, P. (2000). Mendeleyev’s Dream – the Quest for the Elements. New York: Berkley Books. [31] Boyle, Robert (1661). The Sceptical Chymist. New York: Dover Publications, Inc. (reprint). ISBN 0-486-42825-7. [32] Glaser, Christopher (1663). Traite de la chymie. Paris. as found in: Kim, Mi Gyung (2003). Affinity, That Elusive Dream - A Genealogy of the Chemical Revolution. The MIT Press. ISBN 0-262-11273-6. [33] Stahl, George, E. (1730). Philosophical Principles of Universal Chemistry. London. [34] Dumas, J. B. (1837). Affinite (lecture notes), vii, pg 4. “Statique chimique”, Paris: Academie des Sciences [35] Pauling, Linus (1947). General Chemistry. Dover Publications, Inc.. ISBN 0-486-65622-5. [36] Chang, Raymond (1998). Chemistry, 6th Ed.. New York: McGraw Hill. ISBN 0-07-115221-0. [37] "General Chemistry Online - Companion Notes: Matter" (http:/ / antoine. frostburg. edu/ chem/ senese/ 101/ matter/ ). . Retrieved 2011-06-12. [38] Hill, J.W.; Petrucci, R.H.; McCreary, T.W.; Perry, S.S. (2005). General Chemistry (4th ed.). Upper Saddle River, NJ: Pearson Prentice Hall. p. 37. [39] "IUPAC Nomenclature of Organic Chemistry" (http:/ / www. acdlabs. com/ iupac/ nomenclature/ ). . Retrieved 2011-06-12. [40] IUPAC Provisional Recommendations for the Nomenclature of Inorganic Chemistry (2004) (http:/ / www. iupac. org/ reports/ provisional/ abstract04/ connelly_310804. html) [41] "Official SI Unit definitions" (http:/ / www. bipm. org/ en/ si/ base_units/ ). . Retrieved 2011-06-12. [42] "The Lewis Acid-Base Concept" (http:/ / web. archive. org/ web/ 20080527132328/ http:/ / www. apsidium. com/ theory/ lewis_acid. htm). Apsidium. May 19, 2003. Archived from the original (http:/ / www. apsidium. com/ theory/ lewis_acid. htm) on 2008-05-27. . Retrieved 2010-07-31. [43] "History of Acidity" (http:/ / www. bbc. co. uk/ dna/ h2g2/ A708257). 2004-05-27. . Retrieved 2011-06-12. [44] Visionlearning. "Chemical Bonding by Anthony Carpi, Ph" (http:/ / www. visionlearning. com/ library/ module_viewer. php?mid=55). visionlearning. . Retrieved 2011-06-12. [45] Chemical Reaction Equation (http:/ / goldbook. iupac. org/ C01034. html)- IUPAC Goldbook [46] Gold Book Chemical Reaction (http:/ / goldbook. iupac. org/ C01033. html) IUPAC Goldbook [47] Reilly, Michael. (2007). Mechanical force induces chemical reaction (http:/ / www. newscientisttech. com/ article/ dn11427), news service, Reilly [48] Changing States of Matter (http:/ / www. chem4kids. com/ files/ matter_changes. html) - [49] W.G. Laidlaw; D.E. Ryan And Gary Horlick; H.C. Clark, Josef Takats, And Martin Cowie; R.U. Lemieux (1986-12-10). "Chemistry Subdisciplines" (http:/ / www. thecanadianencyclopedia. com/ index. cfm?PgNm=TCE& Params=A1ARTA0001555). The Canadian Encyclopedia. . Retrieved 2011-06-12. [50] Herbst, Eric (May 12, 2005). "Chemistry of Star-Forming Regions". Journal of Physical Chemistry A 109 (18): 4017–4029. doi:10.1021/jp050461c. PMID 16833724. [51] "Top 50 Chemical Producers" (http:/ / pubs. acs. org/ cen/ coverstory/ 83/ 8329globaltop50. html). Chemical & Engineering News 83 (29): 20–23. July 18, 2005. . Further reading Popular reading • Atkins, P.W. Galileos Finger (Oxford University Press) ISBN 0-19-860941-8 • Atkins, P.W. Atkins Molecules (Cambridge University Press) ISBN 0-521-82397-8 • Kean, Sam. The Disappearing Spoon - and other true tales from the Periodic Table (Black Swan) London, 2010 ISBN 978-0-552-77750-6 • Levi, Primo The Periodic Table (Penguin Books) [1975] translated from the Italian by Raymond Rosenthal (1984) ISBN 978-0-14-139944-7 • Stwertka, A. A Guide to the Elements (Oxford University Press) ISBN 0-19-515027-9 Introductory undergraduate text books • Atkins, P.W., Overton, T., Rourke, J., Weller, M. and Armstrong, F. Shriver and Atkins inorganic chemistry (4th edition) 2006 (Oxford University Press) ISBN 0-19-926463-5 • Chang, Raymond. Chemistry 6th ed. Boston: James M. Smith, 1998. ISBN 0-07-115221-0. • Clayden, Jonathan; Greeves, Nick; Warren, Stuart; Wothers, Peter (2001). Organic Chemistry (1st ed.). Oxford University Press. ISBN 978-0-19-850346-0. • Voet and Voet Biochemistry (Wiley) ISBN 0-471-58651-X Advanced undergraduate-level or graduate text books • Atkins, P.W. Physical Chemistry (Oxford University Press) ISBN 0-19-879285-9
  • 17. Chemistry 15 • Atkins, P.W. et al. Molecular Quantum Mechanics (Oxford University Press) • McWeeny, R. Coulsons Valence (Oxford Science Publications) ISBN 0-19-855144-4 • Pauling, L. The Nature of the chemical bond (Cornell University Press) ISBN 0-8014-0333-2 • Pauling, L., and Wilson, E. B. Introduction to Quantum Mechanics with Applications to Chemistry (Dover Publications) ISBN 0-486-64871-0 • Smart and Moore Solid State Chemistry: An Introduction (Chapman and Hall) ISBN 0-412-40040-5 • Stephenson, G. Mathematical Methods for Science Students (Longman) ISBN 0-582-44416-0 History of chemistry By 1000 BC, ancient civilizations used technologies that would eventually form the basis of the various branches of chemistry. Examples include extracting metals from ores, making pottery and glazes, fermenting beer and wine, making pigments for cosmetics and painting, extracting chemicals from plants for medicine and perfume, making cheese, dying cloth, tanning leather, rendering fat into soap, making glass, and making alloys like bronze. Early attempts to explain the nature of matter and its transformations failed. The protoscience of chemistry, Alchemy, was also unsuccessful in explaining the nature of matter. However, by performing experiments and recording the results the alchemist set the stage for modern chemistry. This distinction begins to emerge when a clear differentiation was made between chemistry and alchemy by Robert Boyle in his work The Sceptical Chymist (1661). Chemistry then becomes a full-fledged science when Antoine Lavoisier develops his law of conservation of mass, which demands careful measurements and quantitative observations of chemical phenomena. So, while both alchemy and chemistry are concerned with the nature of matter and its transformations, it is only the chemists who apply the scientific method. The history of chemistry is intertwined with the history of thermodynamics, especially through the work of Willard Gibbs.[1] From fire to atomism Arguably the first chemical reaction used in a controlled manner was fire. However, for millennia fire was simply a mystical force that could transform one substance into another (burning wood, or boiling water) while producing heat and light. Fire affected many aspects of early societies. These ranged from the most simple facets of everyday life, such as cooking and habitat lighting, to more advanced technologies, such as pottery, bricks, and melting of metals to make tools. Philosophical attempts to rationalize why different substances have different properties (color, density, smell), exist in different states (gaseous, liquid, and solid), and react in a different manner when exposed to environments, for example to water or fire or temperature changes, led ancient philosophers to postulate the first theories on nature and chemistry. The history of such philosophical theories that relate to chemistry, can probably be traced back to every single ancient civilization. The common aspect in all these theories was the attempt to identify a small number of primary elements that make up all the various substances in nature. Substances like air, water, and soil/earth, energy forms, such as fire and light, and more abstract concepts such as ideas, aether, and heaven, were common in ancient civilizations even in absence of any cross-fertilization; for example in Greek, Indian, Mayan, and ancient Chinese philosophies all considered air, water, earth and fire as primary elements. Atomism can be traced back to ancient Greece and ancient India.[2] Greek atomism dates back to 440 BC, as what might be indicated by the book De Rerum Natura (The Nature of Things)[3] written by the Roman Lucretius[4] in 50 BC. In the book was found ideas traced back to Democritus and Leucippus, who declared that atoms were the most indivisible part of matter. This coincided with a similar declaration by Indian philosopher Kanada in his Vaisheshika sutras around the same time period.[2] In much the same fashion he discussed the existence of gases. What Kanada declared by sutra, Democritus declared by philosophical musing. Both suffered from a lack of empirical data.
  • 18. History of chemistry 16 Without scientific proof, the existence of atoms was easy to deny. Aristotle opposed the existence of atoms in 330 BC. Much of the early development of purification methods is described by Pliny the Elder in his Naturalis Historia. He made attempts to explain those methods, as well as making acute observations of the state of many minerals. The rise of metallurgy It was fire that led to the discovery of glass and the purification of metals which in turn gave way to the rise of metallurgy. During the early stages of metallurgy, methods of purification of metals were sought, and gold, known in ancient Egypt as early as 2600 BC, became a precious metal. The discovery of alloys heralded the Bronze Age. After the Bronze Age, the history of metallurgy was marked by which army had better weaponry. Countries in Eurasia had their heyday when they made the superior alloys, which, in turn, made better armour and better weapons. This often determined the outcomes of battles. Significant progress in metallurgy and alchemy was made in ancient India.[5] The philosophers stone and the rise of alchemy Alchemy is defined by the Hermetic quest for the philosopher’s stone, the study of which is steeped in symbolic mysticism, and differs greatly from modern science. Alchemists toiled to make transformations on an esoteric (spiritual) and/or exoteric (practical) level.[6] It was the protoscientific, exoteric aspects of alchemy that contributed heavily to the evolution of chemistry in Greco-Roman Egypt, the Islamic Golden Age, and then in Europe. Alchemy and chemistry share an interest in the composition and properties of matter, and prior to the eighteenth century were not separated into distinct disciplines. The term chymistry has been used to describe the blend of alchemy and chemistry that existed before this time.[7] The earliest Western alchemists, who lived in the first centuries of the common era, invented chemical apparatus. The bain-marie, or water bath is named for Mary the Jewess. Her work also gives the first descriptions of the tribikos and kerotakis.[8] Cleopatra the Alchemist "The Alchemist", by Sir William Douglas, 1855 described furnaces and has been credited with the invention of the alembic.[9] Later, the experimental framework established by Jabir ibn Hayyan influenced alchemists as the discipline migrated through the Islamic world, then to Europe in the twelfth century. During the Renaissance, exoteric alchemy remained popular in the form of Paracelsian iatrochemistry, while spiritual alchemy flourished, realigned to its Platonic, Hermetic, and Gnostic roots. Consequently, the symbolic quest for the philosopher’s stone was not superseded by scientific advances, and was still the domain of respected scientists and doctors until the early eighteenth century. Early modern alchemists who are renowned for their scientific contributions include Jan Baptist van Helmont, Robert Boyle, and Isaac Newton.
  • 19. History of chemistry 17 Problems encountered with alchemy There were several problems with alchemy, as seen from todays standpoint. There was no systematic naming system for new compounds, and the language was esoteric and vague to the point that the terminologies meant different things to different people. In fact, according to The Fontana History of Chemistry (Brock, 1992): The language of alchemy soon developed an arcane and secretive technical vocabulary designed to conceal information from the uninitiated. To a large degree, this language is incomprehensible to us today, though it is apparent that readers of Geoffery Chaucers Canons Yeomans Tale or audiences of Ben Jonsons The Alchemist were able to construe it sufficiently to laugh at it.[10] Chaucers tale exposed the more fraudulent side of alchemy, especially the manufacture of counterfeit gold from cheap substances. Less than a century earlier, Dante Alighieri also demonstrated an awareness of this fraudulence, causing him to consign all alchemists to the Inferno in his writings. Soon after, in 1317, the Avignon Pope John XXII ordered all alchemists to leave France for making counterfeit money. A law was passed in England in 1403 which made the "multiplication of metals" punishable by death. Despite these and other apparently extreme measures, alchemy did not die. Royalty and privileged classes still sought to discover the philosophers stone and the elixir of life for themselves.[11] There was also no agreed-upon scientific method for making experiments reproducible. Indeed many alchemists included in their methods irrelevant information such as the timing of the tides or the phases of the moon. The esoteric nature and codified vocabulary of alchemy appeared to be more useful in concealing the fact that they could not be sure of very much at all. As early as the 14th century, cracks seemed to grow in the facade of alchemy; and people became sceptical. Clearly, there needed to be a scientific method where experiments can be repeated by other people, and results needed to be reported in a clear language that laid out both what is known and unknown. From alchemy to chemistry Ambix, cucurbit and retort of Zosimus, from Marcelin Berthelot, Collection des anciens alchimistes grecs (3 vol., Paris, 1887-1888).
  • 20. History of chemistry 18 Early chemists In the Islamic World, the Muslims were translating the works of the ancient Greeks and Egyptians into Arabic and were experimenting with scientific ideas.[12] The development of the modern scientific method was slow and arduous, but an early scientific method for chemistry began emerging among early Muslim chemists, beginning with the 9th century chemist Jābir ibn Hayyān (known as "Geber" in Europe), who is considered as "the father of chemistry".[13][14][15][16] He introduced a systematic and experimental approach to scientific research based in the laboratory, in contrast to the ancient Greek and Egyptian alchemists whose works were largely allegorical and often unintelligble.[17] He also invented and named the alembic (al-anbiq), chemically analyzed many chemical substances, composed lapidaries, distinguished between alkalis and acids, and manufactured hundreds of drugs.[18] He also refined the theory of five classical elements into the theory of seven alchemical elements after identifying mercury and sulfur as Jābir ibn Hayyān (Geber), a Persian alchemist whose experimental research laid the foundations chemical elements.[19] of chemistry. Among other influential Muslim chemists, Abū al-Rayhān al-Bīrūnī,[20] Avicenna[21] and Al-kindi refuted the theories of alchemy, particularly the theory of the transmutation of metals; and al-Tusi described a version of the conservation of mass, noting that a body of matter is able to change but is not able to disappear.[22] Rhazes refuted Aristotles theory of four classical elements for the first time and set up the firm foundations of modern chemistry, using the laboratory in the modern sense, designing and describing more than twenty instruments, many parts of which are still in use today, such as a crucible, cucurbit or retort for distillation, and the head of a still with a delivery tube (ambiq, Latin alembic), and various types of furnace or stove. For the more honest practitioners in Europe, alchemy became an intellectual pursuit after early Arabic alchemy became available through Latin translation, and over time, they got better at it. Paracelsus (1493–1541), for example, rejected the 4-elemental theory and with only a vague understanding of his chemicals and medicines, formed a hybrid of alchemy and science in what was to be called iatrochemistry. Paracelsus was not perfect in making his experiments truly scientific. For example, as an extension of his theory that new compounds could be made by combining mercury with sulfur, he once made what he thought was "oil of sulfur". This was actually dimethyl ether, which had neither mercury nor sulfur. Practical attempts to improve the refining of ores and their extraction to smelt metals was an important source of information for early chemists, among them Georg Agricola (1494–1555), who published his great work De re Agricola, author of De re metallica metallica in 1556. His approach removed the mysticism associated with the subject, creating the practical base upon which others could build. The work describes the many kinds of furnace used to smelt ore, and stimulated interest in minerals and their composition. It is no coincidence that he gives numerous references to the earlier author, Pliny the Elder and his Naturalis Historia. In 1605, Sir Francis Bacon published The Proficience and Advancement of Learning, which contains a description of what would later be known as the scientific method.[23] In 1615 Jean Beguin publishes the Tyrocinium Chymicum, an early chemistry textbook, and in it draws the first-ever chemical equation.[24]
  • 21. History of chemistry 19 Robert Boyle (1627–1691) is considered to have refined the modern scientific method for alchemy and to have separated chemistry further from alchemy.[25] Robert Boyle was an atomist, but favoured the word corpuscle over atoms. He comments that the finest division of matter where the properties are retained is at the level of corpuscles. Boyle was credited with the discovery of Boyles Law. He is also credited for his landmark publication The Sceptical Chymist, where he attempts to develop an atomic theory of matter, with no small degree of success. He laid the foundations for the Chemical Revolution with his mechanical corpuscular philosophy, which in turn relied heavily on the alchemical corpuscular theory and experimental method dating back to the alchemist Jābir ibn Hayyān.[26] Despite all these advances, the person celebrated as the "father of modern chemistry" is Antoine Lavoisier who developed his law of conservation of mass in 1789, also called Lavoisiers Law.[27] With Robert Boyle, one of the co-founders of modern chemistry through his use of proper this, chemistry acquired a strict quantitative nature, allowing reliable experimentation, which further separated predictions to be made. chemistry from alchemy In 1754, Joseph Black isolated carbon dioxide, which he called "fixed air".[28] Carl Wilhelm Scheele and Joseph Priestley independently isolated oxygen, called by Priestley "dephlogisticated air" and Scheele "fire air".[29][30] Joseph Proust proposed the law of definite proportions, which states that elements always combine in small, whole number ratios to form compounds.[31] In 1800, Alessandro Volta devised the first chemical battery, thereby founding the discipline of electrochemistry.[32] In 1803, John Dalton proposed Daltons Law, which describes relationship between the components in a mixture of gases and the relative pressure each contributes to that of the overall mixture.[33] Antoine Lavoisier Although the archives of chemical research draw upon work from ancient Babylonia, Egypt, and especially the Arabs and Persians after Islam, modern chemistry flourished from the time of Antoine Lavoisier, who is regarded as the "father of modern chemistry", particularly for his discovery of the law of conservation of mass, and his refutation of the phlogiston theory of combustion in 1783. (Phlogiston was supposed to be an imponderable substance liberated by flammable materials in burning.) Mikhail Lomonosov independently established a tradition of chemistry in Russia in the 18th century. Lomonosov also rejected the phlogiston theory, and anticipated the kinetic theory of gases. He regarded heat as a form of motion, and stated the idea of conservation of matter. Portrait of Monsieur Lavoisier and his wife, by Jacques-Louis David
  • 22. History of chemistry 20 The vitalism debate and organic chemistry After the nature of combustion (see oxygen) was settled, another dispute, about vitalism and the essential distinction between organic and inorganic substances, was revolutionized by Friedrich Wöhlers accidental synthesis of urea from inorganic substances in 1828. Never before had an organic compound been synthesized from inorganic material. This opened a new research field in chemistry, and by the end of the 19th century, scientists were able to synthesize hundreds of organic compounds. The most important among them are mauve, magenta, and other synthetic dyes, as well as the widely used drug aspirin. The discovery of the artificial synthesis of urea contributed greatly to the theory of isomerism, as the empirical chemical formulas for urea and ammonium cyanate are identical (see Wöhler synthesis). Disputes about atomism after Lavoisier Throughout the 19th century, chemistry was divided between those who followed the atomic theory of John Dalton and those who did not, such as Wilhelm Ostwald and Ernst Mach.[34] Although such proponents of the atomic theory as Amedeo Avogadro and Ludwig Boltzmann made great advances in explaining the behavior of gases, this dispute was not finally settled until Jean Perrins experimental investigation of Einsteins atomic explanation of Brownian motion in the first decade of the 20th century.[34] Well before the dispute had been settled, many had already applied the concept of atomism to chemistry. A major example was the ion theory of Svante Arrhenius which anticipated ideas about atomic substructure that did not fully develop until the 20th century. Michael Faraday was another early worker, whose major contribution to chemistry was electrochemistry, in which (among other things) a certain quantity of electricity during electrolysis or electrodeposition of metals was shown to be associated with certain quantities of chemical elements, and fixed quantities of the elements therefore Bust of John Dalton by Chantrey with each other, in specific ratios. These findings, like those of Daltons combining ratios, were early clues to the atomic nature of matter. The periodic table For many decades, the list of known chemical elements had been steadily increasing. A great breakthrough in making sense of this long list (as well as in understanding the internal structure of atoms as discussed below) was Dmitri Mendeleev and Lothar Meyers development of the periodic table, and particularly Mendeleevs use of it to predict the existence and the properties of germanium, gallium, and scandium, which Mendeleev called ekasilicon, ekaaluminium, and ekaboron respectively. Mendeleev made his prediction in 1870; gallium was discovered in 1875, and was found to have roughly the same properties that Mendeleev Dmitri Mendeleev, responsible for the periodic table. predicted for it. The modern definition of chemistry
  • 23. History of chemistry 21 Classically, before the 20th century, chemistry was defined as the science of the nature of matter and its transformations. It was therefore clearly distinct from physics which was not concerned with such dramatic transformation of matter. Moreover, in contrast to physics, chemistry was not using much of mathematics. Even some were particularly reluctant to using mathematics within chemistry. For example, Auguste Comte wrote in 1830: Every attempt to employ mathematical methods in the study of chemical questions must be considered profoundly irrational and contrary to the spirit of chemistry.... if mathematical analysis should ever hold a prominent place in chemistry -- an aberration which is happily almost impossible -- it would occasion a rapid and widespread degeneration of that science. However, in the second part of the 19th century, the situation changed and August Kekule wrote in 1867: I rather expect that we shall someday find a mathematico-mechanical explanation for what we now call atoms which will render an account of their properties. After the discovery by Ernest Rutherford and Niels Bohr of the atomic structure in 1912, and by Marie and Pierre Curie of radioactivity, scientists had to change their viewpoint on the nature of matter. The experience acquired by chemists was no longer pertinent to the study of the whole nature of matter but only to aspects related to the electron cloud surrounding the atomic nuclei and the movement of the latter in the electric field induced by the former (see Born-Oppenheimer approximation). The range of chemistry was thus restricted to the nature of matter around us in conditions which are not too far (or exceptionally far) from standard conditions for temperature and pressure and in cases where the exposure to radiation is not too different from the natural microwave, visible or UV radiations on Earth. Chemistry was therefore re-defined as the science of matter that deals with the composition, structure, and properties of substances and with the transformations that they undergo. However the meaning of matter used here relates explicitly to substances made of atoms and molecules, disregarding the matter within the atomic nuclei and its nuclear reaction or matter within highly ionized plasmas. This does not mean that chemistry is never involved with plasma or nuclear sciences or even bosonic fields nowadays, since areas such as Quantum Chemistry and Nuclear Chemistry are currently well developed and formally recognized sub-fields of study under the Chemical sciences (Chemistry), but what is now formally recognized as subject of study under the Chemistry category as a science is always based on the use of concepts that describe or explain phenomena either from matter or to matter in the atomic or molecular scale, including the study of the behavior of many molecules as an aggregate or the study of the effects of a single proton on a single atom, but excluding phenomena that deal with different (more "exotic") types of matter (e.g. Bose-Einstein condensate, Higgs Boson, dark matter, naked singularity, etc.) and excluding principles that refer to intrinsic abstract laws of nature in which their concepts can be formulated completely without a precise formal molecular or atomic paradigmatic view (e.g. Quantum Chromodynamics, Quantum Electrodynamics, String Theory, parts of Cosmology (see Cosmochemistry), certain areas of Nuclear Physics (see Nuclear Chemistry), etc.). Nevertheless the field of chemistry is still, on our human scale, very broad and the claim that chemistry is everywhere is accurate. Quantum chemistry Some view the birth of quantum chemistry in the discovery of the Schrödinger equation and its application to the hydrogen atom in 1926. However, the 1927 article of Walter Heitler and Fritz London[35] is often recognised as the first milestone in the history of quantum chemistry.[36] This is the first application of quantum mechanics to the diatomic hydrogen molecule, and thus to the phenomenon of the chemical bond. In the following years much progress was accomplished by Edward Teller, Robert S. Mulliken, Max Born, J. Robert Oppenheimer, Linus Pauling, Erich Hückel, Douglas Hartree, Vladimir Aleksandrovich Fock, to cite a few. Still, skepticism remained as to the general power of quantum mechanics applied to complex chemical systems. The situation around 1930 is described by Paul Dirac:[37]
  • 24. History of chemistry 22 The underlying physical laws necessary for the mathematical theory of a large part of physics and the whole of chemistry are thus completely known, and the difficulty is only that the exact application of these laws leads to equations much too complicated to be soluble. It therefore becomes desirable that approximate practical methods of applying quantum mechanics should be developed, which can lead to an explanation of the main features of complex atomic systems without too much computation. Hence the quantum mechanical methods developed in the 1930s and 1940s are often referred to as theoretical molecular or atomic physics to underline the fact that they were more the application of quantum mechanics to chemistry and spectroscopy than answers to chemically relevant questions. In the 1940s many physicists turned from molecular or atomic physics to nuclear physics (like J. Robert Oppenheimer or Edward Teller). In 1951, a milestone article in quantum chemistry is the seminal paper of Clemens C. J. Roothaan on Roothaan equations.[38] It opened the avenue to the solution of the self-consistent field equations for small molecules like hydrogen or nitrogen. Those computations were performed with the help of tables of integrals which were computed on the most advanced computers of the time. Molecular biology and biochemistry By the mid 20th century, in principle, the integration of physics and chemistry was extensive, with chemical properties explained as the result of the electronic structure of the atom; Linus Paulings book on The Nature of the Chemical Bond used the principles of quantum mechanics to deduce bond angles in ever-more complicated molecules. However, though some principles deduced from quantum mechanics were able to predict qualitatively some chemical features for biologically relevant molecules, they were, till the end of the 20th century, more a collection of rules, observations, and recipes than rigorous ab initio quantitative methods. This heuristic approach triumphed in 1953 when James Watson and Francis Crick deduced the double helical structure of DNA by constructing models constrained by and informed by the knowledge of the chemistry of the constituent parts and the X-ray diffraction patterns obtained by Rosalind Franklin.[39] This discovery lead to an explosion of research into the biochemistry of life. In the same year, the Miller-Urey experiment demonstrated that basic constituents of protein, simple amino acids, could themselves be built up from simpler molecules in a simulation of primordial processes on Earth. Though many questions remain about the true nature of the origin of life, this was the first attempt by chemists to study hypothetical processes in the laboratory under controlled conditions. In 1983 Kary Mullis devised a method for the in-vitro Diagrammatic representation of some key structural features of DNA amplification of DNA, known as the polymerase chain reaction (PCR), which revolutionized the chemical processes used in the laboratory to manipulate it. PCR could be used to synthesize specific pieces of DNA and made possible the sequencing of DNA of organisms, which culminated in the huge human genome project. An important piece in the double helix puzzle was solved by one of Paulings student Matthew Meselson and Frank Stahl, the result of their collaboration (Meselson-Stahl experiment) has been called as "the most beautiful experiment in biology". They used a centrifugation technique that sorted molecules according to differences in weight. Because nitrogen atoms are a component of DNA, they were labelled and therefore tracked in replication in bacteria.
  • 25. History of chemistry 23 Chemical industry The later part of the nineteenth century saw a huge increase in the exploitation of petroleum extracted from the earth for the production of a host of chemicals and largely replaced the use of whale oil, coal tar and naval stores used previously. Large scale production and refinement of petroleum provided feedstocks for liquid fuels such as gasoline and diesel, solvents, lubricants, asphalt, waxes, and for the production of many of the common materials of the modern world, such as synthetic fibers, plastics, paints, detergents, pharmaceuticals, adhesives and ammonia as fertilizer and for other uses. Many of these required new catalysts and the utilization of chemical engineering for their cost-effective production. In the mid-twentieth century, control of the electronic structure of semiconductor materials was made precise by the creation of large ingots of extremely pure single crystals of silicon and germanium. Accurate control of their chemical composition by doping with other elements made the production of the solid state transistor in 1951 and made possible the production of tiny integrated circuits for use in electronic devices, especially computers. Notes [1] Selected Classic Papers from the History of Chemistry (http:/ / web. lemoyne. edu/ ~giunta/ papers. html) [2] Will Durant (1935), Our Oriental Heritage: "Two systems of Hindu thought propound physical theories suggestively similar to those of Greece. Kanada, founder of the Vaisheshika philosophy, held that the world was composed of atoms as many in kind as the various elements. The Jains more nearly approximated to Democritus by teaching that all atoms were of the same kind, producing different effects by diverse modes of combinations. Kanada believed light and heat to be varieties of the same substance; Udayana taught that all heat comes from the sun; and Vachaspati, like Newton, interpreted light as composed of minute particles emitted by substances and striking the eye." [3] Lucretius (50 BCE). "de Rerum Natura (On the Nature of Things)" (http:/ / classics. mit. edu/ Carus/ nature_things. html). The Internet Classics Archive. Massachusetts Institute of Technology. . Retrieved 2007-01-09. [4] Simpson, David (29 June 2005). "Lucretius (c. 99 - c. 55 BCE)" (http:/ / www. iep. utm. edu/ l/ lucretiu. htm). The Internet History of Philosophy. . Retrieved 2007-01-09. [5] Will Durant wrote in The Story of Civilization I: Our Oriental Heritage: "Something has been said about the chemical excellence of cast iron in ancient India, and about the high industrial development of the Gupta times, when India was looked to, even by Imperial Rome, as the most skilled of the nations in such chemical industries as dyeing, tanning, soap-making, glass and cement... By the sixth century the Hindus were far ahead of Europe in industrial chemistry; they were masters of calcinations, distillation, sublimation, steaming, fixation, the production of light without heat, the mixing of anesthetic and soporific powders, and the preparation of metallic salts, compounds and alloys. The tempering of steel was brought in ancient India to a perfection unknown in Europe till our own times; King Porus is said to have selected, as a specially valuable gift from Alexander, not gold or silver, but thirty pounds of steel. The Moslems took much of this Hindu chemical science and industry to the Near East and Europe; the secret of manufacturing "Damascus" blades, for example, was taken by the Arabs from the Persians, and by the Persians from India." [6] Holmyard, E.J. (1957). Alchemy. New York: Dover, 1990. pp. 15,16. [7] William Royall Newman. Atoms and Alchemy: Chymistry and the experimental origins of the scientific revolution. University of Chicago Press, 2006. p.xi [8] Holmyard, E.J. (1957). Alchemy. New York: Dover, 1990. pp. 48,49. [9] Stanton J. Linden. The alchemy reader: from Hermes Trismegistus to Isaac Newton Cambridge University Press. 2003. p.44 [10] Brock, William H. (1992). The Fontana History of Chemistry. London, England: Fontana Press. pp. 32–33. ISBN 0-00-686173-3. [11] Brock, William H. (1992). The Fontana History of Chemistry. London, England: Fontana Press. ISBN 0-00-686173-3. [12] The History of Ancient Chemistry (http:/ / realscience. breckschool. org/ upper/ fruen/ files/ Enrichmentarticles/ files/ History. html) [13] Derewenda, ZS (2007). "On wine, chirality and crystallography". Acta Crystallographica Section A: Foundations of Crystallography 64 (Pt 1): 246–258 [247]. doi:10.1107/S0108767307054293. PMID 18156689.
  • 26. History of chemistry 24 [14] John Warren (2005). "War and the Cultural Heritage of Iraq: a sadly mismanaged affair", Third World Quarterly, Volume 26, Issue 4 & 5, p. 815-830. [15] Dr. A. Zahoor (1997), JABIR IBN HAIYAN (Jabir) (http:/ / www. unhas. ac. id/ ~rhiza/ saintis/ haiyan. html), University of Indonesia [16] Paul Vallely, How Islamic inventors changed the world (http:/ / news. independent. co. uk/ world/ science_technology/ article350594. ece), The Independent [17] Kraus, Paul, Jâbir ibn Hayyân, Contribution à lhistoire des idées scientifiques dans lIslam. I. Le corpus des écrits jâbiriens. II. Jâbir et la science grecque,. Cairo (1942-1943). Repr. By Fuat Sezgin, (Natural Sciences in Islam. 67-68), Frankfurt. 2002: “To form an idea of the historical place of Jabir’s alchemy and to tackle the problem of its sources, it is advisable to compare it with what remains to us of the alchemical literature in the Greek language. One knows in which miserable state this literature reached us. Collected by Byzantine scientists from the tenth century, the corpus of the Greek alchemists is a cluster of incoherent fragments, going back to all the times since the third century until the end of the Middle Ages.” “The efforts of Berthelot and Ruelle to put a little order in this mass of literature led only to poor results, and the later researchers, among them in particular Mrs. Hammer-Jensen, Tannery, Lagercrantz , von Lippmann, Reitzenstein, Ruska, Bidez, Festugiere and others, could make clear only few points of detail… The study of the Greek alchemists is not very encouraging. An even surface examination of the Greek texts shows that a very small part only was organized according to true experiments of laboratory: even the supposedly technical writings, in the state where we find them today, are unintelligible nonsense which refuses any interpretation. It is different with Jabir’s alchemy. The relatively clear description of the processes and the alchemical apparatuses, the methodical classification of the substances, mark an experimental spirit which is extremely far away from the weird and odd esotericism of the Greek texts. The theory on which Jabir supports his operations is one of clearness and of an impressive unity. More than with the other Arab authors, one notes with him a balance between theoretical teaching and practical teaching, between the `ilm and the `amal. In vain one would seek in the Greek texts a work as systematic as that which is presented for example in the Book of Seventy.” (cf. Ahmad Y Hassan. "A Critical Reassessment of the Geber Problem: Part Three" (http:/ / www. history-science-technology. com/ Geber/ Geber 3. htm). . Retrieved 2008-08-09.) [18] Will Durant (1980). The Age of Faith (The Story of Civilization, Volume 4), p. 162-186. Simon & Schuster. ISBN 0-671-01200-2. [19] Strathern, Paul. (2000), Mendeleyev’s Dream – the Quest for the Elements, New York: Berkley Books [20] Marmura Michael E., Nasr Seyyed Hossein (1965). "An Introduction to Islamic Cosmological Doctrines. Conceptions of Nature and Methods Used for Its Study by the Ikhwan Al-Safaan, Al-Biruni, and Ibn Sina by Seyyed Hossein Nasr". Speculum 40 (4): 744–746. doi:10.2307/2851429. JSTOR 2851429. [21] Robert Briffault (1938). The Making of Humanity, p. 196-197. [22] Alakbarov Farid (2001). "A 13th-Century Darwin? Tusis Views on Evolution" (http:/ / azer. com/ aiweb/ categories/ magazine/ 92_folder/ 92_articles/ 92_tusi. html). Azerbaijan International 9: 2. . [23] Asarnow, Herman (2005-08-08). "Sir Francis Bacon: Empiricism" (http:/ / faculty. up. edu/ asarnow/ eliz4. htm). An Image-Oriented Introduction to Backgrounds for English Renaissance Literature. University of Portland. . Retrieved 2007-02-22. [24] Crosland, M.P. (1959). "The use of diagrams as chemical equations in the lectures of William Cullen and Joseph Black." Annals of Science, Vol 15, No. 2, Jun. [25] Robert Boyle (http:/ / understandingscience. ucc. ie/ pages/ sci_robertboyle. htm) [26] Ursula Klein (July 2007). "Styles of Experimentation and Alchemical Matter Theory in the Scientific Revolution". Metascience (Springer) 16 (2): 247–256 [247]. doi:10.1007/s11016-007-9095-8. ISSN 1467-9981 [27] Lavoisier, Antoine (1743-1794) -- from Eric Weissteins World of Scientific Biography (http:/ / scienceworld. wolfram. com/ biography/ Lavoisier. html), ScienceWorld [28] Cooper, Alan (1999). "Joseph Black" (http:/ / web. archive. org/ web/ 20060410074412/ http:/ / www. chem. gla. ac. uk/ dept/ black. htm). History of Glasgow University Chemistry Department. University of Glasgow Department of Chemistry. Archived from the original (http:/ / www. chem. gla. ac. uk/ dept/ black. htm) on 2006-04-10. . Retrieved 2006-02-23. [29] "Joseph Priestley" (http:/ / www. chemheritage. org/ classroom/ chemach/ forerunners/ priestley. html). Chemical Achievers: The Human Face of Chemical Sciences. Chemical Heritage Foundation. 2005. . Retrieved 2007-02-22. [30] "Carl Wilhelm Scheele" (http:/ / mattson. creighton. edu/ History_Gas_Chemistry/ Scheele. html). History of Gas Chemistry. Center for Microscale Gas Chemistry, Creighton University. 2005-09-11. . Retrieved 2007-02-23.
  • 27. History of chemistry 25 [31] "Proust, Joseph Louis (1754-1826)" (http:/ / www. euchems. org/ Distinguished/ 19thCentury/ proustlouis. asp). 100 Distinguished Chemists. European Association for Chemical and Molecular Science. 2005. . Retrieved 2007-02-23. [32] "Inventor Alessandro Volta Biography" (http:/ / www. ideafinder. com/ history/ inventors/ volta. htm). The Great Idea Finder. The Great Idea Finder. 2005. . Retrieved 2007-02-23. [33] "John Dalton" (http:/ / www. chemheritage. org/ classroom/ chemach/ periodic/ dalton. html). Chemical Achievers: The Human Face of Chemical Sciences. Chemical Heritage Foundation. 2005. . Retrieved 2007-02-22. [34] Pullman, Bernard (2004). The Atom in the History of Human Thought. Reisinger, Axel. USA: Oxford University Press Inc. ISBN 0-19-511447-7. [35] W. Heitler and F. London, Wechselwirkung neutraler Atome und Homöopolare Bindung nach der Quantenmechanik, Z. Physik, 44, 455 (1927). [36] Quantum chemistry (http:/ / www. fact-archive. com/ encyclopedia/ Quantum_chemistry) [37] P.A.M. Dirac, Quantum Mechanics of Many-Electron Systems, Proc. R. Soc. London, A 123, 714 (1929). [38] C.C.J. Roothaan, A Study of Two-Center Integrals Useful in Calculations on Molecular Structure, J. Chem. Phys., 19, 1445 (1951). [39] Watson, J. and Crick, F., "Molecular Structure of Nucleic Acids" (http:/ / www. nature. com/ nature/ dna50/ watsoncrick. pdf) Nature, April 25, 1953, p 737–8 References • Selected classic papers from the history of chemistry ( • Biographies of chemists ( • Eric R. Scerri, The Periodic Table: Its Story and Its Significance, Oxford University Press, 2006. Further reading • Servos, John W., Physical chemistry from Ostwald to Pauling : the making of a science in America (http://books., Princeton, N.J. : Princeton University Press, 1990. ISBN 0-691-08566-8 Documentaries • BBC (2010). Chemistry: A Volatile History. External links • ChemisLab ( - Chemists of the Past • SHAC: Society for the History of Alchemy and Chemistry (
  • 28. Atom 26 Atom Helium atom An illustration of the helium atom, depicting the nucleus (pink) and the electron cloud distribution (black). The nucleus (upper right) in helium-4 is in reality spherically symmetric and closely resembles the electron cloud, although for more complicated nuclei this is not always the case. The black bar is one angstrom ( × 10−10 m or 100 pm). Classification Smallest recognized division of a chemical element Properties Mass range: 1.67 × 10−27 to 4.52 × 10−25 kg Electric charge: zero (neutral), or ion charge Diameter range: 62 pm (He) to 520 pm (Cs) (data page) Components: Electrons and a compact nucleus of protons and neutrons The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons (except in the case of hydrogen-1, which is the only stable nuclide with no neutrons). The electrons of an atom are bound to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain bound to each other, forming a molecule. An atom containing an equal number of protons and electrons is electrically neutral, otherwise it has a positive charge if there are fewer electrons (electron deficiency) or negative charge if there are more electrons (electron excess). A positively or negatively charged atom is known as an ion. An atom is classified according to the number of protons and neutrons in its nucleus: the number of protons determines the chemical element, and the number of neutrons determines the isotope of the element.[1] The name atom comes from the Greek ἄτομος (atomos, "indivisible") from ἀ- (a-, "not") and τέμνω (temnō, "I cut"),[2] which means uncuttable, or indivisible, something that cannot be divided further.[3] The concept of an atom as an indivisible component of matter was first proposed by early Indian and Greek philosophers. In the 17th and 18th centuries, chemists provided a physical basis for this idea by showing that certain substances could not be
  • 29. Atom 27 further broken down by chemical methods. During the late 19th and early 20th centuries, physicists discovered subatomic components and structure inside the atom, thereby demonstrating that the atom was divisible. The principles of quantum mechanics were used to successfully model the atom.[4][5] Atoms are minuscule objects with proportionately tiny masses. Atoms can only be observed individually using special instruments such as the scanning tunneling microscope. Over 99.94% of an atoms mass is concentrated in the nucleus,[6] with protons and neutrons having roughly equal mass. Each element has at least one isotope with an unstable nucleus that can undergo radioactive decay. This can result in a transmutation that changes the number of protons or neutrons in a nucleus.[7] Electrons that are bound to atoms possess a set of stable energy levels, or orbitals, and can undergo transitions between them by absorbing or emitting photons that match the energy differences between the levels. The electrons determine the chemical properties of an element, and strongly influence an atoms magnetic properties. History Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny quantities has been around for millennia, but these ideas were founded in abstract, philosophical reasoning rather than experimentation and empirical observation. The nature of atoms in philosophy varied considerably over time and between cultures and schools, and often had spiritual elements. Nevertheless, the basic idea of the atom was adopted by scientists thousands of years later because it elegantly explained new discoveries in the field of chemistry.[8] References to the concept of atoms date back to ancient Greece and India. In India, the Ājīvika, Jain, and Cārvāka schools of atomism may date back to the 6th century BCE.[9] The Nyaya and Vaisheshika schools later developed theories on how atoms combined into more complex objects.[10] In the West, the references to atoms emerged in the 5th century BCE with Leucippus, whose student, Democritus, systematized his views. In approximately 450 BCE, Democritus coined the term átomos (Greek: ἄτομος), which means "uncuttable" or "the smallest indivisible particle of matter". Although the Indian and Greek concepts of the atom were based purely on philosophy, modern science has retained the name coined by Democritus.[8] Corpuscularianism is the postulate, expounded in the 13th-century by the alchemist Pseudo-Geber (Geber),[11] sometimes identified with Paul of Taranto, that all physical bodies possess an inner and outer layer of minute particles or corpuscles.[12] Corpuscularianism is similar to the theory of atomism, except that where atoms were supposed to be indivisible, corpuscles could in principle be divided. In this manner, for example, it was theorized that mercury could penetrate into metals and modify their inner structure.[13] Corpuscularianism stayed a dominant theory over the next several hundred years. In 1661, natural philosopher Robert Boyle published The Sceptical Chymist in which he argued that matter was composed of various combinations of different "corpuscules" or atoms, rather than the classical elements of air, earth, fire and water.[14] During the 1670s corpuscularianism was used by Isaac Newton in his development of the corpuscular theory of light.[12][15]
  • 30. Atom 28 Origin of scientific theory Further progress in the understanding of atoms did not occur until the science of chemistry began to develop. In 1789, French nobleman and scientific researcher Antoine Lavoisier discovered the law of conservation of mass and defined an element as a basic substance that could not be further broken down by the methods of chemistry.[16] In 1805, English instructor and natural philosopher John Dalton used the concept of atoms to explain why elements always react in ratios of small whole numbers (the law of multiple proportions) and why certain gases dissolved better in water than others. He proposed that each element consists of atoms of a single, unique type, and that these atoms Various atoms and molecules as depicted in John can join together to form chemical compounds.[17][18] Dalton is Daltons A New System of Chemical Philosophy considered the originator of modern atomic theory.[19] (1808), one of the earliest scientific works on atomic theory Daltons atomic hypothesis did not specify the size of atoms. Common sense indicated they must be very small, but nobody knew how small. Therefore it was a major landmark when in 1865 Johann Josef Loschmidt measured the size of the molecules that make up air. An additional line of reasoning in support of particle theory (and by extension atomic theory) began in 1827 when botanist Robert Brown used a microscope to look at dust grains floating in water and discovered that they moved about erratically—a phenomenon that became known as "Brownian motion". J. Desaulx suggested in 1877 that the phenomenon was caused by the thermal motion of water molecules, and in 1905 Albert Einstein produced the first mathematical analysis of the motion.[20][21][22] French physicist Jean Perrin used Einsteins work to experimentally determine the mass and dimensions of atoms, thereby conclusively verifying Daltons atomic theory.[23] In 1869, building upon earlier discoveries by such scientists as Lavoisier, Dmitri Mendeleev published the first functional periodic table.[24] The table itself is a visual representation of the periodic law, which states that certain chemical properties of elements repeat periodically when arranged by atomic number.[25] Subcomponents and quantum theory The physicist J. J. Thomson, through his work on cathode rays in 1897, discovered the electron, and concluded that they were a component of every atom. Thus he overturned the belief that atoms are the indivisible, ultimate particles of matter.[26] Thomson postulated that the low mass, negatively charged electrons were distributed throughout the atom, possibly rotating in rings, with their charge balanced by the Mendeleevs first periodic table (1869) presence of a uniform sea of positive charge. This later became known as the plum pudding model. In 1909, Hans Geiger and Ernest Marsden, under the direction of physicist Ernest Rutherford, bombarded a sheet of gold foil with alpha rays—by then known to be positively charged helium atoms—and discovered that a small percentage of these particles were deflected through much larger angles than was predicted using Thomsons proposal. Rutherford interpreted the gold foil experiment as suggesting that the positive charge of a heavy gold atom and most of its mass was concentrated in a nucleus at the center of the atom—the Rutherford model.[27]
  • 31. Atom 29 While experimenting with the products of radioactive decay, in 1913 radiochemist Frederick Soddy discovered that there appeared to be more than one type of atom at each position on the periodic table.[28] The term isotope was coined by Margaret Todd as a suitable name for different atoms that belong to the same element. J.J. Thomson created a technique for separating atom types through his work on ionized gases, which subsequently led to the discovery of stable isotopes.[29] Meanwhile, in 1913, physicist Niels Bohr suggested that the electrons were confined into clearly defined, quantized orbits, and could jump between these, but could not freely spiral inward or outward in intermediate states.[30] An electron must absorb or emit specific amounts of energy to transition between these fixed orbits. When the light from a heated material was passed through a prism, it produced a multi-colored spectrum. The appearance of fixed lines in this spectrum was successfully explained by these orbital transitions.[31] Later in the same year Henry Moseley provided additional experimental evidence in favor of Niels Bohrs theory. These results A Bohr model of the hydrogen atom, showing an refined Ernest Rutherfords and Antonius Van den Broeks model, electron jumping between fixed orbits and which proposed that the atom contains in its nucleus a number of emitting a photon of energy with a specific positive nuclear charges that is equal to its (atomic) number in the frequency periodic table. Until these experiments, atomic number was not known to be a physical and experimental quantity. That it is equal to the atomic nuclear charge remains the accepted atomic model today.[32] Chemical bonds between atoms were now explained, by Gilbert Newton Lewis in 1916, as the interactions between their constituent electrons.[33] As the chemical properties of the elements were known to largely repeat themselves according to the periodic law,[34] in 1919 the American chemist Irving Langmuir suggested that this could be explained if the electrons in an atom were connected or clustered in some manner. Groups of electrons were thought to occupy a set of electron shells about the nucleus.[35] The Stern–Gerlach experiment of 1922 provided further evidence of the quantum nature of the atom. When a beam of silver atoms was passed through a specially shaped magnetic field, the beam was split based on the direction of an atoms angular momentum, or spin. As this direction is random, the beam could be expected to spread into a line. Instead, the beam was split into two parts, depending on whether the atomic spin was oriented up or down.[36] In 1924, Louis de Broglie proposed that all particles behave to an extent like waves. In 1926, Erwin Schrödinger used this idea to develop a mathematical model of the atom that described the electrons as three-dimensional waveforms rather than point particles. A consequence of using waveforms to describe particles is that it is mathematically impossible to obtain precise values for both the position and momentum of a particle at the same time; this became known as the uncertainty principle, formulated by Werner Heisenberg in 1926. In this concept, for a given accuracy in measuring a position one could only obtain a range of probable values for momentum, and vice versa. This model was able to explain observations of atomic behavior that previous models could not, such as certain structural and spectral patterns of atoms larger than hydrogen. Thus, the planetary model of the atom was discarded in favor of one that described atomic orbital zones around the nucleus where a given electron is most likely to be observed.[37][38]
  • 32. Atom 30 The development of the mass spectrometer allowed the exact mass of atoms to be measured. The device uses a magnet to bend the trajectory of a beam of ions, and the amount of deflection is determined by the ratio of an atoms mass to its charge. The chemist Francis William Aston used this instrument to show that isotopes had different masses. The atomic mass of these isotopes varied by integer amounts, called the whole number rule.[39] The explanation for these different isotopes awaited the discovery of the neutron, a neutral-charged particle with a mass similar to the proton, by the physicist James Chadwick in 1932. Isotopes were then explained as elements with the same number of protons, but different numbers of neutrons within the nucleus.[40] Schematic diagram of a simple mass spectrometer Fission, high-energy physics and condensed matter In 1938, the German chemist Otto Hahn, a student of Rutherford, directed neutrons onto uranium atoms expecting to get transuranium elements. Instead, his chemical experiments showed barium as a product.[41] A year later, Lise Meitner and her nephew Otto Frisch verified that Hahns result were the first experimental nuclear fission.[42][43] In 1944, Hahn received the Nobel prize in chemistry. Despite Hahns efforts, the contributions of Meitner and Frisch were not recognized.[44] In the 1950s, the development of improved particle accelerators and particle detectors allowed scientists to study the impacts of atoms moving at high energies.[45] Neutrons and protons were found to be hadrons, or composites of smaller particles called quarks. Standard models of nuclear physics were developed that successfully explained the properties of the nucleus in terms of these sub-atomic particles and the forces that govern their interactions.[46] Components Subatomic particles Though the word atom originally denoted a particle that cannot be cut into smaller particles, in modern scientific usage the atom is composed of various subatomic particles. The constituent particles of an atom are the electron, the proton and the neutron. However, the hydrogen-1 atom has no neutrons and a positive hydrogen ion has no electrons. The electron is by far the least massive of these particles at 9.11 × 10−31 kg, with a negative electrical charge and a size that is too small to be measured using available techniques.[47] Protons have a positive charge and a mass 1,836 times that of the electron, at 1.6726 × 10−27 kg, although this can be reduced by changes to the energy binding the proton into an atom. Neutrons have no electrical charge and have a free mass of 1,839 times the mass of electrons,[48] or 1.6929 × 10−27 kg. Neutrons and protons have comparable dimensions—on the order of 2.5 × 10−15 m—although the surface of these particles is not sharply defined.[49] In the Standard Model of physics, electrons are truly elementary particles with no internal structure. However, both protons and neutrons are composite particles composed of elementary particles called quarks. There are two types of quarks in atoms, each having a fractional electric charge. Protons are composed of two up quarks (each with charge +2⁄3) and one down quark (with a charge of −1⁄3). Neutrons consist of one up quark and two down quarks. This distinction accounts for the difference in mass and charge between the two particles.[50][51] The quarks are held together by the strong interaction (or strong force), which is mediated by gluons. The protons and neutrons, in turn, are held to each other in the nucleus by the nuclear force, which is a residuum of the strong force that has somewhat different range-properties (see the article on the nuclear force for more). The gluon is a
  • 33. Atom 31 member of the family of gauge bosons, which are elementary particles that mediate physical forces.[50][51] Nucleus All the bound protons and neutrons in an atom make up a tiny atomic nucleus, and are collectively called nucleons. The radius of a nucleus is approximately equal to , where A is the total number of nucleons.[52] This is much smaller than the radius of the atom, which is on the order of 105 fm. The nucleons are bound together by a short-ranged attractive potential called the residual strong force. At distances smaller than 2.5 fm this force is much more powerful than the electrostatic force The binding energy needed for a nucleon to escape the nucleus, for various isotopes that causes positively charged protons to repel each other.[53] Atoms of the same element have the same number of protons, called the atomic number. Within a single element, the number of neutrons may vary, determining the isotope of that element. The total number of protons and neutrons determine the nuclide. The number of neutrons relative to the protons determines the stability of the nucleus, with certain isotopes undergoing radioactive decay.[54] The neutron and the proton are different types of fermions. The Pauli exclusion principle is a quantum mechanical effect that prohibits identical fermions, such as multiple protons, from occupying the same quantum physical state at the same time. Thus every proton in the nucleus must occupy a different state, with its own energy level, and the same rule applies to all of the neutrons. This prohibition does not apply to a proton and neutron occupying the same quantum state.[55] For atoms with low atomic numbers, a nucleus that has a different number of protons than neutrons can potentially drop to a lower energy state through a radioactive decay that causes the number of protons and neutrons to more closely match. As a result, atoms with roughly matching numbers of protons and neutrons are more stable against decay. However, with increasing atomic number, the mutual repulsion of the protons requires an increasing proportion of neutrons to maintain the stability of the nucleus, which modifies this trend. Thus, there are no stable nuclei with equal proton and neutron numbers above atomic number Z = 20 (calcium); and as Z increases toward the heaviest nuclei, the ratio of neutrons per proton required for stability increases to about 1.5.[55]
  • 34. Atom 32 The number of protons and neutrons in the atomic nucleus can be modified, although this can require very high energies because of the strong force. Nuclear fusion occurs when multiple atomic particles join to form a heavier nucleus, such as through the energetic collision of two nuclei. For example, at the core of the Sun protons require energies of 3–10 keV to overcome their mutual repulsion—the coulomb barrier—and fuse together into a single nucleus.[56] Nuclear fission is the opposite process, causing a nucleus to split into two smaller nuclei—usually through radioactive decay. The nucleus can also be modified through bombardment by high energy subatomic particles or photons. If this modifies the number of protons in a nucleus, the atom changes to a different chemical element.[57][58] If the mass of the nucleus following a fusion reaction is less than the Illustration of a nuclear fusion process that forms sum of the masses of the separate particles, then the difference between a deuterium nucleus, consisting of a proton and a these two values can be emitted as a type of usable energy (such as a neutron, from two protons. A positron (e+)—an gamma ray, or the kinetic energy of a beta particle), as described by antimatter electron—is emitted along with an 2 electron neutrino. Albert Einsteins mass–energy equivalence formula, E = mc , where m is the mass loss and c is the speed of light. This deficit is part of the binding energy of the new nucleus, and it is the non-recoverable loss of the energy that causes the fused particles to remain together in a state that requires this energy to separate.[59] The fusion of two nuclei that create larger nuclei with lower atomic numbers than iron and nickel—a total nucleon number of about 60—is usually an exothermic process that releases more energy than is required to bring them together.[60] It is this energy-releasing process that makes nuclear fusion in stars a self-sustaining reaction. For heavier nuclei, the binding energy per nucleon in the nucleus begins to decrease. That means fusion processes producing nuclei that have atomic numbers higher than about 26, and atomic masses higher than about 60, is an endothermic process. These more massive nuclei can not undergo an energy-producing fusion reaction that can sustain the hydrostatic equilibrium of a star.[55] Electron cloud The electrons in an atom are attracted to the protons in the nucleus by the electromagnetic force. This force binds the electrons inside an electrostatic potential well surrounding the smaller nucleus, which means that an external source of energy is needed for the electron to escape. The closer an electron is to the nucleus, the greater the attractive force. Hence electrons bound near the center of the potential well require more energy to escape than those at greater separations. Electrons, like other particles, have properties of both a particle and a A potential well, showing, according to classical wave. The electron cloud is a region inside the potential well where mechanics, the minimum energy V(x) needed to each electron forms a type of three-dimensional standing wave—a reach each position x. Classically, a particle with energy E is constrained to a range of positions wave form that does not move relative to the nucleus. This behavior is between x1 and x2. defined by an atomic orbital, a mathematical function that characterises the probability that an electron appears to be at a particular location when its position is measured.[61] Only a discrete (or quantized) set of these orbitals exist around the nucleus, as other possible wave patterns rapidly decay into a more stable form.[62] Orbitals can have one or more ring or node structures, and they differ from each other in size, shape and orientation.[63]
  • 35. Atom 33 Each atomic orbital corresponds to a particular energy level of the electron. The electron can change its state to a higher energy level by absorbing a photon with sufficient energy to boost it into the new quantum state. Likewise, through spontaneous emission, an electron in Wave functions of the first five atomic orbitals. a higher energy state can drop to a lower energy state while radiating The three 2p orbitals each display a single the excess energy as a photon. These characteristic energy values, angular node that has an orientation and a defined by the differences in the energies of the quantum states, are minimum at the center. responsible for atomic spectral lines.[62] The amount of energy needed to remove or add an electron—the electron binding energy—is far less than the binding energy of nucleons. For example, it requires only 13.6 eV to strip a ground-state electron from a hydrogen atom,[64] compared to 2.23 million eV for splitting a deuterium nucleus.[65] Atoms are electrically neutral if they have an equal number of protons and electrons. Atoms that have either a deficit or a surplus of electrons are called ions. Electrons that are farthest from the nucleus may be transferred to other nearby atoms or shared between atoms. By this mechanism, atoms are able to bond into molecules and other types of chemical compounds like ionic and covalent network crystals.[66] Properties Nuclear properties By definition, any two atoms with an identical number of protons in their nuclei belong to the same chemical element. Atoms with equal numbers of protons but a different number of neutrons are different isotopes of the same element. For example, all hydrogen atoms admit exactly one proton, but isotopes exist with no neutrons (hydrogen-1, by far the most common form,[67] also called protium), one neutron (deuterium), two neutrons (tritium) and more than two neutrons. The known elements form a set of atomic numbers, from the single proton element hydrogen up to the 118-proton element ununoctium.[68] All known isotopes of elements with atomic numbers greater than 82 are radioactive.[69][70] About 339 nuclides occur naturally on Earth,[71] of which 255 (about 75%) have not been observed to decay, and are referred to as "stable isotopes". However, only 90 of these nuclides are stable to all decay, even in theory. Another 165 (bringing the total to 255) have not been observed to decay, even though in theory it is energetically possible. These are also formally classified as "stable". An additional 33 radioactive nuclides have half-lives longer than 80 million years, and are long-lived enough to be present from the birth of the solar system. This collection of 288 nuclides are known as primordial nuclides. Finally, an additional 51 short-lived nuclides are known to occur naturally, as daughter products of primordial nuclide decay (such as radium from uranium), or else as products of natural energetic processes on Earth, such as cosmic ray bombardment (for example, carbon-14).[72][73] For 80 of the chemical elements, at least one stable isotope exists. As a rule, there is only a handful of stable isotopes for each of these elements, the average being 3.2 stable isotopes per element. Twenty-six elements have only a single stable isotope, while the largest number of stable isotopes observed for any element is ten, for the element tin. Elements 43, 61, and all elements numbered 83 or higher have no stable isotopes.[74] Stability of isotopes is affected by the ratio of protons to neutrons, and also by the presence of certain "magic numbers" of neutrons or protons that represent closed and filled quantum shells. These quantum shells correspond to a set of energy levels within the shell model of the nucleus; filled shells, such as the filled shell of 50 protons for tin, confers unusual stability on the nuclide. Of the 255 known stable nuclides, only four have both an odd number of protons and odd number of neutrons: hydrogen-2 (deuterium), lithium-6, boron-10 and nitrogen-14. Also, only four naturally occurring, radioactive odd-odd nuclides have a half-life over a billion years: potassium-40, vanadium-50, lanthanum-138 and tantalum-180m. Most odd-odd nuclei are highly unstable with respect to beta decay, because the
  • 36. Atom 34 decay products are even-even, and are therefore more strongly bound, due to nuclear pairing effects.[74] Mass The large majority of an atoms mass comes from the protons and neutrons that make it up. The total number of these particles (called "nucleons") in a given atom is called the mass number. The mass number is a simple whole number, and has units of "nucleons." An example of use of a mass number is "carbon-12," which has 12 nucleons (six protons and six neutrons). The actual mass of an atom at rest is often expressed using the unified atomic mass unit (u), which is also called a dalton (Da). This unit is defined as a twelfth of the mass of a free neutral atom of carbon-12, which is approximately 1.66 × 10−27 kg.[75] Hydrogen-1, the lightest isotope of hydrogen and the atom with the lowest mass, has an atomic weight of 1.007825 u.[76] The value of this number is called the atomic mass. A given atom has an atomic mass approximately equal (within 1%) to its mass number times the mass of the atomic mass unit. However, this number will not be an exact whole number except in the case of carbon-12 (see below)[77] The heaviest stable atom is lead-208,[69] with a mass of 207.9766521 u.[78] As even the most massive atoms are far too light to work with directly, chemists instead use the unit of moles. One mole of atoms of any element always has the same number of atoms (about 6.022 × 1023). This number was chosen so that if an element has an atomic mass of 1 u, a mole of atoms of that element has a mass close to one gram. Because of the definition of the unified atomic mass unit, each carbon-12 atom has an atomic mass of exactly 12 u, and so a mole of carbon-12 atoms weighs exactly 0.012 kg.[75] Shape and size Atoms lack a well-defined outer boundary, so their dimensions are usually described in terms of an atomic radius. This is a measure of the distance out to which the electron cloud extends from the nucleus. However, this assumes the atom to exhibit a spherical shape, which is only obeyed for atoms in vacuum or free space. Atomic radii may be derived from the distances between two nuclei when the two atoms are joined in a chemical bond. The radius varies with the location of an atom on the atomic chart, the type of chemical bond, the number of neighboring atoms (coordination number) and a quantum mechanical property known as spin.[79] On the periodic table of the elements, atom size tends to increase when moving down columns, but decrease when moving across rows (left to right).[80] Consequently, the smallest atom is helium with a radius of 32 pm, while one of the largest is caesium at 225 pm.[81] When subjected to external fields, like an electrical field, the shape of an atom may deviate from that of a sphere. The deformation depends on the field magnitude and the orbital type of outer shell electrons, as shown by group-theoretical considerations. Aspherical deviations might be elicited for instance in crystals, where large crystal-electrical fields may occur at low-symmetry lattice sites.[82] Significant ellipsoidal deformations have recently been shown to occur for sulfur ions in pyrite-type compounds.[83] Atomic dimensions are thousands of times smaller than the wavelengths of light (400–700 nm) so they can not be viewed using an optical microscope. However, individual atoms can be observed using a scanning tunneling microscope. To visualize the minuteness of the atom, consider that a typical human hair is about 1 million carbon atoms in width.[84] A single drop of water contains about 2 sextillion (2 × 1021) atoms of oxygen, and twice the number of hydrogen atoms.[85] A single carat diamond with a mass of 2 × 10−4 kg contains about 10 sextillion (1022) atoms of carbon.[86] If an apple were magnified to the size of the Earth, then the atoms in the apple would be approximately the size of the original apple.[87]
  • 37. Atom 35 Radioactive decay Every element has one or more isotopes that have unstable nuclei that are subject to radioactive decay, causing the nucleus to emit particles or electromagnetic radiation. Radioactivity can occur when the radius of a nucleus is large compared with the radius of the strong force, which only acts over distances on the order of 1 fm.[88] The most common forms of radioactive decay are:[89][90] • Alpha decay is caused when the nucleus emits an alpha particle, which is a helium nucleus consisting of two protons and two neutrons. The result of the emission is a new element with a lower atomic number. • Beta decay is regulated by the weak force, and results from a transformation of a neutron into a proton, or a proton into a neutron. The first is accompanied by the emission of an electron and an antineutrino, while the second causes the This diagram shows the half-life (T½) of various isotopes with Z protons and N emission of a positron and a neutrino. neutrons. The electron or positron emissions are called beta particles. Beta decay either increases or decreases the atomic number of the nucleus by one. • Gamma decay results from a change in the energy level of the nucleus to a lower state, resulting in the emission of electromagnetic radiation. This can occur following the emission of an alpha or a beta particle from radioactive decay. Other more rare types of radioactive decay include ejection of neutrons or protons or clusters of nucleons from a nucleus, or more than one beta particle, or result (through internal conversion) in production of high-speed electrons that are not beta rays, and high-energy photons that are not gamma rays. Each radioactive isotope has a characteristic decay time period—the half-life—that is determined by the amount of time needed for half of a sample to decay. This is an exponential decay process that steadily decreases the proportion of the remaining isotope by 50% every half-life. Hence after two half-lives have passed only 25% of the isotope is present, and so forth.[88] Magnetic moment Elementary particles possess an intrinsic quantum mechanical property known as spin. This is analogous to the angular momentum of an object that is spinning around its center of mass, although strictly speaking these particles are believed to be point-like and cannot be said to be rotating. Spin is measured in units of the reduced Planck constant (ħ), with electrons, protons and neutrons all having spin ½ ħ, or "spin-½". In an atom, electrons in motion around the nucleus possess orbital angular momentum in addition to their spin, while the nucleus itself possesses angular momentum due to its nuclear spin.[91]
  • 38. Atom 36 The magnetic field produced by an atom—its magnetic moment—is determined by these various forms of angular momentum, just as a rotating charged object classically produces a magnetic field. However, the most dominant contribution comes from spin. Due to the nature of electrons to obey the Pauli exclusion principle, in which no two electrons may be found in the same quantum state, bound electrons pair up with each other, with one member of each pair in a spin up state and the other in the opposite, spin down state. Thus these spins cancel each other out, reducing the total magnetic dipole moment to zero in some atoms with even number of electrons.[92] In ferromagnetic elements such as iron, an odd number of electrons leads to an unpaired electron and a net overall magnetic moment. The orbitals of neighboring atoms overlap and a lower energy state is achieved when the spins of unpaired electrons are aligned with each other, a process known as an exchange interaction. When the magnetic moments of ferromagnetic atoms are lined up, the material can produce a measurable macroscopic field. Paramagnetic materials have atoms with magnetic moments that line up in random directions when no magnetic field is present, but the magnetic moments of the individual atoms line up in the presence of a field.[92][93] The nucleus of an atom can also have a net spin. Normally these nuclei are aligned in random directions because of thermal equilibrium. However, for certain elements (such as xenon-129) it is possible to polarize a significant proportion of the nuclear spin states so that they are aligned in the same direction—a condition called hyperpolarization. This has important applications in magnetic resonance imaging.[94][95] Energy levels When an electron is bound to an atom, it has a potential energy that is inversely proportional to its distance from the nucleus. This is measured by the amount of energy needed to unbind the electron from the atom, and is usually given in units of electronvolts (eV). In the quantum mechanical model, a bound electron can only occupy a set of states centered on the nucleus, and each state corresponds to a specific energy level. The lowest energy state of a bound electron is called the ground state, while an electron at a higher energy level is in an excited state.[96] For an electron to transition between two different states, it must absorb or emit a photon at an energy matching the difference in the potential energy of those levels. The energy of an emitted photon is proportional to its frequency, so these specific energy levels appear as distinct bands in the electromagnetic spectrum.[97] Each element has a characteristic spectrum that can depend on the nuclear charge, subshells filled by electrons, the electromagnetic interactions between the electrons and other factors.[98] When a continuous spectrum of energy is passed through a gas or plasma, some of the photons are absorbed by atoms, causing electrons to change their energy level. Those excited electrons that remain bound to their atom spontaneously emit this energy as a photon, traveling in a random direction, and An example of absorption lines in a spectrum so drop back to lower energy levels. Thus the atoms behave like a filter that forms a series of dark absorption bands in the energy output. (An observer viewing the atoms from a view that does not include the continuous spectrum in the background, instead sees a series of emission lines from the photons emitted by the atoms.) Spectroscopic measurements of the strength and width of spectral lines allow the composition and physical properties of a substance to be determined.[99] Close examination of the spectral lines reveals that some display a fine structure splitting. This occurs because of spin-orbit coupling, which is an interaction between the spin and motion of the outermost electron.[100] When an atom is in an external magnetic field, spectral lines become split into three or more components; a phenomenon called the Zeeman effect. This is caused by the interaction of the magnetic field with the magnetic moment of the atom and its electrons. Some atoms can have multiple electron configurations with the same energy level, which thus appear as a single spectral line. The interaction of the magnetic field with the atom shifts these electron
  • 39. Atom 37 configurations to slightly different energy levels, resulting in multiple spectral lines.[101] The presence of an external electric field can cause a comparable splitting and shifting of spectral lines by modifying the electron energy levels, a phenomenon called the Stark effect.[102] If a bound electron is in an excited state, an interacting photon with the proper energy can cause stimulated emission of a photon with a matching energy level. For this to occur, the electron must drop to a lower energy state that has an energy difference matching the energy of the interacting photon. The emitted photon and the interacting photon then move off in parallel and with matching phases. That is, the wave patterns of the two photons are synchronized. This physical property is used to make lasers, which can emit a coherent beam of light energy in a narrow frequency band.[103] Valence and bonding behavior The outermost electron shell of an atom in its uncombined state is known as the valence shell, and the electrons in that shell are called valence electrons. The number of valence electrons determines the bonding behavior with other atoms. Atoms tend to chemically react with each other in a manner that fills (or empties) their outer valence shells.[104] For example, a transfer of a single electron between atoms is a useful approximation for bonds that form between atoms with one-electron more than a filled shell, and others that are one-electron short of a full shell, such as occurs in the compound sodium chloride and other chemical ionic salts. However, many elements display multiple valences, or tendencies to share differing numbers of electrons in different compounds. Thus, chemical bonding between these elements takes many forms of electron-sharing that are more than simple electron transfers. Examples include the element carbon and the organic compounds.[105] The chemical elements are often displayed in a periodic table that is laid out to display recurring chemical properties, and elements with the same number of valence electrons form a group that is aligned in the same column of the table. (The horizontal rows correspond to the filling of a quantum shell of electrons.) The elements at the far right of the table have their outer shell completely filled with electrons, which results in chemically inert elements known as the noble gases.[106][107] States Quantities of atoms are found in different states of matter that depend on the physical conditions, such as temperature and pressure. By varying the conditions, materials can transition between solids, liquids, gases and plasmas. [108] Within a state, a material can also exist in different phases. An example of this is solid carbon, which can exist as graphite or diamond.[109] At temperatures close to absolute zero, atoms can form a Snapshots illustrating the formation of a Bose–Einstein condensate, at which point quantum mechanical effects, Bose–Einstein condensate which are normally only observed at the atomic scale, become apparent on a macroscopic scale.[110][111] This super-cooled collection of atoms then behaves as a single super atom, which may allow fundamental checks of quantum mechanical behavior.[112]
  • 40. Atom 38 Identification The scanning tunneling microscope is a device for viewing surfaces at the atomic level. It uses the quantum tunneling phenomenon, which allows particles to pass through a barrier that would normally be insurmountable. Electrons tunnel through the vacuum between two planar metal electrodes, on each of which is an adsorbed atom, providing a tunneling-current density that can be measured. Scanning one atom (taken as the tip) as it moves past the other (the sample) permits plotting of tip displacement versus lateral separation for a constant current. The calculation shows the extent to which scanning-tunneling-microscope images of an individual atom are visible. It confirms that for low bias, the microscope images the space-averaged dimensions of the electron orbitals across closely Scanning tunneling microscope image showing packed energy levels—the Fermi level local density of states.[113][114] the individual atoms making up this gold (100) surface. Reconstruction causes the surface atoms An atom can be ionized by removing one of its electrons. The electric to deviate from the bulk crystal structure and arrange in columns several atoms wide with pits charge causes the trajectory of an atom to bend when it passes through between them. a magnetic field. The radius by which the trajectory of a moving ion is turned by the magnetic field is determined by the mass of the atom. The mass spectrometer uses this principle to measure the mass-to-charge ratio of ions. If a sample contains multiple isotopes, the mass spectrometer can determine the proportion of each isotope in the sample by measuring the intensity of the different beams of ions. Techniques to vaporize atoms include inductively coupled plasma atomic emission spectroscopy and inductively coupled plasma mass spectrometry, both of which use a plasma to vaporize samples for analysis.[115] A more area-selective method is electron energy loss spectroscopy, which measures the energy loss of an electron beam within a transmission electron microscope when it interacts with a portion of a sample. The atom-probe tomograph has sub-nanometer resolution in 3-D and can chemically identify individual atoms using time-of-flight mass spectrometry.[116] Spectra of excited states can be used to analyze the atomic composition of distant stars. Specific light wavelengths contained in the observed light from stars can be separated out and related to the quantized transitions in free gas atoms. These colors can be replicated using a gas-discharge lamp containing the same element.[117] Helium was discovered in this way in the spectrum of the Sun 23 years before it was found on Earth.[118] Origin and current state Atoms form about 4% of the total energy density of the observable universe, with an average density of about 0.25 atoms/m3.[119] Within a galaxy such as the Milky Way, atoms have a much higher concentration, with the density of matter in the interstellar medium (ISM) ranging from 105 to 109 atoms/m3.[120] The Sun is believed to be inside the Local Bubble, a region of highly ionized gas, so the density in the solar neighborhood is only about 103 atoms/m3.[121] Stars form from dense clouds in the ISM, and the evolutionary processes of stars result in the steady enrichment of the ISM with elements more massive than hydrogen and helium. Up to 95% of the Milky Ways atoms are concentrated inside stars and the total mass of atoms forms about 10% of the mass of the galaxy.[122] (The remainder of the mass is an unknown dark matter.)[123]
  • 41. Atom 39 Nucleosynthesis Stable protons and electrons appeared one second after the Big Bang. During the following three minutes, Big Bang nucleosynthesis produced most of the helium, lithium, and deuterium in the universe, and perhaps some of the beryllium and boron.[124][125][126] The first atoms (complete with bound electrons) were theoretically created 380,000 years after the Big Bang—an epoch called recombination, when the expanding universe cooled enough to allow electrons to become attached to nuclei.[127] Since the Big Bang, which produced no carbon, atomic nuclei have been combined in stars through the process of nuclear fusion to produce more of the element helium, and (via the triple alpha process) the sequence of elements from carbon up to iron.[128] Isotopes such as lithium-6, as well as some beryllium and boron are generated in space through cosmic ray spallation.[129] This occurs when a high-energy proton strikes an atomic nucleus, causing large numbers of nucleons to be ejected. Elements heavier than iron were produced in supernovae through the r-process and in AGB stars through the s-process, both of which involve the capture of neutrons by atomic nuclei.[130] Elements such as lead formed largely through the radioactive decay of heavier elements.[131] Earth Most of the atoms that make up the Earth and its inhabitants were present in their current form in the nebula that collapsed out of a molecular cloud to form the Solar System. The rest are the result of radioactive decay, and their relative proportion can be used to determine the age of the Earth through radiometric dating.[132][133] Most of the helium in the crust of the Earth (about 99% of the helium from gas wells, as shown by its lower abundance of helium-3) is a product of alpha decay.[134] There are a few trace atoms on Earth that were not present at the beginning (i.e., not "primordial"), nor are results of radioactive decay. Carbon-14 is continuously generated by cosmic rays in the atmosphere.[135] Some atoms on Earth have been artificially generated either deliberately or as by-products of nuclear reactors or explosions.[136][137] Of the transuranic elements—those with atomic numbers greater than 92—only plutonium and neptunium occur naturally on Earth.[138][139] Transuranic elements have radioactive lifetimes shorter than the current age of the Earth[140] and thus identifiable quantities of these elements have long since decayed, with the exception of traces of plutonium-244 possibly deposited by cosmic dust.[132] Natural deposits of plutonium and neptunium are produced by neutron capture in uranium ore.[141] The Earth contains approximately 1.33 × 1050 atoms.[142] In the planets atmosphere, small numbers of independent atoms of noble gases exist, such as argon and neon. The remaining 99% of the atmosphere is bound in the form of molecules, including carbon dioxide and diatomic oxygen and nitrogen. At the surface of the Earth, atoms combine to form various compounds, including water, salt, silicates and oxides. Atoms can also combine to create materials that do not consist of discrete molecules, including crystals and liquid or solid metals.[143][144] This atomic matter forms networked arrangements that lack the particular type of small-scale interrupted order associated with molecular matter.[145]
  • 42. Atom 40 Rare and theoretical forms While isotopes with atomic numbers higher than lead (82) are known to be radioactive, an "island of stability" has been proposed for some elements with atomic numbers above 103. These superheavy elements may have a nucleus that is relatively stable against radioactive decay.[146] The most likely candidate for a stable superheavy atom, unbihexium, has 126 protons and 184 neutrons.[147] Each particle of matter has a corresponding antimatter particle with the opposite electrical charge. Thus, the positron is a positively charged antielectron and the antiproton is a negatively charged equivalent of a proton. When a matter and corresponding antimatter particle meet, they annihilate each other. Because of this, along with an imbalance between the number of matter and antimatter particles, the latter are rare in the universe. (The first causes of this imbalance are not yet fully understood, although the baryogenesis theories may offer an explanation.) As a result, no antimatter atoms have been discovered in nature.[148][149] However, in 1996, antihydrogen, the antimatter counterpart of hydrogen, was synthesized at the CERN laboratory in Geneva.[150][151] Other exotic atoms have been created by replacing one of the protons, neutrons or electrons with other particles that have the same charge. For example, an electron can be replaced by a more massive muon, forming a muonic atom. These types of atoms can be used to test the fundamental predictions of physics.[152][153][154] Notes [1] Leigh, G. J., ed. (1990). International Union of Pure and Applied Chemistry, Commission on the Nomenclature of Inorganic Chemistry, Nomenclature of Organic Chemistry – Recommendations 1990. Oxford: Blackwell Scientific Publications. p. 35. ISBN 0-08-022369-9. "An atom is the smallest unit quantity of an element that is capable of existence whether alone or in chemical combination with other atoms of the same or other elements." [2] Liddell, Henry George; Scott, Robert. "A Greek-English Lexicon" (http:/ / www. perseus. tufts. edu/ hopper/ text?doc=Perseus:text:1999. 04. 0057:entry=te/ mnw1). Perseus Digital Library. . [3] Liddell, Henry George; Scott, Robert. "ἄτομος" (http:/ / www. perseus. tufts. edu/ hopper/ text?doc=Perseus:text:1999. 04. 0057:entry=a)/ tomos). A Greek-English Lexicon. Perseus Digital Library. . Retrieved 2010-06-21. [4] Haubold, Hans; Mathai, A.M. (1998). "Microcosmos: From Leucippus to Yukawa" (http:/ / web. archive. org/ web/ 20090505115001/ http:/ / www. columbia. edu/ ~ah297/ unesa/ universe/ universe-chapter3. html). Structure of the Universe. . Retrieved 2008-01-17. [5] Harrison 2003, pp. 123–139 [6] In the case of hydrogen-1, with a single electron and nucleon, the proton is , or 99.95% of the total atomic mass. All other nuclides (isotopes of hydrogen and all other elements) have more nucleons than electrons, so the fraction of mass taken by the nucleus is closer to 100% for all of these types of atoms, than for hydrogen-1. [7] "Radioactive Decays" (http:/ / www2. slac. stanford. edu/ vvc/ theory/ nuclearstability. html). Stanford Linear Accelerator Center. 15 June 2009. Archived (http:/ / web. archive. org/ web/ 20090607115741/ http:/ / www2. slac. stanford. edu/ vvc/ theory/ nuclearstability. html) from the original on 7 June 2009. . Retrieved 2009-07-04. [8] Ponomarev 1993, pp. 14–15 [9] McEvilley 2002, p. 317 [10] King 1999, pp. 105–107 [11] Moran 2005, p. 146 [12] Levere 2001, p. 7 [13] Pratt, Vernon (September 28, 2007). "The Mechanical Philosophy" (http:/ / www. vernonpratt. com/ conceptualisations/ d06bl2_1mechanical. htm). Reason, nature and the human being in the West. . Retrieved 2009-06-28. [14] Siegfried 2002, pp. 42–55 [15] Kemerling, Garth (August 8, 2002). "Corpuscularianism" (http:/ / www. philosophypages. com/ dy/ c9. htm). Philosophical Dictionary. . Retrieved 2009-06-17. [16] "Lavoisiers Elements of Chemistry" (http:/ / web. lemoyne. edu/ ~GIUNTA/ EA/ LAVPREFann. HTML). Elements and Atoms. Le Moyne College, Department of Chemistry. . Retrieved 2007-12-18. [17] Wurtz 1881, pp. 1–2 [18] Dalton 1808 [19] Roscoe 1895, pp. 129 [20] Einstein, Albert (1905). "Über die von der molekularkinetischen Theorie der Wärme geforderte Bewegung von in ruhenden Flüssigkeiten suspendierten Teilchen" (http:/ / www. zbp. univie. ac. at/ dokumente/ einstein2. pdf) (in German) (PDF). Annalen der Physik 322 (8): 549–560. Bibcode 1905AnP...322..549E. doi:10.1002/andp.19053220806. . Retrieved 2007-02-04. [21] Mazo 2002, pp. 1–7
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  • 48. Atom 46 References Book references • LAnnunziata, Michael F. (2003). Handbook of Radioactivity Analysis. Academic Press. ISBN 0-12-436603-1. OCLC 16212955. • Beyer, H. F.; Shevelko, V. P. (2003). Introduction to the Physics of Highly Charged Ions. CRC Press. ISBN 0-7503-0481-2. OCLC 47150433. • Choppin, Gregory R.; Liljenzin, Jan-Olov; Rydberg, Jan (2001). Radiochemistry and Nuclear Chemistry. Elsevier. ISBN 0-7506-7463-6. OCLC 162592180. • Dalton, J. (1808). A New System of Chemical Philosophy, Part 1. London and Manchester: S. Russell. • Demtröder, Wolfgang (2002). Atoms, Molecules and Photons: An Introduction to Atomic- Molecular- and Quantum Physics (1st ed.). Springer. ISBN 3-540-20631-0. OCLC 181435713. • Feynman, Richard (1995). Six Easy Pieces. The Penguin Group. ISBN 978-0-14-027666-4. OCLC 40499574. • Fowles, Grant R. (1989). Introduction to Modern Optics. Courier Dover Publications. ISBN 0-486-65957-7. OCLC 18834711. • Gangopadhyaya, Mrinalkanti (1981). Indian Atomism: History and Sources. Atlantic Highlands, New Jersey: Humanities Press. ISBN 0-391-02177-X. OCLC 10916778. • Goodstein, David L. (2002). States of Matter. Courier Dover Publications. ISBN 0-13-843557-X. • Harrison, Edward Robert (2003). Masks of the Universe: Changing Ideas on the Nature of the Cosmos. Cambridge University Press. ISBN 0-521-77351-2. OCLC 50441595. • Iannone, A. Pablo (2001). Dictionary of World Philosophy. Routledge. ISBN 0-415-17995-5. OCLC 44541769. • Jevremovic, Tatjana (2005). Nuclear Principles in Engineering. Springer. ISBN 0-387-23284-2. OCLC 228384008. • King, Richard (1999). Indian philosophy: an introduction to Hindu and Buddhist thought. Edinburgh University Press. ISBN 0-7486-0954-7. • Lequeux, James (2005). The Interstellar Medium. Springer. ISBN 3-540-21326-0. OCLC 133157789. • Levere, Trevor, H. (2001). Transforming Matter – A History of Chemistry for Alchemy to the Buckyball. The Johns Hopkins University Press. ISBN 0-8018-6610-3. • Liang, Z.-P.; Haacke, E. M. (1999). Webster, J. G.. ed (PDF). Encyclopedia of Electrical and Electronics Engineering: Magnetic Resonance Imaging ( pdf?arnumber=1233976). vol. 2. John Wiley & Sons. pp. 412–26. ISBN 0-471-13946-7. Retrieved 2008-01-09. • McEvilley, Thomas (2002). The shape of ancient thought: comparative studies in Greek and Indian philosophies. Allworth Press. ISBN 1-58115-203-5. • MacGregor, Malcolm H. (1992). The Enigmatic Electron. Oxford University Press. ISBN 0-19-521833-7. OCLC 223372888. • Manuel, Oliver (2001). Origin of Elements in the Solar System: Implications of Post-1957 Observations. Springer. ISBN 0-306-46562-0. OCLC 228374906. • Mazo, Robert M. (2002). Brownian Motion: Fluctuations, Dynamics, and Applications. Oxford University Press. ISBN 0-19-851567-7. OCLC 48753074. • Mills, Ian; Cvitaš, Tomislav; Homann, Klaus; Kallay, Nikola; Kuchitsu, Kozo (1993). Quantities, Units and Symbols in Physical Chemistry (2nd ed.). Oxford: International Union of Pure and Applied Chemistry, Commission on Physiochemical Symbols Terminology and Units, Blackwell Scientific Publications. ISBN 0-632-03583-8. OCLC 27011505. • Moran, Bruce T. (2005). Distilling Knowledge: Alchemy, Chemistry, and the Scientific Revolution. Harvard University Press. ISBN 0-674-01495-2. • Myers, Richard (2003). The Basics of Chemistry. Greenwood Press. ISBN 0-313-31664-3. OCLC 50164580.
  • 49. Atom 47 • Padilla, Michael J.; Miaoulis, Ioannis; Cyr, Martha (2002). Prentice Hall Science Explorer: Chemical Building Blocks. Upper Saddle River, New Jersey USA: Prentice-Hall, Inc.. ISBN 0-13-054091-9. OCLC 47925884. • Pais, Abraham (1986). Inward Bound: Of Matter and Forces in the Physical World. New York: Oxford University Press. ISBN 0-19-851971-0. • Pauling, Linus (1960). The Nature of the Chemical Bond. Cornell University Press. ISBN 0-8014-0333-2. OCLC 17518275. • Pfeffer, Jeremy I.; Nir, Shlomo (2000). Modern Physics: An Introductory Text. Imperial College Press. ISBN 1-86094-250-4. OCLC 45900880. • Ponomarev, Leonid Ivanovich (1993). The Quantum Dice. CRC Press. ISBN 0-7503-0251-8. OCLC 26853108. • Roscoe, Henry Enfield (1895). John Dalton and the Rise of Modern Chemistry ( books?id=FJMEAAAAYAAJ). Century science series. New York: Macmillan. Retrieved 2011-04-03. • Scerri, Eric R. (2007). The periodic table: its story and its significance. Oxford University Press US. ISBN 0-19-530573-6. • Shultis, J. Kenneth; Faw, Richard E. (2002). Fundamentals of Nuclear Science and Engineering. CRC Press. ISBN 0-8247-0834-2. OCLC 123346507. • Siegfried, Robert (2002). From Elements to Atoms: A History of Chemical Composition. DIANE. ISBN 0-87169-924-9. OCLC 186607849. • Sills, Alan D. (2003). Earth Science the Easy Way. Barrons Educational Series. ISBN 0-7641-2146-4. OCLC 51543743. • Smirnov, Boris M. (2003). Physics of Atoms and Ions. Springer. ISBN 0-387-95550-X. • Teresi, Dick (2003). Lost Discoveries: The Ancient Roots of Modern Science ( ?id=pheL_ubbXD0C&dq). Simon & Schuster. pp. 213–214. ISBN 0-7432-4379-X. • Various (2002). Lide, David R.. ed. Handbook of Chemistry & Physics ( (88th ed.). CRC. ISBN 0-8493-0486-5. OCLC 179976746. Archived ( from the original on 23 May 2008. Retrieved 2008-05-23. • Woan, Graham (2000). The Cambridge Handbook of Physics. Cambridge University Press. ISBN 0-521-57507-9. OCLC 224032426. • Wurtz, Charles Adolphe (1881). The Atomic Theory. New York: D. Appleton and company. ISBN 0-559-43636-X. • Zaider, Marco; Rossi, Harald H. (2001). Radiation Science for Physicians and Public Health Workers. Springer. ISBN 0-306-46403-9. OCLC 44110319. • Zumdahl, Steven S. (2002). Introductory Chemistry: A Foundation ( zumdahl/intro_chemistry/5e/students/protected/periodictables/pt/pt/pt_ar5.html) (5th ed.). Houghton Mifflin. ISBN 0-618-34342-3. OCLC 173081482. Archived ( pt/pt_ar5.html) from the original on 4 March 2008. Retrieved 2008-02-05. External links • Francis, Eden (2002). "Atomic Size" ( Clackamas Community College. Archived ( ch104-07/atomic_size.htm) from the original on 4 February 2007. Retrieved 2007-01-09. • Freudenrich, Craig C.. "How Atoms Work" ( How Stuff Works. Archived ( from the original on 8 January 2007. Retrieved 2007-01-09. • "The Atom" ( Free High School Science Texts: Physics. Wikibooks. Retrieved 2010-07-10.
  • 50. Atom 48 • Anonymous (2007). "The atom" ( Science aid+. Retrieved 2010-07-10.—a guide to the atom for teens. • Anonymous (2006-01-03). "Atoms and Atomic Structure" ( BBC. Archived ( A6672963) from the original on 2 January 2007. Retrieved 2007-01-11. • Various (2006-01-03). "Physics 2000, Table of Contents" ( pl?Type=TOC). University of Colorado. Archived ( from the original on 14 January 2008. Retrieved 2008-01-11. • Various (2006-02-03). "What does an atom look like?" ( einleitung_hauptseite_uk.html). University of Karlsruhe. Retrieved 2008-05-12. Chemical element A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. They are divided into metals and non-metals. Familiar examples of elements include carbon, oxygen (non-metals) together with aluminium, iron, copper, gold, mercury, and lead (metals). As of November 2011, 118 elements have been identified, the latest being The periodic table of the chemical elements [1] ununseptium in 2010. Of the 118 known elements, only the first 98 are known to occur naturally on Earth; 80 of them are stable, while the others are radioactive, decaying into lighter elements over various timescales from fractions of a second to billions of years. Those elements that do not occur naturally on Earth have been produced artificially as the synthetic products of man-made nuclear reactions. Hydrogen and helium are by far the most abundant elements in the universe. However, iron is the most abundant element (by mass) making up the Earth, and oxygen is the most common element in the Earths crust.[2] Although all known chemical matter is composed of these elements, chemical matter itself constitutes only about 15% of the matter in the universe. The remainder is dark matter, a mysterious substance which is not composed of chemical elements since it lacks protons, neutrons or electrons.[3] The chemical elements are thought to have been produced by various cosmic processes, including hydrogen, helium (and smaller amounts of lithium, beryllium and boron) created during the Big Bang and cosmic-ray spallation. Production of heavier elements, from carbon to the very heaviest elements, proceeds by stellar nucleosynthesis, and these were made available for later solar system and planetary formation by planetary nebulae and supernovae, which blast these elements into space.[4] The high abundance of oxygen, silicon, and iron on Earth reflect their common production in such stars, after the lighter gaseous elements and their compounds have been subtracted. While most elements are generally viewed as stable, a small amount of natural transformation of one element to another also occurs in the present time, through decay of radioactive elements as well as other natural nuclear processes.
  • 51. Chemical element 49 Relatively pure samples of isolated elements are uncommon in nature. While all of the 98 naturally occurring elements have been identified in mineral samples from the Earths crust, only a small minority of elements are found as recognizable, relative pure minerals. Among the more common of such "native elements" are copper, silver, gold, carbon (as coal, graphite, or diamonds), sulfur, and mercury. All but a few of the most inert elements, such as noble gases and noble metals, are usually found on Earth in chemically combined form, as chemical compounds. While about 32 of the chemical elements occur on Earth in native uncombined form, most of these occur as mixtures. For example, atmospheric air is primarily a mixture of nitrogen, oxygen, and argon, and native solid elements occur in alloys, such as that of iron and nickel. When two distinct elements are chemically combined, with the atoms held together by chemical bonds, the result is termed a chemical compound. Two thirds of the chemical elements occur on Earth only as compounds, and in the remaining third, often the compound forms of the element are most common. Chemical compounds may be composed of elements combined in exact whole-number ratios of atoms, as in water, table salt, and minerals as quartz, calcite, and some ores. However, chemical bonding of many types of elements results in crystalline solids and metallic alloys for which exact chemical formulas do not exist. The history of discovery and use of the elements began with primitive human societies that found native elements like copper and gold, and extracted (smelted) iron and a few other metals from their ores. Alchemists and chemists subsequently identified many more, with nearly all of the naturally-occurring elements known by 1900. The properties of the chemical elements are often summarized using the periodic table that organizes the elements by increasing atomic number into rows ("periods") in which the columns ("groups") share recurring ("periodic") physical and chemical properties. Either in its pure forms, or in various chemical compounds or mixtures, almost every element has at least one important human use. Save for short half-lived radioactive elements, all of the elements are available industrially, most to high degrees of purity. Around two dozen of the elements are essential to various kinds of biological life. Most rare elements on Earth are not needed by life (exceptions being selenium and iodine), while a few quite common ones (aluminium and titanium) are not used. Most organisms share element needs, with a few differences. For example, ocean algae use bromine but land plants and animals seem to need none, and all animals require sodium, but some plants do not. Just six elements—carbon, hydrogen, nitrogen, oxygen, calcium, and phosphorus—make up almost 99% of the mass of a human body (see composition of the human body for a complete list). In addition to the six major elements that compose most of the human body, humans require consumption of at least a dozen more elements in the form of certain chemical compounds. Description The lightest of the chemical elements are hydrogen and helium, both created by Big Bang nucleosynthesis during the first 20 minutes of the universe[5] in a ratio of around 3:1 by mass (approximately 12:1 by number of atoms). Almost all other elements found in nature, including some further hydrogen and helium created since then, were made by various natural or (at times) artificial methods of nucleosynthesis. On Earth, small amounts of new atoms are naturally produced in nucleogenic reactions, or in cosmogenic processes, such as cosmic ray spallation. New atoms are also naturally produced on Earth as radiogenic daughter isotopes of ongoing radioactive decay processes such as alpha decay, beta decay, spontaneous fission, cluster decay, and other rarer modes of decay. Of the 98 naturally occurring elements, those with atomic numbers 1 through 40 are all considered to be stable. Elements with atomic numbers 41 through 82 are apparently stable (except technetium, element 43 and promethium, element 61, which are unstable) but theoretically unstable, and thus possibly mildly radioactive. The half-lives of elements 41 through 82 are so long however that their radioactive decay has yet to be detected by experiment. These "theoretical radionuclides" have half-lives at least 100 million times longer than the estimated age of the universe. Elements with atomic numbers 83 through 98 are unstable to the point that their radioactive decay can be detected. Some of these elements, notably thorium (atomic number 90) and uranium (atomic number 92), have one or more
  • 52. Chemical element 50 isotopes with half-lives long enough to survive as remnants of the explosive stellar nucleosynthesis that produced the heavy elements before the formation of our solar system. For example, at over 1.9×1019 years, over a billion times longer than the current estimated age of the universe, bismuth-209 (atomic number 83) has the longest known alpha decay half-life of any naturally occurring element.[6][7] The very heaviest elements (those beyond californium, atomic number 98) undergo radioactive decay with half-lives so short that they do not occur in nature and have to be synthesized. As of 2010, there are 118 known elements (in this context, "known" means observed well-enough, even from just a few decay products, to have been differentiated from any other element).[8][9] Of these 118 elements, 98 occur naturally on Earth. Ten of these occur in extreme trace quantities: technetium, atomic number 43; promethium, number 61; astatine, number 85; francium, number 87; neptunium, number 93; plutonium, number 94; americium, number 95; curium, number 96; berkelium, number 97; and californium, number 98. These 98 elements have been detected in the universe at large, in the spectra of stars and also supernovae, where short-lived radioactive elements are newly being made. The first 98 elements have been detected directly on Earth as primordial nuclides present from the formation of the solar system, or as naturally-occurring fission or transmutation products of uranium and thorium. The remaining 24 heavier elements, not found today either on Earth or in astronomical spectra, have been derived artificially. All of the heavy elements that are derived solely through artificial means are radioactive, with very short half-lives; if any atoms of these elements were present at the formation of Earth, they are extremely likely to have already decayed, and if present in novae, have been in quantities too small to have been noted. Technetium was the first purportedly non-naturally occurring element to be synthesized, in 1937, although trace amounts of technetium have since been found in nature (and also the element may have been discovered naturally in 1925). This pattern of artificial production and later natural discovery has been repeated with several other radioactive naturally-occurring rare elements. Lists of the elements are available by name, by symbol, by atomic number, by density, by melting point, and by boiling point as well as Ionization energies of the elements. The nuclides of stable and radioactive elements are also available as a list of nuclides, sorted by length of half-life for those that are unstable. One of the most convenient, and certainly the most traditional presentation of the elements, is in form of periodic table, which groups elements with similar chemical properties (and usually also similar electronic structures) together. Atomic number The atomic number of an element is equal to the number of protons that defines the element. For example, all carbon atoms contain 6 protons in their nucleus; so the atomic number of carbon is 6. Carbon atoms may have different numbers of neutrons; atoms of the same element having different numbers of neutrons are known as isotopes of the element. The number of protons in the atomic nucleus also determines its electric charge, which in turn determines the number of electrons of the atom in its non-ionized state. The electrons are placed into atomic orbitals which determine the atoms various chemical properties. The number of neutrons in a nucleus usually has very little effect on an elements chemical properties (except in the case of hydrogen and deuterium). Thus, all carbon isotopes have nearly identical chemical properties because they all have six protons and six electrons, even though carbon atoms may differ in number of neutrons. It is for this reason that atomic number rather than mass number or atomic weight is considered the identifying characteristic of a chemical element. The symbol for atomic number is Z.
  • 53. Chemical element 51 Atomic mass and atomic weight The mass number of an element, A, is the number of nucleons (protons and neutrons) in the atomic nucleus. Different isotopes of a given element are distinguished by their mass numbers, which are conventionally written as a super-index on the left hand side of the atomic symbol (e.g., 238U). The mass number is always a simple whole number and has units of "nucleons." An example of use of a mass number is "magnesium-24," which has 24 nucleons (12 protons and 12 neutrons). Whereas the mass number simply counts the total number of neutrons and protons and is thus a natural (or whole) number, the atomic mass of a single isotope is a real number. In general, it differs in value when expressed in u for a given nuclide (or isotope) slightly from the mass number, since the mass of the protons and neutrons is not exactly 1 u, the electrons contribute a lesser share to the atomic mass as neutron number exceeds proton number, and (finally) because of the nuclear binding energy. For example, the atomic weight of chlorine-35 to five significant digits is 34.969 u and that of chlorine-37 is 36.966 u. However, the atomic mass in u of pure isotope atoms is quite close (always within 1%) to its simple mass number. The only exception to the atomic mass of an isotope atom not being a natural number is 12C, which has a mass of exactly 12 by definition, because u is defined as 1/12 of the mass of a free neutral carbon-12 atom in the ground state. The relative atomic mass (historically and commonly also called "atomic weight") of an element is the average of the atomic masses of all the chemical elements isotopes as found in a particular environment, weighted by isotopic abundance, relative to the atomic mass unit (u). This number may be a fraction that is not close to a whole number, due to the averaging process. For example, the relative atomic mass of chlorine is 35.453 u, which differs greatly from a whole number due to being made of an average of 76% chlorine-35 and 24% chlorine-37. Whenever a relative atomic mass value differs by more than 1% from a whole number, it is due to this averaging effect resulting from significant amounts of more than one isotope being naturally present in the sample of the element in question. Isotopes Isotopes are atoms of the same element (that is, with the same number of protons in their atomic nucleus), but having different numbers of neutrons. Most (66 of 94) naturally occurring elements have more than one stable isotope. Thus, for example, there are three main isotopes of carbon. All carbon atoms have 6 protons in the nucleus, but they can have either 6, 7, or 8 neutrons. Since the mass numbers of these are 12, 13 and 14 respectively, the three isotopes of carbon are known as carbon-12, carbon-13, and carbon-14, often abbreviated to 12C, 13C, and 14C. Carbon in everyday life and in chemistry is a mixture of 12C, 13C, and (a very small fraction of) 14C atoms. Except in the case of the isotopes of hydrogen (which differ greatly from each other in relative mass—enough to cause chemical effects), the isotopes of the various elements are typically chemically nearly indistinguishable from each other. All of the elements have some isotopes that are radioactive (radioisotopes), although not all of these radioisotopes occur naturally. The radioisotopes typically decay into other elements upon radiating an alpha or beta particle. If an element has isotopes that are not radioactive, they are termed "stable." All of the known stable isotopes occur naturally (see primordial isotope). The many radioisotopes that are not found in nature have been characterized from being artificially made. Certain elements have no stable isotopes and are composed only of radioactive isotopes: specifically the elements without any stable isotopes are technetium (atomic number 43), promethium (atomic number 61), and all observed elements with atomic numbers greater than 82. Of the 80 elements with at least one stable isotope, 26 have only one stable isotope, and the mean number of stable isotopes for the 80 stable elements is 3.1 stable isotopes per element. The largest number of stable isotopes that occur for an element is 10 (for tin, element 50).
  • 54. Chemical element 52 Allotropes Atoms of pure elements may bond to each other chemically in more than one way, allowing the pure element to exist in multiple structures (spacial arrangements of atoms), known as allotropes, which differ in their properties. For example, carbon can be found as diamond, which has a tetrahedral structure around each carbon atom; graphite, which has layers of carbon atoms with a hexagonal structure stacked on top of each other; graphene, which is a single layer of graphite that is incredibly strong; fullerenes, which have nearly spherical shapes; and carbon nanotubes, which are tubes with a hexagonal structure (even these may differ from each other in electrical properties). The ability for an element to exist in one of many structural forms is known as allotropy. The standard state, or reference state, of an element is defined as its thermodynamically most stable state at 1 bar at a given temperature (typically at 298.15 K). In thermochemistry, an element is defined to have an enthalpy of formation of zero in its standard state. For example, the reference state for carbon is graphite, because it is more stable than the other allotropes. Properties Several kinds of descriptive categorizations can be applied broadly to the elements, including consideration of their general physical and chemical properties, their states of matter under familiar conditions, their melting and boiling points, their densities, their crystal structures as solids, and their origins. General properties Several terms are commonly used to characterize the general physical and chemical properties of the chemical elements. A first distinction is between the metals, which readily conduct electricity, and the nonmetals, which do not, with a small group (the metalloids) having intermediate properties, often behaving as semiconductors. A more refined classification is often shown in colored presentations of the periodic table; this system restricts the terms "metal" and "nonmetal" to only certain of the more broadly defined metals and nonmetals, adding additional terms for certain sets of the more broadly viewed metals and nonmetals. The version of this classification used in the periodic tables presented here includes: actinides, alkali metals, alkaline earth metals, halogens, lanthanides, post-transition metals (or "other metals"), metalloids, noble gases, nonmetals (or "other nonmetals"), and transition metals. In this system, the alkali metals, alkaline earth metals, and transition metals, as well as the lanthanides and the actinides, are special groups of the metals viewed in a broader sense. Similarly, the halogens and the noble gases are nonmetals, viewed in the broader sense. In some presentations, the halogens are not distinguished, with astatine identified as a metalloid and the others identified as nonmetals. States of matter Another commonly used basic distinction among the elements is their state of matter (phase), solid, liquid, or gas, at a selected standard temperature and pressure (STP). Most of the elements are solids at conventional temperatures and atmospheric pressure, while several are gases. Only bromine and mercury are liquids at 0 degrees Celsius (32 degrees Fahrenheit) and normal atmospheric pressure; caesium and gallium are solids at that temperature, but melt at 28.4 °C (83.2 °F) and 29.8 °C (85.6 °F), respectively. Melting and boiling points Melting and boiling points, typically expressed in degrees Celsius at a pressure of one atmosphere, are commonly used in characterizing the various elements. While known for most elements, either or both of these measurements is still undetermined for some of the radioactive elements available in only tiny quantities. Since helium remains a liquid even at absolute zero at atmospheric pressure, it has only a boiling point, and not a melting point, in conventional presentations.
  • 55. Chemical element 53 Densities The density at a selected standard temperature and pressure (STP) is frequently used in characterizing the elements. Density is often expressed in grams per cubic centimeter (g/cm3). Since several elements are gases at commonly encountered temperatures, their densities are usually stated for their gaseous forms; when liquefied or solidified, the gaseous elements have densities similar to those of the other elements. When an element has allotropes with different densities, one representative allotrope is typically selected in summary presentations, while densities for each allotrope can be stated where more detail is provided. For example, the three familiar allotropes of carbon (amorphous carbon, graphite, and diamond) have densities of 1.8–2.1, 2.267, and 3.515 g/cm3, respectively. Crystal structures The elements studied to date as solid samples have eight kinds of crystal structures: cubic, body-centered cubic, face-centered cubic, hexagonal, monoclinic, orthorhombic, rhombohedral, and tetragonal. For some of the synthetically produced transuranic elements, available samples have been too small to determine crystal structures. Occurrence and origin on Earth Chemical elements may also be categorized by their origin on Earth, with the first 98 considered to be naturally occurring, while those with atomic numbers beyond 98 have only been produced artificially as the synthetic products of man-made nuclear reactions. Of the 98 naturally occurring elements, 84 are considered to be primordial and either stable or metastable (apparently stable but theoretically unstable, or radioactive). The remaining 14 naturally occurring elements possess half lives too short for them to have been present at the beginning of the Solar System, and are therefore considered to be transient elements. Of these 14 transient elements, 7 (polonium, astatine, radon, francium, radium, actinium, and protactinium) are relatively common decay products of thorium, uranium, and plutonium. The remaining 7 transient elements (technetium, promethium, neptunium, americium, curium, berkelium, and californium) occur only rarely, as products of rare nuclear reaction processes from uranium or other heavy elements. Elements with atomic numbers 1 through 40 are all stable, while those with atomic numbers 41 through 82 (except technetium and promethium) are metastable. The half-lives of these metastable "theoretical radionuclides" are so long (at least 100 million times longer than the estimated age of the universe) that their radioactive decay has yet to be detected by experiment. Elements with atomic numbers 83 through 98 are unstable to the point that their radioactive decay can be detected. Some of these elements, notably thorium (atomic number 90) and uranium (atomic number 92), have one or more isotopes with half-lives long enough to survive as remnants of the explosive stellar nucleosynthesis that produced the heavy elements before the formation of our Solar System. For example, at over 1.9×1019 years, over a billion times longer than the current estimated age of the universe, bismuth-209 (atomic number 83) has the longest known alpha decay half-life of any naturally occurring element.[6][7] The very heaviest elements (those beyond californium, atomic number 98) undergo radioactive decay with half-lives so short that they do not occur in nature and have to be synthesized. The periodic table
  • 56. Chemical element 54 Periodic table (standard form) Group → 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 ↓ Period 1 1 2 H He 2 3 4 5 6 7 8 9 10 Li Be B C N O F Ne 3 11 12 13 14 15 16 17 18 Na Mg Al Si P S Cl Ar 4 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 5 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 6 55 56 * 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 Cs Ba lanthanides Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 7 87 88 ** 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 Fr Ra actinides Rf Db Sg Bh Hs Mt Ds Rg Cn Uut Fl Uup Lv Uus Uuo * Lanthanides 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu ** Actinides 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr This is an 18-column periodic table layout, which has come to be referred to as the common or standard form, on account of its [10] popularity. It is also sometimes referred to as the long form, in comparison to the short form or Mendeleev-style , which omits groups 3–12. The wide periodic table incorporates the lanthanides and the actinides, rather than separating them from the main body of the table. The extended periodic table adds the 8th and 9th periods, including the superactinides. Some element categories in the periodic table Metals Metalloids Nonmetals Unknown chemical Alkali Alkaline Inner transition metals Transition Post-transition Other Halogens Noble properties metals earth metals metals metals nonmetals gases Lanthanides Actinides (at standard conditions: 0 °C and 1 atm): Primordial From decay Synthetic black=Solid green=Liquid red=Gas grey=Unknown The properties of the chemical elements are often summarized using the periodic table, which powerfully and elegantly organizes the elements by increasing atomic number into rows ("periods") in which the columns ("groups") share recurring ("periodic") physical and chemical properties. The current standard table contains 118 confirmed elements as of 10 April 2010. Although earlier precursors to this presentation exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869, who intended the table to illustrate recurring trends in the properties of the elements. The layout of the table has been refined and extended over time, as new elements have been discovered, and new theoretical models have been developed to explain chemical behavior.
  • 57. Chemical element 55 Use of the periodic table is now ubiquitous within the academic discipline of chemistry, providing an extremely useful framework to classify, systematize and compare all the many different forms of chemical behavior. The table has also found wide application in physics, geology, biology, materials science, engineering, agriculture, medicine, nutrition, environmental health, and astronomy. Its principles are especially important in chemical engineering. Nomenclature and symbols The various chemical elements are formally identified by their unique atomic numbers, by their accepted names, and by their symbols. Atomic numbers The known elements have atomic numbers from 1 through 118, conventionally presented as Arabic numerals. Since the elements can be uniquely sequenced by atomic number, conventionally from lowest to highest (as in a periodic table), sets of elements are sometimes specified by such notation as "through", "beyond", or "from ... through", as in "through iron", "beyond uranium", or "from lanthanum through lutetium". The terms "light" and "heavy" are sometimes also used informally to indicate relative atomic numbers (not densities!), as in "lighter than carbon" or "heavier than lead", although technically the weight or mass of atoms of an element (their atomic weights or atomic masses) do not always increase monotonically with their atomic numbers. Element names The naming of various substances now known as elements precedes the atomic theory of matter, as names were given locally by various cultures to various minerals, metals, compounds, alloys, mixtures, and other materials, although at the time it was not known which chemicals were elements and which compounds. As they were identified as elements, the existing names for anciently-known elements (e.g., gold, mercury, iron) were kept in most countries. National differences emerged over the names of elements either for convenience, linguistic niceties, or nationalism. For a few illustrative examples: German speakers use "Wasserstoff" (water substance) for "hydrogen", "Sauerstoff" (acid substance) for "oxygen" and "Stickstoff" (smothering substance) for "nitrogen", while English and some romance languages use "sodium" for "natrium" and "potassium" for "kalium", and the French, Italians, Greeks, Portuguese and Poles prefer "azote/azot/azoto" (from roots meaning "no life") for "nitrogen". For purposes of international communication and trade, the official names of the chemical elements both ancient and more recently recognized are decided by the International Union of Pure and Applied Chemistry (IUPAC), which has decided on a sort of international English language, drawing on traditional English names even when an elements chemical symbol is based on a Latin or other traditional word, for example adopting "gold" rather than "aurum" as the name for the 79th element (Au). IUPAC prefers the British spellings "aluminium" and "caesium" over the U.S. spellings "aluminum" and "cesium", and the U.S. "sulfur" over the British "sulphur". However, elements that are practical to sell in bulk in many countries often still have locally used national names, and countries whose national language does not use the Latin alphabet are likely to use the IUPAC element names. According to IUPAC, chemical elements are not proper nouns in English; consequently, the full name of an element is not routinely capitalized in English, even if derived from a proper noun, as in californium and einsteinium. Isotope names of chemical elements are also uncapitalized if written out, e.g., carbon-12 or uranium-235. Chemical element symbols are always capitalized (see below). In the second half of the twentieth century, physics laboratories became able to produce nuclei of chemical elements with half-lives too short for an appreciable amount of them to exist at any time. These are also named by IUPAC, which generally adopts the name chosen by the discoverer. This practice can lead to the controversial question of which research group actually discovered an element, a question that has delayed naming of elements with atomic number of 104 and higher for a considerable time. (See element naming controversy).
  • 58. Chemical element 56 Precursors of such controversies involved the nationalistic namings of elements in the late 19th century. For example, lutetium was named in reference to Paris, France. The Germans were reluctant to relinquish naming rights to the French, often calling it cassiopeium. Similarly, the British discoverer of niobium originally named it columbium, in reference to the New World. It was used extensively as such by American publications prior to international standardization. Chemical symbols Specific chemical elements Before chemistry became a science, alchemists had designed arcane symbols for both metals and common compounds. These were however used as abbreviations in diagrams or procedures; there was no concept of atoms combining to form molecules. With his advances in the atomic theory of matter, John Dalton devised his own simpler symbols, based on circles, which were to be used to depict molecules. The current system of chemical notation was invented by Berzelius. In this typographical system chemical symbols are not used as mere abbreviations – though each consists of letters of the Latin alphabet – they are symbols intended to be used by peoples of all languages and alphabets. The first of these symbols were intended to be fully universal; since Latin was the common language of science at that time, they were abbreviations based on the Latin names of metals – Cu comes from Cuprum, Fe comes from Ferrum, Ag from Argentum. The symbols were not followed by a period (full stop) as abbreviations were. Later chemical elements were also assigned unique chemical symbols, based on the name of the element, but not necessarily in English. For example, sodium has the chemical symbol Na after the Latin natrium. The same applies to "W" (wolfram) for tungsten, "Fe" (ferrum) for iron, "Hg" (hydrargyrum) for mercury, "Sn" (stannum) for tin, "K" (kalium) for potassium, "Au" (aurum) for gold, "Ag" (argentum) for silver, "Pb" (plumbum) for lead, "Cu" (Cuprum) for copper, and "Sb" (stibium) for antimony. Chemical symbols are understood internationally when element names might need to be translated. There are sometimes differences; for example, the Germans have used "J" instead of "I" for iodine, so the character would not be confused with a Roman numeral. The first letter of a chemical symbol is always capitalized, as in the preceding examples, and the subsequent letters, if any, are always lower case (small letters). Thus, the symbols for californium or einsteinium are Cf and Es. General chemical symbols There are also symbols for series of chemical elements, for comparative formulas. These are one capital letter in length, and the letters are reserved so they are not permitted to be given for the names of specific elements. For example, an "X" is used to indicate a variable group amongst a class of compounds (though usually a halogen), while "R" is used for a radical, meaning a compound structure such as a hydrocarbon chain. The letter "Q" is reserved for "heat" in a chemical reaction. "Y" is also often used as a general chemical symbol, although it is also the symbol of yttrium. "Z" is also frequently used as a general variable group. "L" is used to represent a general ligand in inorganic and organometallic chemistry. "M" is also often used in place of a general metal. At least one additional, two-letter generic chemical symbol is also in informal usage, "Ln" for any lanthanide element.
  • 59. Chemical element 57 Isotope symbols Isotopes are distinguished by the atomic mass number (total protons and neutrons) for a particular isotope of an element, with this number combined with the pertinent elements symbol. IUPAC prefers that isotope symbols be written in superscript notation when practical, for example 12C and 235U. However, other notations, such as carbon-12 and uranium-235, or C-12 and U-235, are also used. As a special case, the three naturally occurring isotopes of the element hydrogen are often specified as H for 1H (protium), D for 2H (deuterium), and T for 3H (tritium). This convention is easier to use in chemical equations, replacing the need to write out the mass number for each atom. For example, the formula for heavy water may be written D2O instead of 2H2O. Origin of the elements Only about 4% of the total mass of the universe is made of atoms or ions, and thus represented by chemical elements. This fraction is about 15% of the total matter, with the remainder of the matter (85%) being dark matter. The nature of dark matter is unknown, but it is not composed of atoms of chemical elements because it contains no protons, neutrons, or electrons. (The remaining non-matter part of the mass of the universe is composed of the even more mysterious dark energy). The universes 94 naturally occurring chemical elements are thought to have been produced by at least four cosmic processes. Most of the hydrogen and helium in the universe was produced primordially in the first few minutes of the Big Bang. Three recurrently occurring later processes are thought to have produced the remaining elements. Stellar nucleosynthesis, an ongoing process, produces all elements from carbon through iron in atomic number, but little lithium, beryllium, or boron. Elements heavier in atomic number than iron, as heavy as uranium and plutonium, are produced by explosive nucleosynthesis in supernovas and other cataclysmic Estimated distribution of dark matter and dark energy in the universe. Only the fraction of the mass and energy in the universe labeled cosmic events. Cosmic ray spallation (fragmentation) "atoms" is composed of chemical elements. of carbon, nitrogen, and oxygen is important to the production of lithium, beryllium and boron. During the early phases of the Big Bang, nucleosynthesis of hydrogen nuclei resulted in the production of hydrogen-1 (protonium, 1H) and helium-4 (4He), as well as a smaller amount of deuterium (2H) and very minuscule amounts (on the order of 10−10) of lithium and beryllium. Even smaller amounts of boron may have been produced in the Big Bang, since it has been observed in some very old stars, while carbon has not.[11] It is generally agreed that no heavier elements than boron were produced in the Big Bang. As a result, the primordial abundance of atoms (or ions) consisted of roughly 75% 1H, 25% 4He, and 0.01% deuterium, with only tiny traces of lithium, beryllium, and perhaps boron.[12] Subsequent enrichment of galactic halos occurred due to stellar nucleosynthesis and supernova nucleosynthesis.[13] However, the element abundance in intergalactic space can still closely resemble
  • 60. Chemical element 58 primordial conditions, unless it has been enriched by some means. On Earth (and elsewhere), trace amounts of various elements continue to be produced from other elements as products of natural transmutation processes. These include some produced by cosmic rays or other nuclear reactions (see cosmogenic and nucleogenic nuclides), and others produced as decay products of long-lived primordial nuclides.[14] For example, trace (but detectable) amounts of carbon-14 (14C) are continually produced in the atmosphere by cosmic rays impacting nitrogen atoms, and argon-40 (40Ar) is continually produced by the decay of primordially occurring but unstable potassium-40 (40K). Also, three primordially occurring but radioactive actinides, thorium, uranium, and plutonium, decay through a series of recurrently produced but unstable radioactive elements such as radium and radon, which are transiently present in any sample of these metals or their ores or compounds. Seven other radioactive elements, technetium, promethium, neptunium, americium, curium, berkelium, and californium, occur only incidentally in natural materials, produced as individual atoms by natural fission of the nuclei of various heavy elements or in other rare nuclear processses. Human technology has produced various additional elements beyond these first 98, with those through atomic number 118 now known. Abundance The following graph (note log scale) shows abundance of elements in our solar system. The table shows the twelve most common elements in our galaxy (estimated spectroscopically), as measured in parts per million, by mass.[15] Nearby galaxies that have evolved along similar lines have a corresponding enrichment of elements heavier than hydrogen and helium. The more distant galaxies are being viewed as they appeared in the past, so their abundances of elements appear closer to the primordial mixture. As physical laws and processes appear common throughout the visible universe, however, it is expected that these galaxies will likewise have evolved similar abundances of elements. The abundance of elements in the Solar System is in keeping with their origin from nucleosynthesis in the Big Bang and a number of progenitor supernova stars. Very abundant hydrogen and helium are products of the Big Bang, but the next three elements are rare since they had little time to form in the Big Bang and are not made in stars (they are, however, produced in small quantities by breakup of heavier elements in interstellar dust, as a result of impact by cosmic rays). Beginning with carbon, elements are produced in stars by buildup from alpha particles (helium nuclei), resulting in an alternatingly-larger abundance of elements with even atomic numbers (these are also more stable). In general, such elements up to iron are made in large stars in the process of becoming supernovas. Iron-56 is particularly common, since it is the most stable element that can easily be made from alpha particles (being a product of decay of radioactive nickel-56, ultimately made from 14 helium nuclei). Elements heavier than iron are made in energy-absorbing processes in large stars, and their abundance in the universe (and on Earth) generally decreases with their atomic number. The abundance of the chemical elements on Earth varies from air to crust to ocean, and in various types of life. The abundance of elements in Earths crust differs from those in the universe (and also the Sun and heavy planets like Jupiter) mainly in selective loss of the very lightest elements (hydrogen and helium) and also volatile neon, carbon, nitrogen and sulfur, as a result of solar heating in the early formation of the solar system. Aluminum is also far more common in the Earth and Earths crust than the universe and solar system, but the composition of Earths mantle (which has more magnesium and iron in place of aluminum) more closely mirrors that of the universe, save for the noted loss of volatile elements. The composition of the human body, by contrast, more closely follows the composition of seawater, save that the human body has additional stores of carbon and nitrogen which are necessary to form the proteins and nucleic acids that are characteristic of living organisms. Certain kinds of organisms require particular additional elements, for example the magnesium in chlorophyll in green plants, the calcium in mollusc shells, or the iron in the hemoglobin in vertebrate animals red blood cells.
  • 61. Chemical element 59 Abundances of the chemical elements in the Solar system. Hydrogen and helium are most common, from the Big Bang. The next three elements (Li, Be, B) are rare because they are poorly synthesized in the Big Bang and also in stars. The two general trends in the remaining stellar-produced elements are: (1) an alternation of abundance in elements as they have even or odd atomic numbers, and (2) a general decrease in abundance, as elements become heavier. Iron is especially common because it represents the minimum energy nuclide that can be made by fusion of helium in supernovae. Elements in our galaxy Parts per million by mass Hydrogen 739,000 Helium 240,000 Oxygen 10,400 Carbon 4,600 Neon 1,340 Iron 1,090 Nitrogen 960 Silicon 650 Magnesium 580 Sulfur 440 Potassium 210 Nickel 100 Periodic table highlighting dietary elements[16] H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La * Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac ** Rf Db Sg Bh Hs Mt Ds Rg * Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu ** Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
  • 62. Chemical element 60   Four organic basic elements   Quantity elements   Essential trace elements   Suggested function from biochemistry and metabolic handling in mammals, but no identified specific function History Evolving definitions The concept of an "element" as an undivisible substance has developed through three major historical phases: Classical definitions (such as those of the ancient Greeks), chemical definitions, and atomic definitions. Classical definitions Ancient philosophy posited a set of classical elements to explain observed patterns in nature. These elements originally referred to earth, water, air and fire rather than the chemical elements of modern science. The term elements (stoicheia) was first used by the Greek philosopher Plato in about 360 BCE, in his dialogue Timaeus, which includes a discussion of the composition of inorganic and organic bodies and is a speculative treatise on chemistry. Plato believed the elements introduced a century earlier by Empedocles were composed of Mendeleevs 1869 periodic table small polyhedral forms: tetrahedron (fire), octahedron (air), icosahedron (water), and cube (earth).[17][18] Aristotle, c. 350 BCE, also used the term stoicheia and added a fifth element called aether, which formed the heavens. Aristotle defined an element as: Element – one of those bodies into which other bodies can decompose, and that itself is not capable of being divided into other.[19] Chemical definitions In 1661, Robert Boyle showed that there were more than just the four classical elements that the ancients had assumed.[20] The first modern list of chemical elements was given in Antoine Lavoisiers 1789 Elements of Chemistry, which contained thirty-three elements, including light and caloric.[21] By 1818, Jöns Jakob Berzelius had determined atomic weights for forty-five of the forty-nine then-accepted elements. Dmitri Mendeleev had sixty-six elements in his periodic table of 1869.
  • 63. Chemical element 61 From Boyle until the early 20th century, an element was defined as a pure substance that could not be decomposed into any simpler substance.[20] Put another way, a chemical element cannot be transformed into other chemical elements by chemical processes. Elements during this time were generally distinguished by their atomic weights, a property measurable with fair accuracy by available analytical techniques. Dmitri Mendeleev Atomic definitions The 1913 discovery by Henry Moseley that the nuclear charge is the physical basis for an atoms atomic number, further refined when the nature of protons and neutrons became appreciated, eventually led to the current definition of an element, based on atomic number (number of protons per atomic nucleus). The use of atomic numbers, rather than atomic weights, to distinguish elements has greater predictive value (since these numbers are integers), and also resolves some ambiguities in the chemistry-based view due to varying properties of isotopes and allotropes within the same element. Currently IUPAC defines an element to exist if it has isotopes with a lifetime longer than the 10−14 seconds which takes the nucleus to form an electronic cloud.[22] By 1914, seventy-two elements were known, all naturally occurring.[23] The remaining naturally occurring elements were discovered or isolated is subsequent decades, and various additional elements have also been produced synthetically, Henry Moseley with much of that work pioneered by Glenn T. Seaborg. In 1955, element 101 was discovered and named mendelevium in honor of D.I. Mendeleev, the first to arrange the elements in a periodic manner. Most recently, the synthesis of element 118 was reported in October 2006, and the synthesis of element 117 was reported in April 2010.[24] Discovery and recognition of various elements Ten materials familiar to various prehistoric cultures are now known to be chemical elements: Carbon, copper, gold, iron, lead, mercury, silver, sulfur, tin, and zinc. Three additional materials now accepted as elements, arsenic, antimony, and bismuth, were recognized as distinct substances prior to 1500 AD. Phosphorus, cobalt, and platinum were isolated before 1750. Most of the remaining naturally occurring chemical elements were identified and characterized by 1900, including: • Such now-familiar industrial materials as aluminium, silicon, nickel, chromium, magnesium, and tungsten • Reactive metals such as lithium, sodium, potassium, and calcium • The halogens fluorine, chlorine, bromine, and iodine • Gases such as hydrogen, oxygen, nitrogen, helium, argon, and neon • Most of the rare-earth elements, including cerium, lanthanum, gadolinium, and neodymium, and
  • 64. Chemical element 62 • The more common radioactive elements, including uranium, thorium, radium, and radon Elements isolated or produced since 1900 include: • The three remaining undiscovered regularly occurring stable natural elements: hafnium, lutetium, and rhenium • Plutonium, first produced synthetically but now also known from a few long-persisting natural occurrences • The three incidentally occurring natural elements (neptunium, promethium, and technetium), all first produced synthetically but later discovered in trace amounts in certain geological samples • Three scarcer decay products of uranium or thorium (astatine, francium, and protactinium), • Various synthetic transuranic elements, beginning with americium, curium, berkelium, and californium Recently discovered elements The first transuranium element (element with atomic number greater than 92) discovered was neptunium in 1940. As of May 2012, only the elements up to 112, copernicium, as well as element 114 Flerovium and element 116 Livermorium have been confirmed as discovered by IUPAC, while claims have been made for synthesis of elements 113, 115, 117[25] and 118. The discovery of element 112 was acknowledged in 2009, and the name copernicium and the atomic symbol Cn were suggested for it.[26] The name and symbol were officially endorsed by IUPAC on 19 February 2010.[27] The heaviest element that is believed to have been synthesized to date is element 118, ununoctium, on 9 October 2006, by the Flerov Laboratory of Nuclear Reactions in Dubna, Russia.[9][28] Element 117 was the latest element claimed to be discovered, in 2009.[25] IUPAC officially recognized flerovium and livermorium, elements 114 and 116, in June 2011 and approved their names in May 2012.[29] List of the 118 known chemical elements The following sortable table includes the 118 known chemical elements, with the names linking to the Wikipedia articles on each. • Atomic number, name, and symbol all serve independently as unique identifiers. • Names are those accepted by IUPAC; provisional names for recently produced elements not yet formally named are in parentheses. • Group, period, and block refer to an elements position in the periodic table. • State of matter (solid, liquid, or gas) applies at standard temperature and pressure conditions (STP). • Occurrence distinguishes naturally occurring elements, categorized as either primordial or transient (from decay), and additional synthetic elements that have been produced technologically, but are not known to occur naturally. • Description summarizes an elements properties using the broad categories commonly presented in periodic tables: Actinide, alkali metal, alkaline earth metal, halogen, lanthanide, metal, metalloid, noble gas, non-metal, and transition metal. List of elements Atomic Name Symbol Group Period Block State Occurrence Description no. at STP 1 Hydrogen H 1 1 s Gas Primordial Non-metal 2 Helium He 18 1 s Gas Primordial Noble gas 3 Lithium Li 1 2 s Solid Primordial Alkali metal 4 Beryllium Be 2 2 s Solid Primordial Alkaline earth metal 5 Boron B 13 2 p Solid Primordial Metalloid 6 Carbon C 14 2 p Solid Primordial Non-metal
  • 65. Chemical element 63 7 Nitrogen N 15 2 p Gas Primordial Non-metal 8 Oxygen O 16 2 p Gas Primordial Non-metal 9 Fluorine F 17 2 p Gas Primordial Halogen 10 Neon Ne 18 2 p Gas Primordial Noble gas 11 Sodium Na 1 3 s Solid Primordial Alkali metal 12 Magnesium Mg 2 3 s Solid Primordial Alkaline earth metal 13 Aluminium Al 13 3 p Solid Primordial Metal 14 Silicon Si 14 3 p Solid Primordial Metalloid 15 Phosphorus P 15 3 p Solid Primordial Non-metal 16 Sulfur S 16 3 p Solid Primordial Non-metal 17 Chlorine Cl 17 3 p Gas Primordial Halogen 18 Argon Ar 18 3 p Gas Primordial Noble gas 19 Potassium K 1 4 s Solid Primordial Alkali metal 20 Calcium Ca 2 4 s Solid Primordial Alkaline earth metal 21 Scandium Sc 3 4 d Solid Primordial Transition metal 22 Titanium Ti 4 4 d Solid Primordial Transition metal 23 Vanadium V 5 4 d Solid Primordial Transition metal 24 Chromium Cr 6 4 d Solid Primordial Transition metal 25 Manganese Mn 7 4 d Solid Primordial Transition metal 26 Iron Fe 8 4 d Solid Primordial Transition metal 27 Cobalt Co 9 4 d Solid Primordial Transition metal 28 Nickel Ni 10 4 d Solid Primordial Transition metal 29 Copper Cu 11 4 d Solid Primordial Transition metal 30 Zinc Zn 12 4 d Solid Primordial Transition metal 31 Gallium Ga 13 4 p Solid Primordial Metal 32 Germanium Ge 14 4 p Solid Primordial Metalloid 33 Arsenic As 15 4 p Solid Primordial Metalloid 34 Selenium Se 16 4 p Solid Primordial Non-metal 35 Bromine Br 17 4 p Liquid Primordial Halogen 36 Krypton Kr 18 4 p Gas Primordial Noble gas 37 Rubidium Rb 1 5 s Solid Primordial Alkali metal 38 Strontium Sr 2 5 s Solid Primordial Alkaline earth metal 39 Yttrium Y 3 5 d Solid Primordial Transition metal 40 Zirconium Zr 4 5 d Solid Primordial Transition metal 41 Niobium Nb 5 5 d Solid Primordial Transition metal 42 Molybdenum Mo 6 5 d Solid Primordial Transition metal 43 Technetium Tc 7 5 d Solid Transient Transition metal 44 Ruthenium Ru 8 5 d Solid Primordial Transition metal 45 Rhodium Rh 9 5 d Solid Primordial Transition metal
  • 66. Chemical element 64 46 Palladium Pd 10 5 d Solid Primordial Transition metal 47 Silver Ag 11 5 d Solid Primordial Transition metal 48 Cadmium Cd 12 5 d Solid Primordial Transition metal 49 Indium In 13 5 p Solid Primordial Metal 50 Tin Sn 14 5 p Solid Primordial Metal 51 Antimony Sb 15 5 p Solid Primordial Metalloid 52 Tellurium Te 16 5 p Solid Primordial Metalloid 53 Iodine I 17 5 p Solid Primordial Halogen 54 Xenon Xe 18 5 p Gas Primordial Noble gas 55 Caesium Cs 1 6 s Solid Primordial Alkali metal 56 Barium Ba 2 6 s Solid Primordial Alkaline earth metal 57 Lanthanum La 3 6 f Solid Primordial Lanthanide 58 Cerium Ce 3 6 f Solid Primordial Lanthanide 59 Praseodymium Pr 3 6 f Solid Primordial Lanthanide 60 Neodymium Nd 3 6 f Solid Primordial Lanthanide 61 Promethium Pm 3 6 f Solid Transient Lanthanide 62 Samarium Sm 3 6 f Solid Primordial Lanthanide 63 Europium Eu 3 6 f Solid Primordial Lanthanide 64 Gadolinium Gd 3 6 f Solid Primordial Lanthanide 65 Terbium Tb 3 6 f Solid Primordial Lanthanide 66 Dysprosium Dy 3 6 f Solid Primordial Lanthanide 67 Holmium Ho 3 6 f Solid Primordial Lanthanide 68 Erbium Er 3 6 f Solid Primordial Lanthanide 69 Thulium Tm 3 6 f Solid Primordial Lanthanide 70 Ytterbium Yb 3 6 f Solid Primordial Lanthanide 71 Lutetium Lu 3 6 d Solid Primordial Lanthanide 72 Hafnium Hf 4 6 d Solid Primordial Transition metal 73 Tantalum Ta 5 6 d Solid Primordial Transition metal 74 Tungsten W 6 6 d Solid Primordial Transition metal 75 Rhenium Re 7 6 d Solid Primordial Transition metal 76 Osmium Os 8 6 d Solid Primordial Transition metal 77 Iridium Ir 9 6 d Solid Primordial Transition metal 78 Platinum Pt 10 6 d Solid Primordial Transition metal 79 Gold Au 11 6 d Solid Primordial Transition metal 80 Mercury Hg 12 6 d Liquid Primordial Transition metal 81 Thallium Tl 13 6 p Solid Primordial Metal 82 Lead Pb 14 6 p Solid Primordial Metal 83 Bismuth Bi 15 6 p Solid Primordial Metal 84 Polonium Po 16 6 p Solid Transient Metalloid
  • 67. Chemical element 65 85 Astatine At 17 6 p Solid Transient Halogen 86 Radon Rn 18 6 p Gas Transient Noble gas 87 Francium Fr 1 7 s Solid Transient Alkali metal 88 Radium Ra 2 7 s Solid Transient Alkaline earth metal 89 Actinium Ac 3 7 f Solid Transient Actinide 90 Thorium Th 3 7 f Solid Primordial Actinide 91 Protactinium Pa 3 7 f Solid Transient Actinide 92 Uranium U 3 7 f Solid Primordial Actinide 93 Neptunium Np 3 7 f Solid Transient Actinide 94 Plutonium Pu 3 7 f Solid Primordial Actinide 95 Americium Am 3 7 f Solid Transient Actinide 96 Curium Cm 3 7 f Solid Transient Actinide 97 Berkelium Bk 3 7 f Solid Transient Actinide 98 Californium Cf 3 7 f Solid Transient Actinide 99 Einsteinium Es 3 7 f Solid Synthetic Actinide 100 Fermium Fm 3 7 f Solid Synthetic Actinide 101 Mendelevium Md 3 7 f Solid Synthetic Actinide 102 Nobelium No 3 7 f Solid Synthetic Actinide 103 Lawrencium Lr 3 7 d Solid Synthetic Actinide 104 Rutherfordium Rf 4 7 d Synthetic Transition metal 105 Dubnium Db 5 7 d Synthetic Transition metal 106 Seaborgium Sg 6 7 d Synthetic Transition metal 107 Bohrium Bh 7 7 d Synthetic Transition metal 108 Hassium Hs 8 7 d Synthetic Transition metal 109 Meitnerium Mt 9 7 d Synthetic 110 Darmstadtium Ds 10 7 d Synthetic 111 Roentgenium Rg 11 7 d Synthetic 112 Copernicium Cn 12 7 d Synthetic Transition metal 113 (Ununtrium) Uut 13 7 p Synthetic 114 Flerovium Fl 14 7 p Synthetic 115 (Ununpentium) Uup 15 7 p Synthetic 116 Livermorium Lv 16 7 p Synthetic 117 (Ununseptium) Uus 17 7 p Synthetic 118 (Ununoctium) Uuo 18 7 p Synthetic
  • 68. Chemical element 66 References [1] Yu. Ts. Oganessian; Abdullin, F. Sh.; Bailey, P. D.; Benker, D. E.; Bennett, M. E.; Dmitriev, S. N.; Ezold, J. G.; Hamilton, J. H. et al. (2010). "Synthesis of a New Element with Atomic Number Z=117". Physical Review Letters (Physical Review Letter) 104 (14). Bibcode 2010PhRvL.104n2502O. doi:10.1103/PhysRevLett.104.142502. PMID 20481935. [2] Los Alamos National Laboratory (2011). "Periodic Table of Elements: Oxygen" (http:/ / periodic. lanl. gov/ 8. shtml). Los Alamos, New Mexico: Los Alamos National Security, LLC. . Retrieved 7 May 2011. [3] Oerter, Robert (2006). The Theory of Almost Everything: The Standard Model, the Unsung Triumph of Modern Physics. Penguin. p. 223. ISBN 978-0-452-28786-0. [4] E. M. Burbidge, G. R. Burbidge, W. A. Fowler, F. Hoyle (1957). "Synthesis of the Elements in Stars". Reviews of Modern Physics 29 (4): 547–650. Bibcode 1957RvMP...29..547B. doi:10.1103/RevModPhys.29.547. [5] See the timeline on p.10 of Oganessian, Yu.; Utyonkov, V.; Lobanov, Yu.; Abdullin, F.; Polyakov, A.; Sagaidak, R.; Shirokovsky, I.; Tsyganov, Yu. et al. (2006). "Evidence for Dark Matter" (http:/ / gaitskell. brown. edu/ physics/ talks/ 0408_SLAC_SummerSchool/ Gaitskell_DMEvidence_v16. pdf). Physical Review C 74 (4): 044602. Bibcode 2006PhRvC..74d4602O. doi:10.1103/PhysRevC.74.044602. . [6] Dumé, B (23 April 2003). "Bismuth breaks half-life record for alpha decay" (http:/ / physicsweb. org/ articles/ news/ 7/ 4/ 16). (Bristol, England: Institute of Physics). . Retrieved 7 May 2011. [7] de Marcillac, P; Coron N, Dambier G, Leblanc J, and Moalic J-P (2003). "Experimental detection of alpha-particles from the radioactive decay of natural bismuth". Nature 422 (6934): 876–8. Bibcode 2003Natur.422..876D. doi:10.1038/nature01541. PMID 12712201. [8] Sanderson, K (17 October 2006). "Heaviest element made – again" (http:/ / www. nature. com/ news/ 2006/ 061016/ full/ 061016-4. html). Nature News. doi:10.1038/news061016-4. . [9] Schewe, P; Stein, B (17 October 200). "Elements 116 and 118 Are Discovered" (http:/ / www. aip. org/ pnu/ 2006/ 797. html). Physics News Update. American Institute of Physics. . Retrieved 19 October 2006. [10] http:/ / flerovlab. jinr. ru/ flnr/ dimg/ Periodic_Table. jpg [11] Wilford, JN (14 January 1992). "Hubble Observations Bring Some Surprises" (http:/ / query. nytimes. com/ gst/ fullpage. html?res=9E0CE5D91F3AF937A25752C0A964958260). New York Times. . [12] Wright, EL (12 September 2004). "Big Bang Nucleosynthesis" (http:/ / www. astro. ucla. edu/ ~wright/ BBNS. html). UCLA, Division of Astronomy. . Retrieved 22 February 2007. [13] Wallerstein, George; Iben, Icko; Parker, Peter; Boesgaard, Ann; Hale, Gerald; Champagne, Arthur; Barnes, Charles; Käppeler, Franz et al. (1999). "Synthesis of the elements in stars: forty years of progress" (http:/ / www. cococubed. com/ papers/ wallerstein97. pdf). Reviews of Modern Physics 69 (4): 995–1084. Bibcode 1997RvMP...69..995W. doi:10.1103/RevModPhys.69.995. . [14] Earnshaw, A; Greenwood, N (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. [15] Croswell, K (1996). Alchemy of the Heavens (http:/ / kencroswell. com/ alchemy. html). Anchor. ISBN 0-385-47214-5. . [16] Ultratrace minerals. Authors: Nielsen, Forrest H. USDA, ARS Source: Modern nutrition in health and disease/editors, Maurice E. Shils ... et al.. Baltimore : Williams & Wilkins, c1999., p. 283-303. Issue Date: 1999 URI: (http:/ / hdl. handle. net/ 10113/ 46493) [17] Plato (2008) [c. 360 BC]. Timaeus (http:/ / books. google. com/ ?id=xSjvowNydN8C& lpg=PP1& dq=Plato timaeus& pg=PA45#v=onepage& q=cube& f=false). Forgotten Books. p. 45. ISBN 978-1-60620-018-6. . [18] Hillar, M (2004). "The Problem of the Soul in Aristotles De anima" (http:/ / www. socinian. org/ aristotles_de_anima. html). NASA/WMAP. . Retrieved 10 August 2006. [19] Partington, JR (1937). A Short History of Chemistry. New York: Dover Publications. ISBN 0-486-65977-1. [20] Boyle, R (1661). The Sceptical Chymist. London. ISBN 0-922802-90-4. [21] Lavoisier, AL (1790). Elements of chemistry translated by Robert Kerr (http:/ / books. google. com/ ?id=4BzAjCpEK4gC& pg=PA175). Edinburgh. pp. 175–6. ISBN 978-0-415-17914-0. . [22] Transactinide-2 (http:/ / www. kernchemie. de/ Transactinides/ Transactinide-2/ transactinide-2. html). [23] Carey, GW (1914). The Chemistry of Human Life. Los Angeles. ISBN 0-7661-2840-7. [24] Glanz, J (6 April 2010). "Scientists Discover Heavy New Element" (http:/ / www. nytimes. com/ 2010/ 04/ 07/ science/ 07element. html?hp). New York Times. . [25] Greiner, W. "Recommendations" (http:/ / www. jinr. ru/ img_sections/ PAC/ NP/ 31/ PAK_NP_31_recom_eng. pdf). 31st meeting, PAC for Nuclear Physics. Joint Institute for Nuclear Research. . [26] "IUPAC Announces Start of the Name Approval Process for the Element of Atomic Number 112" (http:/ / media. iupac. org/ news/ 112_Naming_Process_20090720. pdf). IUPAC. 20 July 2009. . Retrieved 27 August 2009. [27] "IUPAC (International Union of Pure and Applied Chemistry): Element 112 is Named Copernicium" (http:/ / www. iupac. org/ web/ nt/ 2010-02-20_112_Copernicium). IUPAC. 20 February 2010. . [28] Oganessian, YT; Utyonkov, V.; Lobanov, Yu.; Abdullin, F.; Polyakov, A.; Sagaidak, R.; Shirokovsky, I.; Tsyganov, Yu. et al. (2006). "Synthesis of the isotopes of elements 118 and 116 in the 249Cf and 245Cm+48Ca fusion reactions". Physical Review C 74 (4): 044602. Bibcode 2006PhRvC..74d4602O. doi:10.1103/PhysRevC.74.044602. [29] "Two ultra-heavy elements added to the periodic table" (http:/ / www. wired. co. uk/ news/ archive/ 2011-06/ 06/ new-elements-added). 6 June 2011. .
  • 69. Chemical element 67 Further reading • Ball, P (2004). The Elements: A Very Short Introduction. Oxford University Press. ISBN 0-19-284099-1. • Emsley, J (2003). Natures Building Blocks: An A-Z Guide to the Elements. Oxford University Press. ISBN 0-19-850340-7. • Gray, T (2009). The Elements: A Visual Exploration of Every Known Atom in the Universe. Black Dog & Leventhal Publishers Inc. ISBN 1-57912-814-9. • Scerri, ER (2007). The Periodic Table, Its Story and Its Significance. Oxford University Press. • Strathern, P (2000). Mendeleyevs Dream: The Quest for the Elements. Hamish Hamilton Ltd. ISBN 0-241-14065-X. External links • Videos for each element ( by the University of Nottingham Chemical compound A chemical compound is a pure chemical substance consisting of two or more different chemical elements[1][2][3] that can be separated into simpler substances by chemical reactions.[4] Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms[3] that are held together in a defined spatial arrangement by chemical bonds. Chemical compounds can be molecular compounds held together by covalent bonds, salts held together by ionic bonds, intermetallic compounds held together by metallic bonds, or complexes held together by coordinate covalent bonds. Pure chemical elements are not considered chemical compounds, even if they consist of molecules which contain only multiple atoms of a single element (such as H2, S8, etc.),[5] which are called diatomic molecules or polyatomic A water molecule is an example of a chemical molecules. compound, consisting of two parts hydrogen and one part oxygen. Wider definitions There are exceptions to the definition above, and large amounts of the solid chemical matter familiar on Earth do not have simple formulas. Certain crystalline compounds are called "non-stoichiometric" because they vary in composition due to either the presence of foreign elements trapped within the crystal structure or a deficit or excess of the constituent elements. Such non-stoichiometric chemical compounds form most of the crust and mantle of the Earth. Other compounds regarded as chemically identical may have varying amounts of heavy or light isotopes of the constituent elements, which will make the ratio of elements by mass vary slightly.
  • 70. Chemical compound 68 Elementary concepts Characteristic properties of compounds: • Elements in a compound are present in a definite proportion Example- 2 atoms of hydrogen + 1 atom of oxygen becomes 1 molecule of compound-water. • Compounds have a definite set of properties Elements comprising a compound do not retain their original properties. Example: hydrogen (element, which is combustible and non-supporter of combustion) + oxygen (element, which is non-combustible and supporter of combustion) becomes water (compound, which is non-combustible and non-supporter of combustion) Valency is the number of hydrogen atoms which can combine with one atom of the element forming a compound. Compounds compared to mixtures The physical and chemical properties of compounds are different from those of their constituent elements. This is one of the main criteria for distinguishing a compound from a mixture of elements or other substances because a mixtures properties are generally closely related to and dependent on the properties of its constituents. Another criterion for distinguishing a compound from a mixture is that the constituents of a mixture can usually be separated by simple, mechanical means such as filtering, evaporation, or use of a magnetic force, but the components of a compound can only be separated by a chemical reaction. Conversely, mixtures can be created by mechanical means alone, but a compound can only be created (either from elements or from other compounds, or a combination of the two) by a chemical reaction. Some mixtures are so intimately combined that they have some properties similar to compounds and may easily be mistaken for compounds. One example is alloys. Alloys are made mechanically, most commonly by heating the constituent metals to a liquid state, mixing them thoroughly, and then cooling the mixture quickly so that the constituents are trapped in the base metal. Other examples of compound-like mixtures include intermetallic compounds and solutions of alkali metals in a liquid form of ammonia. Formula Chemists describe compounds using formulas in various formats. For compounds that exist as molecules, the formula for the molecular unit is shown. For polymeric materials, such as minerals and many metal oxides, the empirical formula is normally given, e.g. NaCl for table salt. The elements in a chemical formula are normally listed in a specific order, called the Hill system. In this system, the carbon atoms (if there are any) are usually listed first, any hydrogen atoms are listed next, and all other elements follow in alphabetical order. If the formula contains no carbon, then all of the elements, including hydrogen, are listed alphabetically. There are, however, several important exceptions to the normal rules. For ionic compounds, the positive ion is almost always listed first and the negative ion is listed second. For oxides, oxygen is usually listed last. Organic acids generally follow the normal rules with C and H coming first in the formula. For example, the formula for trifluoroacetic acid is usually written as C2HF3O2. More descriptive formulas can convey structural information, such as writing the formula for trifluoroacetic acid as CF3CO2H. On the other hand, the chemical formulas for most inorganic acids and bases are exceptions to the normal rules. They are written according to the rules for ionic compounds (positive first, negative second), but they also follow rules that emphasize their Arrhenius definitions. Specifically, the formula for most inorganic acids begins with hydrogen and the formula for most bases ends with the hydroxide ion (OH-). Formulas for inorganic compounds do not often convey structural information, as illustrated by the common use of the formula H2SO4 for a molecule (sulfuric acid) that contains no H-S bonds. A more descriptive
  • 71. Chemical compound 69 presentation would be O2S(OH)2, but it is almost never written this way. Phases and thermal properties Compounds may have several possible phases. All compounds can exist as solids, at least at low enough temperatures. Molecular compounds may also exist as liquids, gases, and, in some cases, even plasmas. All compounds decompose upon applying heat. The temperature at which such fragmentation occurs is often called the decomposition temperature. Decomposition temperatures are not sharp and depend on the rate of heating. CAS number Every chemical substance, including chemical compounds, that has been described in the literature carries a unique numerical identifier, its CAS number. References [1] Brown, Theodore L.; LeMay, H. Eugene; Bursten, Bruce E.; Murphy, Catherine J.; Woodward, Patrick (2009), Chemistry: The Central Science, AP Edition (http:/ / www. pearsonschool. com/ index. cfm?locator=PSZ16f& PMDBSUBCATEGORYID=& PMDBSITEID=2781& PMDBSUBSOLUTIONID=& PMDBSOLUTIONID=6724& PMDBSUBJECTAREAID=& PMDBCATEGORYID=814& PMDbProgramId=52962) (11th ed.), Upper Saddle River, NJ: Pearson/Prentice Hall, pp. 5–6, ISBN 0-13-236489-1, [2] Hill, John W.; Petrucci, Ralph H.; McCreary, Terry W.; Perry, Scott S. (2005), General Chemistry (http:/ / www. pearsonhighered. com/ educator/ academic/ product/ 0,3110,0131402838,00. html) (4th ed.), Upper Saddle River, NJ: Pearson/Prentice Hall, p. 6, ISBN 978-0-13-140283-6, [3] Whitten, Kenneth W.; Davis, Raymond E.; Peck, M. Larry (2000), General Chemistry (6th ed.), Fort Worth, TX: Saunders College Publishing/Harcourt College Publishers, p. 15, ISBN 978-0-03-072373-5 [4] Wilbraham, Antony; Matta, Michael; Staley, Dennis; Waterman, Edward (2002), Chemistry (1st ed.), Upper Saddle River, NJ: Pearson/Prentice Hall, p. 36, ISBN 0-13-251210-6 [5] Halal, John (2008), "Chapter 8: General Chemistry" (http:/ / www. wadsworthmedia. com/ marketing/ sample_chapters/ 156253629X_ch08. pdf), Miladys Hair Structure and Chemistry Simplified (5 ed.), Milady Publishing, pp. 96–98, ISBN 1-4283-3558-7, Further reading • Robert Siegfried (2002). From elements to atoms: a history of chemical composition. American Philosophical Society. ISBN 978-0-87169-924-4.
  • 72. Chemical substance 70 Chemical substance In chemistry, a chemical substance is a form of matter that has constant chemical composition and characteristic properties.[1] It cannot be separated into components by physical separation methods, i.e. without breaking chemical bonds. They can be solids, liquids or gases. Chemical substances are often called pure to set them apart from mixtures. A common example of a chemical substance is pure water; it has the same properties and the same ratio of hydrogen to oxygen whether it is isolated from a river or made in a laboratory. Other chemical substances commonly encountered in pure form are diamond (carbon), gold, table salt (sodium chloride) and refined sugar (sucrose). However, simple or seemingly pure substances found in nature can in Steam and liquid water are two different forms of fact be mixtures of chemical substances. For example, tap water may the same chemical substance, water. contain small amounts of dissolved sodium chloride and compounds containing iron, calcium and many other chemical substances. Chemical substances exist as solids, liquids, gases, or plasma and may change between these phases of matter with changes in temperature or pressure. Chemical reactions convert one chemical substance into another. Forms of energy, such as light and heat, are not considered to be matter, and thus they are not "substances" in this regard. Definition Chemical substances (also called pure substances) are often defined as "any material with a definite chemical composition" in most introductory general chemistry textbooks.[2] According to this definition a chemical substance can either be a pure chemical element or a pure chemical compound. But, there are exceptions to this definition; a pure substance can also be defined as a form of matter that has both definite composition and distinct properties.[3] The chemical substance index published by CAS also includes several alloys of uncertain composition.[4] Non-stoichiometric compounds are a special Colors of a single chemical (Nile red) in different solvents, under visible and UV light. case (in inorganic chemistry) that violates the law of constant composition, and for them, it is sometimes difficult to draw the line between a mixture and a compound, as in the case of palladium hydride. Broader definitions of chemicals or chemical substances can be found, for example: "the term chemical substance means any organic or inorganic substance of a particular molecular identity, including – (i) any combination of such substances occurring in whole or in part as a result of a chemical reaction or occurring in nature"[5] In geology, substances of uniform composition are called minerals, while physical mixtures (aggregates) of several minerals (different substances) are defined as rocks. Many minerals, however, mutually dissolve into solid solutions, such that a single rock is a uniform substance despite being a mixture. Feldspars are a common example: anorthoclase is an alkali aluminum silicate, where the alkali metal is interchangeably either sodium or potassium.
  • 73. Chemical substance 71 History The concept of a "chemical substance" became firmly established in the late eighteenth century after work by the chemist Joseph Proust on the composition of some pure chemical compounds such as basic copper carbonate.[6] He deduced that, "All samples of a compound have the same composition; that is, all samples have the same proportions, by mass, of the elements present in the compound." This is now known as the law of constant composition.[7] Later with the advancement of methods for chemical synthesis particularly in the realm of organic chemistry; the discovery of many more chemical elements and new techniques in the realm of analytical chemistry used for isolation and purification of elements and compounds from chemicals that led to the establishment of modern chemistry, the concept was defined as is found in most chemistry textbooks. However, there are some controversies regarding this definition mainly because the large number of chemical substances reported in chemistry literature need to be indexed. Isomerism caused much consternation to early researchers, since isomers have exact the same composition, but differ in configuration (arrangement) of the atoms. For example, there was much speculation for the chemical identity of benzene, until the correct structure was described by Friedrich August Kekulé. Likewise, the idea of stereoisomerism - that atoms have rigid three-dimensional structure and can thus form isomers that differ only in their three-dimensional arrangement - was another crucial step in understanding the concept of distinct chemical substances. For example, tartaric acid has three distinct isomers, a pair of diastereomers with one diastereomer forming two enantiomers. Chemical elements An element is a chemical substance that is made up of a particular kind of atoms and hence cannot be broken down or transformed by a chemical reaction into a different element, though it can be transmutated into another element through a nuclear reaction. This is so, because all of the atoms in a sample of an element have the same number of protons, though they may be different isotopes, with differing numbers of neutrons. As of 2012, there are 118 known elements, about 80 of which are stable – that is, they do not change by radioactive decay into other Native sulfur crystals. Sulfur occurs naturally as elements. Some elements can occur as more than a single chemical elemental sulfur, in sulfide and sulfate minerals substance (allotropes). For instance, oxygen exists as both diatomic and in hydrogen sulfide. oxygen (O2) and ozone (O3). The majority of elements are classified as metals. These are elements with a characteristic lustre such as iron, copper, and gold. Metals typically conduct electricity and heat well, and they are malleable and ductile.[8] Around a dozen elements,[9] such as carbon, nitrogen, and oxygen, are classified as non-metals. Non-metals lack the metallic properties described above, they also have a high electronegativity and a tendency to form negative ions. Certain elements such as silicon sometimes resemble metals and sometimes resemble non-metals, and are known as metalloids.
  • 74. Chemical substance 72 Chemical compounds A pure chemical compound is a chemical substance that is composed of a particular set of molecules or ions. Two or more elements combined into one substance through a chemical reaction form a chemical compound. All compounds are substances, but not all substances are compounds. A chemical compound can be either atoms bonded together in molecules or crystals in which atoms, molecules or ions form a crystalline lattice. Compounds based primarily on carbon and hydrogen Potassium ferricyanide is a compound of atoms are called organic compounds, and all others are called inorganic potassium, iron, carbon and nitrogen; although it compounds. Compounds containing bonds between carbon and a metal contains cyanide anions, it does not release them are called organometallic compounds. and is nontoxic. Compounds in which components share electrons are known as covalent compounds. Compounds consisting of oppositely charged ions are known as ionic compounds, or salts. In organic chemistry, there can be more than one chemical compound with the same composition and molecular weight. Generally, these are called isomers. Isomers usually have substantially different chemical properties, may be isolated and do not spontaneously convert to each other. A common example is glucose vs. fructose. The former is an aldehyde, the latter is a ketone. Their interconversion requires either enzymatic or acid-base catalysis. However, there are also tautomers, where isomerization occurs spontaneously, such that a pure substance cannot be isolated into its tautomers. A common example is glucose, which has open-chain and ring forms. One cannot manufacture pure open-chain glucose because glucose spontaneously cyclizes to the hemiacetal form. Substances versus mixtures All matter consists of various elements and chemical compounds, but these are often intimately mixed together. Mixtures contain more than one chemical substance, and they do not have a fixed composition. In principle, they can be separated into the component substances by purely mechanical processes. Butter, soil and wood are common examples of mixtures. Grey iron metal and yellow sulfur are both chemical elements, and they can be mixed together in any ratio to form a yellow-grey mixture. No chemical process occurs, and the material can be identified as a mixture by the fact that the sulfur and the iron can be separated by a Cranberry glass, while it looks homogeneous, is a mechanical process, such as using a magnet to attract the iron away mixture consisting of glass and gold colloidal from the sulfur. particles of ca. 40 nm diameter, which give it a red color. In contrast, if iron and sulfur are heated together in a certain ratio (1 atom of iron for each atom of sulfur, or by weight, 56 grams (1 mol) of iron to 32 grams (1 mol) of sulfur), a chemical reaction takes place and a new substance is formed, the compound iron(II) sulfide, with chemical formula FeS. The resulting compound has all the properties of a chemical substance and is not a mixture. Iron(II) sulfide has its own distinct properties such as melting point and solubility, and the two elements cannot be separated using normal mechanical processes; a magnet will be unable to recover the iron, since there is no metallic iron present in the compound.
  • 75. Chemical substance 73 Chemicals versus chemical substances While the term chemical substance is a precise technical term that is synonymous with "chemical" for professional chemists, the meaning of the word chemical varies for non-chemists within the English speaking world or those using English. For industries, government and society in general in some countries,[10] the word chemical includes a wider class of substances that contain many mixtures of such chemical substances, often finding application in many vocations.[11] In countries that require a list of ingredients in products, the "chemicals" listed would be equated with "chemical substances".[12] Within the chemical industry, manufactured "chemicals" are chemical substances, which can be classified by production volume into bulk chemicals, fine chemicals and chemicals found in research only. Bulk chemicals are produced in very large quantities, usually with highly optimized continuous processes and to a relatively low price. Fine chemicals are produced at a high cost in small quantities for special low-volume applications such as biocides, pharmaceuticals and speciality chemicals for technical applications. Research chemicals are produced individually for research, such as when searching for synthetic routes or screening substances for pharmaceutical activity. In effect, their price per gram is very high, although they are not sold. The cause of the difference in production volume is the complexity of the molecular structure of the chemical. Bulk chemicals are usually much less complex. While fine chemicals may be more complex, many of them are simple enough to be sold as "building blocks" in the synthesis of more complex molecules targeted for single use, as named above. The production of a chemical includes not only its synthesis but also its purification to eliminate by-products and impurities involved in the synthesis. The last step in production should be the analysis of batch lots of chemicals in order to identify and quantify the percentages of impurities for the buyer of the chemicals. The required purity and analysis depends on the application, but higher tolerance of impurities is usually expected in the production of bulk chemicals. Thus, the user of the chemical in the US might choose between the bulk or "technical grade" with higher amounts of impurities or a much purer "pharmaceutical grade" (labeled "USP", United States Pharmacopeia). Naming and indexing Every chemical substance has one or more systematic names, usually named according to the IUPAC rules for naming. An alternative system is used by the Chemical Abstracts Service (CAS). Many compounds are also known by their more common, simpler names, many of which predate the systematic name. For example, the long-known sugar glucose is now systematically named 6-(hydroxymethyl)oxane-2,3,4,5-tetrol. Natural products and pharmaceuticals are also given simpler names, for example the mild pain-killer Naproxen is the more common name for the chemical compound (S)-6-methoxy-α-methyl-2-naphthaleneacetic acid. Chemists frequently refer to chemical compounds using chemical formulae or molecular structure of the compound. There has been a phenomenal growth in the number of chemical compounds being synthesized (or isolated), and then reported in the scientific literature by professional chemists around the world.[13] An enormous number of chemical compounds are possible through the chemical combination of the known chemical elements. As of May 2011, about sixty million chemical compounds are known.[14] The names of many of these compounds are often nontrivial and hence not very easy to remember or cite accurately. Also it is difficult to keep the track of them in the literature. Several international organizations like IUPAC and CAS have initiated steps to make such tasks easier. CAS provides the abstracting services of the chemical literature, and provides a numerical identifier, known as CAS registry number to each chemical substance that been reported in the chemical literature (such as chemistry journals and patents). This information is compiled as a database and is popularly known as the Chemical substances index. Other computer-friendly systems that have been developed for substance information, are: SMILES and the International Chemical Identifier or InChI.
  • 76. Chemical substance 74 Identification of a typical chemical substance Common name Systematic name Chemical formula Chemical structure CAS registry number InChI alcohol, or ethanol C2H5OH [64-17-5] 1/C2H6O/c1-2-3/h3H,2H2,1H3 ethyl alcohol Isolation, purification, characterization, and identification Often a pure substance needs to be isolated from a mixture, for example from a natural source (where a sample often contains numerous chemical substances) or after a chemical reaction (which often give mixtures of chemical substances). External links • eChemPortal substance and property search [15] Notes and references [1] Nic, M.; Jirat, J.; Kosata, B., eds. (2006–). "Chemical Substance" (http:/ / goldbook. iupac. org/ C01039. html). IUPAC Compendium of Chemical Terminology (Online ed.). doi:10.1351/goldbook.C01039. ISBN 0-9678550-9-8. . [2] Hill, J. W.; Petrucci, R. H.; McCreary, T. W.; Perry, S. S. General Chemistry, 4th ed., p5, Pearson Prentice Hall, Upper Saddle River, New Jersey, 2005 [3] Pure Substance – DiracDelta Science & Engineering Encyclopedia (http:/ / www. diracdelta. co. uk/ science/ source/ p/ u/ pure substance/ source. html) [4] Appendix IV: Chemical Substance Index Names (http:/ / www. cas. org/ ASSETS/ 58D34DD3892142D18F5C3B0A004D3A0C/ indexguideapp. pdf) [5] "What is the TSCA Chemical Substance Inventory?" (http:/ / www. epa. gov/ oppt/ newchems/ pubs/ invntory. htm). US Environmental Protection Agency. . Retrieved 2009-10-19. [6] Hill, J. W.; Petrucci, R. H.; McCreary, T. W.; Perry, S. S. General Chemistry, 4th ed., p37, Pearson Prentice Hall, Upper Saddle River, New Jersey, 2005. [7] Law of Definite Proportions (http:/ / dbhs. wvusd. k12. ca. us/ webdocs/ AtomicStructure/ LawofDefiniteProportion. html) [8] Hill, J. W.; Petrucci, R. H.; McCreary, T. W.; Perry, S. S. General Chemistry, 4th ed., pp 45–46, Pearson Prentice Hall, Upper Saddle River, New Jersey, 2005. [9] The boundary between metalloids and non-metals is imprecise, as explained in the previous reference. [10] What is a chemical (http:/ / www. nicnas. gov. au/ Industry/ New_Chemicals/ Does_My_Chemical_Require_Notification/ What_Is_A_Chemical. asp) [11] BfR – Chemicals (http:/ / www. bfr. bund. de/ cd/ 569) [12] There is only one definition for "chemical", that of a substance, in the US Unabridged Edition of the Random House Dictionary of the English Language, New York, 1966. [13] Coping with the Growth of Chemical Knowledge: Challenges for Chemistry Documentation, Education, and Working Chemists (http:/ / www. rz. uni-karlsruhe. de/ ~ed01/ Jslit/ eduquim. htm) [14] Chemical Abstracts substance count (http:/ / www. cas. org/ newsevents/ releases/ 60millionth052011. html) [15] http:/ / www. echemportal. org
  • 77. Molecule 75 Molecule A molecule (  /ˈmɒlɪkjuːl/) is an electrically neutral group of two or more atoms held together by covalent chemical bonds.[1][2][3][4][5][6] Molecules are distinguished from ions by their lack of electrical charge. However, in quantum physics, organic 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane chemistry, and biochemistry, the term molecule is often used less strictly, also being applied to polyatomic ions. In the kinetic theory of gases, the term molecule is often used for any gaseous particle regardless of its composition. According to this definition noble gas atoms are considered molecules despite the fact that they are composed of a single non-bonded atom.[7] A molecule may consist of atoms of a single chemical element, as with oxygen (O2), or of different elements, as with water (H2O). Atoms and complexes connected by non-covalent bonds such as hydrogen bonds or ionic bonds are generally not considered single molecules.[8] Molecules as components of matter are common in organic substances (and therefore biochemistry). They also make up most of the oceans and atmosphere. However, the majority of familiar solid substances on Earth, including most of the minerals that make up the crust, mantle, and core of the Earth, contain many chemical bonds, but are not made of identifiable molecules. Also, no typical molecule can be defined for ionic crystals (salts) and covalent crystals (network solids), although these are often composed of repeating unit cells that extend either in a plane (such as in graphene) or three-dimensionally (such as in diamond, quartz, or sodium chloride). The theme of repeated unit-cellular-structure also holds for most condensed phases with metallic bonding, which means that solid metals are also not made of molecules. In glasses (solids that exist in a vitreous disordered state), atoms may also be held together by chemical bonds without presence of any definable molecule, but also without any of the regularity of repeating units that characterises crystals. Molecular science The science of molecules is called molecular chemistry or molecular physics, depending on whether the focus is on chemistry or physics. Molecular chemistry deals with the laws governing the interaction between molecules that results in the formation and breakage of chemical bonds, while molecular physics deals with the laws governing their structure and properties. In practice, however, this distinction is vague. In molecular sciences, a molecule consists of a stable system (bound state) comprising two or more atoms. Polyatomic ions may sometimes be usefully thought of as electrically charged molecules. The term unstable molecule is used for very reactive species, i.e., short-lived assemblies (resonances) of electrons and nuclei, such as radicals, molecular ions, Rydberg molecules, transition states, van der Waals complexes, or systems of colliding atoms as in Bose-Einstein condensate
  • 78. Molecule 76 History and etymology According to Merriam-Webster and the Online Etymology Dictionary, the word "molecule" derives from the Latin "moles" or small unit of mass. • Molecule (1794) – "extremely minute particle," from Fr. molécule (1678), from Mod.L. molecula, dim. of L. moles "mass, barrier". A vague meaning at first; the vogue for the word (used until late 18th century only in Latin form) can be traced to the philosophy of Descartes. Although the existence of molecules has been accepted by many chemists since the early 19th century as a result of Daltons laws of Definite and Multiple Proportions (1803–1808) and Avogadros law (1811), there was some resistance among positivists and physicists such as Mach, Boltzmann, Maxwell, and Gibbs, who saw molecules merely as convenient mathematical constructs. The work of John Dalton Perrin on Brownian motion (1911) is considered to be the final proof of the existence of molecules. The definition of the molecule has evolved as knowledge of the structure of molecules has increased. Earlier definitions were less precise, defining molecules as the smallest particles of pure chemical substances that still retain their composition and chemical properties.[9] This definition often breaks down since many substances in ordinary experience, such as rocks, salts, and metals, are composed of large networks of chemically bonded atoms or ions, but are not made of discrete molecules. Molecular size Most molecules are far too small to be seen with the naked eye, but there are exceptions. DNA, a macromolecule, can reach macroscopic sizes, as can molecules of many polymers. The smallest molecule is the diatomic hydrogen (H2), with a bond length of 0.74 Å.[10] Molecules commonly used as building blocks for organic synthesis have a dimension of a few Å to several dozen Å. Single molecules cannot usually be observed by light (as noted above), but small molecules and even the outlines of individual atoms may be traced in some circumstances by use of an atomic force microscope. Some of the largest molecules are macromolecules or supermolecules. Radius Effective molecular radius is the size a molecule displays in solution.[11][12] The table of permselectivity for different substances contains examples. Molecular formula A compounds empirical formula is the simplest integer ratio of the chemical elements that constitute it. For example, water is always composed of a 2:1 ratio of hydrogen to oxygen atoms, and ethyl alcohol or ethanol is always composed of carbon, hydrogen, and oxygen in a 2:6:1 ratio. However, this does not determine the kind of molecule uniquely – dimethyl ether has the same ratios as ethanol, for instance. Molecules with the same atoms in different arrangements are called isomers. Also carbohydrates, for example, have the same ratio (carbon:hydrogen:oxygen = 1:2:1) (and thus the same empirical formula) but different total numbers of atoms in the molecule. The molecular formula reflects the exact number of atoms that compose the molecule and so characterizes different molecules. However different isomers can have the same atomic composition while being different molecules. The empirical formula is often the same as the molecular formula but not always. For example, the molecule acetylene has molecular formula C2H2, but the simplest integer ratio of elements is CH.
  • 79. Molecule 77 The molecular mass can be calculated from the chemical formula and is expressed in conventional atomic mass units equal to 1/12 of the mass of a neutral carbon-12 (12C isotope) atom. For network solids, the term formula unit is used in stoichiometric calculations. Molecular geometry Molecules have fixed equilibrium geometries—bond lengths and angles— about which they continuously oscillate through vibrational and rotational motions. A pure substance is composed of molecules with the same average geometrical structure. The chemical formula and the structure of a molecule are the two important factors that determine its properties, particularly its reactivity. Isomers share a chemical formula but normally have very different properties because of their different structures. Stereoisomers, a particular type of isomers, may have very similar physico-chemical properties and at the same time different biochemical activities. Molecular spectroscopy Molecular spectroscopy deals with the response (spectrum) of molecules interacting with probing signals of known energy (or frequency, according to Plancks formula). Molecules have quantized energy levels that can be analyzed by detecting the molecules energy exchange through absorbance or emission.[13] Spectroscopy does not generally refer to diffraction studies where particles such as neutrons, electrons, or high energy X-rays interact with a regular arrangement of molecules (as in a crystal). Theoretical aspects The study of molecules by molecular physics and theoretical chemistry is largely based on quantum mechanics and is essential for the understanding of the chemical bond. The simplest of molecules is the hydrogen molecule-ion, H2+, and the simplest of all the chemical bonds is the one-electron bond. H2+ is composed of two positively charged protons and one negatively charged electron, which means that the Schrödinger equation for the system can be solved more easily due to the lack of electron–electron repulsion. With the development of fast digital computers, approximate solutions for more complicated molecules became possible and are one of the main aspects of computational chemistry. When trying to define rigorously whether an arrangement of atoms is "sufficiently stable" to be considered a molecule, IUPAC suggests that it "must correspond to a depression on the potential energy surface that is deep enough to confine at least one vibrational state".[1] This definition does not depend on the nature of the interaction between the atoms, but only on the strength of the interaction. In fact, it includes weakly bound species that would not traditionally be considered molecules, such as the helium dimer, He2, which has one vibrational bound state[14] and is so loosely bound that it is only likely to be observed at very low temperatures. References [1] Nic, M.; Jirat, J.; Kosata, B., eds. (2006–). "molecule" (http:/ / goldbook. iupac. org/ M04002. html). IUPAC Compendium of Chemical Terminology (Online ed.). doi:10.1351/goldbook.{{{file}}}. ISBN 0-9678550-9-8. . [2] Pauling, Linus (1970). General Chemistry. New York: Dover Publications, Inc.. ISBN 0-486-65622-5. [3] Ebbin, Darrell, D. (1990). General Chemistry, 3rd Ed.. Boston: Houghton Mifflin Co.. ISBN 0-395-43302-9. [4] Brown, T.L. (2003). Chemistry – the Central Science, 9th Ed.. New Jersey: Prentice Hall. ISBN 0-13-066997-0. [5] Chang, Raymond (1998). Chemistry, 6th Ed.. New York: McGraw Hill. ISBN 0-07-115221-0. [6] Zumdahl, Steven S. (1997). Chemistry, 4th ed.. Boston: Houghton Mifflin. ISBN 0-669-41794-7. [7] Chandra, Sulekh. Comprehensive Inorganic Chemistry. New Age Publishers. ISBN 81-224-1512-1. [8] Molecule (http:/ / www. britannica. com/ EBchecked/ topic/ 388236/ molecule), Encyclopaedia Britannica on-line [9] Molecule Definition (http:/ / antoine. frostburg. edu/ chem/ senese/ 101/ glossary/ m. shtml#molecule) (Frostburg State University) [10] Roger L. DeKock, Harry B. Gray (1989). Chemical structure and bonding (http:/ / books. google. com/ ?id=q77rPHP5fWMC& pg=PA199). University Science Books. p. 199. ISBN 0-935702-61-X. .
  • 80. Molecule 78 [11] Chang RL, Deen WM, Robertson CR, Brenner BM. (1975). "Permselectivity of the glomerular capillary wall: III. Restricted transport of polyanions". Kidney Int. 8 (4): 212–218. doi:10.1038/ki.1975.104. PMID 1202253. [12] Chang RL, Ueki IF, Troy JL, Deen WM, Robertson CR, Brenner BM. (1975). "Permselectivity of the glomerular capillary wall to macromolecules. II. Experimental studies in rats using neutral dextran". Biophys J. 15 (9): 887–906. Bibcode 1975BpJ....15..887C. doi:10.1016/S0006-3495(75)85863-2. PMC 1334749. PMID 1182263. [13] Nic, M.; Jirat, J.; Kosata, B., eds. (2006–). "spectroscopy" (http:/ / goldbook. iupac. org/ {{{file}}}. html). IUPAC Compendium of Chemical Terminology (Online ed.). doi:10.1351/goldbook.{{{file}}}. ISBN 0-9678550-9-8. . [14] Anderson JB (May 2004). "Comment on "An exact quantum Monte Carlo calculation of the helium-helium intermolecular potential" [J. Chem. Phys. 115, 4546 (2001)]". J Chem Phys 120 (20): 9886–7. Bibcode 2004JChPh.120.9886A. doi:10.1063/1.1704638. PMID 15268005. External links • Molecule of the Month ( – School of Chemistry, University of Bristol Chemical bond A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electrostatic force of attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction. The strength of chemical bonds varies considerably; there are "strong bonds" such as covalent or ionic bonds and "weak bonds" such as dipole–dipole interactions, the London dispersion force and hydrogen bonding. Since opposite charges attract via a simple electromagnetic force, the negatively charged electrons that are orbiting the nucleus and the positively charged protons in the nucleus attract each other. Also, an electron positioned between two nuclei will be attracted to both of them. Thus, the most stable configuration of nuclei and electrons is one in which the electrons spend more time between nuclei, than anywhere else in space. These electrons cause the nuclei to be attracted to each other, and this attraction results in the bond. However, this assembly cannot collapse to a size dictated by the volumes of these individual particles. Due to the matter wave nature of electrons and their smaller mass, they occupy a much larger amount of volume compared with the nuclei, and this volume occupied by the electrons keeps the atomic nuclei relatively far apart, as compared with the size of the nuclei themselves. In general, strong chemical bonding is associated with the sharing or transfer of electrons between the participating atoms. The atoms in molecules, crystals, metals and diatomic gases— indeed most of the physical environment around us— are held together by chemical bonds, which dictate the structure and the bulk properties of matter.
  • 81. Chemical bond 79 Overview of main types of chemical bonds A chemical bond is an attraction between atoms. This attraction may be seen as the result of different behaviors of the outermost electrons of atoms. Although all of these behaviors merge into each other seamlessly in various bonding situations so that there is no clear line to be drawn between them, nevertheless behaviors of atoms become so qualitatively different as the character of the bond changes quantitatively, that it remains useful and customary to differentiate between the bonds that cause these different properties of condensed Examples of Lewis dot-style chemical bonds between carbon C, hydrogen H, and matter. oxygen O. Lewis dot depictures represent an early attempt to describe chemical bonding and are still widely used today. In the simplest view of a so-called covalent bond, one or more electrons (often a pair of electrons) are drawn into the space between the two atomic nuclei. Here the negatively charged electrons are attracted to the positive charges of both nuclei, instead of just their own. This overcomes the repulsion between the two positively charged nuclei of the two atoms, and so this overwhelming attraction holds the two nuclei in a fixed configuration of equilibrium, even though they will still vibrate at equilibrium position. Thus, covalent bonding involves sharing of electrons in which the positively charged nuclei of two or more atoms simultaneously attract the negatively charged electrons that are being shared between them. These bonds exist between two particular identifiable atoms, and have a direction in space, allowing them to be shown as single connecting lines between atoms in drawings, or modeled as sticks between spheres in models. In a polar covalent bond, one or more electrons are unequally shared between two nuclei. Covalent bonds often result in the formation of small collections of better-connected atoms called molecules, which in solids and liquids are bound to other molecules by forces that are often much weaker than the covalent bonds that hold the molecules internally together. Such weak intermolecular bonds give organic molecular substances, such as waxes and oils, their soft bulk character, and their low melting points (in liquids, molecules must cease most structured or oriented contact with each other). When covalent bonds link long chains of atoms in large molecules, however (as in polymers such as nylon), or when covalent bonds extend in networks though solids that are not composed of discrete molecules (such as diamond or quartz or the silicate minerals in many types of rock) then the structures that result may be both strong and tough, at least in the direction oriented correctly with networks of covalent bonds. Also, the melting points of such covalent polymers and networks increase greatly. In a simplified view of an ionic bond, the bonding electron is not shared at all, but transferred. In this type of bond, the outer atomic orbital of one atom has a vacancy which allows addition of one or more electrons. These newly added electrons potentially occupy a lower energy-state (effectively closer to more nuclear charge) than they experience in a different atom. Thus, one nucleus offers a more tightly bound position to an electron than does another nucleus, with the result that one atom may transfer an electron to the other. This transfer causes one atom to assume a net positive charge, and the other to assume a net negative charge. The bond then results from electrostatic attraction between atoms, and the atoms become positive or negatively charged ions. Ionic bonds may be seen as extreme examples of polarization in covalent bonds. Often, such bonds have no particular orientation in space, since
  • 82. Chemical bond 80 they result from equal electrostatic attraction of each ion to all ions around them. Ionic bonds are strong (and thus ionic substances require high temperatures to melt) but also brittle, since the forces between ions are short-range, and do not easily bridge cracks and fractures. This type of bond gives a charactistic physical character to crystals of classic mineral salts, such as table salt. A less often mentioned type of bonding is the metallic bond. In this type of bonding, each atom in a metal donates one or more electrons to a "sea" of electrons that reside between many metal atoms. In this sea, each electron is free (by virtue of its wave nature) to be associated with a great many atoms at once. The bond results because the metal atoms become somewhat positively charged due to loss of their electrons, while the electrons remain attracted to many atoms, without being part of any given atom. Metallic bonding may be seen as an extreme example of delocalization of electrons over a large system of covalent bonds, in which every atom participates. This type of bonding is often very strong (resulting in the tensile strength of metals). However, metallic bonds are more collective in nature than other types, and so they allow metal crystals to more easily deform, because they are composed of atoms attracted to each other, but not in any particularly-oriented ways. This results in the malliability of metals. The sea of electrons in metallic bonds causes the characteristically good electrical and thermal conductivity of metals, and also their "shiny" reflection of most frequencies of white light. All bonds can be explained by quantum theory, but, in practice, simplification rules allow chemists to predict the strength, directionality, and polarity of bonds. The octet rule and VSEPR theory are two examples. More sophisticated theories are valence bond theory which includes orbital hybridization and resonance, and the linear combination of atomic orbitals molecular orbital method which includes ligand field theory. Electrostatics are used to describe bond polarities and the effects they have on chemical substances. History Early speculations into the nature of the chemical bond, from as early as the 12th century, supposed that certain types of chemical species were joined by a type of chemical affinity. In 1704, Isaac Newton famously outlined his atomic bonding theory, in "Query 31" of his Opticks, whereby atoms attach to each other by some "force". Specifically, after acknowledging the various popular theories in vogue at the time, of how atoms were reasoned to attach to each other, i.e. "hooked atoms", "glued together by rest", or "stuck together by conspiring motions", Newton states that he would rather infer from their cohesion, that "particles attract one another by some force, which in immediate contact is exceedingly strong, at small distances performs the chemical operations, and reaches not far from the particles with any sensible effect." In 1819, on the heels of the invention of the voltaic pile, Jöns Jakob Berzelius developed a theory of chemical combination stressing the electronegative and electropositive character of the combining atoms. By the mid 19th century, Edward Frankland, F.A. Kekulé, A.S. Couper, A.M. Butlerov, and Hermann Kolbe, building on the theory of radicals, developed the theory of valency, originally called "combining power", in which compounds were joined owing to an attraction of positive and negative poles. In 1916, chemist Gilbert N. Lewis developed the concept of the electron-pair bond, in which two atoms may share one to six electrons, thus forming the single electron bond, a single bond, a double bond, or a triple bond; in Lewiss own words, "An electron may form a part of the shell of two different atoms and cannot be said to belong to either one exclusively."[1] That same year, Walther Kossel put forward a theory similar to Lewis only his model assumed complete transfers of electrons between atoms, and was thus a model of ionic bonds. Both Lewis and Kossel structured their bonding models on that of Abeggs rule (1904). In 1927, the first mathematically complete quantum description of a simple chemical bond, i.e. that produced by one electron in the hydrogen molecular ion, H2+, was derived by the Danish physicist Oyvind Burrau.[2] This work showed that the quantum approach to chemical bonds could be fundamentally and quantitatively correct, but the mathematical methods used could not be extended to molecules containing more than one electron. A more practical, albeit less quantitative, approach was put forward in the same year by Walter Heitler and Fritz London. The
  • 83. Chemical bond 81 Heitler-London method forms the basis of what is now called valence bond theory. In 1929, the linear combination of atomic orbitals molecular orbital method (LCAO) approximation was introduced by Sir John Lennard-Jones, who also suggested methods to derive electronic structures of molecules of F2 (fluorine) and O2 (oxygen) molecules, from basic quantum principles. This molecular orbital theory represented a covalent bond as an orbital formed by combining the quantum mechanical Schrödinger atomic orbitals which had been hypothesized for electrons in single atoms. The equations for bonding electrons in multi-electron atoms could not be solved to mathematical perfection (i.e., analytically), but approximations for them still gave many good qualitative predictions and results. Most quantitative calculations in modern quantum chemistry use either valence bond or molecular orbital theory as a starting point, although a third approach, Density Functional Theory, has become increasingly popular in recent years. In 1935, H. H. James and A. S. Coolidge carried out a calculation on the dihydrogen molecule that, unlike all previous calculation which used functions only of the distance of the electron from the atomic nucleus, used functions which also explicitly added the distance between the two electrons.[3] With up to 13 adjustable parameters they obtained a result very close to the experimental result for the dissociation energy. Later extensions have used up to 54 parameters and give excellent agreement with experiment. This calculation convinced the scientific community that quantum theory could give agreement with experiment. However this approach has none of the physical pictures of the valence bond and molecular orbital theories and is difficult to extend to larger molecules. Valence bond theory In 1927, valence bond theory was formulated and it argues that a chemical bond forms when two valence electrons, in their respective atomic orbitals, work or function to hold two nuclei together, by virtue of effects of lowering system energies. Building on this theory, the chemist Linus Pauling published in 1931 what some consider one of the most important papers in the history of chemistry: "On the Nature of the Chemical Bond". In this paper, elaborating on the works of Lewis, and the valence bond theory (VB) of Heitler and London, and his own earlier works, Pauling presented six rules for the shared electron bond, the first three of which were already generally known: 1. The electron-pair bond forms through the interaction of an unpaired electron on each of two atoms. 2. The spins of the electrons have to be opposed. 3. Once paired, the two electrons cannot take part in additional bonds. His last three rules were new: 4. The electron-exchange terms for the bond involves only one wave function from each atom. 5. The available electrons in the lowest energy level form the strongest bonds. 6. Of two orbitals in an atom, the one that can overlap the most with an orbital from another atom will form the strongest bond, and this bond will tend to lie in the direction of the concentrated orbital. Building on this article, Paulings 1939 textbook: On the Nature of the Chemical Bond would become what some have called the "Bible" of modern chemistry. This book helped experimental chemists to understand the impact of quantum theory on chemistry. However, the later edition in 1959 failed to adequately address the problems that appeared to be better understood by molecular orbital theory. The impact of valence theory declined during the 1960s and 1970s as molecular orbital theory grew in usefulness as it was implemented in large digital computer programs. Since the 1980s, the more difficult problems of implementing valence bond theory into computer programs have been solved largely, and valence bond theory has seen a resurgence.
  • 84. Chemical bond 82 Comparison of valence bond and molecular orbital theory In some respects valence bond theory is superior to molecular orbital theory. When applied to the simplest two-electron molecule, H2, valence bond theory, even at the simplest Heitler-London approach, gives a much closer approximation to the bond energy, and it provides a much more accurate representation of the behavior of the electrons as chemical bonds are formed and broken. In contrast simple molecular orbital theory predicts that the hydrogen molecule dissociates into a linear superposition of hydrogen atoms and positive and negative hydrogen ions, a completely unphysical result. This explains in part why the curve of total energy against interatomic distance for the valence bond method lies below the curve for the molecular orbital method at all distances and most particularly so for large distances. This situation arises for all homonuclear diatomic molecules and is particularly a problem for F2, where the minimum energy of the curve with molecular orbital theory is still higher in energy than the energy of two F atoms. The concepts of hybridization are so versatile, and the variability in bonding in most organic compounds is so modest, that valence bond theory remains an integral part of the vocabulary of organic chemistry. However, the work of Friedrich Hund, Robert Mulliken, and Gerhard Herzberg showed that molecular orbital theory provided a more appropriate description of the spectroscopic, ionization and magnetic properties of molecules. The deficiencies of valence bond theory became apparent when hypervalent molecules (e.g. PF5) were explained without the use of d orbitals that were crucial to the bonding hybridisation scheme proposed for such molecules by Pauling. Metal complexes and electron deficient compounds (e.g. diborane) also appeared to be well described by molecular orbital theory, although valence bond descriptions have been made. In the 1930s the two methods strongly competed until it was realised that they are both approximations to a better theory. If we take the simple valence bond structure and mix in all possible covalent and ionic structures arising from a particular set of atomic orbitals, we reach what is called the full configuration interaction wave function. If we take the simple molecular orbital description of the ground state and combine that function with the functions describing all possible excited states using unoccupied orbitals arising from the same set of atomic orbitals, we also reach the full configuration interaction wavefunction. It can be then seen that the simple molecular orbital approach gives too much weight to the ionic structures, while the simple valence bond approach gives too little. This can also be described as saying that the molecular orbital approach is too delocalised, while the valence bond approach is too localised. The two approaches are now regarded as complementary, each providing its own insights into the problem of chemical bonding. Modern calculations in quantum chemistry usually start from (but ultimately go far beyond) a molecular orbital rather than a valence bond approach, not because of any intrinsic superiority in the former but rather because the MO approach is more readily adapted to numerical computations. However better valence bond programs are now available. Bonds in chemical formulas The fact that atoms and molecules are three-dimensional makes it difficult to use a single technique for indicating orbitals and bonds. In molecular formulas the chemical bonds (binding orbitals) between atoms are indicated by various methods according to the type of discussion. Sometimes, they are completely neglected. For example, in organic chemistry chemists are sometimes concerned only with the functional groups of the molecule. Thus, the molecular formula of ethanol may be written in a paper in conformational, three-dimensional, full two-dimensional (indicating every bond with no three-dimensional directions), compressed two-dimensional (CH3–CH2–OH), separating the functional group from another part of the molecule (C2H5OH), or by its atomic constituents (C2H6O), according to what is discussed. Sometimes, even the non-bonding valence shell electrons (with the two-dimensional approximate directions) are marked, i.e. for elemental carbon .C. Some chemists may also mark the respective orbitals, i.e. the hypothetical ethene−4 anion (/C=C/ −4) indicating the possibility of bond formation.
  • 85. Chemical bond 83 Strong chemical bonds Typical bond lengths in pm and bond energies in kJ/mol. Bond lengths can be converted to Åby division by 100 (1 Å = 100 pm). Data taken from [4]. Bond Length Energy (pm) (kJ/mol) H — Hydrogen H–H 74 436 H–O 96 366 H–F 92 568 H–Cl 127 432 C — Carbon C–H 109 413 C–C 154 348 C–C= 151 =C–C≡ 147 =C–C= 148 C=C 134 614 C≡C 120 839 C–N 147 308 C–O 143 360 C–F 134 488 C–Cl 177 330 N — Nitrogen N–H 101 391 N–N 145 170 N≡N 110 945 O — Oxygen O–O 148 145 O=O 121 498 F, Cl, Br, I — Halogens F–F 142 158 Cl–Cl 199 243 Br–H 141 366 Br–Br 228 193 I–H 161 298 I–I 267 151
  • 86. Chemical bond 84 Strong chemical bonds are the intramolecular forces which hold atoms together in molecules. A strong chemical bond is formed from the transfer or sharing of electrons between atomic centers and relies on the electrostatic attraction between the protons in nuclei and the electrons in the orbitals. Although these bonds typically involve the transfer of integer numbers of electrons (this is the bond order, which represents one transferred electron or two shared electrons), some systems can have intermediate numbers of bonds. An example of this is the organic molecule benzene, where the bond order is 1.5 for each carbon atom, meaning that it has 1.5 bonds (shares three electrons) with each one of its two neighbors. The types of strong bond differ due to the difference in electronegativity of the constituent elements. A large difference in electronegativity leads to more polar (ionic) character in the bond. Covalent bond Covalent bonding is a common type of bonding, in which the electronegativity difference between the bonded atoms is small or nonexistent. Bonds within most organic compounds are described as covalent. See sigma bonds and pi bonds for LCAO-description of such bonding. A polar covalent bond is a covalent bond with a significant ionic character. This means that the electrons are closer to one of the atoms than the other, creating an imbalance of charge. They occur as a bond between two atoms with moderately different electronegativities, and give rise to dipole-dipole interactions. The electronegativity of these bonds is 0.3 to 1.7 . A coordinate covalent bond is one where both bonding electrons are from one of the atoms involved in the bond. These bonds give rise to Lewis acids and bases. The electrons are shared roughly equally between the atoms in contrast to ionic bonding. Such bonding occurs in molecules such as the ammonium ion (NH4+) and are shown by an arrow pointing to the Lewis acid. Also known as non-polar covalent bond, the electronegativity of these bonds range from 0 to 0.3. Molecules which are formed primarily from non-polar covalent bonds are often immiscible in water or other polar solvents, but much more soluble in non-polar solvents such as hexane. Ionic bond Ionic bonding is a type of electrostatic interaction between atoms which have a large electronegativity difference. There is no precise value that distinguishes ionic from covalent bonding, but a difference of electronegativity of over 1.7 is likely to be ionic, and a difference of less than 1.7 is likely to be covalent.[5] Ionic bonding leads to separate positive and negative ions. Ionic charges are commonly between −3e to +3e. Ionic bonding commonly occurs in metal salts such as sodium chloride (table salt). A typical feature of ionic bonds is that the species form into ionic crystals, in which no ion is specifically paired with any single other ion, in a specific directional bond. Rather, each species of ion is surrounded by ions of the opposite charge, and the spacing between it and each of the oppositely charged ions near it, is the same for all surrounding atoms of the same type. It is thus no longer possible to associate an ion with any specific other single ionized atom near it. This is a situation unlike that in covalent crystals, where covalent bonds between specific atoms are still discernible from the shorter distances between them, as measured by with such techniques as X-ray diffraction. Ionic crystals may contain a mixture of covalent and ionic species, as for example salts of complex acids, such as sodium cyanide, NaCN. Many minerals are of this type. X-ray diffration shows that in NaCN, for example, the bonds between sodium cations (Na+) and the cyanide anions (CN-) are ionic, with no sodium ion associated with any particular cyanide. However, the bonds between C and N atoms in cyanide are of the covalent type, making each of the carbon and nitrogen associated with just one of its opposite type, to which it is physically much closer than it is to other carbons or nitrogens in a sodium cyanide crystal. When such crystals are melted into liquids, the ionic bonds are broken first because they are non-directional and allow the charged species to move freely. Similarly, when such salts dissolve into water, the ionic bonds are typically
  • 87. Chemical bond 85 broken by the interaction with water, but the covalent bonds continue to hold. For example, in solution, the cyanide ions, still bound together as single CN- ions, move independently through the solution, as do sodium ions, as Na+. In water, charged ions move apart because each of them are more strongly attracted to a number of water molecules, than to each other. The attraction between ions and water molecules in such solutions is due to a type of weak dipole-dipole type chemical bond. In melted ionic compounds, the ions continue to be attracted to each other, but not in any ordered or crystalline way. One- and three-electron bonds Bonds with one or three electrons can be found in radical species, which have an odd number of electrons. The simplest example of a 1-electron bond is found in the dihydrogen cation, H2+. One-electron bonds often have about half the bond energy of a 2-electron bond, and are therefore called "half bonds". However, there are exceptions: in the case of dilithium, the bond is actually stronger for the 1-electron Li2+ than for the 2-electron Li2. This exception can be explained in terms of hybridization and inner-shell effects.[6] One-electron bonding in the dihydrogen cation. The simplest example of three-electron bonding can be found in the helium dimer cation, He2+, and can also be considered a "half bond" because, in molecular orbital terms, the third electron is in an anti-bonding orbital Three-electron bonding in chlorine dioxide. which cancels out half of the bond formed by the other two electrons. Another example of a molecule containing a 3-electron bond, in addition to two 2-electron bonds, is nitric oxide, NO. The oxygen molecule, O2 can also be regarded as having two 3-electron bonds and one 2-electron bond, which accounts for its paramagnetism and its formal bond order of 2.[7] Chlorine dioxide and its heavier analogues bromine dioxide and iodine dioxide also contain three-electron bonds. Molecules with odd-electron bonds are usually highly reactive. These types of bond are only stable between atoms with similar electronegativities.[7]
  • 88. Chemical bond 86 Bent bonds Bent bonds, also known as banana bonds, are bonds in strained or otherwise sterically hindered molecules whose binding orbitals are forced into a banana-like form. Bent bonds are often more susceptible to reactions than ordinary bonds. 3c-2e and 3c-4e bonds In three-center two-electron bonds ("3c–2e") three atoms share two electrons in bonding. This type of bonding occurs in electron deficient compounds like diborane. Each such bond (2 per molecule in diborane) contains a pair of electrons which connect the boron atoms to each other in a banana shape, with a proton (nucleus of a hydrogen atom) in the middle of the bond, sharing electrons with both boron atoms. Three-center four-electron bonds ("3c–4e") also exist which explain the bonding in hypervalent molecules. In certain cluster compounds, so-called four-center two-electron bonds also have been postulated. In certain conjugated π (pi) systems, such as benzene and other aromatic compounds (see below), and in conjugated network solids such as graphite, the electrons in the conjugated system of π-bonds are spread over as many nuclear centers as exist in the molecule, or the network. Aromatic bond In organic chemistry, certain configurations of electrons and orbitals infer extra stability to a molecule. This occurs when π orbitals overlap and combine with others on different atomic centres, forming a long range bond. For a molecule to be aromatic, it must obey Hückels rule, where the number of π electrons fit the formula 4n + 2, where n is an integer. The bonds involved in the aromaticity are all planar. In benzene, the prototypical aromatic compound, 18 (n = 4) bonding electrons bind 6 carbon atoms together to form a planar ring structure. The bond "order" (average number of bonds) between the different carbon atoms may be said to be (18/6)/2=1.5, but in this case the bonds are all identical from the chemical point of view. They may sometimes be written as single bonds alternating with double bonds, but the view of all ring bonds as being equivalently about 1.5 bonds in strength, is much closer to truth. In the case of heterocyclic aromatics and substituted benzenes, the electronegativity differences between different parts of the ring may dominate the chemical behaviour of aromatic ring bonds, which otherwise are equivalent. Metallic bond In a metallic bond, bonding electrons are delocalized over a lattice of atoms. By contrast, in ionic compounds, the locations of the binding electrons and their charges are static. The freely-moving or delocalization of bonding electrons leads to classical metallic properties such as luster (surface light reflectivity), electrical and thermal conductivity, ductility, and high tensile strength. Intermolecular bonding There are four basic types of bonds that can be formed between two or more (otherwise non-associated) molecules, ions or atoms. Intermolecular forces cause molecules to be attracted or repulsed by each other. Often, these define some of the physical characteristics (such as the melting point) of a substance. • A large difference in electronegativity between two bonded atoms will cause a permanent charge separation, or dipole, in a molecule or ion. Two or more molecules or ions with permanent dipoles can interact in dipole-dipole interactions. The bonding electrons in a molecule or ion will, on average, be closer to the more electronegative atom more frequently than the less electronegative one, giving rise to partial charges on each atom, and causing electrostatic forces between molecules or ions.
  • 89. Chemical bond 87 • A hydrogen bond is effectively a strong example of an interaction between two permanent dipoles. The large difference in electronegativities between hydrogen and any of fluorine, nitrogen and oxygen, coupled with their lone pairs of electrons cause strong electrostatic forces between molecules. Hydrogen bonds are responsible for the high boiling points of water and ammonia with respect to their heavier analogues. • The London dispersion force arises due to instantaneous dipoles in neighbouring atoms. As the negative charge of the electron is not uniform around the whole atom, there is always a charge imbalance. This small charge will induce a corresponding dipole in a nearby molecule; causing an attraction between the two. The electron then moves to another part of the electron cloud and the attraction is broken. • A cation–pi interaction occurs between a pi bond and a cation. Summary: electrons in chemical bonds In the (unrealistic) limit of "pure" ionic bonding, electrons are perfectly localized on one of the two atoms in the bond. Such bonds can be understood by classical physics. The forces between the atoms are characterized by isotropic continuum electrostatic potentials. Their magnitude is in simple proportion to the charge difference. Covalent bonds are better understood by valence bond theory or molecular orbital theory. The properties of the atoms involved can be understood using concepts such as oxidation number. The electron density within a bond is not assigned to individual atoms, but is instead delocalized between atoms. In valence bond theory, the two electrons on the two atoms are coupled together with the bond strength depending on the overlap between them. In molecular orbital theory, the linear combination of atomic orbitals (LCAO) helps describe the delocalized molecular orbital structures and energies based on the atomic orbitals of the atoms they came from. Unlike pure ionic bonds, covalent bonds may have directed anisotropic properties. These may have their own names, such as sigma bond and pi bond. In the general case, atoms form bonds that are intermediates between ionic and covalent, depending on the relative electronegativity of the atoms involved. This type of bond is sometimes called polar covalent. References [1] Lewis, Gilbert N. (1916). "The Atom and the Molecule". Journal of the American Chemical Society 38: 772. [2] Laidler, K. J. (1993). The World of Physical Chemistry. Oxford University Press. p. 347. [3] James, H. H.; A. S. Coolidge (1933). "The Ground State of the Hydrogen Molecule". Journal of Chemical Physics (American Institute of Physics) 1 (12): 825–835. doi:10.1063/1.1749252. [4] http:/ / www. science. uwaterloo. ca/ ~cchieh/ cact/ c120/ bondel. html [5] Atkins, Peter; Loretta Jones (1997). Chemistry: Molecules, Matter and Change. New York: W. H. Freeman & Co.. pp. 294–295. ISBN 0-7167-3107-X. [6] Weinhold, F.; Landis, C. (2005). Valency and bonding. Cambridge. pp. 96–100. ISBN 0-521-83128-8. [7] Pauling, L. The Nature of the Chemical Bond. Cornell University Press, 1960. External links • W. Locke (1997). Introduction to Molecular Orbital Theory ( mo_theory/main.html). Retrieved May 18, 2005. • Carl R. Nave (2005). HyperPhysics ( Retrieved May 18, 2005. • Linus Pauling and the Nature of the Chemical Bond: A Documentary History (http://osulibrary.oregonstate. edu/specialcollections/coll/pauling/bond/index.html). Retrieved February 29, 2008.
  • 90. Chemical reaction 88 Chemical reaction A chemical reaction is a process that leads to the transformation of one set of chemical substances to another.[1] Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity. Classically, chemical reactions encompass changes that strictly involve the motion of electrons in the forming and breaking of chemical bonds, although the general concept of a chemical reaction, in particular the notion of a chemical equation, is applicable to transformations of elementary particles (such as illustrated by Feynman diagrams), as well as nuclear reactions. The substance (or substances) initially involved in a chemical reaction are called reactants or reagents. Chemical reactions are usually characterized by a chemical change, and they yield one or more A thermite reaction using iron(III) oxide. The products, which usually have properties different from the reactants. sparks flying outwards are globules of molten iron trailing smoke in their wake. Reactions often consist of a sequence of individual sub-steps, the so-called elementary reactions, and the information on the precise course of action is part of the reaction mechanism. Chemical reactions are described with chemical equations, which graphically present the starting materials, end products, and sometimes intermediate products and reaction conditions. Different chemical reactions are used in combination in chemical synthesis in order to obtain a desired product. In biochemistry, series of chemical reactions catalyzed by enzymes form metabolic pathways, by which syntheses and decompositions impossible under ordinary conditions are performed within a cell. Video demonstrating a chemical reaction.
  • 91. Chemical reaction 89 History Chemical reactions such as combustion in the fire, fermentation and the reduction of ores to metals were known since antiquity. Initial theories of transformation of materials were developed by Greek philosophers, such as the Four-Element Theory of Empedocles stating that any substance is composed of the four basic elements – fire, water, air and earth. In the Middle Ages, chemical transformations were studied by Alchemists. They attempted, in particular, to convert lead into gold, for which purpose they used reactions of lead and lead-copper alloys with sulfur.[2] The production of chemical substances that do not normally occur in nature has long been tried, such as the synthesis of sulfuric and nitric acids attributed to the controversial alchemist Jābir ibn Hayyān. The process involved heating of sulfate and nitrate minerals such as copper sulfate, alum and saltpeter. In the 17th century, Johann Rudolph Glauber produced hydrochloric acid and sodium sulfate by reacting sulfuric acid and sodium chloride. With the development of the lead chamber process in 1746 and the Leblanc process, allowing large-scale Antoine Lavoisier developed the theory of production of sulfuric acid and sodium carbonate, respectively, combustion as a chemical reaction with oxygen chemical reactions became implemented into the industry. Further optimization of sulfuric acid technology resulted in the contact process in 1880s,[3] and the Haber process was developed in 1909–1910 for ammonia synthesis.[4] From the 16th century, researchers including Jan Baptist van Helmont, Robert Boyle and Isaac Newton tried to establish theories of the experimentally observed chemical transformations. The phlogiston theory was proposed in 1667 by Johann Joachim Becher. It postulated the existence of a fire-like element called "phlogiston", which was contained within combustible bodies and released during combustion. This proved to be false in 1785 by Antoine Lavoisier who found the correct explanation of the combustion as reaction with oxygen from the air.[5] Joseph Louis Gay-Lussac recognized in 1808 that gases always react in a certain relationship with each other. Based on this idea and the atomic theory of John Dalton, Joseph Proust had developed the law of definite proportions, which later resulted in the concepts of stoichiometry and chemical equations.[6] Regarding the organic chemistry, it was long believed that compounds obtained from living organisms were too complex to be obtained synthetically. According to the concept of vitalism, organic matter was endowed with a "vital force" and distinguished from inorganic materials. This separation was ended however by the synthesis of urea from inorganic precursors by Friedrich Wöhler in 1828. Other chemists who brought major contributions to organic chemistry include Alexander William Williamson with his synthesis of ethers and Christopher Kelk Ingold, who, among many discoveries, established the mechanisms of substitution reactions. Equations Chemical equations are used to graphically illustrate chemical reactions. They consist of chemical or structural formulas of the reactants on the left and those of the products on the right. They are separated by an arrow (→) which indicates the direction and type of the reaction. The tip of the arrow points in the direction in which the reaction proceeds. A double arrow ( ) pointing in opposite directions is used for equilibrium reactions. Equations should be balanced according to the stoichiometry, the number of atoms of each species should be the same on both sides of the equation. This is achieved by scaling the number of involved molecules (A, B, C and D in a schematic example below) by the appropriate integers a, b, c and d.[7]
  • 92. Chemical reaction 90 More elaborate reactions are represented by reaction schemes, which in addition to starting materials and products show important intermediates or transition states. Also, some relatively minor additions to the reaction can be indicated above the reaction arrow; examples of such additions are water, heat, illumination, a catalyst, etc. Similarly, some minor products can be placed below the arrow, often with a minus sign. An example of organic reaction: oxidation of ketones to esters with a peroxycarboxylic acid Retrosynthetic analysis can be applied to design a complex synthesis reaction. Here the analysis starts from the products, for example by splitting selected chemical bonds, to arrive at plausible initial reagents. A special arrow (⇒) is used in retro reactions.[8] Elementary reactions The elementary reaction is the smallest division into which a chemical reaction can be decomposed to, it has no intermediate products.[9] Most experimentally observed reactions are built up from many elementary reactions that occur in parallel or sequentially. The actual sequence of the individual elementary reactions is known as reaction mechanism. An elementary reaction involves a few molecules, usually one or two, because of the low probability for several molecules to meet at a certain time.[10] The most important elementary reactions are unimolecular and bimolecular reactions. Only one molecule is involved in a unimolecular reaction; it is transformed by an isomerization or a dissociation in one or more other molecules. Such reaction requires addition of energy in the form of heat or light. A typical example of a Isomerization of azobenzene, induced by light (hν) or heat (Δ) unimolecular reaction is the cis–trans isomerization, in which the cis-form of a compound converts to the trans-form or vice versa.[11] In a typical dissociation reaction, a bond in a molecule splits (ruptures) resulting in two molecular fragments. The splitting can be homolytic or heterolytic. In the first case, the bond is divided so that each product retains an electron and becomes a neutral radical. In the second case, both electrons of the chemical bond remain with one of the products, resulting in charged ions. Dissociation plays an important role in triggering chain reactions, such as hydrogen–oxygen or polymerization reactions. Dissociation of a molecule AB into fragments A and B For bimolecular reactions, two molecules collide and react with each other. Their merger is called chemical synthesis or an addition reaction. Another possibility is that only a portion of one molecule is transferred to the other molecule. This type of reaction occurs, for example, in redox and acid-base reactions. In redox reactions, the transferred particle is an electron,
  • 93. Chemical reaction 91 whereas in acid-base reactions it is a proton. This type of reaction is also called metathesis. for example NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s) Chemical equilibrium Most chemical reactions are reversible, that is they can and do run in both directions. The forward and reverse reactions are competing with each other and differ in reaction rates. These rates depend on the concentration and therefore change with time of the reaction: the reverse rate gradually increases and becomes equal to the rate of the forward reaction, establishing the so-called chemical equilibrium. The time to reach equilibrium depends on such parameters as temperature, pressure and the materials involved, and is determined by the minimum free energy. In equilibrium, the Gibbs free energy must be zero. The pressure dependence can be explained with the Le Chateliers principle. For example, an increase in pressure due to decreasing volume causes the reaction to shift to the side with the fewer moles of gas.[12] The reaction yield stabilized at equilibrium, but can be increased by removing the product from the reaction mixture or increasing temperature or pressure. Change in the initial concentrations of the substances does not affect the equilibrium. Thermodynamics Chemical reactions are determined by the laws of thermodynamics. Reactions can proceed by themselves if they are exergonic, that is if they release energy. The associated free energy of the reaction is composed of two different thermodynamic quantities, enthalpy and entropy:[13] G: free energy, H: enthalpy, T: temperature, S: entropy, Δ: difference(change between original and product) Reactions can be exothermic, where ΔH is negative and energy is released. Typical examples of exothermic reactions are precipitation and crystallization, in which ordered solids are formed from disordered gaseous or liquid phases. In contrast, in endothermic reactions, heat is consumed from the environment. This can occur by increasing the entropy of the system, often through the formation of gaseous reaction products, which have high entropy. Since the entropy increases with temperature, many endothermic reactions preferably take place at high temperatures. On the contrary, many exothermic reactions such as crystallization occur at low temperatures. Changes in temperature can sometimes reverse the direction of a reaction, as in the Boudouard reaction: This reaction between carbon dioxide and carbon to form carbon monoxide is endothermic at temperatures above approximately 800 °C and is exothermic below this temperature.[14] Reactions can also be characterized by the internal energy which takes into account changes in the entropy, volume and chemical potential. The latter depends, among other things, on the activities of the involved substances.[15] U: internal energy, S: entropy, p: pressure, μ: chemical potential, n: number of molecules, d: small change sign
  • 94. Chemical reaction 92 Kinetics The speed at which a reactions takes place is studied by reaction kinetics. The rate depends on various parameters, such as: • Reactant concentrations, which usually make the reaction happen at a faster rate if raised through increased collisions per unit time. Some reactions, however, have rates that are independent of reactant concentrations. These are called zero order reactions. • Surface area available for contact between the reactants, in particular solid ones in heterogeneous systems. Larger surface areas lead to higher reaction rates. • Pressure – increasing the pressure decreases the volume between molecules and therefore increases the frequency of collisions between the molecules. • Activation energy, which is defined as the amount of energy required to make the reaction start and carry on spontaneously. Higher activation energy implies that the reactants need more energy to start than a reaction with a lower activation energy. • Temperature, which hastens reactions if raised, since higher temperature increases the energy of the molecules, creating more collisions per unit time, • The presence or absence of a catalyst. Catalysts are substances which change the pathway (mechanism) of a reaction which in turn increases the speed of a reaction by lowering the activation energy needed for the reaction to take place. A catalyst is not destroyed or changed during a reaction, so it can be used again. • For some reactions, the presence of electromagnetic radiation, most notably ultraviolet light, is needed to promote the breaking of bonds to start the reaction. This is particularly true for reactions involving radicals. Several theories allow calculating the reaction rates at the molecular level. This field is referred to as reaction dynamics. The rate v of a first-order reaction, which could be disintegration of a substance A, is given by: Its integration yields: Here k is first-order rate constant having dimension 1/time, [A](t) is concentration at a time t and [A]0 is the initial concentration. The rate of a first-order reaction depends only on the concentration and the properties of the involved substance, and the reaction itself can be described with the characteristic half-life. More than one time constant is needed when describing reactions of higher order. The temperature dependence of the rate constant usually follows the Arrhenius equation: where Ea is the activation energy and kB is the Boltzmann constant. One of the simplest models of reaction rate is the collision theory. More realistic models are tailored to a specific problem and include the transition state theory, the calculation of the potential energy surface, the Marcus theory and the Rice–Ramsperger–Kassel–Marcus (RRKM) theory.[16]
  • 95. Chemical reaction 93 Reaction types Four basic types Synthesis In a synthesis reaction, two or more simple substances combine to form a more complex substance. Two or more reactants yielding one product is another way to identify a synthesis reaction. These reactions are in the general form: A + B → AB For example, simple hydrogen gas combined with simple oxygen gas can produce a more complex substance, such as water.[17] Decomposition A decomposition reaction is the opposite of a synthesis reaction, where a more complex substance breaks down into its more simple parts. These reactions are in the general form: AB → A + B[17][18] Single replacement In a single replacement reaction, a single uncombined element replaces another in a compound.[17] Double replacement In a double replacement reaction, parts of two compounds switch places to form two new compounds.[17] This is when the anions and cations of two different molecules switch places, forming two entirely different compounds.[18] These reactions are in the general form: AB + CD → AD + CB An example of a double displacement reaction is the reaction of lead(II) nitrate with potassium iodide to form lead(II) iodide and potassium nitrate: Pb(NO3)2 + 2 KI → PbI2 + 2 KNO3 Oxidation and reduction Redox reactions can be understood in terms of transfer of electrons from one involved species (reducing agent) to another (oxidizing agent). In this process, the former species is oxidized and the latter is reduced, thus the term redox. Though sufficient for many purposes, these descriptions are not precisely correct. Oxidation is better defined as an increase in oxidation number, and reduction as a decrease in Illustration of a redox reaction oxidation number. In practice, the transfer of electrons will always change the oxidation number, but there are many reactions that are classed as "redox" even though no electron transfer occurs (such as those involving covalent bonds).[19][20] An example of a redox reaction is: 2 S2O32−(aq) + I2(aq) → S4O62–(aq) + 2 I−(aq) Here I2 is reduced to I– and S2O32– (thiosulfate anion) is oxidized to The two parts of a redox reaction S4O62–. Which of the involved reactants would be reducing or oxidizing agent can be predicted from the electronegativity of their elements. Elements with low electronegativity, such as most metals, easily donate electrons and oxidize – they
  • 96. Chemical reaction 94 are reducing agents. On the contrary, many ions with high oxidation numbers, such as H2O2, MnO, CrO3, Cr2O, OsO4) can gain one or two extra electrons and are strong oxidizing agents. The number of electrons donated or accepted in a redox reaction can be predicted from electron configuration of the reactant element. Elements are trying to reach the low-energy noble gas configuration, and therefore alkali metals and halogens will donate and accept one electron, respectively, and the noble gases themselves are chemically inactive.[21] An important class of redox reactions are the electrochemical reactions, where the electrons from the power supply are used as a reducing agent. These reactions are particularly important for the production of chemical elements, such as chlorine[22] or aluminium. The reverse process in which electrons are released in redox reactions and can be used as electrical energy is possible and is used in the batteries. Complexation In complexation reactions, several ligands react with a metal atom to form a coordination complex. This is achieved by providing lone pairs of the ligand into empty orbitals of the metal atom and forming dipolar bonds. The ligands are Lewis bases, they can be both ions and neutral molecules, such as carbon monoxide, ammonia or water. The number of ligands that react with a central metal atom can be found using the 18-electron rule, saying that the valence shells of a transition metal will collectively accommodate 18 electrons, whereas the symmetry of the resulting complex can be predicted with the crystal field theory and ligand field theory. Complexation reactions also include ligand exchange, in which one or more ligands are replaced by another, and redox processes which change the oxidation state of the central metal atom.[23] Ferrocene – an iron atom sandwiched between two C5H5 ligands Acid-base reactions Acid-base reactions involve transfer of protons from one molecule (acid) to another (base). Here, acids act as proton donors and bases as acceptors. Acid-base reaction, HA: acid, B: Base, A–: conjugated base, HB+: conjugated acid The associated proton transfer results in the so-called conjugate acid and conjugate base.[24] The reverse reaction is possible, and thus the acid/base and conjugated base/acid are always in equilibrium. The equilibrium is determined by the acid and base dissociation constants (Ka and Kb) of the involved substances. A special case of the acid-base reaction is the neutralization where an acid and a base, taken at exactly same amounts, form a neutral salt. Acid-base reactions can have different definitions depending on the acid-base concept employed. Some of the most common are: • Arrhenius definition: Acids dissociate in water releasing H3O+ ions; bases dissociate in water releasing OH– ions. • Brønsted-Lowry definition: Acids are proton (H+) donors, bases are proton acceptors; this includes the Arrhenius definition. • Lewis definition: Acids are electron-pair acceptors, bases are electron-pair donors; this includes the Brønsted-Lowry definition.
  • 97. Chemical reaction 95 Precipitation Precipitation is the formation of a solid in a solution or inside another solid during a chemical reaction. It usually takes place when the concentration of dissolved ions exceeds the solubility limit[25] and forms an insoluble salt. This process can be assisted by adding a precipitating agent or by removal of the solvent. Rapid precipitation results in an amorphous or microcrystalline residue and slow process can yield single crystals. The latter can also be obtained by recrystallization from microcrystalline salts.[26] Solid-state reactions Reactions can take place between two solids. However, because of the Precipitation relatively small diffusion rates in solids, the corresponding chemical reactions are very slow in comparison to liquid and gas phase reactions. They are accelerated by increasing the reaction temperature and finely dividing the reactant to increase the contacting surface area.[27] Photochemical reactions In photochemical reactions, atoms and molecules absorb energy (photons) of the illumination light and convert into an excited state. They can then release this energy by breaking chemical bonds, thereby producing radicals. Photochemical reactions include hydrogen–oxygen In this Paterno–Büchi reaction, a photoexcited reactions, radical polymerization, chain reactions and rearrangement carbonyl group is added to an unexcited olefin, reactions.[28] yielding an oxetane. Many important processes involve photochemistry. The premier example is photosynthesis, in which most plants use solar energy to convert carbon dioxide and water into glucose, disposing of oxygen as a side-product. Humans rely on photochemistry for the formation of vitamin D, and vision is initiated by a photochemical reaction of rhodopsin.[11] In fireflies, an enzyme in the abdomen catalyzes a reaction that results in bioluminescence.[29] Many significant photochemical reactions, such as ozone formation, occur in the Earth atmosphere and constitute atmospheric chemistry.
  • 98. Chemical reaction 96 Catalysis Further information: Reaction Progress Kinetic Analysis In catalysis, the reaction does not proceed directly, but through a third substance known as catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself; however, it can be inhibited, deactivated or destroyed by secondary processes. Catalysts can be used in a different phase (heterogeneous) or in the same phase (homogenous) as the reactants. In heterogeneous catalysis, typical secondary processes include coking where the catalyst becomes covered by polymeric side products. Additionally, heterogeneous catalysts can dissolve into the solution in a solid–liquid system or evaporate in a solid–gas system. Catalysts can only speed up Schematic potential energy diagram showing the the reaction – chemicals that slow down the reaction are called effect of a catalyst in an endothermic chemical inhibitors.[30][31] Substances that increase the activity of catalysts are reaction. The presence of a catalyst opens a different reaction pathway (in red) with a lower called promoters, and substances that deactivate catalysts are called activation energy. The final result and the overall catalytic poisons. With a catalyst, a reaction which is kinetically thermodynamics are the same. inhibited by a high activation energy can take place in circumvention of this activation energy. Heterogeneous catalysts are usually solids, powdered in order to maximize their surface area. Of particular importance in heterogeneous catalysis are the platinum group metals and other transition metals, which are used in hydrogenations, catalytic reforming and in the synthesis of commodity chemicals such as nitric acid and ammonia. Acids are an example of a homogeneous catalyst, they increase the nucleophilicity of carbonyls, allowing a reaction that would not Solid heterogeneous catalysts are plated on otherwise proceed with electrophiles. The advantage of homogeneous meshes in ceramic catalytic converters in order to maximize their surface area. This exhaust catalysts is the ease of mixing them with the reactants, but they may converter is from a Peugeot 106 S2 1100 also be difficult to separate from the products. Therefore, heterogeneous catalysts are preferred in many industrial processes.[32] Reactions in organic chemistry In organic chemistry, in addition to oxidation, reduction or acid-base reactions, a number of other reactions can take place which involve covalent bonds between carbon atoms or carbon and heteroatoms (such as oxygen, nitrogen, halogens, etc.). Many specific reactions in organic chemistry are name reactions designated after their discoverers.
  • 99. Chemical reaction 97 Substitution In a substitution reaction, a functional group in a particular chemical compound is replaced by another group.[33] These reactions can be distinguished by the type of substituting species into a nucleophilic, electrophilic or radical substitution. SN1 mechanism SN2 mechanism In the first type, a nucleophile, an atom or molecule with an excess of electrons and thus a negative charge or partial charge, replaces another atom or part of the "substrate" molecule. The electron pair from the nucleophile attacks the substrate forming a new bond, while the leaving group departs with an electron pair. The nucleophile may be electrically neutral or negatively charged, whereas the substrate is typically neutral or positively charged. Examples of nucleophiles are hydroxide ion, alkoxides, amines and halides. This type of reaction is found mainly in aliphatic hydrocarbons, and rarely in aromatic hydrocarbon. The latter have high electron density and enter nucleophilic aromatic substitution only with very strong electron withdrawing groups. Nucleophilic substitution can take place by two different mechanisms, SN1 and SN2. In their names, S stands for substitution, N for nucleophilic, and the number represents the kinetic order of the reaction, unimolecular or bimolecular.[34] The three steps of an SN2 reaction. The nucleophile is green and the leaving group is red SN2 reaction causes stereo inversion (Walden inversion) The SN1 reaction proceeds in two steps. First, the leaving group is eliminated creating a carbocation. This is followed by a rapid reaction with the nucleophile.[35] In the SN2 mechanism, the nucleophile forms a transition state with the attacked molecule, and only then the leaving group is cleaved. These two mechanisms differ in the stereochemistry of the products. SN1 leads to the
  • 100. Chemical reaction 98 non-stereospecific addition and does not result in a chiral center, but rather in a set of geometric isomers (cis/trans). In contrast, a reversal (Walden inversion) of the previously existing stereochemistry is observed in the SN2 mechanism.[36] Electrophilic substitution is the counterpart of the nucleophilic substitution in that the attacking atom or molecule, an electrophile, has low electron density and thus a positive charge. Typical electrophiles are the carbon atom of carbonyl groups, carbocations or sulfur or nitronium cations. This reaction takes place almost exclusively in aromatic hydrocarbons, where it is called electrophilic aromatic substitution. The electrophile attack results in the so-called σ-complex, a transition state in which the aromatic system is abolished. Then, the leaving group, usually a proton, is split off and the aromaticity is restored. An alternative to aromatic substitution is electrophilic aliphatic substitution. It is similar to the nucleophilic aliphatic substitution and also has two major types, SE1 and SE2[37] Mechanism of electrophilic aromatic substitution In the third type of substitution reaction, radical substitution, the attacking particle is a radical.[33] This process usually takes the form of a chain reaction, for example in the reaction of alkanes with halogens. In the first step, light or heat disintegrates the halogen-containing molecules producing the radicals. Then the reaction proceeds as an avalanche until two radicals meet and recombine.[38] Reactions during the chain reaction of radical substitution Addition and elimination The addition and its counterpart, the elimination, are reactions which change the number of substituents on the carbon atom, and form or cleave multiple bonds. Double and triple bonds can be produced by eliminating a suitable leaving group. Similar to the nucleophilic substitution, there are several possible reaction mechanisms which are named after the respective reaction order. In the E1 mechanism, the leaving group is ejected first, forming a carbocation. The next step, formation of the double bond, takes place with elimination of a proton (deprotonation). The leaving order is reversed in the E1cb mechanism, that is the proton is split off first. This mechanism requires participation of a base.[39] Because of the similar conditions, both reactions in the E1 or E1cb elimination always compete with the SN1 substitution.[40]
  • 101. Chemical reaction 99 E1 elimination E1cb elimination The E2 mechanism also requires a base, but there the attack of the base and the elimination of the leaving group proceed simultaneously and produce no ionic intermediate. In contrast to the E1 eliminations, different stereochemical configurations are possible for the reaction product in the E2 mechanism, because the attack of the base preferentially occurs in the anti-position with respect to the leaving E2 elimination group. Because of the similar conditions and reagents, the E2 elimination is always in competition with the SN2-substitution.[41] The counterpart of elimination is the addition where double or triple bonds are converted into single bonds. Similar to the substitution reactions, there are several types Electrophilic addition of hydrogen bromide of additions distinguished by the type of the attacking particle. For example, in the electrophilic addition of hydrogen bromide, an electrophile (proton) attacks the double bond forming a carbocation, which then reacts with the nucleophile (bromine). The carbocation can be formed on either side of the double bond depending on the groups attached to its ends, and the preferred configuration can be predicted with the Markovnikovs rule.[42] This rule states that "In the heterolytic addition of a polar molecule to an alkene or alkyne, the more electronegative (nucleophilic) atom (or part) of the polar molecule becomes attached to the carbon atom bearing the smaller number of hydrogen atoms."[43] If the addition of a functional group takes place at the less substituted carbon atom of the double bond, then the electrophilic substitution with acids is not possible. In this case, one has to use the hydroboration–oxidation reaction, where in the first step, the boron atom acts as electrophile and adds to the less substituted carbon atom. At the second step, the nucleophilic hydroperoxide or halogen anion attacks the boron atom.[44] While the addition to the electron-rich alkenes and alkynes is mainly electrophilic, the nucleophilic addition plays an important role for the carbon-heteroatom multiple bonds, and especially its most important representative, the carbonyl group. This process is often associated with an elimination, so that after the reaction the carbonyl group is present again. It is therefore called addition-elimination reaction and may occur in carboxylic acid derivatives such as chlorides, esters or anhydrides. This reaction is often catalyzed by acids or bases, where the acids increase by the electrophilicity of the carbonyl group by binding to the oxygen atom, whereas the bases enhance the nucleophilicity of the attacking nucleophile.[45]
  • 102. Chemical reaction 100 Acid-catalyzed addition-elimination mechanism Nucleophilic addition of a carbanion or another nucleophile to the double bond of an alpha, beta unsaturated carbonyl compound can proceed via the Michael reaction, which belongs to the larger class of conjugate additions. This is one of the most useful methods for the mild formation of C-C bonds.[46][47][48] Some additions which can not be executed with nucleophiles and electrophiles, can be succeeded with free radicals. As with the free-radical substitution, the radical addition proceeds as a chain reaction, and such reactions are the basis of the free-radical polymerization.[49] Other organic reaction mechanisms The Cope rearrangement of 3-methyl-1,5-hexadiene Mechanism of a Diels-Alder reaction Orbital overlap in a Diels-Alder reaction In a rearrangement reaction, the carbon skeleton of a molecule is rearranged to give a structural isomer of the original molecule. These include hydride shift reactions such as the Wagner-Meerwein rearrangement, where a hydrogen, alkyl or aryl group migrates from one carbon to a neighboring carbon. Most rearrangements are associated with the breaking and formation of new carbon-carbon bonds. Other examples are sigmatropic reaction such as the Cope rearrangement.[50] Cyclic rearrangements include cycloadditions and, more generally, pericyclic reactions, wherein two or more double bond-containing molecules form a cyclic molecule. An important example of cycloaddition reaction is the Diels–Alder reaction (the so-called [4+2] cycloaddition) between a conjugated diene and a substituted alkene to form a substituted cyclohexene system.[51] Whether or not a certain cycloaddition would proceed depends on the electronic orbitals of the participating species, as only orbitals with the same sign of wave function will overlap and interact constructively to form new bonds.
  • 103. Chemical reaction 101 Cycloaddition is usually assisted by light or heat. These perturbations result in different arrangement of electrons in the excited state of the involved molecules and therefore in different effects. For example, the [4+2] Diels-Alder reactions can be assisted by heat whereas the [2+2] cycloaddition is selectively induced by light.[52] Because of the orbital character, the potential for developing stereoisomeric products upon cycloaddition is limited, as described by the Woodward-Hoffmann rules.[53] Biochemical reactions Biochemical reactions are mainly controlled by enzymes. These proteins can specifically catalyze a single reaction, so that reactions can be controlled very precisely. The reaction takes place in the active site, a small part of the enzyme which is usually found in a cleft or pocket lined by Illustration of the induced fit model of enzyme activity amino acid residues, and the rest of the enzyme is used mainly for stabilization. The catalytic action of enzymes relies on several mechanisms including the molecular shape ("induced fit"), bond strain, proximity and orientation of molecules relative to the enzyme, proton donation or withdrawal (acid/base catalysis), electrostatic interactions and many others.[54] The biochemical reactions that occur in living organisms are collectively known as metabolism. Among the most important of its mechanisms is the anabolism, in which different DNA and enzyme-controlled processes result in the production of large molecules such as proteins and carbohydrates from smaller units.[55] Bioenergetics studies the sources of energy for such reactions. An important energy source is glucose, which can be produced by plants via photosynthesis or assimilated from food. All organisms use this energy to produce adenosine triphosphate (ATP), which can then be used to energize other reactions. Applications Chemical reactions are central to chemical engineering where they are used for the synthesis of new compounds from natural raw materials such as petroleum and mineral ores. It is essential to make the reaction as efficient as possible, maximizing the yield and minimizing the amount of reagents, energy inputs and waste. Catalysts are especially helpful for reducing the energy required for the reaction and increasing its reaction rate.[56][57] Some specific reactions have their niche applications. For example, the thermite reaction is used to generate light and heat in pyrotechnics and Thermite reaction proceeding in railway welding. welding. Although it is less controllable than the more conventional Shortly after this, the liquid iron flows into the oxy-fuel welding, arc welding and flash welding, it requires much less mould around the rail gap equipment and is still used to mend rails, especially in remote areas.[58]
  • 104. Chemical reaction 102 Monitoring Mechanisms of monitoring chemical reactions depend strongly on the reaction rate. Relatively slow processes can be analyzed in situ for the concentrations and identities of the individual ingredients. Important tools of real time analysis are the measurement of pH and analysis of optical absorption (color) and emission spectra. A less accessible but rather efficient method is introduction of a radioactive isotope into the reaction and monitoring how it changes over time and where it moves to; this method is often used to analyze redistribution of substances in the human body. Faster reactions are usually studied with ultrafast laser spectroscopy where utilization of femtosecond lasers allows short-lived transition states to be monitored at time scaled down to a few femtoseconds.[59] References [1] Nic, M.; Jirat, J.; Kosata, B., eds. (2006–). "chemical reaction" (http:/ / goldbook. iupac. org/ C01033. html). IUPAC Compendium of Chemical Terminology (Online ed.). doi:10.1351/goldbook.C01033. ISBN 0-9678550-9-8. . [2] Weyer, Jost (1973). "Neuere Interpretationsmglichkeiten der Alchemie" (in German). Chemie in unserer Zeit 7 (6): 177. doi:10.1002/ciuz.19730070604. [3] Leonard J. Friedman & Samantha J. Friedman The History of the Contact Sulfuric Acid Process (http:/ / www. aiche-cf. org/ Clearwater/ 2008/ Paper2/ 8. 2. 7. pdf), Acid Engineering & Consulting, Inc. Boca Raton, Florida [4] John E. Lesch The German chemical industry in the twentieth century (http:/ / books. google. com/ books?id=VJIztvolC8cC& pg=PA170), Springer, 2000, ISBN 0-7923-6487-2 p. 170 [5] Brock, pp. 34–55 [6] Brock, pp. 104–107 [7] Nic, M.; Jirat, J.; Kosata, B., eds. (2006–). "chemical reaction equation" (http:/ / goldbook. iupac. org/ C01034. html). IUPAC Compendium of Chemical Terminology (Online ed.). doi:10.1351/goldbook.C01034. ISBN 0-9678550-9-8. . [8] Corey, E. J. (1988). "Robert Robinson Lecture. Retrosynthetic thinking?essentials and examples". Chemical Society Reviews 17: 111. doi:10.1039/CS9881700111. [9] Nic, M.; Jirat, J.; Kosata, B., eds. (2006–). "elementary reaction" (http:/ / goldbook. iupac. org/ E02035. html). IUPAC Compendium of Chemical Terminology (Online ed.). doi:10.1351/goldbook.E02035. ISBN 0-9678550-9-8. . [10] Gernot Frenking: Elementarreaktionen. In: Römpp Chemie-Lexikon, Thieme, 2006 [11] Christophe Dugave Cis-trans isomerization in biochemistry (http:/ / books. google. com/ books?id=udSCHPq5Ii0C& pg=PA56), Wiley-VCH, 2006 ISBN 3-527-31304-4 p. 56 [12] Atkins, p. 114. [13] Atkins, pp. 106–108 [14] Wiberg, pp. 810–811 [15] Atkins, p. 150 [16] Atkins, p. 963 [17] To react or not to react? (http:/ / www. schools. utah. gov/ curr/ science/ sciber00/ 8th/ matter/ sciber/ chemtype. htm). Utah State Office of Education. Retrieved 4 June 2011. [18] Six Types of Chemical Reactions (http:/ / misterguch. brinkster. net/ 6typesofchemicalrxn. html) – MrGuch ChemFiesta. [19] Christian B. Anfinsen Advances in protein chemistry (http:/ / books. google. com/ books?id=HvARsi6S-b0C& pg=PA7), Academic Press, 1991 ISBN 0-12-034242-1 p. 7 [20] A. G. Sykes Advances in Inorganic Chemistry, Volume 36 (http:/ / books. google. com/ books?id=qnRkjATn0YUC& pg=PA359), Academic Press, 1991 ISBN 0-12-023636-2 p. 359 [21] Wiberg, pp. 289–290 [22] Wiberg, p. 409 [23] Wiberg, pp. 1180–1205 [24] Nic, M.; Jirat, J.; Kosata, B., eds. (2006–). "conjugate acid–base pair" (http:/ / goldbook. iupac. org/ C01266. html). IUPAC Compendium of Chemical Terminology (Online ed.). doi:10.1351/goldbook.C01266. ISBN 0-9678550-9-8. . [25] Nic, M.; Jirat, J.; Kosata, B., eds. (2006–). "precipitation" (http:/ / goldbook. iupac. org/ P04795. html). IUPAC Compendium of Chemical Terminology (Online ed.). doi:10.1351/goldbook.P04795. ISBN 0-9678550-9-8. . [26] Jörg Wingender, Stefanie Ortanderl Ausfällung. In: Römpp Chemie-Lexikon., Thieme, July 2009 [27] Ralf Alsfasser, Erwin Riedel, C Janiak, HJ Meyer Modern Inorganic Chemistry. 3. Edition. de Gruyter, 2007, ISBN 978-3-11-019060-1, p. 171 [28] Atkins, pp. 937–950 [29] David Stanley Saunders Insect clocks (http:/ / books. google. com/ books?id=3qJOw5Gh_UMC& pg=PA179), Elsevier, 2002, ISBN 0-444-50407-9 p. 179
  • 105. Chemical reaction 103 [30] Nic, M.; Jirat, J.; Kosata, B., eds. (2006–). "catalyst" (http:/ / goldbook. iupac. org/ C00876. html). IUPAC Compendium of Chemical Terminology (Online ed.). doi:10.1351/goldbook.C00876. ISBN 0-9678550-9-8. . [31] Nic, M.; Jirat, J.; Kosata, B., eds. (2006–). "inhibitor" (http:/ / goldbook. iupac. org/ I03035. html). IUPAC Compendium of Chemical Terminology (Online ed.). doi:10.1351/goldbook.I03035. ISBN 0-9678550-9-8. . [32] Christoph Elschenbroich: Organometallchemie. 6th edition, Wiesbaden, 2008, ISBN 978-3-8351-0167-8, p. 263 [33] March, Jerry (1985), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (3rd ed.), New York: Wiley, ISBN 0-471-85472-7 [34] S. R. Hartshorn, Aliphatic Nucleophilic Substitution (http:/ / books. google. com/ books?id=bAo4AAAAIAAJ& printsec=frontcover), Cambridge University Press, London, 1973. ISBN 0-521-09801-7 pp. 1 ff [35] Leslie C. Bateman, Mervyn G. Church, Edward D. Hughes, Christopher K. Ingold and Nazeer Ahmed Taher (1940). "188. Mechanism of substitution at a saturated carbon atom. Part XXIII. A kinetic demonstration of the unimolecular solvolysis of alkyl halides. (Section E) a general discussion". Journal of the Chemical Society: 979. doi:10.1039/JR9400000979. [36] Brückner, pp. 63–77 [37] Brückner, pp. 203–206 [38] Brückner, p. 16 [39] Brückner, p. 192 [40] Brückner, p. 183 [41] Brückner, p. 172 [42] Wiberg, pp. 950, 1602 [43] Nic, M.; Jirat, J.; Kosata, B., eds. (2006–). "Markownikoff rule" (http:/ / goldbook. iupac. org/ M03707. html). IUPAC Compendium of Chemical Terminology (Online ed.). doi:10.1351/goldbook.M03707. ISBN 0-9678550-9-8. . [44] Brückner, p. 125 [45] Hans Peter Latscha, Uli Kazmaier, Helmut Alfons Klein Organische Chemie: Chemie-basiswissen II, Vol. 2. 6th edition, Springer, 2008, ISBN 978-3-540-77106-7, p. 273 [46] Organic Reactions. 2004. doi:10.1002/0471264180. ISBN 0-471-26418-0. [47] Ian Hunt. "Chapter 18: Enols and Enolates — The Michael Addition reaction" (http:/ / www. chem. ucalgary. ca/ courses/ 351/ Carey5th/ Ch18/ ch18-4-3. html). University of Calgary. . [48] Brückner, p. 580 [49] Manfred Lechner, Klaus Gehrke, Eckhard Nordmeier Macromolecular Chemistry 3rd Edition, Birkhauser, Basel 2003, ISBN 3-7643-6952-3, pp. 53–65 [50] Marye Anne Fox, James K. Whitesell Organic chemistry (http:/ / books. google. com/ books?id=xx_uIP5LgO8C& pg=PA699), 2004, ISBN 0-7637-2197-2 p. 699 [51] Diels, Otto; Alder, Kurt (1928). "Synthesen in der hydroaromatischen Reihe". Justus Liebigs Annalen der Chemie 460: 98. doi:10.1002/jlac.19284600106. [52] Brückner, pp. 637–647 [53] Woodward, R. B.; Hoffmann, Roald (1965). Journal of the American Chemical Society 87 (2): 395. doi:10.1021/ja01080a054. [54] Peter Karlson , Detlef Doenecke, Jan Koolman, Georg Fuchs, Wolfgang Gerok. Karlson Biochemistry and Pathobiochemistry, 16th edition, Georg Thieme, 2005, ISBN 978-3-13-357815-8, pp. 55–56 [55] Nic, M.; Jirat, J.; Kosata, B., eds. (2006–). "anabolism" (http:/ / goldbook. iupac. org/ A00314. html). IUPAC Compendium of Chemical Terminology (Online ed.). doi:10.1351/goldbook.A00314. ISBN 0-9678550-9-8. . [56] Gerhard Emig, Elias Klemm. Technical Chemistry. 5th edition, Springer, 2005, ISBN 978-3-540-23452-4, pp. 33–34 [57] Trost, B. (1991). "The atom economy—a search for synthetic efficiency". Science 254 (5037): 1471–7. Bibcode 1991Sci...254.1471T. doi:10.1126/science.1962206. PMID 1962206. [58] John J. McKetta, Guy E Weismantel Encyclopedia of Chemical Processing and Design: Volume 67 – Water and Wastewater Treatment: Protective Coating Systems to Zeolite, Volume 67 (http:/ / books. google. com/ books?id=MfjDlUe8Kc0C& pg=PA109), CRC Press, 1999 ISBN 0-8247-2618-9, p. 109 [59] Atkins, p. 987
  • 106. Chemical reaction 104 Bibliography • Atkins, Peter W. and Julio de Paula Physical Chemistry, 4th Edition, Wiley-VCH, Weinheim 2006, ISBN 978-3-527-31546-8 • Brock, William H. Viewegs Geschichte der Chemie ( pg=PA459). Vieweg, Braunschweig 1997, ISBN 3-540-67033-5. • Brückner, Reinhard Reaktionsmechanismen. 3rd ed., Spektrum Akademischer Verlag, München 2004, ISBN 3-8274-1579-9 • Wiberg, Egon, Wiberg, Nils and Holleman, Arnold Frederick Inorganic chemistry ( books?id=Mtth5g59dEIC&pg=PA287), Academic Press, 2001 ISBN 0-12-352651-5 Chemical equilibrium In a chemical reaction, chemical equilibrium is the state in which both reactants and products are present at concentrations which have no further tendency to change with time.[1] Usually, this state results when the forward reaction proceeds at the same rate as the reverse reaction. The reaction rates of the forward and reverse reactions are generally not zero but, being equal, there are no net changes in the concentrations of the reactant and product. This process is called dynamic equilibrium.[2][3]
  • 107. Chemical equilibrium 105 Introduction The concept of chemical equilibrium was developed after Berthollet (1803) found that some chemical reactions are reversible. For any reaction mixture to exist at equilibrium, the rates of the forward and backward (reverse) reactions are equal. In the following chemical equation with arrows pointing both ways to indicate equilibrium, A and B are reactant chemical species, S and T are product species, and α, β, σ, and τ are the stoichiometric coefficients of the respective reactants and products: The equilibrium position of a reaction is said to lie "far to the right" if, at equilibrium, nearly all the reactants are consumed. Conversely the equilibrium position is said to be "far to the left" if hardly any product is formed from the reactants. Guldberg and Waage (1865), building on Berthollet’s ideas, proposed the law of mass action: where A, B, S and T are active masses and k+ and k− are rate constants. Since at equilibrium forward and backward rates are equal: and the ratio of the rate constants is also a constant, now known as an equilibrium constant. By convention the products form the numerator. However, the law of mass action is valid only for concerted one-step reactions that proceed through a single transition state and is not valid in A burette, an general because rate equations do not, in general, follow the stoichiometry of the reaction as apparatus for carrying out Guldberg and Waage had proposed (see, for example, nucleophilic aliphatic substitution by SN1 or e.g. acid-base reaction of hydrogen and bromine to form hydrogen bromide). Equality of forward and backward titration, is an reaction rates, however, is a necessary condition for chemical equilibrium, though it is not important part sufficient to explain why equilibrium occurs. of equilibrium chemistry. Despite the failure of this derivation, the equilibrium constant for a reaction is indeed a constant, independent of the activities of the various species involved, though it does depend on temperature as observed by the van t Hoff equation. Adding a catalyst will affect both the forward reaction and the reverse reaction in the same way and will not have an effect on the equilibrium constant. The catalyst will speed up both reactions thereby increasing the speed at which equilibrium is reached.[2][4] Although the macroscopic equilibrium concentrations are constant in time, reactions do occur at the molecular level. For example, in the case of acetic acid dissolved in water and forming acetate and hydronium ions, CH3CO2H + H2O ⇌ CH3CO2− + H3O+ a proton may hop from one molecule of acetic acid on to a water molecule and then on to an acetate anion to form another molecule of acetic acid and leaving the number of acetic acid molecules unchanged. This is an example of dynamic equilibrium. Equilibria, like the rest of thermodynamics, are statistical phenomena, averages of microscopic behavior. Le Chateliers principle (1884) gives an idea of the behavior of an equilibrium system when changes to its reaction conditions occur. If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to partially reverse the change. For example, adding more S from the outside will cause an excess of products, and the system will try to counteract this by increasing the reverse reaction and pushing the equilibrium point backward
  • 108. Chemical equilibrium 106 (though the equilibrium constant will stay the same). If mineral acid is added to the acetic acid mixture, increasing the concentration of hydronium ion, the amount of dissociation must decrease as the reaction is driven to the left in accordance with this principle. This can also be deduced from the equilibrium constant expression for the reaction: If {H3O+} increases {CH3CO2H} must increase and {CH3CO2−} must decrease. The H2O is left out as it is a pure liquid and its concentration is undefined. A quantitative version is given by the reaction quotient. J. W. Gibbs suggested in 1873 that equilibrium is attained when the Gibbs energy of the system is at its minimum value (assuming the reaction is carried out under constant pressure). What this means is that the derivative of the Gibbs energy with respect to reaction coordinate (a measure of the extent of reaction that has occurred, ranging from zero for all reactants to a maximum for all products) vanishes, signalling a stationary point. This derivative is called the reaction Gibbs energy (or energy change) and corresponds to the difference between the chemical potentials of reactants and products at the composition of the reaction mixture.[1] This criterion is both necessary and sufficient. If a mixture is not at equilibrium, the liberation of the excess Gibbs energy (or Helmholtz energy at constant volume reactions) is the “driving force” for the composition of the mixture to change until equilibrium is reached. The equilibrium constant can be related to the standard Gibbs energy change for the reaction by the equation where R is the universal gas constant and T the temperature. When the reactants are dissolved in a medium of high ionic strength the quotient of activity coefficients may be taken to be constant. In that case the concentration quotient, Kc, where [A] is the concentration of A, etc., is independent of the analytical concentration of the reactants. For this reason, equilibrium constants for solutions are usually determined in media of high ionic strength. Kc varies with ionic strength, temperature and pressure (or volume). Likewise Kp for gases depends on partial pressure. These constants are easier to measure and encountered in high-school chemistry courses. Thermodynamics The relation between the Gibbs energy and the equilibrium constant can be found by considering chemical potentials.[1] At constant temperature and pressure the function G Gibbs free energy for the reaction, depends only on the extent of reaction: ξ (Greek letter xi), and can only decrease according to the second law of thermodynamics. It means that the derivative of G with ξ must be negative if the reaction happens; at the equilibrium the derivative being equal to zero. : equilibrium At constant volume, one must consider the Helmholtz free energy for the reaction: A. In this article only the constant pressure case is considered. The constant volume case is important in geochemistry and atmospheric chemistry where pressure variations are significant. Note that, if reactants and products were in standard state (completely pure), then there would be no reversibility and no equilibrium. The mixing of the products and reactants contributes a large entropy (known as entropy of mixing) to states containing equal mixture of products and reactants. The combination of the standard Gibbs energy change and the Gibbs energy of mixing determines the
  • 109. Chemical equilibrium 107 equilibrium state.[5][6] In general an equilibrium system is defined by writing an equilibrium equation for the reaction In order to meet the thermodynamic condition for equilibrium, the Gibbs energy must be stationary, meaning that the derivative of G with respect to the extent of reaction: ξ, must be zero. It can be shown that in this case, the sum of chemical potentials of the products is equal to the sum of those corresponding to the reactants. Therefore, the sum of the Gibbs energies of the reactants must be the equal to the sum of the Gibbs energies of the products. where μ is in this case a partial molar Gibbs energy, a chemical potential. The chemical potential of a reagent A is a function of the activity, {A} of that reagent. ,( is the standard chemical potential ). Substituting expressions like this into the Gibbs energy equation: in the case of a closed system. Now ( corresponds to the Stoichiometric coefficient and is the differential of the extent of reaction ). At constant pressure and temperature we obtain: which corresponds to the Gibbs free energy change for the reaction . This results in: . By substituting the chemical potentials: , the relationship becomes: : which is the standard Gibbs energy change for the reaction. It is a constant at a given temperature, which can be calculated, using thermodynamical tables. ( is the reaction quotient when the system is not at equilibrium ). Therefore At equilibrium ; the reaction quotient becomes equal to the equilibrium constant. leading to:
  • 110. Chemical equilibrium 108 and Obtaining the value of the standard Gibbs energy change, allows the calculation of the equilibrium constant Addition of reactants or products For a reactional system at equilibrium: ; . If are modified activities of constituents, the value of the reaction quotient changes and becomes different from the equilibrium constant: and then • If activity of a reagent increases , the reaction quotient decreases. then and : The reaction will shift to the right (i.e. in the forward direction, and thus more products will form). • If activity of a product increases then and : The reaction will shift to the left (i.e. in the reverse direction, and thus less products will form). Note that activities and equilibrium constants are dimensionless numbers.
  • 111. Chemical equilibrium 109 Treatment of activity The expression for the equilibrium constant can be rewritten as the product of a concentration quotient, Kc and an activity coefficient quotient, Γ. [A] is the concentration of reagent A, etc. It is possible in principle to obtain values of the activity coefficients, γ. For solutions, equations such as the Debye-Hückel equation or extensions such as Davies equation[7] Specific ion interaction theory or Pitzer equations[8] may be used.Software (below). However this is not always possible. It is common practice to assume that Γ is a constant, and to use the concentration quotient in place of the thermodynamic equilibrium constant. It is also general practice to use the term equilibrium constant instead of the more accurate concentration quotient. This practice will be followed here. For reactions in the gas phase partial pressure is used in place of concentration and fugacity coefficient in place of activity coefficient. In the real world, for example, when making ammonia in industry, fugacity coefficients must be taken into account. Fugacity, f, is the product of partial pressure and fugacity coefficient. The chemical potential of a species in the gas phase is given by so the general expression defining an equilibrium constant is valid for both solution and gas phases. Concentration quotients In aqueous solution, equilibrium constants are usually determined in the presence of an "inert" electrolyte such as sodium nitrate NaNO3 or potassium perchlorate KClO4. The ionic strength of a solution is given by where ci and zi stands for the concentration and ionic charge of ion type i, and the sum is taken over all the N types of charged species in solution. When the concentration of dissolved salt is much higher than the analytical concentrations of the reagents, the ions originating from the dissolved salt determine the ionic strength, and the ionic strength is effectively constant. Since activity coefficients depend on ionic strength the activity coefficients of the species are effectively independent of concentration. Thus, the assumption that Γ is constant is justified. The concentration quotient is a simple multiple of the equilibrium constant.[9] However, Kc will vary with ionic strength. If it is measured at a series of different ionic strengths the value can be extrapolated to zero ionic strength.[8] The concentration quotient obtained in this manner is known, paradoxically, as a thermodynamic equilibrium constant. To use a published value of an equilibrium constant in conditions of ionic strength different from the conditions used in its determination, the value should be adjustedSoftware (below).
  • 112. Chemical equilibrium 110 Metastable mixtures A mixture may be appear to have no tendency to change, though it is not at equilibrium. For example, a mixture of SO2 and O2 is metastable as there is a kinetic barrier to formation of the product, SO3. 2SO2 + O2 2SO3 The barrier can be overcome when a catalyst is also present in the mixture as in the contact process, but the catalyst does not affect the equilibrium concentrations. Likewise, the formation of bicarbonate from carbon dioxide and water is very slow under normal conditions CO2 + 2H2O HCO3- +H3O+ but almost instantaneous in the presence of the catalytic enzyme carbonic anhydrase. Pure substances When pure substances (liquids or solids) are involved in equilibria they do not appear in the equilibrium equation[10] Applying the general formula for an equilibrium constant to the specific case of acetic acid one obtains It may be assumed that the concentration of water is constant. This assumption will be valid for all but very concentrated solutions. The equilibrium constant expression is therefore usually written as where now a constant factor is incorporated into the equilibrium constant. A particular case is the self-ionization of water itself The self-ionization constant of water is defined as It is perfectly legitimate to write [H+] for the hydronium ion concentration, since the state of solvation of the proton is constant (in dilute solutions) and so does not affect the equilibrium concentrations. Kw varies with variation in ionic strength and/or temperature. The concentrations of H+ and OH- are not independent quantities. Most commonly [OH-] is replaced by Kw[H+]−1 in equilibrium constant expressions which would otherwise include hydroxide ion. Solids also do not appear in the equilibrium equation. An example is the Boudouard reaction[10]: for which the equation (without solid carbon) is written as:
  • 113. Chemical equilibrium 111 Multiple equilibria Consider the case of a dibasic acid H2A. When dissolved in water, the mixture will contain H2A, HA- and A2-. This equilibrium can be split into two steps in each of which one proton is liberated. K1 and K2 are examples of stepwise equilibrium constants. The overall equilibrium constant, , is product of the stepwise constants. Note that these constants are dissociation constants because the products on the right hand side of the equilibrium expression are dissociation products. In many systems, it is preferable to use association constants. β1 and β2 are examples of association constants. Clearly β1 = 1/K2 and β2 = 1/βD; lg β1 = pK2 and lg β2 = pK2 + pK1[11] For multiple equilibrium systems, also see: theory of Response reactions. Effect of temperature The effect of changing temperature on an equilibrium constant is given by the van t Hoff equation Thus, for exothermic reactions, (ΔH is negative) K decreases with an increase in temperature, but, for endothermic reactions, (ΔH is positive) K increases with an increase temperature. An alternative formulation is At first sight this appears to offer a means of obtaining the standard molar enthalpy of the reaction by studying the variation of K with temperature. In practice, however, the method is unreliable because error propagation almost always gives very large errors on the values calculated in this way.
  • 114. Chemical equilibrium 112 Effect of electric and magnetic fields The effect of electric field on equilibrium has been studied by Manfred Eigen among others. Types of equilibrium 1. In the gas phase. Rocket engines[12] 2. The industrial synthesis such as ammonia in the Haber-Bosch process (depicted right) takes place through a succession of equilibrium steps including adsorption processes. 3. atmospheric chemistry 4. Seawater and other natural waters: Chemical oceanography 5. Distribution between two phases 1. LogD-Distribution coefficient: Important for pharmaceuticals where lipophilicity is a significant property of a drug 2. Liquid-liquid extraction, Ion exchange, Chromatography 3. Solubility product 4. Uptake and release of oxygen by haemoglobin in blood 6. Acid/base equilibria: Acid dissociation constant, hydrolysis, buffer solutions, indicators, acid-base homeostasis Haber-Bosch process 7. Metal-ligand complexation: sequestering agents, chelation therapy, MRI contrast reagents, Schlenk equilibrium 8. Adduct formation: Host-guest chemistry, supramolecular chemistry, molecular recognition, dinitrogen tetroxide 9. In certain oscillating reactions, the approach to equilibrium is not asymptotically but in the form of a damped oscillation .[10] 10. The related Nernst equation in electrochemistry gives the difference in electrode potential as a function of redox concentrations. 11. When molecules on each side of the equilibrium are able to further react irreversibly in secondary reactions, the final product ratio is determined according to the Curtin-Hammett principle. In these applications, terms such as stability constant, formation constant, binding constant, affinity constant, association/dissociation constant are used. In biochemistry, it is common to give units for binding constants, which serve to define the concentration units used when the constant’s value was determined.
  • 115. Chemical equilibrium 113 Composition of a mixture When the only equilibrium is that of the formation of a 1:1 adduct as the composition of a mixture, there are any number of ways that the composition of a mixture can be calculated. For example, see ICE table for a traditional method of calculating the pH of a solution of a weak acid. There are three approaches to the general calculation of the composition of a mixture at equilibrium. 1. The most basic approach is to manipulate the various equilibrium constants until the desired concentrations are expressed in terms of measured equilibrium constants (equivalent to measuring chemical potentials) and initial conditions. 2. Minimize the Gibbs energy of the system.[13] 3. Satisfy the equation of mass balance. The equations of mass balance are simply statements that demonstrate that the total concentration of each reactant must be constant by the law of conservation of mass. Mass-balance equations In general, the calculations are rather complicated or complex. For instance, in the case of a dibasic acid, H2A dissolved in water the two reactants can be specified as the conjugate base, A2-, and the proton, H+. The following equations of mass-balance could apply equally well to a base such as 1,2-diaminoethane, in which case the base itself is designated as the reactant A: With TA the total concentration of species A. Note that it is customary to omit the ionic charges when writing and using these equations. When the equilibrium constants are known and the total concentrations are specified there are two equations in two unknown "free concentrations" [A] and [H]. This follows from the fact that [HA]= β1[A][H], [H2A]= β2[A][H]2 and [OH] = Kw[H]−1 so the concentrations of the "complexes" are calculated from the free concentrations and the equilibrium constants. General expressions applicable to all systems with two reagents, A and B would be It is easy to see how this can be extended to three or more reagents.
  • 116. Chemical equilibrium 114 Polybasic acids The composition of solutions containing reactants A and H is easy to calculate as a function of p[H]. When [H] is known, the free concentration [A] is calculated from the mass-balance equation in A. Here is an example of the results that can be obtained. This diagram, for the hydrolysis of the aluminium Lewis acid Al3+aq[14] shows the species concentrations for a 5×10−6M solution of an aluminium salt as a function of pH. Each concentration is shown as a percentage of the total aluminium. Solution and precipitation The diagram above illustrates the point that a precipitate that is not one of the main species in the solution equilibrium may be formed. At pH just below 5.5 the main species present in a 5μM solution of Al3+ are aluminium hydroxides Al(OH)2+, Al(OH)2+ and Al13(OH)327+, but on raising the pH Al(OH)3 precipitates from the solution. This occurs because Al(OH)3 has a very large lattice energy. As the pH rises more and more Al(OH)3 comes out of solution. This is an example of Le Chateliers principle in action: Increasing the concentration of the hydroxide ion causes more aluminium hydroxide to precipitate, which removes hydroxide from the solution. When the hydroxide concentration becomes sufficiently high the soluble aluminate, Al(OH)4-, is formed. Another common instance where precipitation occurs is when a metal cation interacts with an anionic ligand to form an electrically-neutral complex. If the complex is hydrophobic, it will precipitate out of water. This occurs with the nickel ion Ni2+ and dimethylglyoxime, (dmgH2): in this case the lattice energy of the solid is not particularly large, but it greatly exceeds the energy of solvation of the molecule Ni(dmgH)2. Minimization of free energy At equilibrium, G is at a minimum: For a closed system, no particles may enter or leave, although they may combine in various ways. The total number of atoms of each element will remain constant. This means that the minimization above must be subjected to the constraints:
  • 117. Chemical equilibrium 115 where is the number of atoms of element i in molecule j and bi0 is the total number of atoms of element i, which is a constant, since the system is closed. If there are a total of k types of atoms in the system, then there will be k such equations. This is a standard problem in optimisation, known as constrained minimisation. The most common method of solving it is using the method of Lagrange multipliers, also known as undetermined multipliers (though other methods may be used). Define: where the are the Lagrange multipliers, one for each element. This allows each of the to be treated independently, and it can be shown using the tools of multivariate calculus that the equilibrium condition is given by     and     (For proof see Lagrange multipliers) This is a set of (m+k) equations in (m+k) unknowns (the and the ) and may, therefore, be solved for the equilibrium concentrations as long as the chemical potentials are known as functions of the concentrations at the given temperature and pressure. (See Thermodynamic databases for pure substances). This method of calculating equilibrium chemical concentrations is useful for systems with a large number of different molecules. The use of k atomic element conservation equations for the mass constraint is straightforward, and replaces the use of the stoichiometric coefficient equations.[12] References [1] Peter Atkins and Julio de Paula, Atkins Physical Chemistry, 8th edition (W.H. Freeman 2006, ISBN 0-7167-8759-8) p.200-202 [2] Atkins, Peter W and Jones, Loretta Chemical Principles: The Quest for Insight 2nd Ed. ISBN 0-7167-9903-0 [3] Nic, M.; Jirat, J.; Kosata, B., eds. (2006–). "chemical equilibrium" (http:/ / goldbook. iupac. org/ C01023. html). IUPAC Compendium of Chemical Terminology (Online ed.). doi:10.1351/goldbook.C01023. ISBN 0-9678550-9-8. . [4] Chemistry: Matter and Its Changes James E. Brady , Fred Senese 4th Ed. ISBN 0-471-21517-1 [5] Schultz, Mary Jane (1999). "Why Equilibrium? Understanding Entropy of Mixing". Journal of Chemical Education 76 (10): 1391. Bibcode 1999JChEd..76.1391S. doi:10.1021/ed076p1391. [6] Clugston, Michael J. (1990). "A mathematical verification of the second law of thermodynamics from the entropy of mixing". Journal of Chemical Education 67 (3): 203. Bibcode 1990JChEd..67Q.203C. doi:10.1021/ed067p203. [7] C.W. Davies, Ion Association, Butterworths, 1962 [8] I. Grenthe and H. Wanner, Guidelines for the extrapolation to zero ionic strength (http:/ / www. nea. fr/ html/ dbtdb/ guidelines/ tdb2. pdf) [9] F.J.C. Rossotti and H. Rossotti, The Determination of Stability Constants, McGraw-Hill, 1961 [10] Concise Encyclopedia Chemistry 1994 ISBN 0-89925-457-8 [11] M.T. Beck, Chemistry of Complex Equilibria, Van Nostrand, 1970. 2nd. Edition by M.T. Beck and I Nagypál, Akadémiai Kaidó, Budapest, 1990. [12] NASA Reference publication 1311, Computer Program for Calculation of Complex Chemical Equilibrium Compositions and Applications (http:/ / gltrs. grc. nasa. gov/ reports/ 1994/ RP-1311. pdf) [13] This approach is described in detail in W. R. Smith and R. W. Missen, Chemical Reaction Equilibrium Analysis: Theory and Algorithms, , Krieger Publishing, Malabar, Fla, 1991 (a reprint, with corrections, of the same title by John Wiley & Sons, 1982). A comprehensive treatment of the theory of chemical reaction equilibria and its computation. Details at http:/ / www. mathtrek. com/ (http:/ / www. mathtrek. com) [14] The diagram was created with the program HySS (http:/ / www. hyperquad. co. uk/ hyss. htm)
  • 118. Chemical equilibrium 116 Further reading • F. Van Zeggeren and S.H. Storey, The Computation of Chemical Equilibria, Cambridge University Press, 1970. Mainly concerned with gas-phase equilibria. • D. J. Leggett (editor), Computational Methods for the Determination of Formation Constants, Plenum Press, 1985. • A.E. Martell and R.J. Motekaitis, The Determination and Use of Stability Constants, Wiley-VCH, 1992. • P. Gans, Stability Constants: Determination and Uses, an interactive CD, Protonic Software (Leeds), 2004 External links • All about chemical equilibrium ( • Thermodynamics of chemical equilibrium ( • ( Computer programs There are n mass-balance equations in n unknown free concentrations. This constitutes a set of non-linear equations that must be solved by a method of successive approximations. The most commonly-used method is the Newton-Raphson method, which has been the subject of numerous publications. Some general computer programs are listed here. • Geochem-EZ ( home.htm)- (freeware) a multi-purpose chemical speciation program, used in plant nutrition and in soil and environmental chemistry research to perform equilibrium speciation computations, allowing the user to estimate solution ion activities and to consider simple complexes and solid phases. • HySS ( Titration simulation and speciation calculations. • EQS4WIN ( A powerful computer program originally developed for gas-phase equilibria but subsequently extended to general applications. Uses the Gibbs energy minimization approach. • CHEMEQL ( A comprehensive computer program for the calculation of thermodynamic equilibrium concentrations of species in homogeneous and heterogeneous systems. Many geochemical applications. • WinSGW ( A Windows version of the SOLGASWATER computer program. • Visual MINTEQ ( A Windows version of MINTEQA2 (ver 4.0). MINTEQA2 ( is a chemical equilibrium model for the calculation of metal speciation, solubility equilibria etc. for natural waters. • MINEQL+ ( A chemical equilibrium modeling system for aqueous systems. Handles a wide range of pH, redox, solubility and sorption scenarios.
  • 119. Chemical equilibrium 117 Software • Aqua solution software ( (Sukhno Igor, Buzko Vladimir, Polushin Alexey) A set of six computer programs for • Specific Interaction Theory. An editable database of published SIT parameters. Estimation of SIT parameters and adjustment of stability constants for changes in ionic strength. • Calculation of electrolyte activity coefficients, ionic activity coefficients, osmotic coefficients • Calculation of acid-base equilibria in electrolyte solutions and sea water • Calculation of O2 solubility in water, electrolyte solutions, natural fluids, and seawater as a function of temperature, concentration, salinity, altitude, external pressure, humidity • Prediction of temperature dependence of lg K values using various thermodynamic models • JESS ( powerful research tool for thermodynamic and kinetic modelling of chemical speciation in complex aqueous environments, with a focus on determining thermodynamic consistency by automatic means. • Chemical Equilibrium Calculator ( • Mission to Mars – A chemistry tutorial for high school students ( • AIOMFAC model ( calculation of activity coefficients in electrolyte solutions and organic-inorganic mixtures using group-contribution concept. Chemical law Chemical laws are those laws of nature relevant to chemistry. The most fundamental concept in chemistry is the law of conservation of mass, which states that there is no detectable change in the quantity of matter during an ordinary chemical reaction. Modern physics shows that it is actually energy that is conserved, and that energy and mass are related; a concept which becomes important in nuclear chemistry. Conservation of energy leads to the important concepts of equilibrium, thermodynamics, and kinetics. Additional laws of chemistry elaborate on the law of conservation of mass. Joseph Prousts law of definite composition says that pure chemicals are composed of elements in a definite formulation; we now know that the structural arrangement of these elements is also important. Daltons law of multiple proportions says that these chemicals will present themselves in proportions that are small whole numbers (i.e. 1:2 O:H in water); although in many systems (notably biomacromolecules and minerals) the ratios tend to require large numbers, and are frequently represented as a fraction. Such compounds are known as non-stoichiometric compounds More modern laws of chemistry define the relationship between energy and transformations. • In equilibrium, molecules exist in mixture defined by the transformations possible on the timescale of the equilibrium, and are in a ratio defined by the intrinsic energy of the molecules—the lower the intrinsic energy, the more abundant the molecule. • Transforming one structure to another requires the input of energy to cross an energy barrier; this can come from the intrinsic energy of the molecules themselves, or from an external source which will generally accelerate transformations. The higher the energy barrier, the slower the transformation occurs. • There is a hypothetical intermediate, or transition structure, that corresponds to the structure at the top of the energy barrier. The Hammond-Leffler Postulate states that this structure looks most similar to the product or starting material which has intrinsic energy closest to that of the energy barrier. Stabilizing this hypothetical intermediate through chemical interaction is one way to achieve catalysis. • All chemical processes are reversible (law of microscopic reversibility) although some processes have such an energy bias, they are essentially irreversible.
  • 120. Outline of chemistry 118 Outline of chemistry The following outline is provided as an overview of and topical guide to chemistry: Chemistry – science of atomic matter (matter that is composed of chemical elements), especially its chemical reactions, but also including its properties, structure, composition, behavior, and changes as they relate the chemical reactions.[1][2] Chemistry is centrally concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds. Nature of chemistry Chemistry can be described as all of the following: • An academic discipline: one with academic departments, curricula and degrees; national and international societies; and specialized journals. • A scientific field (a branch of science) – widely-recognized category of specialized expertise within science, and typically embodies its own terminology and nomenclature. Such a field will usually be represented by one or more scientific journals, where peer reviewed research is published. There are several geophysics-related scientific journals. • A natural science – one that seeks to elucidate the rules that govern the natural world using empirical and scientific method. • A physical science – one that studies non-living systems. • A biological science – one that studies the role of chemicals and chemical processes in living organisms. See Outline of biochemistry. Branches of chemistry • Analytical chemistry – analysis of material samples to gain an understanding of their chemical composition and structure. Analytical chemistry incorporates standardized experimental methods in chemistry. These methods may be used in all subdisciplines of chemistry, excluding purely theoretical chemistry. • Biochemistry – study of the chemicals, chemical reactions and chemical interactions that take place in living organisms. Biochemistry and organic chemistry are closely related, as in medicinal chemistry or neurochemistry. Biochemistry is also associated with molecular biology and genetics. • Inorganic chemistry – study of the properties and reactions of inorganic compounds. The distinction between organic and inorganic disciplines is not absolute and there is much overlap, most importantly in the sub-discipline of organometallic chemistry. • Materials chemistry – preparation, characterization, and understanding of substances with a useful function. The field is a new breadth of study in graduate programs, and it integrates elements from all classical areas of chemistry with a focus on fundamental issues that are unique to materials. Primary systems of study include the chemistry of condensed phases (solids, liquids, polymers) and interfaces between different phases. • Neurochemistry – study of neurochemicals; including transmitters, peptides, proteins, lipids, sugars, and nucleic acids; their interactions, and the roles they play in forming, maintaining, and modifying the nervous system. • Nuclear chemistry – study of how subatomic particles come together and make nuclei. Modern Transmutation is a large component of nuclear chemistry, and the table of nuclides is an important result and tool for this field. • Organic chemistry – study of the structure, properties, composition, mechanisms, and reactions of organic compounds. An organic compound is defined as any compound based on a carbon skeleton. • Physical chemistry – study of the physical and fundamental basis of chemical systems and processes. In particular, the energetics and dynamics of such systems and processes are of interest to physical chemists. Important areas of study include chemical thermodynamics, chemical kinetics, electrochemistry, statistical
  • 121. Outline of chemistry 119 mechanics, spectroscopy, and more recently, astrochemistry.[3] Physical chemistry has large overlap with molecular physics. Physical chemistry involves the use of infinitesimal calculus in deriving equations. It is usually associated with quantum chemistry and theoretical chemistry. Physical chemistry is a distinct discipline from chemical physics, but again, there is very strong overlap. • Theoretical chemistry – study of chemistry via fundamental theoretical reasoning (usually within mathematics or physics). In particular the application of quantum mechanics to chemistry is called quantum chemistry. Since the end of the Second World War, the development of computers has allowed a systematic development of computational chemistry, which is the art of developing and applying computer programs for solving chemical problems. Theoretical chemistry has large overlap with (theoretical and experimental) condensed matter physics and molecular physics. • Agrochemistry – • Astrochemistry – • Cosmochemistry – • Atmospheric chemistry – • Chemical engineering – • Chemical biology – • Chemo-informatics – • Electrochemistry – • Environmental chemistry – • Femtochemistry – • flavor chemistry – • Flow chemistry – • Geochemistry – • Green chemistry – • Histochemistry – • History of chemistry – • hydrogenation chemistry – • Immunochemistry – • Marine chemistry – • Materials science – • Mathematical chemistry – • Mechanochemistry – • Medicinal chemistry – • Molecular biology – • Molecular mechanics – • Nanotechnology – • Natural product chemistry – • Oenology – • Organometallic chemistry – • Petrochemistry – • Pharmacology – • Photochemistry – • Physical organic chemistry – • Phytochemistry – • Polymer chemistry – • Radiochemistry – • Solid-state chemistry –
  • 122. Outline of chemistry 120 • Sonochemistry – • Supramolecular chemistry – • Surface chemistry – • Synthetic chemistry – • Thermochemistry – The branch of chemistry that studies the relation between chemical action and the amount of heat absorbed or generated. • Calorimetry – The study of heat changes in physical and chemical processes. Atomic Theory The Atomic Model Timeline • The idea of what an atom is has changed over time. • Different scientists and their discoveries have led to the development of the current model of an atom. • Other examples include: • The solar system (BIG made SMALL) • The biological cell (SMALL made BIG) The Democritus Model • A Greek philosopher • He conceived the idea of the atom to describe matter. • Atom comes from the word atomos which means "indivisible". • He believed that matter was finite (had a limit) • He believed the smallest piece of matter was an indestructible and indivisible particle which he called the "atom". The John Dalton Model J.J. Thompson: The Plum Pudding Model Thermochemistry Terminology • Thermochemistry – • Chemical kinetics – • Exothermic – • Endothermic – • Thermochemical equation – • Enthalpy change – • Enthalpy of reaction – • Temperature – • Calorimeter – • Heat – • Joule – • Calorie – • Specific heat – • Specific heat capacity – • Latent heat – • Heat of fusion – • Heat of vaporization – • Collision theory –
  • 123. Outline of chemistry 121 • Activation energy – • Activated complex – • Reaction rate – • Catalyst – Thermochemical Equations • Chemical equations that include the heat involved in a reaction, either on the reactant side or the product side. • Examples: • H2O(l) + 240kJ → H2O(g) • N2 + 3H2 → 2NH3 + 92kJ • Joule (J) – Chemists For more chemists, see: Nobel Prize in Chemistry and List of chemists • Marie Curie • John Dalton • Humphry Davy • Eleuthère Irénée du Pont • George Eastman • Michael Faraday • Dmitriy Mendeleyev • Alfred Nobel • Wilhelm Ostwald • Louis Pasteur • Linus Pauling • Joseph Priestley • Karl Ziegler Chemistry literature • Scientific literature – • Scientific journal – • Academic journal – • List of important publications in chemistry • List of scientific journals in chemistry List of science magazines • Scientific American
  • 124. Outline of chemistry 122 Lists Chemical elements data references • List of elements — atomic mass, atomic number, symbol, name • Electron configurations of the elements (data page) — electron configuration, electrons per shell • Densities of the elements (data page) — density (solid, liquid, gas) • Electron affinity (data page) — electron affinity • Melting points of the elements (data page) — melting point • Boiling points of the elements (data page) — boiling point • Critical points of the elements (data page) — critical point • Heats of fusion of the elements (data page) — heat of fusion • Heats of vaporization of the elements (data page) — heat of vaporization • Heat capacities of the elements (data page) — heat capacity • Vapor pressures of the elements (data page) — vapor pressure • Electronegativities of the elements (data page) — electronegativity (Pauling scale) • Ionization energies of the elements (data page) — ionization energies (in eV) and molar ionization energies (in kJ/mol) • Atomic radii of the elements (data page) — atomic radius (empirical), atomic radius (calculated), van der Waals radius, covalent radius • Electrical resistivities of the elements (data page) — electrical resistivity • Thermal conductivities of the elements (data page) — thermal conductivity • Thermal expansion coefficients of the elements (data page) — thermal expansion • Speeds of sound of the elements (data page) — speed of sound • Elastic properties of the elements (data page) — Youngs modulus, Poisson ratio, bulk modulus, shear modulus • Hardnesses of the elements (data page) — Mohs hardness, Vickers hardness, Brinell hardness • Abundances of the elements (data page) — Earths crust, sea water, Sun and solar system • List of oxidation states of the elements — oxidation states List of compounds • List of CAS numbers by chemical compound • List of Extremely Hazardous Substances • List of inorganic compounds • List of organic compounds • List of alkanes • List of alloys Other • List of thermal conductivities • List of purification methods in chemistry • List of unsolved problems in chemistry
  • 125. Outline of chemistry 123 References [1] "What is Chemistry?" (http:/ / chemweb. ucc. ie/ what_is_chemistry. htm). . Retrieved 2011-06-12. [2] Chemistry (http:/ / dictionary. reference. com/ browse/ Chemistry). (n.d.). Merriam-Websters Medical Dictionary. Retrieved August 19, 2007. [3] Herbst, Eric (May 12, 2005). "Chemistry of Star-Forming Regions". Journal of Physical Chemistry A 109 (18): 4017–4029. doi:10.1021/jp050461c. PMID 16833724. External links • International Union of Pure and Applied Chemistry ( • IUPAC Nomenclature Home Page (, see especially the "Gold Book" containing definitions of standard chemical terms • Interactive [[Mind Map (] of Chemistry] • / Chemical energetics ( pdf) Common chemicals This article is a table of common chemical ingredients and where to find them. Table of common chemical ingredients and where to find them Chemical Chemical formula Common name Where to buy Specific brand or product name Acetic acid CH3COOH + H2O 5% Solution: White vinegar Supermarket Any brand of white vinegar Notes: Acetic acid is also available in concentrations up to 31%. Acetone CH3COCH3 Nail polish remover Discount store Onyx, Cutex Paint remover Notes: While composition varies from product to product, paint removers will contain more acetone per volume than regular nail polish remover, and industrial grade (rather than consumer grade) paint removers used by professionals and sold in bulk will [1] contain more acetone still. Some stores sell pure acetone as well. Ammonium (NH4)2CO3 Bakers ammonia Drugstores None carbonate Notes: Bakers ammonia can be found in drugstores. Ammonium NH4OH 10% Solution: Household Supermarket (for household None hydroxide ammonia ammonia) 27% Solution: Strong Drug store (for strong ammonia ammonia) Notes: Combine household ammonia and strong ammonia with water. Boric acid H3BO3 Boric acid Drug store None Notes: Often sold as a roach killer Calcium CaCO3 Chunks: Marble, limestone Builders supplies (for chunk) None carbonate Powder: Precipitated chalk Drug store (for powder) Notes:
  • 126. Common chemicals 124 Calcium CaCl2 Laundry aid Supermarket None chloride Laundry salt Hardware store Road salt Notes: Many chemicals are used to melt snow. Make certain that if you purchase road salt it is pure calcium chloride. Calcium Ca(OH)2 Slaked lime, garden lime Gardening Department None hydroxide Notes: Used to reduce the acidity of soil. Calcium oxide CaO Quicklime Builders supplies None Notes: Calcium (CaSO4) * H2O Plaster of Paris or Hardware store None sulfate CaSO4 * 2H2O Gypsum Notes: Copper(II) CuSO4 Blue Vitriol Hardware Store Zep Root Kill, Rooto Root Kill sulfate Cupric Sulfate Notes: Sold at Home Depot as Zep Root Kill or at Ace Hardware as Rooto Root Kill. Reacting the Copper II Sulfate dissolved in water with Sodium Bicarbonate (Baking Soda) will produce Copper Carbonate and CO2. Glucose C6H12O6 + H2O Corn syrup Supermarket None Notes: Glucose is a monosaccharide that, as a sweetener, is commonly found as a syrup. It is generally produced from corn starch. Hydrochloric HCl + H2O 25% Solution: Muriatic acid Hardware store The Works acid Notes: Commonly used to bleach concrete. Found in high concentrations in silverware cleaning solutions. It is also less frequently found in high concentrations in drain cleaners such as the works, however, drain cleaners also contain detergents which can introduce destabilizing impurities to chemical compounds. Hydrofluoric HF + H2O Automotive store Aluminum brightener & tire acid cleaner Notes: Best known for its ability to dissolve glass. Found in high concentrations in commercial tire cleaning solutions. Professional grade tire cleaning solutions, such as those bought in bulk by car dealerships, are typically more concentrated than consumer grade products. Must be stored in polyethylene or Teflon containers, and is very hazardous. Magnesium MgSO4 *7H2O Epsom salts Drug store None sulfate Notes: Magnesium MgCl2 Nigari (Japan) or Lushui Asian Market None chloride (China) Notes: Used to make tofu from soy milk. Manganese MnO2 Pyrolusite Hardware stores None dioxide Notes: Pyrolusite can be extracted from certain types of batteries, called dry cells, but its use is becoming rare. Naphthalene C10H8 Mothballs Hardware store None Notes: Mothballs may also be made of (para)dichlorobenzene (1,4-dichlorobenzene). Oxalic acid H2C2O4 + 2H2O Non-chlorine bleach powder Grocery, hardware, and large Bar Keepers Friend cleanser discount stores Notes:
  • 127. Common chemicals 125 Potassium KNO3 Saltpeter, saltpetre Hardware store, garden center, Grants stump remover nitrate supermarket Notes: Potassium nitrate is used as stump remover, fertilizer, and meat preservative. Potassium NaKC4H4O6 * 4H2O Rochelle salt Drug store None sodium tartrate Notes: Sodium NaHCO3 Baking soda, bicarbonate of Supermarket Arm & Hammer bicarbonate soda Notes: Be careful to use only single action baking soda when sodium bicarbonate is required. Baking soda is pure sodium bicarbonate, but baking powder has other ingredients, such as potassium tartrate and sodium monophosphate. Double action baking powder contains single action baking powder, a high temperature acid which is a gas formed at room temperature when moistened, and corn starch, which is added as a drying agent to prevent accidental activation. Sodium Na2CO3 Washing Soda Supermarket Arm & Hammer carbonate Notes: Sodium NaCl Salt, table salt Supermarket None chloride Notes: Canning or pickling salts tend not to have iodine added, so are more pure. Sodium NaOH Lye, caustic soda Hardware Store Drano, Rooto Drain hydroxide Opener(100% Pure) Notes: Keep out of eyes, can cause blindness. Sodium Na2B4O7 * 10H2O Borax Drug stores, supermarket None tetraborate Notes: Sucrose C12H22O11 Table sugar Supermarket None Notes: Sucrose is the name for table sugar, which is made from sugar beets and sugarcane. Sulfuric acid H2SO4 Sulfuric acid, vitriol Hardware store Pro Liquid Drain Cleaner Notes: This is a very difficult chemical to find in concentrated form at a hardware store. Most chemistry experiments or processes require the use of sulfuric acid in concentrations above 85% for optimum results. Car batteries contain only 40% concentration, and depending on state of charge can contain large amounts of lead sulfate. Battery acid can easily be concentrated due to the much higher boiling point of the acid. Zinc chloride ZnClf + H2O Tinners Fluid Hardware store None Notes: Also called "killed acid," zinc chloride can be created by dissolving a small amount of zinc in hydrochloric acid. Used for cleaning copper. References [1] http:/ / www. walmart. com/ catalog/ product. do?product_id=11047134
  • 128. International Year of Chemistry 126 International Year of Chemistry The International Year of Chemistry 2011 (IYC 2011) commemorates the achievements of chemistry, and its contributions to humankind.[1] This recognition for chemistry was made official by the United Nations in December 2008. Events for the year were coordinated by IUPAC, the International Union of Pure and Applied Chemistry, and by UNESCO, the United Nations Educational, Scientific, and Cultural Organization.[2][3] Background International Year of Chemistry Logo The UN resolution calling for the International Year of Chemistry in 2011 was submitted by Ethiopia and co-sponsored by 23 nations. A case was made that chemistry makes a vital contribution towards achieving the goals of the UN Decade of Education for Sustainable Development, 2005-2014. Theme The theme of IYC2011 was "Chemistry–our life, our future," and focused on the “achievements of chemistry and its contributions to the well-being of humankind.”[1] It aimed to raise awareness of chemistry among the general public and to attract young people into the field, as well as to highlight the role of chemistry in solving global problems.[4] Events IYC 2011 events were organized by national chemical societies, such as the American Chemical Society, the Royal Society of Chemistry, the Brazilian Chemical Society, the Society of Chemical Industry [5] and the Royal Australian Chemical Institute, and by regional chemical federations, such as the European Association for Chemical and Molecular Sciences and the Federation of African Societies of Chemistry.[6][7][8][9] The IYC holds a full list of events on its website.[10] Events scheduled were billed as: - conferences, congresses, symposia, fairs, exhibitions, expositions, grand openings, lectures, meetings, open discussions, workshops, celebrations, shows, art exhibitions, and quizzes, The IYC Closing Event was held in Brussels, Belgium on Dec 01, 2011.[10] Some notable events • See the IYC website for a full list [11]. France The official launch ceremony of the IYC 2011 took place on 27–28 January in Paris at the headquarters of the United Nations Educational Scientific & Cultural Organization (UNESCO). It was attended by 1,000+ delegates from 60 countries. Four Nobel Prize Winners attended. UNESCO Director General Irina Bokova delivered the opening address.[12]
  • 129. International Year of Chemistry 127 Switzerland On February 2011 Swiss Post issued a postage stamp bearing a depiction of a model of a molecule of vitamin C to mark the International Year of Chemistry. Swiss chemist Tadeus Reichstein synthesised the vitamin for the first time in 1933.[13] United Kingdom The Royal Society of Chemistry celebrated IYC 2011 by reviewing the most significant chemical advances since the millennium.[14] Australia An international conference was held as an official IYC event at the UNESCO World Heritage Listed Lord Howe Island between 14–18 August entitled Towards Global Artificial Photosynthesis: Energy, Nanochemistry and Governance. [15] Canada Canada had many demonstrations for the year of chemistry. 32 universities all around Canada participated.[16] Dalhousie University made a "chemistry rendezvous" for the 7th of May. It included a tour of the chemistry lab, food and demonstrations.[17] India Iqras H.J. Thim College of Arts And Science, Mehrun, Jalgaon, Maharashtra, INDIA has scheduled to Celebrate International Year of Chemistry 2011 in the Academic Year 2011-2012. References [1] About IYC: Introduction. (http:/ / www. chemistry2011. org/ about-iyc/ introduction) July 9, 2009. Retrieved on July 22, 2009. [2] United Nations Observances. Retrieved on July 27, 2009. (http:/ / www. un. org/ observances/ years. shtml) [3] United Nations Resolution 63/209: International Year of Chemistry. (http:/ / daccessdds. un. org/ doc/ UNDOC/ GEN/ N08/ 483/ 33/ PDF/ N0848333. pdf?OpenElement) February 3, 2009. Retrieved on July 22, 2009. [4] “UNESCO Named Lead Agency for International Year of Chemistry in 2011.” (http:/ / portal. unesco. org/ en/ ev. php-URL_ID=44332& URL_DO=DO_TOPIC& URL_SECTION=201. html) UNESCO News Service press release. December 30, 2008. Retrieved on July 20, 2009. [5] http:/ / www. soci. org [6] About IYC: Background. (http:/ / www. chemistry2011. org/ about-iyc/ background/ ) Retrieved on July 22, 2009. [7] “2011 Will Be International Year of Chemistry.” (http:/ / pubs. acs. org/ cen/ news/ 87/ i01/ 8701notw8. html) Chemical and Engineering News. [8] “2011 To Be International Year of Chemistry.” (http:/ / www. rsc. org/ chemistryworld/ Issues/ 2009/ February/ 2011ToBeInternationalYearOfChemistry. asp) Chemistry World. February 2009. Retrieved on July 21, 2009. [9] “The United Nations Organization Has Proclaimed 2011 the International Year of Chemistry.” (http:/ / www. scielo. br/ scielo. php?script=sci_arttext& pid=S0103-50532009000300001& lng=en& nrm=iso& tlng=en) Journal of the Brazilian Chemical Society, vol. 20 no. 3, São Paulo 2009. Retrieved on July 23, 2009. [10] "Events What is happening and when" (http:/ / www. chemistry2011. org/ participate/ events). IYC 2011 Official website. 2011. . Retrieved 2011-02-23. [11] http:/ / www. chemistry2011. org/ participate/ events [12] "The Year Begins! Echoes from Paris" (http:/ / www. chemistry2011. org/ about-iyc/ news/ The-Year-Begins/ ). IYC 2011 Official website. Feb 11, 2011. . Retrieved 2011-02-23. [13] Stephens, Thomas (Feb 17, 2011). "Let the chemical games begin!" (http:/ / www. swissinfo. ch/ eng/ Specials/ International_year_of_chemistry/ Background/ Let_the_chemical_games_begin!. html?cid=29513206). Swiss Info. Swiss Broadcasting Corporation. . Retrieved 2011-02-23. [14] ChemComm Highlights in Chemistry (http:/ / pubs. rsc. org/ en/ Journals/ ArticleCollectionLanding?sercode=CC& themeId=C0CC00656D-K-C0CC02411B_THEME& journalName=Chemical Communications) - celebrating IYC 2011 by reviewing the most significant chemical advances since the millennium [15] Towards Global Artificial Photosynthesis: Energy, Nanochemistry and Governance http:/ / law. anu. edu. au/ coast/ tgap/ conf. htm (accessed 23 March 2011)
  • 130. International Year of Chemistry 128 [16] http:/ / www. iyc2011. ca [17] http:/ / chemresources. chemistry. dal. ca/ rendezvous. pdf External links • IYC 2011 Home page ( • Stamps Released On IYC 2011 ( • International Year of Chemistry Global Experiment ( List of chemists This is a list of World famous chemists: (alphabetical order). It should include those who have been important to the development or practice of chemistry. Their research have made significant contribution in the area of basic or applied chemistry. For a list of those chemists who are famous because of other accomplishments, see the section Chemists famous in other areas. A • Atul Kumar, (Born 1963), Indian chemist • Emil Abderhalden, (1877–1950), Swiss chemist • Richard Abegg, (1869–1910), German chemist • Frederick Abel, (1827–1902), English chemist • Friedrich Accum, (1769–1838),German chemist, advances in the field of gas lighting • Homer Burton Adkins, (1892–1949), American chemist, known for work in hydrogenation of organic compounds • Peter Agre, (1949-), American chemist and doctor, 2003 Nobel Prize in Chemistry • Georgius Agricola, (1494–1555), German scholar known as "the father of mineralogy" • Arthur Aikin, (1773–1855), English chemist and mineralogist • Adrien Albert, (1907–1989), Australian Medicinal Chemist • Kurt Alder, (1902–1958), German chemist, 1950 Nobel Prize in Chemistry • Sidney Altman, (1939-), 1989 Nobel Prize in Chemistry • Christian B. Anfinsen, (1916–1995), 1972 Nobel Prize in Chemistry • Angelo Angeli, an Italian Chemist • Anthony Joseph Arduengo, III, an American Chemist • Johan August Arfwedson, (1792–1841), Swedish chemist • Anton Eduard van Arkel, (1893–1976), Dutch chemist • Svante Arrhenius, (1859–1927), Swedish chemist, one of the founders of physical chemistry • Francis William Aston, (1877–1945), 1922 Nobel Prize in Chemistry • Amedeo Avogadro,(1776–1856), Italian chemist and physicist, discovered and Avogadros law)
  • 131. List of chemists 129 B • Stephen Moulton Babcock, (1843–1931), worked on the "single-grain experiment" • Werner Emmanuel Bachmann, (1901–1951), American chemist, known for work in steroids and RDX • Leo Baekeland, (1863–1944), Belgian-American chemist • Adolf von Baeyer, (1835–1917), German chemist, 1905 Nobel Prize in Chemistry, synthesis of indigo • Piero Baglioni, Italian Chemist • Hendrik Willem Bakhuis Roozeboom, (1854–1907), Dutch chemist • Allen J. Bard, (born 1933), 2008 Wolf Prize in Chemistry • Neil Bartlett, (1932–2008), English/Canadian/American chemist • Sir Derek Barton, (1918–1998), 1969 Nobel Prize in Chemistry • Fred Basolo, (1920–2007), American inorganic chemist • Antoine Baum, (1728–1804), French chemist • Karl Bayer, (1847–1904), Austrian chemist • Johann Joachim Becher, (1635–1682), Developed the phlogiston theory of combustion • Friedrich Konrad Beilstein, (1838–1906), German-Russian chemist, created Beilstein database • Joseph Achille Le Bel, (1847–1930), French chemist, early work in sterochemistry • Irina Beletskaya, (born 1933), Russian organometallic chemist • Francesco Bellini (1947– ), research scientist, doctor in organic chemistry • Paul Berg, (born 1926), 1980 Nobel Prize in Chemistry • Friedrich Bergius, (1884–1949), 1931 Nobel Prize in Chemistry • Marcellin Berthelot, (1827–1907), French chemist, important work in thermochemistry • Claude Louis Berthollet, (1748–1822), French chemist • Carolyn R. Bertozzi, American Chemist, UC Berkeley • Jöns Jakob Berzelius, (1779–1848), Swedish chemist, coined the term "polymer" in 1833 • Johannes Martin Bijvoet, (1892–1980), Dutch chemist and crystallographer • Joseph Black, (1728–1799), chemist • Dale L. Boger, (born 1953), American organic and medicinal chemist • Paul Emile Lecoq de Boisbaudran, (1838–1912), French chemist • Jan Boldingh, (1915–2003), Dutch chemist • Alexander Borodin, (1833–1887), Russian chemist & composer • Hans-Joachim Born, German radiochemist • Carl Bosch, (1872–1940), German chemist • Jean-Baptiste Boussingault, (1802–1887), French chemist, agricultural chemistry • Paul D. Boyer, (born 1918), 1997 Nobel Prize in Chemistry • Robert Boyer, Employee of Henry Ford focus on soybean use. • Robert Boyle, (1627–1691), English pioneer of modern chemistry • Henri Braconnot, (1780–1855), French chemist and pharmacist • Johannes Nicolaus Brønsted, (1879–1947), Danish chemist • Herbert C. Brown, (1912–2004), 1979 Nobel Prize in Chemistry • Eduard Buchner, (1860–1917), 1907 Nobel Prize in Chemistry • Robert Wilhelm Bunsen, (1811–1899), German inventor, chemist, discovered the elements caesium and rubidium with Gustav Kirchhoff and invented the Bunsen burner • William Merriam Burton, (1865–1954), American chemist, developed the first thermal cracking process for crude oil • Adolf Butenandt, (1903–1995), 1939 Nobel Prize in Chemistry • Aleksandr Butlerov, (1828–1886), Russian chemist, discovered the formose reaction
  • 132. List of chemists 130 C • Melvin Calvin, (1911–1997), American chemist, winner of 1961 Nobel Prize in Chemistry • Georg Ludwig Carius, (1829–1875), German chemist • Heinrich Caro, (1834–1910), German chemist • Wallace Carothers, (1896–1937), American chemist, known for the discovery of nylon • Stanislao Cannizzaro, (1826–1910), Italian Chemist, postulated the Cannizzaro reaction • Henry Cavendish, (1731–1810), British scientist • Thomas Cech, (born 1947), 1989 Nobel Prize in Chemistry • Martin Chalfie, (born 1947), 2008 Nobel Prize in Chemistry • Michelle Chang, (born 1977), American Chemist, Professor of Chemistry, University of California, Berkeley • Yves Chauvin, (born 1930), 2005 Nobel Prize in Chemistry • Michel Eugėne Chevreul, (1786–1889), French chemist, designed an early form of soap, lived to be 102! • Aaron Ciechanover, (born 1947), 2004 Nobel Prize in Chemistry • Giacomo Luigi Ciamician, Italian Chemist, Father of the Solar Panel • Ernst Cohen, (1869–1944), Dutch chemist (murdered in Auschwitz) • Elias James Corey, (born 1928), American organic chemist, winner of the 1990 Nobel Prize in Chemistry • Robert Corey (1897–1971), American biochemist • Carl Ferdinand Cori, (1896–1984), Czech biochemist, Nobel Prize in medicine 1947 • Gerty Cori, (1896–1957), American biochemist, Nobel Prize in medicine 1947 • Charles D. Coryell, (1912–1971), American chemist, co-discovered the element promethium • John Cornforth, (born 1917), Australian winner of the 1975 Nobel Prize in Chemistry • Frank Albert Cotton, (1930–2007), 2000 Wolf Prize in Chemistry • Charles Coulson (1910–1974), British theoretical chemist • Archibald Scott Couper, (1831–1892), English chemist, further developed Tetravalence • James Crafts, (1839–1917), American chemist, developer of Friedel-Crafts reaction • Donald J. Cram, (1919–2001), American chemist, winner of the 1987 Nobel Prize in Chemistry • William Crookes, (1832–1919), British chemist, discovered the element thallium • Paul J. Crutzen, (1933), Dutch chemist, winner of the 1995 Nobel Prize in Chemistry • Marie Curie, (1867–1934), Polish radiation physicist, 1903 Nobel Prize in Physics, 1911 Nobel Prize in Chemistry • Pierre Curie, (1859–1906), 1903 Nobel Prize in Physics • Robert Curl, (born 1933), American chemist, winner of 1996 Nobel Prize in Chemistry • Theodor Curtius, (1857–1928), German chemist D • John Dalton, (1766–1844), physicist and pioneer of the atomic theory • Carl Peter Henrik Dam, (1895–1976), Danish biochemist, winner of the 1943 Nobel Prize in Physiology or Medicine • Vincenzo, Count Dandolo, (1758–1819), Italian Nobleman and Chemist • Samuel J. Danishefsky, (born 1936), American organic chemist, natural product Total synthesis, 1995/6 Wolf Prize in Chemistry • Humphry Davy, (1778–1829), British Chemist, discovered several alkaline earth metals • Raymond Davis, Jr., (1914–2006), American physical chemist • Peter Debye, (1884–1966), Dutch chemist, winner of the 1936 Nobel Prize in Chemistry • Johann Deisenhofer, (born 1943), 1988 Nobel Prize in Chemistry • Francesco DeMaria, (born 1928), Italian-American chemist, working in Chemical engineering
  • 133. List of chemists 131 • Sir James Dewar, (1842–1923) • François Diederich, (born 1952), Luxembourg chemist • Otto Diels, (1876–1954), German chemist, winner of the 1950 Nobel Prize in Chemistry • Edward Doisy, (1893– 1986), American biochemist, winner of the 1943 Nobel Prize in Physiology or Medicine • Davorin Dolar, (1921–2005), chemist from Univ. of Ljubljana • David Adriaan van Dorp, (1915–1995), Dutch chemist • Herbert Henry Dow, (1866–1930), American industrial chemist, known for bromine extraction • Cornelius Drebbel, (1572–1633), Dutch inventor, alchemist and chemist • Vratislav Ducháček, (born 1941), Czech chemist • Carl Duisberg, (1861–1935), German chemist, early administrative industrial chemist • Jean Baptiste Dumas, (1800–1884), French chemist, work on atomic weights E • Paul Ehrlich, (1854–1915), German chemist, winner of the 1908 Nobel Prize in Physiology or Medicine • Arthur Eichengrün, (1867–1949) • Manfred Eigen, (born 1927), German chemist, winner of the 1967 Nobel Prize in Chemistry • Mostafa El-Sayed, Egyptian-American physical chemist • Fausto Elhuyar, (1755–1833), Spanish chemist, discoverer of tungsten • Conrad Elvehjem, (1901–1962), American biochemist, discovered niacin • Harry Julius Emeléus (1903–1993), British inorganic chemist • Emil Erlenmeyer, (1825–1909), German chemist • Richard R. Ernst, (born 1933), 1991 Nobel Prize in Chemistry • Gerhard Ertl, (born 1936), German physical chemist, 2007 Nobel prize in chemistry • Hans von Euler-Chelpin, (1873–1964), Swedish chemist, winner of the 1929 Nobel Prize in Chemistry • Henry Eyring, (1901–1981), Mexican-American theoretical chemist F • Kazimierz Fajans, (1887–1975), Polish-American physical chemist • Michael Faraday (1791–1867), chemist and physicist, discovered Benzene • Hermann von Fehling, (1812–1885), German chemist • John Bennett Fenn, (born 1917), 2002 Nobel Prize in Chemistry • Enrico Fermi, (born 1901), Nuclear Chemist and Elementary Particle Physicist, Nobel Prize in Physics 1938 • Hermann Emil Fischer (1852–1919), 1902 Nobel Prize in Chemistry, (actual name Hermann Emil Fischer, see below) not to be confused with: • Franz Joseph Emil Fischer (1877–1947), German chemist, co-discovered the Fischer-Tropsch process • Ernst Gottfried Fischer (1754–1831), German chemist • Ernst Otto Fischer (1918–2007), German chemist, 1973 Nobel Prize in Chemistry winner • Hans Fischer (1881–1945), German organic chemist, 1930 Nobel Prize in Chemistry winner • Antoine François, comte de Fourcroy,(1775–1809), co-discovered the element Iridium and developed modern chemical notation • Nicolas Flamel, French alchemist • Paul Flory, (1910–1985), 1974 Nobel Prize in Chemistry • Edward Frankland,(1825–1899), English chemist, originated the concept of valence • Rosalind Franklin (1920–1958), British Chemist and Crystallographer • Herman Frasch, (1851–1914), German mining engineer and inventor, pioneered the Frasch process • Carl Remigius Fresenius (1818–1897), German chemist
  • 134. List of chemists 132 • Charles Friedel, (1832–1899), French chemist, developer of Friedel-Crafts reaction • Alexander Naumovich Frumkin (1895–1976), electrochemist and chemist • Kenichi Fukui, (1918–1998), 1981 Nobel Prize in Chemistry G • Johan Gadolin, (1760–1852), Finnish chemist • Merrill Garnett, (born 1930), American biochemist • Joseph Louis Gay-Lussac, (1778–1850), French chemist and physicist, discovered the Gay-Lussac law • Charles Frédéric Gerhardt, (1816–1856), French chemist, synthesized acetylsalicylic acid • William Giauque, (1895–1982), 1949 Nobel Prize in Chemistry • Josiah Willard Gibbs (1839–1903), American engineer, chemist and physicist • Walter Gilbert, (born 1932), 1980 Nobel Prize in Chemistry • Johann Rudolf Glauber, (1604–1670), Dutch-German alchemist and chemist • Lawrence E. Glendenin, (1918–2008), American chemist, co-discovered the element promethium • Leopold Gmelin, (1788–1853), German chemist, discovered potassium ferricyanide. • Theodore Nicolas Gobley, (1811–1874), French chemist, pioneer in brain tissues analysis, discoverer of lecithin • Victor Goldschmidt, (1888–1947) Father of Modern Geochemistry • Moses Gomberg, (1866–1947), Russian-American chemist, known for pioneering work in radical chemistry • David van Goorle also called Gorlaeus, (1591–1612), Dutch chemist, on of the first modern atomists • Carl Gräbe, (1841–1927), German chemist, discovered the dye alizarin • Thomas Graham, (1805–1869), Scottish chemist, dialysis and diffusion. • Harry B. Gray, (born 1935), 2004 Wolf Prize in Chemistry • Francois Auguste Victor Grignard, (1871–1935), 1912 Nobel Prize in Chemistry corecipient • Robert H. Grubbs, (born 1942), 2005 Nobel Prize in Chemistry H • Fritz Haber, (1868–1934) 1918 Nobel Prize in Chemistry, father of the Haber process. • Otto Hahn, (1879–1968) 1944 Nobel Prize in Chemistry • John Scott Haldane,(1860–1936), British biochemist • Charles Martin Hall, (1863–1914), American chemist, famous for Hall-Héroult process • Arthur Harden, (1865–1940), English biochemist and winner of the shared Nobel Prize in Chemistry in 1929 • Odd Hassel, (1897–1981), Norwegian chemist 1969 Nobel Prize in chemistry • Charles Hatchett, (1765–1847), English chemist who discovered niobium • Herbert A. Hauptman, (born 1917), 1985 Nobel Prize in chemistry • Robert Havemann, (1910–1982), chemist • Walter Haworth, (1883–1950), 1937 Nobel Prize in chemistry • Clayton Heathcock, American Chemist • Alan J. Heeger, (born 1936), 2000 Nobel Prize in chemistry • Jan Baptist van Helmont,(1579–1644), The founder of pneumatic chemistry • Dudley R. Herschbach, (1932-), American chemist, 1986 Nobel Prize in chemistry • Avram Hershko, (born 1937), 2004 Nobel Prize in chemistry • Charles Herty, American Chemist • Gerhard Herzberg, (1904–1999), German-Canadian chemist, 1971 Nobel Prize in Chemistry • Germain Henri Hess, (1802–1850), Swiss-born Russian chemist • George de Hevesy, (1885–1966), Hungarian born chemist, recipient of the Nobel Prize in chemistry 1943 • Jaroslav Heyrovský, (1890–1967), Czech chemist, 1959 Nobel Prize in Chemistry
  • 135. List of chemists 133 • Cyril Norman Hinshelwood, (1897–1967), English physical chemist and winner of the shared Nobel Prize in Chemistry in 1956 • Dorothy Hodgkin, (1910–1994), 1964 Nobel Prize in chemistry • Jacobus Henricus van t Hoff, (1852–1911), Dutch physical chemist, 1901 Nobel Prize in Chemistry • Albert Hofmann, (1906–2008), Swiss chemist, synthesized Lysergic acid diethylamide (LSD) • August Wilhelm Hofmann, (1818–1892), German chemist, first to isolate sorbic acid • Darleane C. Hoffman, (born 1926), American Nuclear Chemist • Friedrich Hoffmann, (1660–1742), physician and chemist • Roald Hoffmann, (born 1937), Polish-born American chemist, 1981 Nobel Prize in chemistry • Frederick Gowland Hopkins, (1861–1947), British biochemist, known for discovery of vitamins, Nobel Prize in Physiology or Medicine in 1929 • Linda Hsieh-Wilson, American chemist, California Institute of Technology • Heinrich Hubert Maria Josef Houben, (1875–1940) German organic chemist • Coenraad Johannes van Houten, (1801–1887), Dutch chemist and chocolate maker, invented cocoa powder • Amir H. Hoveyda, US-based chemist working in asymmetric catalysis • Benjamin Hsiao, Asian American chemist at Stony Brook University, Fellow of the American Physical Society, Fellow of the American Chemical Society, Fellow of the American Association for the Advancement of Science[1] • Robert Huber, (born 1937), 1988 Nobel Prize in chemistry I • Sir Christopher Kelk Ingold (1893–1970), English chemist • Vladimir Ipatieff, (1867–1952), Russian-American chemist, known for organic synthesis J • Paul Janssen (1926–2003), Belgian founder of Janssen Pharmaceutica. • Frédéric Joliot-Curie (1900–1958), French chemist and physicist, 1935 Nobel Prize in Chemistry • Irène Joliot-Curie (1897–1956), French chemist and physicist, 1935 Nobel Prize in Chemistry K • Henri B. Kagan, (born 1930), 2001 Wolf Prize in Chemistry • Jerome Karle, (born 1918), 1985 Nobel Prize in Chemistry • Paul Karrer, (1889–1971), 1937 Nobel Prize in Chemistry • Karl Wilhelm Gottlob Kastner (1783–1857) • August Kekulé, (1829–1896), German organic chemist • John Kendrew, (1917–1997), 1962 Nobel Prize in Chemistry • Petrus Jacobus Kipp, (1808–1864), Dutch chemist, inventor of Kipp-generator • Johan Kjeldahl, (1849–1900), Danish chemist, head chemist at Carlsberg Brewery, methods still in use • Martin Heinrich Klaproth, (1743–1817), German chemist, discovered the element Uranium • Trevor Kletz (born 1922) British promoter of industrial safety • Aaron Klug, (born in 1926), winner of the 1982 Nobel Prize in Chemistry • Emil Knoevenagel, (1865–1921) • William Standish Knowles, (born 1917), 2001 Nobel Prize in Chemistry • Walter Kohn, (born 1923), 1998 Nobel Prize in Chemistry. • Adolph Wilhelm Hermann Kolbe, (1818–1884), German chemist known for Kolbe nitrile synthesis • Izaak Kolthoff, (1894–1993), Dutch-American chemist, the "Father of Analytical Chemistry"
  • 136. List of chemists 134 • Roger D. Kornberg, (born 1947), 2006 Nobel Prize in Chemistry • Hans A. Krebs, (1900–1981), German biochemist, work on metabolic cycles • Harold Kroto, (born 1939), English chemist, 1996 Nobel Prize in Chemistry • Richard Kuhn (1900–1967), 1938 Nobel Prize in Chemistry. L • Irving Langmuir, (1881–1957), chemist, physicist, 1932 Nobel Prize in Chemistry • Auguste Laurent, (1807–1853), French chemist, discovered anthracene • Paul Lauterbur, (1929–2007), American chemist • Antoine Lavoisier, (1743–1794), French pioneer chemist • Nicolas Leblanc, (1742–1806), French chemist and surgeon • Henri Louis Le Chatelier, (1850–1936) • Yuan T. Lee, (born 1936), winner of 1986 Nobel Prize in Chemistry • Jean-Marie Lehn, (born 1939), French chemist, shared 1987 Nobel Prize in Chemistry • Luis Federico Leloir, (1906–1987), Argentine biochemist and winner of the 1970 Nobel Prize in Chemistry • Raymond Lemieux, (1920–2000), 1999 Wolf Prize in Chemistry • Gilbert Newton Lewis, (1875–1946), American chemist and first Dean of the Berkeley College of Chemistry • Andreas Libavius, (1555–1616), German doctor and chemist • Carl Theodore Liebermann, (1842–1914), German chemist, known for synthesis of alizarin • Willard Libby (1908–1980), American chemist, winner of 1960 Nobel Prize in Chemistry • Justus von Liebig, (1803–1873), German inventor and pioneer in agricultural and biological chemistry • Karl Paul Link, (1901–1978), American biochemist, discovered the anticoagulant warfarin. • William Lipscomb, (born 1919), 1976 Nobel Prize in Chemistry • Joseph Lister, 1st Baron Lister, (1827–1912), English surgeon • Arthur H. Livermore, (1915–2009), Science Educator and chemist • Mikhail Lomonosov, (1711–1765), Russian scientist, anticipated the kinetic-molecular theory by 100 years • H. Christopher Longuet-Higgins, British Chemist • Martin Lowry, (1874–1936), British chemist • Sima Lozanić (1847–1935), Serbian Chemist • Ignacy Łukasiewicz, (1802–1882), Polish pharmacist M • Alan MacDiarmid, (1927–2007), 2000 Nobel Prize in Chemistry • Carolina Henriette Mac Gillavry, (1904–1993), Dutch chemist and crystallographer • Roderick MacKinnon, (born 1956), 2003 Nobel Prize in Chemistry • Pierre Macquer, (1718–1784), influential French chemist • Rudolph A. Marcus, (born 1923), 1992 Nobel Prize in Chemistry • Jacob A. Marinsky, (1918–2005), American chemist, co-discovered the element promethium • Jean Charles Galissard de Marignac, (1817–1894), Swiss chemist, discovered ytterbium and co-discovered gadolinium. • Vladimir Vasilevich Markovnikov, (1838–1904) • Tobin J. Marks, (1944), American inorganic chemist and material scientist • Alan G. Marshall, American chemist, co-inventor of Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry • Archer John Porter Martin, (1910–2002), 1952 Nobel Prize in Chemistry • Martinus van Marum, (1750–1837), Dutch chemist
  • 137. List of chemists 135 • Elmer McCollum, (1879–1967), American Biochemist, known for work of diet on health • Edwin McMillan, (1907–1991), 1951 Nobel Prize in Chemistry • Lise Meitner, (1878–1968), German physicist • Dmitri Ivanovich Mendeleev, (1834–1907), Russian chemist, creator of the Periodic table of elements • John Mercer, (1791–1866), chemist and industrialist • Robert Bruce Merrifield, (1921–2006), solid-phase chemist, 1984 Nobel Prize in Chemistry • Julius Lothar Meyer, (1830–1895),German chemist, important work on The periodic table of elements; not to be confused with: • Viktor Meyer, (1848–1897) • August Michaelis (1847–1916), German chemist • Hartmut Michel, (born 1948), 1988 Nobel Prize in Chemistry • Stanley Miller (born 1930), American chemist, best known for the Miller-Urey experiment • Luis E. Miramontes (1925–2004), co-inventor of the combined oral contraceptive pill • Peter D. Mitchell, (1920–1992), 1978 Nobel Prize in Chemistry • William A. Mitchell, (1911–2004), key inventor behind Pop Rocks, Tang, and Kool Whip • Eilhardt Mitscherlich, (1794–1863) German chemist, remembered for the law of isomorphism. • Alexander Mitscherlich, (1836–1918), chemist • Karl Friedrich Mohr, (1806–1879), German chemist famous for first musings on the Conservation of energy • Henri Moissan, (1852–1907), French chemist and the winner of the 1906 Nobel Prize in Chemistry • Mario J. Molina, (born 1943), 1995 Nobel Prize in Chemistry • Jacques Monod, (1910–1976), biochemist, winner of Nobel Prize in Physiology or Medicine in 1965 • Peter Moore (born 1939), American biochemist, Sterling Professor of Chemistry at Yale University • Stanford Moore, (1913–1982), 1972 Nobel Prize in Chemistry • Henry Gwyn Jeffreys Moseley (1887–1915), English physicist, discovered Moseleys law • Gerardus Johannes Mulder, (1802–1880), Dutch organic chemist • Paul Müller, Swiss chemist, (1899–1965), discovered DDT, won the Nobel Prize in Physiology or Medicine in 1939 • Robert S. Mulliken, (1896–1986), American physicist, chemist, 1966 Nobel Prize in Chemistry • Kary Mullis, (born 1944), 1993 Nobel Prize in Chemistry • Earl Muetterties, (1927–1984) American chemist N • Robert Nalbandyan, (1937–2002), Armenian protein chemist • Giulio Natta, (1903–1979), Italian chemist, 1963 Nobel Prize in Chemistry • Costin Nenitescu, (1902–1970), Romanian chemist • Antonio Neri, (1500s–1614), Florentine chemist and glassmaker • Walther Nernst, (1864–1941), German chemist, 1920 Nobel Prize in Chemistry • John Alexander Reina Newlands, (1837–1898), English analytical chemist • William Nicholson, (1753–1815), English chemist • Kyriacos Costa Nicolaou, American chemist • Julius Nieuwland, (1878–1936), American chemist, work on synthetic rubber leading to neoprene • Alfred Nobel, (1833–1896), Swedish chemist • Ronald George Wreyford Norrish, (1897–1978), 1967 Nobel Prize in Chemistry • John Howard Northrop, (1891–1987), 1946 Nobel Prize in Chemistry • Ryōji Noyori, (born 1938), 2001 Wolf Prize in Chemistry, 2001 Nobel Prize in Chemistry • Ralph Nuzzo, American chemist and materials scientists
  • 138. List of chemists 136 O • George Andrew Olah, (born 1927), 1994 Nobel Prize in Chemistry • Lars Onsager, (1903–1976), physical chemist, 1968 Nobel Prize in Chemistry • Joan Oró, (1923–2004), Catalan biochemist, one of his most important contributions was the prebiotic synthesis of the nucleobase adenine from hydrogen cyanide. • Hans Christian Ørsted, First to isolate aluminium • Wilhelm Ostwald, (1853–1932), 1909 Nobel Prize in Chemistry P • Paracelsus, (1493–1541), alchemist • Rudolph Pariser, (born 1923), theoretical and organic chemist • Robert G. Parr, (born 1921), theoretical chemist • Louis Pasteur, (1822–1895), French biochemist, father of pasteurization • Linus Pauling, (1901–1994), Nobel Prizes in chemistry and peace • Charles J. Pedersen, (1904–1989), 1987 Nobel Prize in Chemistry • Eugène-Melchior Péligot, (1811–1890) French chemist who isolated the uranium metal • William Henry Perkin, (1838–1907) British organic chemist and inventor of mauveine (dye) • William Henry Perkin, Jr., (1860–1929) British organic chemist, son of Sir William Henry Perkin • Max Perutz, (1914–2002), 1962 Nobel Prize in Chemistry • David Andrew Phoenix, (born 1966), Biochemist • Roy J. Plunkett, (1910–1994), discoverer of Teflon • John Charles Polanyi, (born 1929), Canadian chemist, Nobel Prize in Chemistry 1986. • John A. Pople, (1925–2004), theoretical chemist, 1998 Nobel Prize in Chemistry • George Porter, (1920–2002), 1967 Nobel Prize in Chemistry • Fritz Pregl, (1869–1930), Slovene-German chemist, Nobel Prize in Chemistry 1923. • Vladimir Prelog, (1906–1998), 1975 Nobel Prize in Chemistry • Joseph Priestley, (1733–1804), no formal training as a scientist, discovered the element oxygen • Ilya Prigogine, (1917–2003), 1977 Nobel Prize in Chemistry • Joseph Louis Proust, (1754–1826), discovered the Law of definite proportions R • Venkatraman Ramakrishnan, (born 1952), 2009 Nobel Prize in Chemistry • William Ramsay, (1852–1916), Scottish chemist, 1904 Nobel Prize in Chemistry • François-Marie Raoult, (1830–1901), French chemist, known for Raoults law • Henry Rapoport, American chemist, UC Berkeley • William Sage Rapson, South African Chemist and co-author of Gold Usage • Ken Raymond, American Inorganic and Bioinorganic Chemist, UC Berkeley • Julius Rebek, (1944), Hungarian_American chemist. • Henri Victor Regnault (1810–1878), French chemist and physicist • Tadeus Reichstein, (1897–1996), chemist, 1950 Nobel Prize in Physiology or Medicine • Rhazes (Razi), Iranian Chemist .(865–925) • Stuart A. Rice, (born 1932), physical chemist • Theodore William Richards, (1868–1928), 1914 Nobel Prize in Chemistry • Wim Richter, South Africa • Ellen Swallow Richards, (1842–1911), industrial and environmental chemist. • Jeremias Benjamin Richter, (1762–1807), German chemist, first used the term stoichiometry
  • 139. List of chemists 137 • Nikolaus Riehl, Germany (1901–1990) • Andrés Manuel del Río, (1764–1849), Spanish-Mexican geochemist, discovered vanadium • Robert Robinson (1886–1975), 1947 Nobel Prize in Chemistry • Pierre Jean Robiquet (1780–1840), French chemist, discovered caffeine, alizarin, cantharidin • Hillar Rootare (1928) Estonian-American Physical Chemist • Irwin Rose, (born 1926), 2004 Nobel Prize in Chemistry • Guillaume-François Rouelle, (1703–1770), French chemist • H. M. Rouell, (1718–1779), French chemist • Frank Sherwood Rowland, (born 1927), 1995 Nobel Prize in Chemistry • Daniel Rutherford, (1749–1819), Scottish chemist • Ernest Rutherford, (1871–1937), New Zealand born chemist and nuclear physicist. Discovered the Proton. Nobel Prize in Chemistry 1908 • Leopold Ruzicka (Lavoslav Ružička), (1887–1976), 1939 Nobel Prize in Chemistry S • Paul Sabatier, (1854–1941), 1912 Nobel Prize in Chemistry corecipient • Frederick Sanger, (born 1918), 1958 and 1980 Nobel Prize in Chemistry • Carl Wilhelm Scheele, (1742–1786), Swedish 18th century chemist, discovered numerous elements • Christian Friedrich Schönbein, (1799–1868), German-Swiss chemist, invented the fuel cell, and discovered gun cotton and ozone. • Stuart L. Schreiber, (born 1956), American chemist, a pioneer in a field of chemical biology • Richard R. Schrock, (born 1945), 2005 Nobel Prize in Chemistry • Peter Schultz, American chemist • Glenn T. Seaborg, (1912–1999), 1951 Nobel Prize in Chemistry • Nils Gabriel Sefström, (1787–1845), chemist. • Francesco Selmi, (1817–1881), Italian chemist. • Nikolay Nikolayevich Semyonov, (1896–1986), physicist and chemist, 1956 Nobel Prize in Chemistry • K. Barry Sharpless, (born 1941), 2001 Wolf Prize in Chemistry, 2001 Nobel Prize in Chemistry • Patsy O. Sherman (born 1930), 12 US Patents • Nevil Vincent Sidgwick, (1873–1952), English theoretical chemist, known for work in valency • Osamu Shimomura, (born 1928), 2008 Nobel Prize in Chemistry • Hideki Shirakawa, (born 1936), 2000 Nobel Prize in Chemistry • Alexander Shulgin, (born 1925), Pioneer researcher in Psychopharmacology and Entheogens • Salimuzzaman Siddiqui, (1897–1994), Pakistani chemist, pioneer in natural products chemistry • Oktay Sinanoglu, (born 1935), Turkish chemist • Jens Christian Skou, (born 1918), 1997 Nobel Prize in Chemistry • Richard Smalley, (1943–2005), 1996 Nobel Prize in Chemistry • Michael Smith, (1932–2000), 1993 Nobel Prize in Chemistry • Ascanio Sobrero, (1812–1888), Italian chemist, discoverer of nitroglycerin • Frederick Soddy, (1877–1956), British chemist, 1921 Nobel Prize in Chemistry • Susan Solomon, American atmospheric chemist • Ernest Solvay, (1838–1922), Belgian chemist and industrialist • S.P.L. Sørensen, (1868–1939), Danish chemist • Gabor A. Somorjai, (born 1935), 1998 Wolf Prize in Chemistry • Georg Ernst Stahl, (1659–1734), Important work on fermentation • Wendell Meredith Stanley, (1904–1971), 1946 Nobel Prize in Chemistry • Jean Servais Stas, (1813–1891), Belgian analytical chemist
  • 140. List of chemists 138 • Branko Stanovnik, (born 1938), chemist. • Hermann Staudinger, (1881–1965), polymer chemist, 1953 Nobel Prize in Chemistry • Harry Steenbock, (1886–1967), American biochemist, work on ultra violet irradiation. • William Howard Stein, (1911–1980), 1972 Nobel Prize in Chemistry • Thomas A. Steitz, (born 1940), 2009 Nobel Prize in Chemistry • Alfred Stock, (1876–1946), German inorganic chemist, known for work in mercury poisoning • Fraser Stoddart, (born 1945), Scottish chemist, a pioneer in the field of the mechanical bond • F. Gordon A. Stone (1925–2011), British inorganic chemist • S. Donald Stookey (born 1915), American glass and ceramic chemist • Gilbert Stork, (born 1921), 1995/6 Wolf Prize in Chemistry • Friedrich August Kekulé von Stradonitz, (1829–1896), German organic chemist,principal founder of chemical structure • James B. Sumner, (1887–1955), 1946 Nobel Prize in Chemistry • Edwin Sutermeister, American chemist, known for its work on papermaking • Theodor Svedberg, (1884–1971), 1926 Nobel Prize in Chemistry • Joseph Swan, (1828–1914), English physicist, chemist & inventor • Frédéric Swarts, (1866–1940), Belgian chemist, prepared the first chlorofluorocarbon compound • Richard Laurence Millington Synge, (1914–1994), 1952 Nobel Prize in Chemistry T • Koichi Tanaka, (born 1959), 2002 Nobel Prize in Chemistry • Henry Taube, (1915–2005), 1983 Nobel Prize in Chemistry • Louis Jacques Thénard, (1777–1857), French chemist, discovered hydrogen peroxide and Thenards Blue. • J. J. Thomson, (1856–1940), British physicist, Known in chemistry for discovery of Isotopes • Arne Tiselius, (1902–1971), 1948 Nobel Prize in Chemistry • Max Tishler, (1906–1989), 1970 Priestley Medal • Alexander R. Todd, Baron Todd, (1907–1997), 1957 Nobel Prize in Chemistry • Evangelista Torricelli, Italian Physicist and Chemist who invented the Barometer, pupil of Galileo • Roger Y. Tsien, (born 1952), 2008 Nobel Prize in Chemistry • Mikhail Tsvet, (1872–1919), Russian botanist, known for adsorption chromatography U • Georges Urbain, (1872–1938), French chemist, discovered the element Lutetium • Harold Clayton Urey, (1893–1981), 1934 Nobel Prize in Chemistry V • Lauri Vaska, (born 1925), Estonian/American chemist • Louis Nicolas Vauquelin, (1763–1829), Discovered the elements Beryllium and Chromium • Vincent du Vigneaud, (1901–1978), 1955 Nobel Prize in Chemistry • Artturi Ilmari Virtanen, (1895–1973), chemist, Nobel Prize laureate • Max Volmer, Germany (1885–1965) • Alessandro Volta, (1745–1827), electrochemist, Invented the Voltaic Cell
  • 141. List of chemists 139 W • Johannes Diderik van der Waals, (1837–1923) • Sir James Walker (1863–1935), Scottish physical chemist • John E. Walker, (born 1941), 1997 Nobel Prize in Chemistry • Otto Wallach, (1847–1931), German chemist, 1910 Nobel Prize in Chemistry • Alfred Werner, (1866–1919), Swiss chemist, 1913 Nobel Prize in Chemistry • Thomas Summers West (1927–2010), British analytical chemist. • Peter Jaffrey Wheatley (1921–1997) • Chaim Weizmann, (1874–1952), Russian chemist, developed the ABE-process • George M. Whitesides, (born 1939), American chemist • John Rex Whinfield (1901–1966), British chemist, discovered polyester fibres • Heinrich Otto Wieland (1877–1957) German chemist 1927 Nobel Prize in Chemistry • Julius Wilbrand - inventor of TNT • Harvey W. Wiley, (1844–1930), US chemist, Pure food & drug advocate • Sir Geoffrey Wilkinson, (1921–1996), 1973 Nobel Prize in Chemistry • Alexander William Williamson, English chemist, famous for Williamson ether synthesis • Thomas Willson, (1860–1915), Canadian chemist, discovered an economically efficient process for creating calcium carbide • Richard Willstätter, (1872–1942), 1915 Nobel Prize in Chemistry • Adolf Otto Reinhold Windaus, (1876–1959), 1928 Nobel Prize in Chemistry • Günter Wirths, Germany • Georg Wittig, 1897–1987), 1979 Nobel Prize in Chemistry • Friedrich Wöhler, (1800–1882), German chemist, best known for his synthesis of urea. • William Hyde Wollaston, (1766–1828), English chemist, discovered the element Palladium and the element Rhodium • Robert B. Woodward (1917–1979), 1965 Nobel Prize in Chemistry • Charles-Adolphe Wurtz, (1817–1884), Alsatian French chemist, discovered the Wurtz reaction • Kurt Wüthrich, (born 1938), 2002 Nobel Prize in Chemistry X • Xiaoliang Sunney Xie, (born 1962), chemist at Harvard University. A pioneer in the field of Single Molecule Microscopy and CARS (Coherent Anti-Stokes Raman Spectroscopy) microscopy. Y • Ada Yonath, (born 1939), 2006/7 Wolf Prize in Chemistry, 2009 Nobel Prize in Chemistry • Sabir Yunusov, (1909–1995), Soviet chemist (alkaloids) Z • Richard Zare, (born 1939), 2005 Wolf Prize in Chemistry • Ahmed H. Zewail, (born 1946), Egyptian, 1999 Nobel Prize in Chemistry for his work on femtochemistry. • Karl Ziegler, (1898–1973), 1963 Nobel Prize in Chemistry • Richard Adolf Zsigmondy, (1865–1929), 1925 Nobel Prize in Chemistry
  • 142. List of chemists 140 Chemists famous in other areas • Marion Barry (born 1936), Masters in Organic Chemistry, American politician • Alexander Borodin (1833–1887), Russian chemist & composer • Jerry Buss (born 1934), PhD in Physical Chemistry, owner of the NBA LA Lakers and other sports franchises • Emmanuel Dongala (born 1941), Congolese chemist and novelist • Dolph Lundgren (born 1957), Masters in Chemistry, Swedish actor • Primo Levi (1919–1987), resistance fighter, chemist and novelist • Mikhail Lomonosov (1711–1765), Russian chemist, historian, philologist, and poet. • Angela Merkel (born 1954), Doctorate in Quantum Chemistry, Chancellor of Germany 2005- • Gaspard Monge (1746–1818), invented descriptive geometry • Francis Muguet (1955–2009), advocate of open information access • Edward Williams Morley (1838–1923), performed the Michelson-Morley experiment • Knute Rockne (1888–1931), head football coach of Notre Dame • Elio Di Rupo (born 1951),Prime Minister of Belgium • Israel Shahak (1933–2001) • Margaret Thatcher (born 1925), Prime Minister of the United Kingdom (1979–1990), Research chemist at BX Plastics References [1] "Benjamin S. Hsiao Named Vice President for Research at Stony Brook University" (http:/ / commcgi. cc. stonybrook. edu/ am2/ publish/ General_University_News_2/ Benjamin_S_Hsiao_Named_Vice_President_for_Research_at_Stony_Brook_University. shtml). . Retrieved 12 July 2012. List of compounds Compounds are organized into the following three lists: • List of inorganic compounds, compounds without a C-H bond • List of organic compounds, compounds with a C-H bond • List of bio molecules. External links Relevant links for chemical compounds are: • The CAS Substance Databases [1], which contains information on about 23 million compounds. Keep in mind users need to actually pay to even look at these, otherwise they may find the most common ones by CAS at Common Chemistry [2] • Chemfinder [3] is helpful for finding information about a chemical • ChemSpider [4] • R&D Chemicals [5] • ChemIDplus [6] is a useful non-commercial source for chemical lookups • PubChem [7] • Material Data Safety Sheets [8], plus other relevant links These (commercial) links may also provide useful information: • Acros Organics [9] • Alfa Aesar [10] • Sigma Aldrich Fluka [11]
  • 143. List of compounds 141 References [1] http:/ / www. cas. org [2] http:/ / www. commonchemistry. org/ [3] http:/ / chemfinder. cambridgesoft. com/ [4] http:/ / www. ChemSpider. com/ [5] http:/ / www. rdchemicals. com/ [6] http:/ / chem. sis. nlm. nih. gov/ chemidplus/ [7] http:/ / pubchem. ncbi. nlm. nih. gov/ [8] http:/ / physchem. ox. ac. uk/ MSDS/ [9] http:/ / www. acros. com/ [10] http:/ / www. alfa. com/ [11] http:/ / www. sigmaaldrich. com/ List of important publications in chemistry This is a list of important publications in chemistry, organized by field. Some reasons why a particular publication might be regarded as important: • Topic creator – A publication that created a new topic • Breakthrough – A publication that changed scientific knowledge significantly • Influence – A publication which has significantly influenced the world or has had a massive impact on the teaching of chemistry. Foundations The Sceptical Chymist • Robert Boyle 1661 Description: Boyle, in the form of a dialogue, argued that chemical theories should be firmly grounded in experiment before their acceptance, and for the foundation of chemistry as a science separate from medicine and alchemy. Importance: Topic Creator, Influence. Boyle, in this book, became the first to argue that experiment should form the basis of all theory, a common practice in chemistry today. He also expounded on a rudimentary atomic theory and the existence of chemical elements beyond the classic earth, fire, air, and water.[1] He is seen as the father of chemistry,[2] and this is his most celebrated book,[3] with continued relevance to the present day.[4] Traité Élémentaire de Chimie (Elementary Treatise of Chemistry) • Antoine Lavoisier • Traité Élémentaire de Chimie, 1789, available in English as Elementary Treatise of Chemistry Description: This book was intended as an introduction to new theories in chemistry and as such, was one of the first Chemistry textbooks.[5] Importance: Introduction, Influence. Aside from being one of the first chemistry textbooks, the book was one of the first to state the Law of conservation of mass, define a chemical element, and contain a list of known elements.[6][7][8]
  • 144. List of important publications in chemistry 142 Méthode de Nomenclature Chimique • Guyton de Morveau, L. B.; Lavoisier, A. L.; Berthollet, C. L.; de Fourcroy, A. F. • Méthode de Nomenclature Chimique, Paris, 1787, available in English as Chymical Nomenclature. • Some details and a picture available at IUPAC nomenclature#History Description: This publication laid out a logical system for naming chemical substances (mainly chemical elements and inorganic compounds). Importance: Prior to this publication, a multitude of names were often used for the same substance. This publication led to an international consensus on how to name chemical substances. A New System of Chemical Philosophy • John Dalton, 1808–1827 Description: This book explained Daltons theory of atoms and its applications to chemistry. Importance: Topic Creator, Breakthrough, Influence. The book was one of the first to describe a modern atomic theory, a theory that lies at the basis of modern chemistry.[9] It is the first to introduce a table of atomic and molecular weights.[10] Surprisingly, given the period in which the book was written, of the five properties of atoms that Dalton listed, only two have been shown to be incorrect. The Dependence Between the Properties of the Atomic Weights of the Elements • Dmitri Mendeleev • Zeitschrift für Chemie 12, 405-406 (1869) • Online version [11] Description and Importance: In this paper the periodic table was introduced.[12] Notice that the table in the above link is the original one. Since then the table structure was slightly changed and new elements were added to it. Organic chemistry Science of Synthesis: Houben-Weyl Methods of Molecular Transformations • Volume editors are here [13]. Article authors for each volume can be found here [14]. • Thieme: Stuttgart, 48 volumes, 2000 - 2009 (print and electronic version available) Description: Contains synthetic models selected by world-renowned experts, with full experimental procedures and background information. Considers methods from journals, books, and patent literature from the early 19th century up to the present day and presents important synthetic methods for all classes of compounds. Critically evaluates the preparative applicability and significance of the synthetic methods. Importance: A reference publication.[15]
  • 145. List of important publications in chemistry 143 Marchs Advanced Organic Chemistry: Reactions, Mechanisms, and Structure • Michael B. Smith, Jerry March • Wiley-Interscience, 5th edition, 2001, ISBN 0-471-58589-0 • Wiley-Interscience, 6th edition, 2007, ISBN 978-0-471-72091-1 Description: A comprehensive reference for organic chemistry with over 25,000 references. Importance: A reference publication.[16] The Logic of Chemical Synthesis • Elias James Corey, Xue-Min Cheng • Wiley-Interscience, 1995, ISBN 0-471-11594-0 Description: Describes the logic underlying the rational design of complex organic synthesis. Importance: Breakthrough, Influence Protective Groups in Organic Synthesis • Theodora W. Greene, Peter G. M. Wuts • Wiley-Interscience, 3rd edition, 1999, ISBN 0-471-16019-9 Description: A comprehensive reference for the usage of protecting groups in organic synthesis. Importance: A reference publication. Comprehensive Organic Transformations • Richard C. Larock • Wiley-VCH • 1st edition: • 2nd edition: 1999, ISBN 0-471-19031-4 Description: A standard reference for the practicing organic chemist. These books are just enormous lists of key references indexed by functional group transformations. Importance: A reference publication. Stereochemistry of Carbon Compounds • Ernest L. Eliel • 1st edition: 1962 • Current edition: 1994 Description: systematic and complete exposition of all aspects of organic stereochemistry Importance: standard advanced text for organic stereochemistry.[17]
  • 146. List of important publications in chemistry 144 Classics in Total Synthesis • K.C. Nicolaou and E.J. Sorensen • Current edition: 1996 Description. The synthesis of famous molecules done by the masters of organic chemistry Importance. A standard postgraduate text book for the study of total synthesis and a valuable reference work for experts. "..destined to become a classic itself".[18] Inorganic chemistry Chemical Applications of Group Theory • F. Albert Cotton • Wiley, John & Sons, Incorporated, 1st Ed. 1963, 3rd Ed. 1990. Description: The group theory book for chemists Importance: Significant influence by introducing group theory to a much wider group of chemists. Advanced Inorganic Chemistry • F. Albert Cotton and Geoffrey Wilkinson • Wiley, John & Sons, Incorporated, 1st Ed. 1962, 6th Ed. 1999 Description: A classic general textbook for an undergraduate course in inorganic chemistry Importance: This book is not only a good introduction to the subject, it was very different from earlier texts and "led to a fundamental shift in the way in which inorganic chemistry was studied".[19] It seemed to be symbolic of the renaissance in inorganic chemistry starting in the 1950s. Every new text in inorganic chemistry since this text has had to respond to it. Physical chemistry Physical Chemistry • P. W. Atkins • Oxford University Press, 1st Ed. 1978, 7th Ed. 2002 (with Julio de Paula) Description: A classic general textbook for an undergraduate course in physical chemistry Importance: This book is not only a good introduction to the subject, it was very different from earlier texts and altered the way physical chemistry was taught. The first edition was very widely used where English is the language of instruction. Other texts had to respond to the lead from Atkins. The current edition is the 9th edition. Physical Chemistry • R. Stephen Berry, Stuart A. Rice, and John Ross • Oxford University Press, 1st Ed. 1980, 2nd Ed. 2000 Description: An encyclopedic text and reference suitable for advanced undergraduate or graduate study. Importance: This massive text by outstanding research workers begins with simple systems and proceeds logically to the more complex phenomena of physical chemistry. The original literature is cited extensively, making the work useful as a reference as well as a textbook. Many topics of current research are treated. Its advanced and exhaustive coverage of the field, together with extensive coverage of modern topics, eclipses the former champion, the text by E. A. Moelwyn-Hughes.
  • 147. List of important publications in chemistry 145 Biochemistry A Structure for Deoxyribose Nucleic Acid • James D. Watson and Francis Crick • Nature 171, 737-738 (1953) © Macmillan Publishers Ltd. • Online version [20] Description: In this paper the structure of DNA was proposed. It consisted of a double helix with a phosphate backbone, unlike Linus Pauling and R.B. Coreys double helix where the backbone consisted of the bases. They conclude with the sly remark: "It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material." Importance: Topic creator, Breakthrough, Influence Polymer chemistry Principles of Polymer Chemistry • Flory, Paul J.(1953) • Cornell University Press. 1953, ISBN 0-8014-0134-8. Importance: First major text on polymer chemistry; presents both organic and physical chemistry aspects. Written by a chemist who made major contributions to the physical chemistry of polymers, for which he won the Nobel prize in 1974. Description: Discusses structure and stereochemistry of synthetic polymers, polymerization kinetics, behaviour of polymers in solution, chain dimensions. Environmental chemistry Aquatic Chemistry, Chemical Equilibria and Rates in Natural Waters • Stumm, Werner and James J. Morgan. • John Wiley and Sons, Inc., 1st Edition 1970, 3rd Edition 1996, ISBN 0-471-51185-4. Description. This book covers the full spectrum of the discipline including acid/base equilibria, carbonate chemistry, mass transfer, complexation, sorption phenomenon, oxidation/reduction, colloid chemistry, and flocculation/coagulation. The authors generally present the material using a ground up approach that emphasizes fundamental principles of thermodynamics and kinetics. Importance. The publication is one of the most widely cited texts in environmental chemistry. In 1999, Stumm and Morgan received the Stockholm Water Prize for their contributions in the field. The citation specifically mentioned Aquatic Chemistry where it was described as a "seminal book" which is "used in education all over the world".[21]
  • 148. List of important publications in chemistry 146 Stratospheric sink for chlorofluoromethanes: chlorine atom-catalysed destruction of ozone Mario J. Molina and F. S. Rowland, Nature 249, 810-812 (1974) Description: This paper warned of the danger of ozone depletion due to man-made chlorofluorocarbons. The main atmospheric sink for these compounds was identified as ultraviolet photolysis, liberating chlorine atoms which catalyze the destruction of stratospheric ozone and have the potential to significantly deplete the ozone layer. Importance: Influence, as described in the presentation speech for the Nobel Prize in Chemistry 1995: “The findings presented by this years laureates in chemistry have had an enormous political and industrial impact. This was because they clearly identified unacceptable environmental hazards in a large, economically important sector.” [22] Chemical thermodynamics On the Equilibrium of Heterogeneous Substances • Gibbs, Willard • Trans. Conn. Acad., Vol. III, pp. 108–248, 1876; pp. 343–524, 1878. Description: paper applied the thermodynamic theory of steam engines to atomic level chemical reactions; i.e., it established equilibrium criteria necessary to predict the thermodynamic tendency of chemical reactions at constant temperature and pressure. Importance: topic creator; historian Bill Bryson states, in his A Short History of Nearly Everything, that Gibbs’ Equilibrium paper is "the Principia of thermodynamics".[23] In addition, this paper, in many ways, functions as the mathematical foundation of physical chemistry. Theoretical chemistry, Quantum chemistry and Computational Chemistry Valence and the structure of atoms and molecules • Gilbert N. Lewis • New York, The Chemical Catalog Company, Inc., 1923. Description: Discusses ionic and covalent bonding (polar and non-polar). Importance: The book that introduced the modern concept of the covalent bond as the sharing of electron pairs, and tried to reconcile the chemists empirical view of the atom with the physicists and spectroscopists quantum mechanical view. It could be considered a precursor to Paulings books. Introduction to Quantum Mechanics with Applications to Chemistry • Linus Pauling, E. Bright Wilson • New York, London, McGraw-Hill book company, 1935. Description: A classic and excellent introduction to quantum mechanics. Importance: One of the earliest books that introduced quantum mechanics to chemists. It remains well loved by many to this day.[24]
  • 149. List of important publications in chemistry 147 Valence • C. A Coulson • Oxford, Clarendon Press, 1952. • The latest edition is called Coulsons Valence, 3rd Edition, Roy McWeeny, Oxford University Press, 1980 Description: A classic introduction to valence and the theory of chemical binding. Importance: This book is credited with causing the expansion of interest in molecular orbital theory from the 1950s.[25] The Nature of the Chemical Bond and the Structure of Molecules and Crystals; An Introduction to Modern Structural Chemistry • Linus Pauling • Ithaca, N.Y., London, Cornell University Press; H. Milford, Oxford University Press, 1940. Description: A classic that was the first general book to introduce quantum mechanics to chemists. Importance: Probably more than any other book, introduced quantum mechanics and, in particular, valence bond theory to experimental chemists.[24][26] Density-Functional Theory of Atoms and Molecules • R. G. Parr and W. Yang, • Oxford University Press, New York, 1989. Description: A very thorough and scholarly account of density functional theory. Importance: This is a good introduction to the subject, but has particular significance in the way it describes how the theory throws new light on old chemical concepts such as electronegativity. Supramolecular chemistry Supramolecular Chemistry - Concepts and Perspectives • Jean-Marie Lehn • ISBN 3-527-29311-6, VCH, Description: Comprenhensive textbook written by topic creator. Importance: Most-popular textbook on subject (according to Lehn coined the term "supermolecule" in 73, developed the concept of supramolecular chemistry in 78, and won the Nobel Prize for his supramolecular chemistry work in ’87. Supramolecular Medicinal Chemistry • Michael J. Zaworotko • Brian D. Moulton Description: Selected articles: "Supramolecular Medicinal Chemistry: Mixed-Ligand Coordination Complexes".Mol. Pharmaceutics, 2007, 4 (3), pp 373–385;"Pharmaceutical co-crystals".Journal of Pharmaceutical Sciences, 2006, 95 (3), pp 499–516;"Crystal engineering of pharmaceutical co-crystals from polymorphic active pharmaceutical ingredients". Chem. Commun, 2005, pp 4601 – 4603; "Recent advances of discrete coordination complexes and coordination polymers in drug delivery". Coord. Chem. Rev., 2011, 255, pp 1623–1641. Importance: Breakthrough, Influence
  • 150. List of important publications in chemistry 148 Medicinal chemistry The Practice of Medicinal Chemistry • Camille Georges Wermuth editor • Academic Press, 1996, ISBN 0-12-744640-0 • 2nd edition, Academic Press, 2003, ISBN 0-12-744481-5 Description: A great overview of the theory, methodology, and techniques of drug design. Importance: Introduction, Influence References [1] "From the mazy and incoherent alchemical and iatrochemical doctrines, the former based on false conceptions of matter, the latter on erroneous views of life processes and physiology, a new science arose - the study of the composition of substances. The formulation of this definition of chemistry was due to Robert Boyle. In his Sceptical Chemist (1662) he freely criticized the prevailing scientific views and methods, with the object of showing that true knowledge could only be gained by the logical application of the principles of experiment and deduction." 1911 Britannica (http:/ / www. 1911encyclopedia. org/ Chemistry#Boyle) [2] Famous Chemists, Sir William A. Tilden, George Routledge & Sons Ltd., (1921), pg 1 - 21. [3] A History of Chemistry, Volume 2, J. R. Partington, Macmillan, reprinted 1969, pg 497. [4] Doubts and paradoxes, Mike Sutton, Chemistry World, Volume 6, Number 4, April 2011, Page 46 - 49, Royal Society of Chemistry, ISSN 1473-7604 [5] Traité Élémentaire de Chimie - Details and contents (in French) (http:/ / histsciences. univ-paris1. fr/ i-corpus/ lavoisier/ book-detail. php?bookId=89) [6] "The spread of Lavoisiers doctrines was greatly facilitated by the defined and logical form in which he presented them in his Traite Elementaire de Chimie (presente dans un ordre nouveau et dapres les decouvertes modernes) (1789)." 1911 Britannica (http:/ / www. 1911encyclopedia. org/ Antoine_Laurent_Lavoisier) [7] Leicester & Klickstein 1969, p. 154 [8] McKenzie 1988, p. 410 [9] Leicester & Klickstein 1969, p. 251 [10] McKenzie 1988, p. 437 [11] http:/ / webserver. lemoyne. edu/ faculty/ giunta/ EA/ MENDELEEVann. HTML [12] Leicester & Klickstein 1969, p. 438 [13] http:/ / www. thieme-chemistry. com/ thieme-chemistry/ sos/ info/ print/ sos/ people/ voled. shtml [14] http:/ / www. thieme-chemistry. com/ thieme-chemistry/ sos/ info/ print/ sos/ people/ authors. shtml [15] Issues in Science and Technology Librarianship review by Judith N. Currano (http:/ / www. istl. org/ 07-summer/ electronic1. html) [16] "His seminal reference-Advanced Organic Chemistry-is known worldwide and has been a mainstay among chemists for 30 years". New York Times obituary (http:/ / query. nytimes. com/ gst/ fullpage. html?res=9402E5DF123CF93BA15751C1A961958260). [17] Book review of Stereochemistry of Carbon Compounds in Journal of Chemical Education (http:/ / www. jce. divched. org/ Journal/ issues/ 1996/ Aug/ absA174_2. html) [18] Myers, Andrew G. (1997). "Review of "Classics in Total Synthesis"". Journal of the American Chemical Society 119 (33): 7906–7907. [19] An Obituary of F. Albert Cotton (http:/ / www. telegraph. co. uk/ news/ obituaries/ 1544265/ Professor-F-Albert-Cotton. html) [20] http:/ / www. nature. com/ nature/ dna50/ watsoncrick. pdf [21] The Stockholm International Water Institute (http:/ / www. siwi. org/ ) Follow links to "Stockholm Water Prize", "Laureates", "1999", and "Read more". [22] http:/ / nobelprize. org/ nobel_prizes/ chemistry/ laureates/ 1995/ presentation-speech. html [23] Bryson, Bill (2005). A Short History of Nearly Everything. Broadway Books. ISBN 0-7679-0817-1. [24] Linus Pauling as an Evangelical Chemist, Dudley Herschbach (http:/ / osulibrary. oregonstate. edu/ specialcollections/ events/ 2007paulingconference/ video-s2-5-herschbach. html) [25] Textbooks as Manifestos: C. A. Coulson after Linus Pauling and R. S. Mulliken, Ana Simões (http:/ / osulibrary. oregonstate. edu/ specialcollections/ events/ 2007paulingconference/ video-s1-3-simoes. html) A lecture by video and transcript by a historian of science that clearly and in detail discusses the importance of Coulsons book in relation to the earlier work of Pauling and Mulliken. [26] Textbooks as Manifestos: C. A. Coulson after Linus Pauling and R. S. Mulliken, Ana Simões (http:/ / osulibrary. oregonstate. edu/ specialcollections/ events/ 2007paulingconference/ video-s1-3-simoes. html) A lecture by video and transcript by a historian of science that clearly and in detail discusses the importance of Paulings book. • Guinta, Carmen. "Selected classic papers from the history of chemistry" ( papers.html). Le Moyne College. Retrieved 24 October 2011.
  • 151. List of important publications in chemistry 149 • Bolton, Henry Carrington (1904). A select bibliography of chemistry, 1492–1902 ( details/cu31924014491389). Smithsonian Institution. • Leicester, Henry M.; Klickstein, Herbert S., eds. (1969). A Source Book in Chemistry, 1400-1900 (http://books. books in chemistry&pg=PR4#v=onepage& q=source books in chemistry&f=false). Harvard University Press. ISBN 978-0-674-82230-6. Retrieved 24 October 2011. • Leicester, Henry Marshall (1968). Source book in chemistry: 1900-1950. Source books in the history of the sciences. Cambridge, Massachusetts: Harvard University Press. OCLC 438301. • McKenzie, A. E. E. (1988). The major achievements of science : the development of science from ancient times to the Present. History of science and technology reprint series (1st reprint ed.). Ames: Iowa State University Press. ISBN 978-0-8138-0092-9. • Williams, Henry Smith (1999). A history of science volume 1–4 ( catalogs/bysubject-sci-history.html). The Worldwide School. List of software for molecular mechanics modeling This is a list of computer programs that are predominantly used for molecular mechanics calculations. Min - Optimization, MD - Molecular Dynamics, MC - Monte Carlo, REM - Replica exchange method, QM - Quantum mechanics, Imp - Implicit water, HA - Hardware accelerated. Y - Yes. I - Has interface. Name View Model Min MD MC REM QM Imp HA Comments License Website 3D Builder Abalone Y Y Y Y Y Y I Y Y Biomolecular simulations, Free Agile Molecule protein folding. [1] [2] Y Y Y Molecular dynamics with Basic version ACEMD Acellera Ltd CHARMM, Amber forcefields. free. [3] Running on NVIDIA GPUs. Commercial Heavily optimized with CUDA. version available. [4] Y Y Y Y Charmm, AMBER, user Free ADUN specified (through force field [5] markup language, FFML), QM/MM calculations with Empirical Valence Bond (EVB); Framework based (GNUStep/cocoa); SCAAS for spherical boundary conditions [6] Y Y Y Y Y Not free AMBER [7] Ascalaph Y Y Y Y Y Y I Y Y Molecular building (DNA, Free & Ascalaph Designer proteins, hydrocarbons, Commercial [8] Project nanotubes). Molecular dynamics. GPU acceleration.
  • 152. List of software for molecular mechanics modeling 150 Automated Y Y Automated molecular topology Free for Automated Topology building service for small academic use Topology Builder (ATB) molecules (< 99 atoms). [9] Builder GROMOS, GROMACS, CNS formats with validation Repository for molecular topologies and pre-equilibrated systems Avogadro Y Y Y I Molecule building, editing Free, open [10] Avogadro (Peptides, small molecules, source crystals), Conformational analysis, 2D/3D conversion. Extensible interfaces to other tools. Balloon Y Y 2D/3D conversion and Free to use, Åbo Akademi conformational analysis. closed source [11] BOSS Y Y Y OPLS Commercial Yale University [12] CHARMM Y Y Y Y I I Y Commercial version with Not free multiple graphical front ends is [13] sold by Accelrys (as CHARMm) Chemitorium Y Y Free 2D/3D graphical organic Free [14] link molecule builder, viewer and visualisation tool. ChemSketch Y Y Y Fast 2-D graphical molecule Free Advanced builder and 3-D viewer. Contains Chemistry simplified CHARMM for fast Development, stable inaccurate optimization of [15] Inc. single molecules up to 1000 atoms COSMOS Y Y Y Y Y I Hybrid QM/MM Free (without COSMOS COSMOS-NMR force field with GUI) and [16] Software fast semi-empirical calculation of commercial electrostatic and/or NMR properties. 3-D graphical molecule builder and viewer. Culgi Y Y Y Y Y Atomistic simulations and Not free [17] Culgi BV mesoscale methods. Desmond Y Y Y Y Y High Performance MD. Comes Free and D. E. Shaw with a comprehensive GUI for commercial [18] Research building, visualizing, and reviewing results as well as calculation setup up and launching.
  • 153. List of software for molecular mechanics modeling 151 Discovery Y Y Y Y Y Y Y Discovery Studio is a Closed [19] Accelrys Studio comprehensive life science source/Trial modeling and simulation suite of available applications focused on optimizing the drug discovery process. Capabilities include, small molecule simulations, QM/MM, pharmacophore modeling, QSAR, protein-ligand docking, protein homology modeling, sequence analysis, protein-protein docking, antibody modeling, etc. Y/I Y Y Y Y Y I University of Washington and Free, The Baker Labs. Structure download download page prediction. Protein folding. [20] FoldX I Y Y Energy calculations and protein Free for [21] CRG design academic use GoVASP Y I I I GoVASP is a sophisticated Closed Windiks graphical user interface for the source/Not [22] Consulting Vienna Ab-Initio Simulation free/Trial Package (VASP). GoVASP available comprises tools to prepare, perform and monitor VASP calculations and to evaluate and visualize the computed data. GPIUTMD I I Y Y I Y GPIUTMD stands for Graphic Closed GPIUTMD Processors at Isfahan University source/Not [23] of Technology for Many-particle free/Demo Dynamics. It performs general available purpose particle dynamics simulations on a single workstation, taking the advantage of NVIDIA CUDA GPUs to attain a level of performance equivalent to hundreds of processors on a fast cluster. GROMACS Y Y ? High performance MD Free [24] GROMOS Y Y Geared towards biomolecules Not free GROMOS [25] Homepage GULP Y Y Molecular dynamics and Lattice Free for [26] optimization academic use Y Y Y General-purpose Molecular Free, open [27] HOOMD-blue [27] Dynamics highly optimized for source GPUs. Includes various pair potentials, Brownian dynamics, dissipative particle dynamics, rigid body constraints, energy minimization, etc...
  • 154. List of software for molecular mechanics modeling 152 ICM Y Y Y Y Y Powerful global optimizer in an Not free [28] Molsoft arbitrary subset of internal variables, NOEs, Protein docking, Ligand docking, Peptide docking, EM, Density placement LAMMPS Y Y Y I Y Has potentials for soft and Free [29] Sandia solid-state materials and coarse-grain systems MacroModel Y Y Y Y Y I Y OPLS-AA, MMFF, GBSA Not free Schrödinger, solvent model, conformational [30] LLC sampling, minimization, MD. Includes the Maestro GUI which provides visualization, molecule building, calculation setup, job launching and monitoring, project-level organization of results and access to a suite of other modelling programs. MAPS Y Y Y Y Y Y Y Building, visualization and Closed Scienomics analysis tools in a single user source/Trial [31] interface together with access to available multiple simulation engines. Materials Y Y Y Y Y Y Y Y Materials Studio is a software Closed [32] Accelrys Studio environment that brings the source/Trial materials simulation technology available to desktop computing, solving key problems throughout the R&D process. MedeA Y Y Y Y Y Y MedeA combines leading Closed Materials experimental databases and source/Trial [33] Design major computational programs available like the Vienna Ab-Initio Simulation Package (VASP), LAMMPS, GIBBS with sophisticated materials property prediction, analysis, and visualization. MCCCS Y Originally designed for the Free Towhee Project Towhee prediction of fluid phase [34] equilibria MDynaMix Y Parallel MD Free Stockholm [35] University MOE Y Y Y Y I Y Molecular Operating Commercial Chemical Environment Computing [36] Group MOIL Y Y Y Y Also includes action-based Free [37] link algorithms (Stochastic Difference Equation in Time and Stochastic Difference Equation in Length) and locally enhanced sampling.
  • 155. List of software for molecular mechanics modeling 153 molecools Y Y Simple Javascript molecular [38] link visualization tool MOLDY Y Parallel, only pair-potentials, Free [39] Moldy Cell lists, modified Beemans algorithm ORAC Y Y Y A Molecular Dynamics Free, open ORAC Simulation Program to Explore source download page Free Energy Surfaces in [40] Biomolecular Systems at the Atomistic Level [41] Y Generation of Models for Free NAB Case group "Unusual" DNA and RNA [42] Packmol Y Builds complex initial [43] link configurations for Molecular Dynamics Prime Y Y Y Y I Y Homology modeling, loop and [44] link side chain optimization, minimization, OPLS-AA, SGB solvent model, parallalized Protein Local Y Y Y Y Helix, loop, and side chain Not free [45] link Optimization optimization. Fast energy Program minimization. p4vasp Y Y Python-based viewer, structure Free, open [46] builder and VASP results source browser. Shows band-structure, charge densities and simulates STM images. PyMol Y Y Python-based viewer, many Free, open [47] plugins to other software. Some source mutagenisis. QMOL Y Protein viewer, provided by Free DNASTAR, DNASTAR [48] Inc. RasMol Y Fast viewer Free [49] RasMol Raster3D Y High quality raster images Free University of Washington [50] [51] I Y Y Y Y Reduced MD. Package for Free on GNU RedMD University of coarse-grained simulations. Licence Warsaw, ICM [52] StruMM3D Y Y Y Y Sophisticated 3-D molecule The 200 atom Exorga, Inc. (STR3DI32) builder and viewer, advanced version is free [53] structural analytical algorithms, full featured molecular modeling and quantitation of stereo-electronic effects, docking and the handling of complexes. Selvita Protein Y Y Y Y Protein structure prediction, Commercial [54] Selvita Ltd Modeling homology modeling, ab initio Platform modeling, loop modeling, protein threading
  • 156. List of software for molecular mechanics modeling 154 SimBioSys Y Y Y Y molecular docking, scoring Not Free SimBioSys Inc. MoDeST functions for docking, [55] (Molecular "ligand-based", Design "fragment-based", "de-novo" Software Toolkit) Spartan Y Y Y Y Y Y Small molecule (< 2000 a.m.u.) Commercial, Wavefunction, MM and QM tools for Trial Available Inc. [56] determining conformation, structure, property, spectra, reactivity, and selectivity. SwissParam Web server to determine Free for SwissParam. automatically parameters and academic. [57] topologies for small organic CHARMm molecules, for use with the licence CHARMM all atoms force field. required for Files can be used with commercial CHARMM and GROMACS. usage. TeraChem Y Y Y Y High performance Closed source PetaChem LLC GPU-accelerated ab initio / Trial licenses [58] Molecular Dynamics and available TD/DFT software package for very large molecular or even nanoscale systems. The software runs on NVIDIA GPUs and 64-bit Linux, and is based on heavily optimized CUDA code. TINKER I Y Y Y Y I Y Software tools for molecular Free Washington design [59] University Tremolo-X I Y Y Fast, parallel MD Not Free Tremolo-X [60] UCSF Chimera Y Y Y Visually appealing viewer, University of amino acid rotamers and other [61] California building, includes Antechamber and MMTK, Ambertools plugins in development. VEGA ZZ Y Y Y I Y Y Y 3D viewer, multiple file format Free for VEGA ZZ Web support, 2D and 3D editor, academic use [62] site surface calculation, conformational analysis, MOPAC and NAMD interfaces, MD trajectory analysis, molecular docking, virtual screening, database engine, parallel design, OpenCL acceleration, etc. VLifeMDS Y Y Y Y I Y Complete Molecular Modelling Not free Vlife Sciences Software, QSAR, Combinetorial Technologies Library generation, [63] Pharmacophore, Cheminformatics, docking, etc. VMD + NAMD Y Y Y Y Y Y Y Fast, parallel MD, CUDA Open source, Beckman free to [64] Institute academics
  • 157. List of software for molecular mechanics modeling 155 WHAT IF Y Y I I I Visualizer for MD. Interface to Not free [65] WHAT IF GROMACS. xeo Y Y open project management for [66] link nanostructures YASARA Y Y Y Y Molecular-graphics, -modeling Not free and -simulation program [67] Zodiac Y Y Y Drug design suite [68] link References [1] http:/ / www. biomolecular-modeling. com/ Abalone/ index. html [2] M. J. Harvey, G. Giupponi and G. De Fabritiis (2009). "ACEMD: Accelerating Biomolecular Dynamics in the Microsecond Time Scale". Journal of Chemical Theory and Computation 5 (6): 1632–1639. doi:10.1021/ct9000685. [3] http:/ / www. acellera. com/ acemd [4] Johnston, MA, Fernández-Galván, I, Villà-Freixa, J (2005). "Framework-based design of a new all-purpose molecular simulation application: the Adun simulator". J. Comp. Chem. 26 (15): 1647–1659. doi:10.1002/jcc.20312. PMID 16175583. [5] http:/ / adun. imim. es [6] Cornell WD, Cieplak P, Bayly CI, Gould IR, Merz KM Jr, Ferguson DM, Spellmeyer DC, Fox T, Caldwell JW, Kollman PA (1995). "A second generation force field for the simulation of proteins, nucleic acids, and organic molecules". J. Am. Chem. Soc. 117 (19): 5179–5197. doi:10.1021/ja00124a002. [7] http:/ / ambermd. org [8] http:/ / www. biomolecular-modeling. com/ Ascalaph/ Packages. html [9] http:/ / compbio. biosci. uq. edu. au/ atb [10] http:/ / avogadro. openmolecules. net/ wiki/ [11] http:/ / www. abo. fi/ ~mivainio/ balloon/ [12] http:/ / zarbi. chem. yale. edu/ software. html#boss [13] http:/ / www. charmm. org/ [14] http:/ / weltweitimnetz. de/ software/ Chemistry. en. page [15] http:/ / www. acdlabs. com/ resources/ freeware/ chemsketch/ [16] http:/ / www. cosmos-software. de/ ce_intro. html [17] http:/ / www. culgi. com [18] http:/ / deshawresearch. com/ resources. html [19] http:/ / accelrys. com/ products/ discovery-studio/ [20] http:/ / fold. it/ portal/ [21] http:/ / foldx. crg. es [22] http:/ / www. govasp. com [23] http:/ / gpiutmd. iut. ac. ir/ index. php [24] http:/ / www. gromacs. org [25] http:/ / www. igc. ethz. ch/ GROMOS/ index [26] https:/ / projects. ivec. org/ gulp/ [27] http:/ / codeblue. umich. edu/ hoomd-blue/ index. html [28] http:/ / www. molsoft. com/ [29] http:/ / lammps. sandia. gov/ [30] http:/ / www. schrodinger. com/ ProductDescription. php?mID=6& sID=8& cID=0 [31] http:/ / www. scienomics. com/ products/ molecular-modeling-platform/ [32] http:/ / accelrys. com/ products/ materials-studio/ [33] http:/ / www. materialsdesign. com [34] http:/ / towhee. sourceforge. net/ [35] http:/ / www. fos. su. se/ ~sasha/ mdynamix/ [36] http:/ / www. chemcomp. com/ [37] http:/ / cbsu. tc. cornell. edu/ software/ moil/ moil. html [38] http:/ / blahbleh. com/ molecools. php [39] http:/ / www. ccp5. ac. uk/ moldy/ moldy. html [40] http:/ / www. chim. unifi. it/ orac [41] Macke T, Case DA (1998). "Modeling unusual nucleic acid structures". Molecular Modeling of Nucleic Acids: 379–393. [42] http:/ / www. scripps. edu/ mb/ case/
  • 158. List of software for molecular mechanics modeling 156 [43] http:/ / www. ime. unicamp. br/ ~martinez/ packmol [44] http:/ / www. schrodinger. com/ ProductDescription. php?mID=6& sID=2& cID=0 [45] http:/ / jacobson. compbio. ucsf. edu/ plop_manual/ plop_overview. htm [46] http:/ / p4vasp. at [47] http:/ / www. pymol. org/ [48] http:/ / www. dnastar. com/ products/ qmol/ index. html [49] http:/ / www. bernstein-plus-sons. com/ software/ rasmol/ [50] http:/ / skuld. bmsc. washington. edu/ raster3d/ raster3d. html [51] A. Górecki, M. Szypowski, M. Długosz and J. Trylska (2009). "RedMD - Reduced molecular dynamics package". J. Comp. Chem. 30 (14): 2364–2373. doi:10.1002/jcc.21223. PMID 19247989. [52] http:/ / bionano. icm. edu. pl/ software/ redmd [53] http:/ / www. exorga. com [54] http:/ / www. selvita. com/ selvita-protein-modeling-platform. html [55] http:/ / www. simbiosys. ca/ products/ index. html [56] http:/ / www. wavefun. com/ products/ spartan. html [57] http:/ / www. swissparam. ch [58] http:/ / petachem. com/ [59] http:/ / dasher. wustl. edu/ tinker/ [60] http:/ / www. tremolo-x. com [61] http:/ / www. cgl. ucsf. edu/ chimera/ index. html [62] http:/ / www. vegazz. net [63] http:/ / www. vlifesciences. com/ [64] http:/ / www. ks. uiuc. edu/ Research/ vmd/ [65] http:/ / swift. cmbi. ru. nl/ whatif/ [66] http:/ / sourceforge. net/ projects/ xeo [67] http:/ / www. yasara. com/ [68] http:/ / www. zeden. org/ External links • SINCRIS ( • Linux4Chemistry ( • Collaborative Computational Project ( • World Index of Molecular Visualization Resources ( • Short list of Molecular Modeling resources ( • OpenScience ( • Biological Magnetic Resonance Data Bank ( • Materials modelling and computer simulation codes ( Materials_modelling_and_computer_simulation_codes) • A few tips on molecular dynamics (
  • 159. List of unsolved problems in chemistry 157 List of unsolved problems in chemistry Unsolved problems in chemistry tend to be questions of the kind "Can we make X chemical compound?", "Can we analyse it?", "Can we purify it?" and are commonly solved rather quickly, but may just as well require considerable efforts to be solved. However, there are also some questions with deeper implications. This article tends to deal with the areas that are the center of new scientific research in chemistry. Problems in chemistry are considered unsolved when an expert in the field considers it unsolved or when several experts in the field disagree about a solution to a problem.[1] Organic chemistry problems • Solvolysis of the norbornyl cation: Why is the norbornyl cation so stable? Is it symmetrical? If so, why? This problem has been largely settled for the unsubstituted norbornyl cation, but not for the substituted cation. See Non-classical ion. • On water reactions: Why are some organic reactions accelerated at the water-organic interface?[2] • What is the origin of the bond rotation barrier in ethane, steric hindrance or hyperconjugation? • What is the origin of the alpha effect? Nucleophiles with an electronegative atom and one or more lone pairs adjacent to the nucleophilic center are particularly reactive. • Many mechanisms proposed for catalytic processes are poorly understood and often fail to explain all relevant phenomena. Biochemistry problems • Better-than perfect enzymes: Why do some enzymes exhibit faster-than-diffusion kinetics?[3] See Enzyme kinetics. • What is the origin of homochirality in amino acids and sugars?[4] • Protein folding problem: Is it possible to predict the secondary, tertiary and quaternary structure of a polypeptide sequence based solely on the sequence and environmental information? Inverse protein-folding problem: Is it possible to design a polypeptide sequence which will adopt a given structure under certain environmental conditions?[4] [5] • RNA folding problem: Is it possible to accurately predict the secondary, tertiary and quaternary structure of a polyribonucleic acid sequence based on its sequence and environment? • What are the chemical origins of life? How did non-living chemical compounds generate self-replicating, complex life forms? Physical chemistry problems • What is the electronic structure of the high temperature superconductors at various points on the phase diagram? Can the transition temperature be brought up to room temperature? See Superconductivity. • Feynmanium: What are the chemical consequences of having an element, with an atomic number above 137, whose 1s electrons must travel faster than the speed of light? Is "Feynmanium" the last chemical element that can physically exist? The problem may actually occur at approximately Element 173, given the finite extension of nuclear-charge distribution. See the article on Extension of the periodic table beyond the seventh period and section Relativistic effects of Atomic orbital. • How can electromagnetic energy (photons) be efficiently converted to chemical energy? (E.g. splitting of water to hydrogen and oxygen using solar energy.)[6][7] • What is the nature of bonding in hypervalent molecules? See Hypervalent molecules.
  • 160. List of unsolved problems in chemistry 158 • What is the structure of water? According to Science Magazine in 2005, one of the 100 outstanding unsolved problems in science revolves around the question of how water forms hydrogen bonds with its neighbors in bulk water.[4] See: water cluster. • What process creates the septaria in septarian nodules? References [1] For relevant citations also see the satellite pages [2] Unique Reactivity of Organic Compounds in Aqueous Suspension Sridhar Narayan, John Muldoon, M. G. Finn, Valery V. Fokin, Hartmuth C. Kolb, [[K. Barry Sharpless (http:/ / www3. interscience. wiley. com/ cgi-bin/ fulltext/ 110473968/ HTMLSTART)] Angew. Chem. Int. Ed. 21/2005 p 3157 ,] [3] Hsieh M, Brenowitz M (August 1997). "Comparison of the DNA association kinetics of the Lac repressor tetramer, its dimeric mutant LacIadi, and the native dimeric Gal repressor" (http:/ / www. jbc. org/ cgi/ pmidlookup?view=long& pmid=9268351). J. Biol. Chem. 272 (35): 22092–6. doi:10.1074/jbc.272.35.22092. PMID 9268351. . [4] "So much more to know" (http:/ / www. sciencemag. org/ cgi/ content/ full/ 309/ 5731/ 78b). Science 309 (5731): 78–102. July 2005. doi:10.1126/science.309.5731.78b. PMID 15994524. . [5] "[[MIT OpenCourseWare (http:/ / ocw. mit. edu/ NR/ rdonlyres/ Biology/ 7-88JProtein-Folding-ProblemFall2003/ 2E446AD3-5702-49F1-9B95-9DC298E2ACB3/ 0/ lec01. pdf)] 7.88J / 5.48J / 7.24J / 10.543J Protein Folding Problem, Fall 2003 Lecture Notes - 1"]. 2003. [6] Duffie, John A. (2006). Solar Engineering of Thermal Processes. Wiley-Interscience. p. 928. ISBN 978-0-471-69867-8. [7] Brabec, Christoph; Vladimir Dyakonov, Jürgen Parisi, Niyazi Serdar Sariciftci (2006). Organic Photovoltaics: Concepts and Realization. Springer. p. 300. ISBN 978-3-540-00405-9. External links • 10 problems for Chemistry in the 21st Century ( - French Chemical Society • "First 25 of 125 big questions that face scientific inquiry over the next quarter-century" (http://www. Science 309 (125th Anniversary). 1 July 2005. • "So much more to know — Next 100 of 125 big questions that face scientific inquiry over the next quarter-century" ( Science 309 (5731): 78–102. July 2005. doi:10.1126/science.309.5731.78b. PMID 15994524. • Unsolved Problems in Nanotechnology: Chemical Processing by Self-Assembly - Matthew Tirrell (http://www. - Departments of Chemical Engineering and Materials, Materials Research Laboratory, California NanoSystems Institute, University of California, Santa Barbara
  • 161. Periodic systems of small molecules 159 Periodic systems of small molecules Periodic systems of molecules are charts of molecules similar to the periodic table of the elements. Construction of such charts was initiated in the early 20th century and is still ongoing. It is commonly believed that the periodic law, represented by the periodic chart, is echoed in the behavior of molecules, at least small molecules. For instance, if one replaces any one of the atoms in a triatomic molecule with a rare gas atom, there will be a drastic change in the molecule’s properties. Several goals could be accomplished by constructing an explicit representation of this periodic law as manifested in molecules: (1) a classification scheme for the vast number of molecules that exist, starting with small ones having just a few atoms, for use as a teaching aid and tool for archiving data, (2) forecasting data for molecular properties based on the classification scheme, and (3) a sort of unity with the periodic chart and the periodic system of fundamental particles.[1] Physical periodic systems of molecules Periodic systems (or charts or tables) of molecules are the subjects of two reviews.[2][3] The systems of diatomic molecules include those of (1) H. D. W. Clark,[4][5] and (2) F.-A. Kong,[6][7] which somewhat resemble the atomic chart. The system of R. Hefferlin et al.[8][9] was developed from (3) a three-dimensional to (4) a four-dimensional system Kronecker product of the element chart with itself. A totally different kind of periodic system is (5) that of G. V. Zhuvikin,[11][12] which is based on group dynamics. In all but the first of these cases, other researchers provided invaluable contributions and some of them are co-authors. The architectures of these systems have been adjusted by Kong[7] and Hefferlin [13] to include ionized species, and expanded by Kong,[7] Hefferlin,[9] and Zhuvikin and Hefferlin[12] to the space of triatomic molecules. These architectures are The Kronecker product of a hypothetical mathematically related to the chart of the elements. They were first four-element periodic chart. The sixteen called “physical” periodic systems.[2] molecules, some of which are redundant, suggest a hypercube, which in turn suggests that the molecules exist in a four-dimentionsl space; the coordinates are the period numbers and group Chemical periodic systems of molecules numbers of the two constituent atoms. [10] Other investigators have focused on building structures that address specific kinds of molecules such as alkanes (Morozov);[14] benzenoids (Dias);[15][16] functional groups containing fluorine, oxygen, nitrogen and sulfur (Haas);[17][18] or a combination of core charge, number of shells, redox potentials, and acid-base tendencies (Gorski).[19][20] These structures are not restricted to molecules with a given number of atoms and they bear little resemblance to the element chart; they are called “chemical” systems. Chemical systems do not start with the element chart, but instead start with, for example, formula enumerations (Dias), the hydrogen-displacement principle (Haas), reduced potential curves (Jenz),[21] a set of molecular descriptors (Gorski), and similar strategies.
  • 162. Periodic systems of small molecules 160 Hyperperiodicity E. V. Babaev[22] has erected a hyperperiodic system which in principle includes all of the systems described above except those of Dias, Gorski, and Jenz. Bases of the element chart and periodic systems of molecules The periodic chart of the elements, like a small stool, is supported by three legs: (a) the Bohr-Sommerfeld “solar system” atomic model (with electron spin and the Madelung principle), which provides the magic-number elements that end each row of the table and gives the number of elements in each row, (b) solutions to the Schroedinger equation, which provide the same information, and (c) data provided by experiment, by the solar system model, and by solutions to the Schroedinger equation. The Bohr-Sommerfeld model should not be ignored: it gave explanations for the wealth of spectroscopic data that were already in existence before the advent of wave mechanics. Each of the molecular systems listed above, and those not cited, is also supported by three legs: (a) physical and chemical data arranged in graphical or tabular patterns (which, for physical periodic systems at least, echo the appearance of the element chart), (b) group dynamic, valence-bond, molecular-orbital, and other fundamental theories, and (c) summing of atomic period and group numbers (Kong), the Kronecker product and exploitation of higher dimensions (Hefferlin), formula enumerations (Dias), the hydrogen-displacement principle (Haas), reduced potential curves (Jenz), and similar strategies. A chronological list of the contributions to this field[3] contains almost thirty entries dated 1862, 1907, 1929, 1935, and 1936; then, after a pause, a higher level of activity beginning with the 100th anniversary of Mendeleev’s publication of his element chart, 1969. Many publications on periodic systems of molecules include some predictions of molecular properties, but starting at the turn of the Century there have been serious attempts to use periodic systems for the prediction of progressively more precise data for various numbers of molecules. Among these attempts are those of Kong,[7] and Hefferlin[23][24] A collapsed-coordinate system for triatomic molecules The collapsed-coordinate system has three independent variables instead of the six demanded by the Kronecker-product system. The reduction of independent variables makes use of three properties of gas-phase, ground-state, triatomic molecules. (1) In general, whatever the total number of constituent atomic valence electrons, data for isoelectronic molecules tend to be more similar than for adjacent molecules that have more or fewer valence electrons; for triatomic molecules, the electron count is the sum of the atomic group numbers (the sum of the column numbers 1 to 8 in the p-block of the periodic chart of the elements, C1+C2+C3). (2) Linear/bent triatomic molecules appear to be slightly more stable, other parameters being equal, if carbon is the central atom. (3) Most physical properties of diatomic molecules (especially spectroscopic constants) are closely monotonic with respect to the product of the two atomic period (or row) numbers, R1 and R2; for triatomic molecules, the monotonicity is close with respect to R1R2+R2R3 (which reduces to R1R2 for diatomic molecules). Therefore, the coordinates x, y, and z of the collapsed-coordinate system are C1+C2+C3, C2, and R1R2+R2R3. Multiple-regression predictions of four property values for molecules with tabulated data agree very well with the tabulated data (the error measures of the predictions include the tabulated data in all but a few cases).[25]
  • 163. Periodic systems of small molecules 161 References [1] Chung, D.-Y. (2000). "The Periodic Table of Elementary Particles". arXiv:0003023. [2] Hefferlin, R. and Burdick, G.W. 1994. Fizicheskie i khimicheskie periodicheskie sistemy Molekul, Zhurnal Obshchei Xhimii, vol. 64, pp 1870–1885. English translation: "Periodic Systems of Molecules: Physical and Chemical". Russ. J. Gen. Chem. 64: 1659–1674. [3] Hefferlin, R. 2006. The Periodic Systems of Molecules pp. 221 ff (http:/ / books. google. com/ books?id=gDSg9VQNIPcC& pg=PA221), in Baird, D., Scerri, E., and McIntyre, L. (Eds.) “The Philosophy of Chemistry, Synthesis of a New Discipline,” Springer, Dordrecht ISBN 1-4020-3256-0. [4] Clark, C. H. D. (1935). "The periodic Groups of Non-Hydride Di-Atoms". Trans. Faraday Soc 31: 1017–1036. doi:10.1039/tf9353101017. [5] Clark, C. H. D (1940). "Systematics of Band-Spectral Constants. Part V. Interrelations of Dissociation Energy and Equilibrium Internuclear Distance of Di-Atoms in Ground States". Trans. Faraday Soc. 36: 370–376. [6] Kong, F (1982). "The Periodicity of Diatomic Molecules". J. Mol. Struct 90: 17–28. doi:10.1016/0022-2860(82)90199-5. [7] Kong, F. and Wu, W. 2010. Periodicity of Diatomic and Triatomic Molecules, Conference Proceedings of the 2010 Workshop on Mathematical Chemistry of the Americas. [8] Hefferlin, R., Campbell, D. Gimbel, H. Kuhlman, and T. Cayton (1979). "The periodic table of diatomic molecules—I an algorithm for retrieval and prediction of spectrophysical properties". Quant. Spectrosc. Radiat. Transfer 21 (4): 315–336. doi:10.1016/0022-4073(79)90063-3. [9] Hefferlin, R (2008). "Kronecker-Product Periodic Systems of Small Gas-Phase Molecules and the Search for Order in Atomic Ensembles of Any Phase". Comb. Chem. High Through. Screen 11: 690–706. [10] G. W. Burdick and R. Hefferlin, Data Location in a Four Dimensional Periodic System of Diatomic Molecules, in M. Putz, Ed., Chemical Information and Computation Challenges in the 21rst Century – A Celebration of 2011, the International Year of Chemistry, NOVA, 2011 [11] Zhuvikin, G.V. and R. Hefferlin (1983). Periodicheskaya Sistema Dvukhatomnykh Molekul: Teoretiko-gruppovoi Podkhod, Vestnik Leningradskovo Universiteta. pp. 10–16. [12] Carlson, C.M., Cavanaugh, R.J, Hefferlin, R.A, and of Zhuvikin, G.V. (1996). "Periodic Systems of Molecular States from the Boson Group Dynamics of SO(3)xSU(2)s". Chem. Inf. Comp. Sci 36: 396–398. [13] Hefferlin, R. et al. (1984). "Periodic Systems of N-atom Molecules". J. Quant. Spectrosc. Radiat. Transfer 32 (4): 257–268. doi:10.1016/0022-4073(84)90098-0. [14] Morozov, N. 1907. Stroeniya Veshchestva, I. D. Sytina Publication, Moscow. [15] Dias, J.R. (1982). "A periodic Table of Polycyclic Aromatic Hydrocarbons. Isomer Enumeration of Fused Polycyclic Aromatic Hydrocarbons". Chem. Inf. Comput. Sci. 22: 15–22. [16] Dias, J. R. (1994). "Benzenoids to Fullerines and the Circumscribing and Leapfrog Algorithms". New J. Chem. 18: 667–673. [17] Haas, A. (1982). "A new classification principle: the periodic system of functional groups". Chemicker-Zeitung 106: 239–248. [18] Haas, A. (1988). "Das Elementverscheibungsprinzip und siene Bedeutung fur die Chemie der p-Block Elemente". Kontakte (Darmstadt) 3: 3–11. [19] Gorski, A (1971). "Morphological Classification of Simple Species. Part I. Fundamental Components of Chemical Structure". Roczniki Chemii 45: 1981–1989. [20] Gorski, A (1973). "Morphological Classification of Simple Species. Part V. Evaluation of Structural Parameters of Species". Roczniki Chemii 47: 211–216. [21] Jenz, F (1996). "The Reduced Potential Curve (RPC) Method and its Applications". Int. Rev. Phys. Chem. 15 (2): 467–523. doi:10.1080/01442359609353191. [22] Babaev, E.V. and R. Hefferlin 1996. The Concepts of Periodicity and Hyper- periodicity: from Atoms to Molecules, in Rouvray, D.H. and Kirby, E.C., “Concepts in Chemistry,” Research Studies Press Limited, Taunton, Somerset, England. [23] Hefferlin, R. (2010). "Vibration Frequencies using Least squares and Neural Networks for 50 new s and p Electron Diatomics". Quant. Spectr. Radiat. Transf. 111: 71–77. doi:10.1016/j.jqsrt.2009.08.004. [24] Hefferlin, R. (2010). Internuclear Separations using Least squares and Neural Networks for 46 new s and p Electron Diatomics. [25] Carlson, C., Gilkeson, J., Linderman, K., LeBlanc, S. Hefferlin, R., and Davis, B (1997). "Estimation of Properties of Triatomic Molecules from Tabulated Data Using Least-Squares Fitting". Croatica Chemica Acta 70: 479–508.
  • 164. Periodic table 162 Periodic table The periodic table is a tabular display of the chemical elements, organized on the basis of their atomic numbers and chemical properties. Elements are presented in increasing atomic number. The main body of the table is a 18 × 7 grid, and elements with the same number of valence electrons are kept together in groups, such as the halogens and the noble gases. Due to this, there are gaps that form four distinct rectangular areas or blocks. The f-block is Standard form of the periodic table. The colors represent different categories of not included in the main table, but rather is elements explained below. usually floated below, as an inline f-block would make the table impractically wide. Using periodic trends, the periodic table can help predict the properties of various elements and the relations between properties. As a result, it provides a useful framework for analyzing chemical behavior, and is widely used in chemistry and other sciences. Although precursors exist, the current table is generally credited to Dmitri Mendeleev, who developed it in 1869 to illustrate periodic trends in the properties of the then-known elements; the layout has been refined and extended as new elements have been discovered and new theoretical models developed to explain chemical behavior. Mendeleevs presentation also predicted some properties of then-unknown elements expected to fill gaps in his arrangement; most of these predictions were proved correct when those elements were discovered and found to have properties close to the predictions. All elements from atomic numbers 1 (hydrogen) to 118 (ununoctium) have been synthesized. Of these, all up to and including californium exist naturally; the rest have only been artificially synthesised in laboratories, along with numerous synthetic radionuclides of naturally occurring elements. Production of elements beyond ununoctium is being pursued, with the question of how the periodic table may need to be modified to accommodate these elements being a matter of ongoing debate. History First attempts of systemization In 1789, Antoine Lavoisier published a list of 33 chemical elements. Although Lavoisier grouped the elements into gases, metals, nonmetals, and earths,[1] chemists spent the following century searching for a more precise classification scheme. In 1829, Johann Wolfgang Döbereiner observed that many of the elements could be grouped into triads (groups of three) based on their chemical properties. Lithium, sodium, and potassium, for example, were grouped together as soft, reactive metals. Döbereiner also observed that, when arranged by atomic weight, the second member of each triad was roughly the average of the first and the third.[2] This became known as the Law of Triads.[3] German chemist Leopold Gmelin worked with this system, and by 1843 he had identified ten triads, three groups of four, and one group of five. Jean-Baptiste Dumas published work in 1857 describing relationships between various groups of metals. Although various chemists were able to identify relationships between small groups of elements, they had yet to build one scheme that encompassed them all.[2]
  • 165. Periodic table 163 German chemist August Kekulé had observed in 1858 that carbon has a tendency to bond with other elements in a ratio of one to four. Methane, for example, has one carbon atom and four hydrogen atoms. This concept eventually became known as valency. In 1864, fellow German chemist Julius Lothar Meyer published a table of the 49 known elements arranged by valency. The table revealed that elements with similar properties often shared the same valency.[4] English chemist John Newlands produced a series of papers in 1864 and 1865 that described his own classification of the elements: He noted that when listed in order of increasing atomic weight, similar physical and chemical properties recurred at intervals of eight, which he likened to the octaves of music.[5][6] This Law of Octaves, however, was ridiculed by his contemporaries, and the Chemical Society refused to publish his work.[7] Nonetheless, Newlands was able to draft an atomic table and use it to predict the existence of missing elements, such as germanium. The Chemical Society only acknowledged the significance of his discoveries some five years after they credited Mendeleev.[8] Mendeleevs table Russian chemistry professor Dmitri Ivanovich Mendeleev and German chemist Julius Lothar Meyer independently published their periodic tables in 1869 and 1870, respectively.[9] They both constructed their tables in a similar manner: By listing the elements in a row or column in order of atomic weight and starting a new row or column when the characteristics of the elements began to repeat.[10] The success of Mendeleevs table came from two decisions he made: The first was to leave gaps in the table when it seemed that the corresponding element had not yet been discovered.[11] Mendeleev was not the first chemist to do so, but he was the first to be recognized as using the trends in his periodic table to predict the properties of those missing elements, such as gallium and germanium.[12] The second decision was to occasionally ignore the order suggested by the atomic weights and switch Dmitri Mendeleev adjacent elements, such as cobalt and nickel, to better classify them into chemical families. With the development of theories of atomic structure, it became apparent that Mendeleev had listed the elements in order of increasing atomic number or nuclear charge.[13] In 1913 Henry Moseley obtained experimental values of atomic number from X-ray spectra of the elements. Further development In the years following publication of Mendeleevs periodic table, the gaps he identified were filled as
  • 166. Periodic table 164 chemists discovered additional naturally occurring elements.[14] It is often stated that the last naturally occurring element to be discovered was francium (referred to by Mendeleev as eka-caesium) in 1939.[15] However, plutonium, produced synthetically in 1940, was identified in trace quantities as a naturally occurring primordial element in 1971,[16] and in 2011 it was found that all the elements up to californium can occur naturally in trace amounts in uranium ores.[17] With the development of modern quantum mechanical theories of electron configurations within atoms, it became apparent that each row (or period) in the table corresponded to the filling of a quantum shell of electrons. In Mendeleevs original table, each period was the same length. However, because larger atoms have more electron sub-shells, modern tables have progressively longer periods further down the table.[18] Mendeleevs 1869 periodic table; note that his arrangement presents the periods vertically, and the groups horizontally. Previously, the groups were known by roman numerals. In America, the roman numerals were followed by either an "A" if the group was in the s- or p-block, or a "B" if the group was in the d-block. The roman numerals used correspond to the last digit of todays naming convention (e.g. the group 4 elements were group IVB, and the carbon group were group IVA). In Europe, the lettering was similar, except that "A" was used if the group was before group 10, and "B" was used for groups including and after group 10. In addition, groups 8, 9 and 10 used to be treated as one triple-sized group, known collectively in both notations as group VIII. In 1988, the new IUPAC naming system was put into use, and the old group names were deprecated.[19] The production of various transuranic elements has expanded the periodic table significantly, the first of these being neptunium, synthesized in 1939.[20] Because many of the transuranic elements are highly unstable and decay quickly, they are challenging to detect and characterize when produced, and there have been controversies concerning the acceptance of competing discovery claims for some elements, requiring independent review to determine which party has priority, and hence naming rights. The most recently accepted and named elements are flerovium (114) and livermorium (116), both named on 31 May 2012.[21] In 2010, a joint Russia–US collaboration at Dubna, Moscow Oblast, Russia, claimed to have synthesized six atoms of ununseptium, making it the most recently claimed discovery.[22] Contents of the periodic table
  • 167. Periodic table 165 Periodic table (standard form) Group → 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 ↓ Period 1 1 2 H He 2 3 4 5 6 7 8 9 10 Li Be B C N O F Ne 3 11 12 13 14 15 16 17 18 Na Mg Al Si P S Cl Ar 4 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 5 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 6 55 56 * 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 Cs Ba lanthanides Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 7 87 88 ** 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 Fr Ra actinides Rf Db Sg Bh Hs Mt Ds Rg Cn Uut Fl Uup Lv Uus Uuo * Lanthanides 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu ** Actinides 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr This is an 18-column periodic table layout, which has come to be referred to as the common or standard form, on account of its [10] popularity. It is also sometimes referred to as the long form, in comparison to the short form or Mendeleev-style , which omits groups 3–12. The wide periodic table incorporates the lanthanides and the actinides, rather than separating them from the main body of the table. The extended periodic table adds the 8th and 9th periods, including the superactinides. Some element categories in the periodic table Metals Metalloids Nonmetals Unknown chemical Alkali Alkaline Inner transition metals Transition Post-transition Other Halogens Noble properties metals earth metals metals metals nonmetals gases Lanthanides Actinides (at standard conditions: 0 °C and 1 atm): Primordial From decay Synthetic black=Solid green=Liquid red=Gas grey=Unknown All versions of the periodic table only include chemical elements, not mixtures, compounds, or subatomic particles, and each isotope of a given element is represented in the same cell. In the standard periodic table, the elements are listed in order of increasing atomic number (the number of protons in the nucleus of an atom). A new row (period) is started when a new electron shell has its first electron. Columns (groups) are determined by the electron configuration of the atom; elements with the same number of electrons in a particular subshell fall into the same columns (e.g. oxygen and selenium are in the same column because they both have 4 electrons in the outermost p-subshell). The periods are longer further down in the periodic table, and the groups get longer on the right (although the alkali metals, the largest group, is on the far left, and the alkaline earth metals, another large group, are next to the alkali metals). In general, elements with similar chemical properties fall into the same group in the
  • 168. Periodic table 166 periodic table, although in the f-block, and to some respect in the d-block, the elements in the same period tend to have similar properties, as well. Thus, it is relatively easy to predict the chemical properties of an element if one knows the properties of the elements around it.[23] As of 2012, the periodic table contains 118 confirmed chemical elements. Of these elements, 114 have been officially recognized and named by the International Union of Pure and Applied Chemistry (IUPAC). A total of 98 of these occur naturally, of which 84 are primordial. The other 14 elements only occur in decay chains of primordial elements.[17] All elements from einsteinium to copernicium, as well as flerovium, and livermorium, while not occurring naturally in the universe, have been officially recognized by the IUPAC as being synthesized, while elements 113, 115, 117 and 118 have reportedly been synthesized in laboratories and are currently known only by their systematic element names, based off their atomic numbers.[24] No element heavier than einsteinium (element 99) has ever been observed in macroscopic quantities in its pure form.[25] No elements past 118 have been synthesized as of 2012.[26] In printed or other formally presented periodic tables, each element is provided a formatted cell that usually provides some of the basic properties of the element. Atomic number, element symbol, and name are almost always included, and atomic weights, densities, melting and boiling points, crystal structure as a solid, origin, abbreviated electron configuration, electronegativity, and most common valence numbers are sometimes included as well.[27] By definition, each chemical element has a unique atomic number representing the number of protons in its nucleus, but most elements have differing numbers of neutrons among different atoms; these are referred to as isotopes. For example, all atoms of carbon have six protons and usually have six neutrons as well, but about 1% have seven neutrons, and a very small amount have eight neutrons; so carbon has three different naturally occurring isotopes. Isotopes are never separated in the periodic table; they are always grouped together under a single element. Elements with no stable isotopes have the atomic masses of their most stable isotopes listed in parentheses.[28] Organization In the modern periodic table, the elements are placed progressively in each period from left to right in the sequence of their atomic numbers, with a new row started after a noble gas. The first element in the next row is always an alkali metal with an atomic number one greater than that of the noble gas (e.g. after krypton, a noble gas with the atomic number 36, a new row is started by rubidium, an alkali metal with the atomic number 37). No gaps currently exist because all elements between hydrogen and ununoctium (element 118) have been discovered. Since the elements are sequenced by atomic number, sets of elements are sometimes specified by terms such as "through" (e.g. through iron), "beyond" (e.g. beyond uranium), or "from ... through" (e.g. from lanthanum through lutetium). The terms "light" and "heavy" are sometimes also used informally to indicate relative atomic numbers (not densities), as in "lighter than carbon" or "heavier than lead", although technically the weight or mass of atoms of an element (their atomic weights or atomic masses) do not always increase monotonically with their atomic numbers. For instance tellurium, element 52, is on average heavier than iodine, element 53.[28] Hydrogen and helium are often placed in different places than their electron configurations would indicate; Hydrogen is usually placed above lithium, in accordance with its electron configuration, but is sometimes placed above fluorine,[29] or even carbon,[29] as it also behaves similarly to them. Helium is almost always placed above neon, as they are very similar chemically.[30] The significance of atomic numbers to the organization of the periodic table was not appreciated until the existence and properties of protons and neutrons became understood. Mendeleevs periodic tables instead used atomic weights, information determinable to fair precision in his time, which worked well enough in most cases to give a powerfully predictive presentation far better than any other comprehensive portrayal of the chemical elements properties then possible. Substitution of atomic numbers, once understood, gave a definitive, integer-based sequence for the elements, still used today even as new synthetic elements are being produced and studied.[31]
  • 169. Periodic table 167 Grouping methods Groups A group or family is a vertical column in the periodic table. Groups are considered the most important method of classifying the elements. In some groups, the elements have very similar properties and exhibit a clear trend in properties down the group. Under the international naming system, the groups are numbered numerically from 1 to 18 from the leftmost column (the alkali metals) to the rightmost column (the noble gases).[32] The older naming systems differed slightly between Europe and America.[33] Some of these groups have been given trivial (unsystematic) names, such as the alkali metals, alkaline earth metals, pnictogens, chalcogens, halogens, and noble gases. However, some other groups, such as group 4, have no trivial names and are referred to simply by their group numbers, since they display fewer similarities and/or vertical trends.[32] Modern quantum mechanical theories of atomic structure explain group trends by proposing that elements within the same group generally have the same electron configurations in their valence shell, which is the most important factor in accounting for their similar properties.[34] Elements in the same group show patterns in atomic radius, ionization energy, and electronegativity. From top to bottom in a group, the atomic radii of the elements increase. Since there are more filled energy levels, valence electrons are found farther from the nucleus. From the top, each successive element has a lower ionization energy because it is easier to remove an electron since the atoms are less tightly bound. Similarly, a group has a top to bottom decrease in electronegativity due to an increasing distance between valence electrons and the nucleus.[35] Periods A period or series is a horizontal row in the periodic table. Although groups are the most common way of classifying elements, there are regions where horizontal trends are more significant than vertical group trends, such as the f-block, where the lanthanides and actinides form two substantial horizontal series of elements.[36] Elements in the same period show trends in atomic radius, ionization energy, electron affinity, and electronegativity. Moving left to right across a period, atomic radius usually decreases. This occurs because each successive element has an added proton and electron which causes the electron to be drawn closer to the nucleus.[37]This decrease in atomic radius also causes the ionization energy to increase when moving from left to right across a period. The more tightly bound an element is, the more energy is required to remove an electron. Electronegativity increases in the same manner as ionization energy because of the pull exerted on the electrons by the nucleus.[35] Electron affinity also shows a slight trend across a period. Metals (left side of a period) generally have a lower electron affinity than nonmetals (right side of a period) with the exception of the noble gases.[38]
  • 170. Periodic table 168 Blocks Because of the importance of the outermost electron shell, the different regions of the periodic table are sometimes referred to as periodic table blocks, named according to the subshell in which the "last" electron resides.[30] The s-block comprises the first two groups (alkali metals and alkaline earth metals) as well as hydrogen and helium. The p-block comprises the last six groups which are groups 13 to 18 in IUPAC (3A to 8A in American) and contains, among others, all of the metalloids. The d-block comprises groups 3 to 12 in IUPAC (or 3B to 2B in A diagram of the periodic table, highlighting the different blocks. American group numbering) and contains all of the transition metals. The f-block, usually offset below the rest of the periodic table, comprises the lanthanides and actinides.[39] Variations and other conventions In presentations of the periodic table, the lanthanides and the actinides are customarily shown as two additional rows below the main body of the table,[40] with placeholders or else a selected single element of each series (either lanthanum or lutetium, and either actinium or lawrencium, respectively) shown in a single cell of the main table, between barium and hafnium, and radium and rutherfordium, respectively. This convention is entirely a matter of aesthetics and formatting practicality; a rarely used wide-formatted periodic table inserts the lanthanide and actinide series in their proper places, as parts of the tables sixth and seventh rows (periods).[41] Many presentations of the periodic table show a dark stair-step diagonal line along the metalloids, with metals to the left of the line and non-metals to the right.[41] Various other groupings of the chemical elements are sometimes also highlighted on a periodic Periodic table with inline f-block. table, such as transition metals, post-transition metals, and metalloids. Other informal groupings of the elements exist, such as the platinum group and the noble metals, but are rarely addressed in periodic tables.[41]
  • 171. Periodic table 169 Periodic trends The primary determinant of an elements chemical properties is its electron configuration, particularly the valence shell electrons. For instance, any atoms with four valence electrons occupying p orbitals will exhibit some similarity. The type of orbital in which the atoms outermost electrons reside determines the "block" to which it belongs. The number of valence shell electrons determines the family, or group, to which the element belongs.[30] The total number of electron shells an atom has Some of the trends in the periodic table. determines the period to which it belongs. Each shell is divided into different subshells, which as atomic number increases are filled roughly in the order depicted in the table at hand (according to the Aufbau principle; see table below).[42] Hence the structure of the periodic table. Since the outermost electrons determine chemical properties, those with the same number of valence electrons are generally grouped together.[43] Subshell s f d p Period 1 1s 2 2s 2p 3 3s 3p 4 4s 3d 4p 5 5s 4d 5p 6 6s 4f 5d 6p 7 7s 5f 6d 7p Progressing through a group from lightest element to heaviest element, the outer-shell electrons (those most readily accessible for participation in chemical reactions) are all in the same type of orbital, with a similar shape, but with increasingly higher energy and average distance from the nucleus. For instance, the outer-shell (or "valence") electrons of the first group, headed by hydrogen, all have one electron in an s orbital. In hydrogen, that s orbital is in the lowest possible energy state of any atom, the first-shell orbital (and represented by hydrogens position in the first period of the table).[44] In francium, the heaviest element of the group, the outer-shell electron is in the seventh-shell orbital, significantly further out on average from the nucleus than those electrons filling all the shells below it in energy. As another example, both carbon and lead have four electrons in their outer shell orbitals.[45] As atomic number (i.e., charge on the atomic nucleus) increases, the spin-orbit coupling between the nucleus and the electrons becomes greater, reducing the validity of the quantum mechanical orbital approximation model, which considers each atomic orbital as a separate entity.[46]
  • 172. Periodic table 170 Atomic and ionic radii Atomic radii vary in a predictable and explicable manner across the periodic table. For instance, the radii generally decrease along each period of the table, from the alkali metals to the noble gases; and increase down each group. The radius increases sharply between the noble gas at the end of each period and the alkali metal at the beginning of the next period. These trends of the atomic radii (and of various other chemical and physical properties of the elements) can be explained by the electron shell theory of the atom; they provided important evidence for the development and confirmation of quantum Atomic number plotted against atomic radius. The noble gases, astatine, francium, theory.[47] and all elements heavier than americium were left out as there is no data for them. The way the atomic radius varies with increasing atomic number (Z) can be explained by the arrangement of electrons in shells of fixed capacity. The shells are generally filled in order of increasing radius, since the negatively charged electrons are attracted by the positively charged protons in the nucleus. As the atomic number increases along each row of the periodic table, the additional electrons go into the same outermost shell; whose radius gradually contracts, due to the increasing nuclear charge. In a noble gas, the outermost shell is completely filled; therefore, the additional electron of next alkali metal will go into the next outer shell, accounting for the sudden increase in the atomic radius.[47] The electrons in the 4f-subshell, which is progressively filled from cerium (Z = 58) to lutetium (Z = 71), are not particularly effective at shielding the increasing nuclear charge from the sub-shells further out. The elements immediately following the lanthanides have atomic radii which are smaller than would be expected and which are almost identical to the atomic radii of the elements immediately above them.[48] Hence hafnium has virtually the same atomic radius (and chemistry) as zirconium, and tantalum has an atomic radius similar to niobium, and so forth. This is known as the lanthanide contraction. The effect of the lanthanide contraction is noticeable up to platinum (Z = 78), after which it is masked by a relativistic effect known as the inert pair effect.[49] The d-block contraction is less pronounced than the lanthanide contraction but arises from a similar cause. In this case, it is the poor shielding capacity of the 3d-electrons which affects the atomic radii and chemistries of the elements immediately following the first row of the transition metals, from gallium (Z = 31) to bromine (Z = 35).[48]
  • 173. Periodic table 171 Ionization energy and reactivity The first ionization energy is the energy it takes to remove an electron from an atom, and the second ionization energy is the energy it takes to remove a second electron from an atom. Future ionization energies follow this same pattern. Higher ionization energies tend to be larger than lower ionization energies. Electrons in the closer orbitals experience greater forces of electrostatic attraction; thus, Periodic trend for ionization energy. Each period begins at a minimum for the alkali their removal requires increasingly metals, and ends at a maximum for the noble gases. more energy. Ionization energy becomes greater up and to the right of the periodic table.[49] Large jumps in the successive molar ionization energies occur when passing noble gas configurations. For example, as can be seen in the table above, the first two molar ionization energies of magnesium (stripping the two 3s electrons from a magnesium atom) are much smaller than the third, which requires stripping off a 2p electron from the very stable neon configuration of Mg2+.[49] Ionization energy is also a periodic trend within the periodic table organization. Moving left to right within a period or upward within a group, the first ionization energy generally increases. As the atomic radius decreases, it becomes harder to remove an electron that is closer to a more positively charged nucleus.[49] Electronegativity In general, electronegativity increases on passing from left to right along a period, and decreases on descending a group. Hence, fluorine is undoubtedly the most electronegative of the elements (not counting noble gases) while caesium is the least electronegative, at least of those elements for which substantial data is available.[50] There are some exceptions to this general rule. Gallium and germanium have higher electronegativities than aluminium and silicon respectively because of the d-block contraction. Elements of the fourth period The variation of Pauling electronegativity (y-axis) as one descends the main groups of the periodic table from the second period to the sixth period. immediately after the first row of the transition metals have unusually small atomic radii because the 3d-electrons are not effective at shielding the increased nuclear charge, and smaller atomic size correlates with higher electronegativity (see Allred-Rochow electronegativity, Sanderson electronegativity above).[50] The anomalously high electronegativity of lead, particularly when compared to thallium and bismuth, appears to be an artifact of data selection (and data availability)—methods of calculation other than the Pauling method show the normal periodic trends for these elements.[51]
  • 174. Periodic table 172 Alternatives While the iconic format presented above is widely used,[30] other alternative periodic tables exist, including not only various rectangular formats, but also circular or cylindrical versions in which the rows (periods) flow from one into another, without the arbitrary breaks required at the margins of the usual printed or screen-formatted versions. Alternative periodic tables are developed often to highlight or emphasize different chemical or physical properties of the elements which are not as apparent in traditional periodic tables. Some tables aim to emphasize both the nucleon and electronic structure of atoms. This can be done by changing the spatial relationship or representation each element has with respect to another element in the table. A common alternate layout is Charles Janets Left Step Periodic Table, which organizes elements according to orbital filling. The modern version, known as the ADOMAH Periodic Table named after the biblical Adam, Adomah,[52], helps with writing electron configurations; the table is oriented 90˚ from the traditional periodic table, with the s-block moved to the end, after the noble gases.[53] The modern version of the Left Step Periodic Table, the ADOMAH Periodic Another alternative layout is Theodor Benfeys periodic table, where elements Table. are arranged in a spiral with hydrogen at the center and spiraling outward, with the transition metals, lanthanides, and actinides as peninsulas.[54] Three-dimensional periodic tables exist as well, such as Paul-Antoine Giguères periodic table, which has four billboards, each representing a block, with elements on the front and back. Hydrogen and helium are omitted.[55] Future developments and the end of the periodic table Although all elements up to ununoctium have been discovered, only elements up to hassium (element 108) have known chemical properties, along with copernicium (element 112). The other elements may behave differently from what would be predicted by extrapolation, due to relativistic effects; for example, flerovium has been predicted to possibly exhibit some noble-gas-like properties, even though it is currently placed in the carbon group.[56] It is unclear whether new elements will continue the pattern of the current periodic table as period 8, or require further adaptations or adjustments. Seaborg expected the eighth period, which includes a two-element s-block for elements 119 and 120, a g-block for the next 18 elements, and 30 additional elements continuing the current f-, d-, and p-blocks.[57] On the other side, some physicists like Pekka Pyykkö have theorized that these additional elements do not follow the Madelung rule, which predicts how electron shells are filled, and thus affect the appearance of the present periodic table.[58] Richard Feynman noted[59] that literally interpreting the relativistic Dirac equation has problems with electron orbitals at Z > 137, suggesting that neutral atoms cannot exist beyond untriseptium, and that a periodic table based on electron orbitals breaks down at this point. A more rigorous analysis calculates the limit to be Z ≈ 173.[60]
  • 175. Periodic table 173 Calculations from the Bohr model The Bohr model has problems for atoms with atomic number greater than 137, because the speed of an electron in a 1s electron orbital, v, is given by where Z is the atomic number, c is the speed of light, and α is the fine-structure constant.[61] Under this model, any element with Z greater than 137 would require 1s electrons to be traveling faster than the speed of light. Thus, relativistic models must be used for Z > 137. Calculations from the Dirac equation The relativistic Dirac equation also has problems for Z > 137, for the ground state energy is where m is the rest mass of the electron. Although for Z > 137, the wave function of the Dirac ground state is oscillatory, rather than bound, and there is no gap between the positive and negative energy spectra, as in the Klein paradox.[62] More accurate calculations taking into account the effects of the finite size of the nucleus indicate that the binding energy first exceeds 2mc2 forZ > Zcr ≈ 173. For Z > Zcr, if the innermost orbital is not filled, the electric field of the nucleus will pull an electron out of the vacuum, resulting in the spontaneous emission of a positron.[63] References [1] Siegfried, Robert (2002). From elements to atoms: a history of chemical composition. Philadelphia, Pennsylvania: Library of Congress Cataloging-in-Publication Data. p. 92. ISBN 0-87169-924-9. [2] Ball, p. 100 [3] Horvitz, Leslie (2002). Eureka!: Scientific Breakthroughs That Changed The World. New York: John Wiley. p. 43. ISBN 978-0-471-23341-1. OCLC 50766822. [4] Ball, p. 101 [5] Newlands, John A. R. (1864-08-20). "On Relations Among the Equivalents" (http:/ / web. lemoyne. edu/ ~giunta/ EA/ NEWLANDSann. HTML#newlands3). Chemical News 10: 94–95. . [6] Newlands, John A. R. (1865-08-18). "On the Law of Octaves" (http:/ / web. lemoyne. edu/ ~giunta/ EA/ NEWLANDSann. HTML#newlands4). Chemical News 12: 83. . [7] Bryson, Bill (2004). A Short History of Nearly Everything. Black Swan. pp. 141–142. ISBN 978-0-552-15174-0. [8] Brock, W. H.; Knight (1965). "The Atomic Debates: Memorable and Interesting Evenings in the Life of the Chemical Society". Isis (The University of Chicago Press) 56 (1): 5–25. [9] Mendelejew, Dimitri (1869). "Über die Beziehungen der Eigenschaften zu den Atomgewichten der Elemente" (in German). Zeitschrift für Chemie: 405–406. [10] Ball, pp. 100–102 [11] Pullman, Bernard (1998). The Atom in the History of Human Thought. Translated by Axel Reisinger. Oxford University Press. p. 227. ISBN 0-19-515040-6. [12] Ball, p. 105 [13] Atkins, P. W. (1995). The Periodic Kingdom. HarperCollins Publishers, Inc.. p. 87. ISBN 0-465-07265-8. [14] Kaji, Masanori (2002). "D.I. Mendeleevs Concept of Chemical Elements and the Principle of Chemistry" (http:/ / www. scs. illinois. edu/ ~mainzv/ HIST/ awards/ OPA Papers/ 2005-Kaji. pdf). Bull. Hist. Chem. (Tokyo Institute of Technology) 27 (1): 4-16. . Retrieved 11 June 2012. [15] Adloff, Jean-Pierre; Kaufman, George B. (25 September 2005). "Francium (Atomic Number 87), the Last Discovered Natural Element" (http:/ / chemeducator. org/ sbibs/ s0010005/ spapers/ 1050387gk. htm). The Chemical Educator. . Retrieved 26 March 2007. [16] Hoffman, D. C.; Lawrence, F. O.; Mewherter, J. L.; Rourke, F. M. (1971). "Detection of Plutonium-244 in Nature" (http:/ / www. nature. com/ nature/ journal/ v234/ n5325/ abs/ 234132a0. html). Nature 234 (5325): 132–134. Bibcode 1971Natur.234..132H. doi:10.1038/234132a0. . [17] Emsley, John (2011). Natures Building Blocks: An A-Z Guide to the Elements (New ed.). New York, NY: Oxford University Press. ISBN 978-0-19-960563-7. [18] Ball, p. 111 [19] Fluck, E. (1988). "New Notations in the Periodic Table" (http:/ / www. iupac. org/ publications/ pac/ 1988/ pdf/ 6003x0431. pdf). Pure Appl. Chem. (IUPAC) 60 (3): 431–436. doi:10.1351/pac198860030431. . Retrieved 24 March 2012.
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Bibcode 2007NuPhA.789..142S. doi:10.1016/j.nuclphysa.2007.04.001. [32] Leigh, G. J. (1990). Nomenclature of Inorganic Chemistry: Recommendations 1990. Blackwell Science. ISBN 0-632-02494-1. [33] Leigh, Jeffery. "Periodic Tables and IUPAC" (http:/ / www. iupac. org/ publications/ ci/ 2009/ 3101/ 1_leigh. html). Chemistry International: The News Magazine of The International Union of Pure and Applied Chemistry (IUPAC). . Retrieved 23 March 2011. [34] Scerri, E. R. (2007). The Periodic Table: Its Story and its Significance. Oxford University Press. ISBN 978-0-19-530573-9. [35] Moore, p. 111 [36] Stoker, Stephen H. (2007). General, organic, and biological chemistry. New York: Houghton Mifflin. p. 68. ISBN 978-0-618-73063-6. OCLC 52445586. [37] Mascetta, Joseph (2003). Chemistry The Easy Way (4th ed.). New York: Hauppauge. p. 50. ISBN 978-0-7641-1978-1. OCLC 52047235. [38] Kotz, John; Treichel, Paul; Townsend, John (2009). Chemistry and Chemical Reactivity, Volume 2 (7th ed.). Belmont: Thomson Brooks/Cole. p. 324. ISBN 978-0-495-38712-1. OCLC 220756597. [39] Jones, Chris (2002). d- and f-block chemistry. New York: J. Wiley & Sons. p. 2. ISBN 978-0-471-22476-1. OCLC 300468713. [40] Gray, p. 11 [41] Guenther, W. B. (1987). "An upward view of the periodic table: Getting to the bottom of it". Journal of Chemical Education 64: 9–8. doi:10.1021/ed064p9. [42] Moore, p. 46 [43] Kahn, L. R. (1976). "Ab initio effective core potentials: Reduction of all-electron molecular structure calculations to calculations involving only valence electrons". The Journal of Chemical Physics 65 (10): 3826–3821. doi:10.1063/1.432900. [44] Hornback, Joseph (2006). Organic Chemistry (2nd ed.). Pacific Grove: Thomson Brooks/Cole. p. 62. ISBN 978-0-534-49317-2. OCLC 66441248. [45] Gray, pp. 25, 189 [46] Bethe, Hans; Salpeter, E. E. (1957). "Quantum Mechanics of One- and Two-Electron Atoms" (http:/ / www. imamu. edu. sa/ Scientific_selections/ abstracts/ Physics/ Quantum mechanics of one and two electron atoms. pdf). Encyclopedia of Physics 35: 347–385. . Retrieved 11 April 2012. [47] Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements (http:/ / books. google. co. nz/ books?id=OezvAAAAMAAJ& q=0-08-022057-6& dq=0-08-022057-6& source=bl& ots=m4tIRxdwSk& sig=XQTTjw5EN9n5z62JB3d0vaUEn0Y& hl=en& sa=X& ei=UoAWUN7-EM6ziQfyxIDoCQ& ved=0CD8Q6AEwBA). Oxford: Pergamon Press. p. 27. ISBN 0-08-022057-6. . [48] Jolly, W. L. (1991). Modern Inorganic Chemistry (2nd ed.). McGraw-Hill. p. 22. ISBN 978-0-07-112651-9. [49] Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements (http:/ / books. google. co. nz/ books?id=OezvAAAAMAAJ& q=0-08-022057-6& dq=0-08-022057-6& source=bl& ots=m4tIRxdwSk& sig=XQTTjw5EN9n5z62JB3d0vaUEn0Y& hl=en& sa=X& ei=UoAWUN7-EM6ziQfyxIDoCQ& ved=0CD8Q6AEwBA). Oxford: Pergamon Press. p. 28. ISBN 0-08-022057-6. . [50] Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements (http:/ / books. google. co. nz/ books?id=OezvAAAAMAAJ& q=0-08-022057-6& dq=0-08-022057-6& source=bl& ots=m4tIRxdwSk& sig=XQTTjw5EN9n5z62JB3d0vaUEn0Y& hl=en& sa=X& ei=UoAWUN7-EM6ziQfyxIDoCQ& ved=0CD8Q6AEwBA). Oxford: Pergamon Press. p. 30. ISBN 0-08-022057-6. . [51] Allred, A. L. (1960). "Electronegativity values from thermochemical data" (http:/ / www. sciencedirect. com/ science/ article/ pii/ 0022190261801425). Journal of Inorganic and Nuclear Chemistry (Northwestern University) 17 (3-4): 215-221. doi:10.1016/0022-1902(61)80142-5. . Retrieved 11 June 2012. [52] Tsimmerman, Valery (19 March 2009). "Periodic Law can be understood in terms of the Tetrahedral Sphere Packing!" (http:/ / perfectperiodictable. com/ ). . Retrieved 5 July 2012.
  • 177. Periodic table 175 [53] Stewart, Philip J. (2009). "Charles Janet: unrecognized genius of the periodic system". Foundations of Chemistry 12 (1). doi:10.1007/s10698-008-9062-5. [54] Seaborg, Glenn (1964). "Plutonium: The Ornery Element". Chemistry 37 (6): 14. [55] Mazurs, E.G. (1974). Graphical Representations of the Periodic System During One Hundred Years. Alabama: University of Alabama Press. ISBN 9780817332006. [56] Schändel, Matthias (2003). The Chemistry of Superheavy Elements. Dordrecht: Kluwer Academic Publishers. p. 277. ISBN 1-4020-1250-0. [57] Frazier, K. (1978). "Superheavy Elements". Science News 113 (15): 236–238. doi:10.2307/3963006. JSTOR 3963006. [58] Pyykkö, Pekka (2011). "A suggested periodic table up to Z ≤ 172, based on Dirac–Fock calculations on atoms and ions". Physical Chemistry Chemical Physics 13 (1): 161–8. Bibcode 2011PCCP...13..161P. doi:10.1039/c0cp01575j. PMID 20967377. [59] Elert, G.. "Atomic Models" (http:/ / physics. info/ atomic-models/ ). The Physics Hypertextbook. . Retrieved 2009-10-09. [60] Greiner, W.; Schramm, S. (2008). American Journal of Physics. 76. p. 509. [61] Eisberg, R.; Resnick, R. (1974). Quantum Physics of Atoms, Molecules, Solids, Nuclei and Particles. John Wiley & Sons. ISBN 9780471873730. [62] Bjorken, J. D.; Drell, S. D. (1965). Relativistic Quantum Mechanics. American Institute of Physics. ISBN 0031-9228. [63] Ruffini, R.; Vereshchagin, G.; Xue, S. S. (2010). "Electron–positron pairs in physics and astrophysics: From heavy nuclei to black holes". Physics Reports 487: 1. doi:10.1016/j.physrep.2009.10.004. Bibliography • Ball, Philip (2002). The Ingredients: A Guided Tour of the Elements. Oxford University Press. ISBN 0-19-284100-9. • Bouma, J. (1989). "An Application-Oriented Periodic Table of the Elements". J. Chem. Ed. 66 (9): 741. Bibcode 1989JChEd..66..741B. doi:10.1021/ed066p741. • Gray, Theodore (2009). The Elements: A Visual Exploration of Every Known Atom in the Universe. New York: Black Dog & Leventhal Publishers. ISBN 978-1-57912-814-2. • Hjørland, Birger (2011). "The periodic table and the philosophy of classification" ( EricScerri/Papers/432740/Forum_The_Philosophy_of_Classification). Knowledge Organization 38 (1): 9–21. Retrieved 2011-03-13. • Kean, Sam (2010). The Disappearing Spoon - and other true tales from the Periodic Table. London: Black Swan. ISBN 978-0-552-77750-6. • Levi, Primo (1984). The Periodic Table [1975]. London: Penguin Books. ISBN 978-0-14-139944-7. • Mazurs, E.G (1974). Graphical Representations of the Periodic System During One Hundred Years. Alabama: University of Alabama Press. • Moore, John (2003). Chemistry For Dummies. New York: Wiley Publications. p. 111. ISBN 978-0-7645-5430-8. OCLC 51168057. • Scerri, Eric (2007). The periodic table: its story and its significance. Oxford: Oxford University Press. ISBN 0-19-530573-6. External links • M. Dayah. "Dynamic Periodic Table" ( Retrieved 14 May 2012. • Brady Haran. "The Periodic Table of Videos" ( University of Nottingham. Retrieved 14 May 2012. • Mark Winter. "WebElements: the periodic table on the web" ( University of Sheffield. Retrieved 14 May 2012. • Mark R. Leach. "The INTERNET Database of Periodic Tables" ( 35_pt/pt_database.php). Retrieved 14 May 2012. • "Periodic Table of the Elements in Four Hundred Languages" ( vyhledav/chemici2.html). Retrieved 14 May 2012.
  • 178. Philosophy of chemistry 176 Philosophy of chemistry The philosophy of chemistry considers the methodology and underlying assumptions of the science of chemistry. It is explored by philosophers, chemists, and philosopher-chemist teams. For much of its history, philosophy of science has been dominated by the philosophy of physics, but the philosophical questions that arise from chemistry have received increasing attention since the latter part of the 20th century.[1][2] Foundations of chemistry Major philosophical questions arise as soon as one attempts to define chemistry and what it studies. Atoms and molecules are often assumed to be the fundamental units of chemical theory,[3] but traditional descriptions of molecular structure and chemical bonding fail to account for the properties of many substances, including metals and metal complexes[4] and aromaticity.[5] Additionally, chemists frequently use non-existent chemical entities like resonance structures[4][5] to explain the structure and reactions of different substances; these explanatory tools use the language and graphical representations of molecules to describe the behavior of chemicals and chemical reactions that in reality do not behave as straightforward molecules. Some chemists and philosophers of chemistry prefer to think of substances, rather than microstructures, as the fundamental units of study in chemistry. There is not always a one-to-one correspondence between the two methods of classifying substances.[3] For example, many rocks exist as mineral complexes composed of multiple ions that do not occur in fixed proportions or spatial relationships to one another.[4] A related philosophical problem is whether chemistry is the study of substances or reactions.[3] Atoms, even in a solid, are in perpetual motion and under the right conditions many chemicals react spontaneously to form new products. A variety of environmental variables contribute to a substances properties, including temperature and pressure, proximity to other molecules and the presence of a magnetic field.[3][4][5] As Schummer puts it, "Substance philosophers define a chemical reaction by the change of certain substances, whereas process philosophers define a substance by its characteristic chemical reactions."[3] Philosophers of chemistry discuss issues of symmetry and chirality in nature. Organic (i.e., carbon-based) molecules are those most often chiral. Amino acids, nucleic acids and sugars, all of which are found exclusively as a single enantiomer in organisms, are the basic chemical units of life. Chemists, biochemists, and biologists alike debate the origins of this homochirality. Philosophers debate facts regarding the origin of this phenomenon, namely whether it emerged contingently, amid a lifeless racemic environment or if other processes were at play. Some speculate that answers can only be found in comparison to extraterrestrial life, if it is ever found. Other philosophers question whether there exists a bias toward assumptions of nature as symmetrical, thereby causing resistance to any evidence to the contrary. One of the most topical issues is determining to what extent physics, specifically, quantum mechanics, explains chemical phenomena. Can chemistry, in fact, be reduced to physics as has been assumed by many, or are there inexplicable gaps? Some authors have recently suggested that a number of difficulties exist in the reductionist program, notwithstanding our increasing knowledge of the microcosmic realm. The noted philosopher of science, Karl Popper, among others, predicted as much.
  • 179. Philosophy of chemistry 177 Methodology Chemistry is in a sense the paradigmatic laboratory science, one that predates both experimental and theoretical physics. While astronomers have to get along without experimenting directly on the distant objects of their attention, and biologists have to experiment within ethical and legal restraints on more available objects, chemistry conforms to, and indeed gave rise to, textbook explanations of what constitutes the scientific method. One theme arising from chemical experiments is the value of ambiguity as a spur to the type of science that chemists do. Emily R. Grosholz and Roald Hoffmann, for example, have argued that equivocations in chemistry have helped bridge the gap between experiment and theory, thereby advancing the field. Such an argument challenges preconceptions to the effect that the more fully concepts are clarified, the more useful they will prove. Philosophers of chemistry Several philosophers and scientists have focused on the philosophy of chemistry in recent years, notably, the Dutch philosopher Jaap van Brakel, who wrote The Philosophy of Chemistry in 2000, and the Maltese philosopher-chemist Eric Scerri, editor of the journal "Foundations of Chemistry" and author of Normative and Descriptive Philosophy of Science and the Role of Chemistry in Philosophy of Chemistry, 2004, among other articles. Scerri is especially interested in the philosophical foundations of the periodic table, and how physics and chemistry intersect in relation to it, which he contends is not merely a matter for science, but for philosophy.[6] Although in other fields of science students of the method are generally not practitioners in the field, in chemistry (particularly in synthetic organic chemistry) intellectual method and philosophical foundations are often explored by investigators with active research programmes. Elias James Corey developed the concept of "retrosynthesis" published a seminal work "The logic of chemical synthesis" which deconstructs these thought processes and speculates on computer-assisted synthesis. Other chemists such as K. C. Nicolaou (co-author of Classics in Total Synthesis). Further reading Review Articles • Philosophy of Chemistry [7] article on the Stanford Encyclopedia of Philosophy Journals • Foundations of Chemistry [8], an international peer-reviewed journal for History and Philosophy of Chemistry as well as Chemical Education published by Springer. • Hyle: International Journal for Philosophy of Chemistry [9], an English-language peer-reviewed journal associated with the University of Karlsruhe, Germany. Books • Philosophy of Chemistry, J. van Brakel, Leuven University Press, 2000. ISBN 90-5867-063-5 • Philosophy of Chemistry : Synthesis of a New Discipline, Davis Baird, Eric Scerri, Lee McIntyre (eds.), Dordrecht: Springer, 2006. ISBN 1-4020-3256-0 • The Periodic Table: Its Story and Its Significance, E.R. Scerri, Oxford University Press, New York, 2006. ISBN 0-19-530573-6 • Of Minds and Molecules: [10] New Philosophical Perspectives on Chemistry, Nalini Bhushan and Stuart Rosenfeld (eds.), Oxford University Press, 2000, Reviewed by Michael Weisberg
  • 180. Philosophy of chemistry 178 Academic Events The International Society for the Philosophy of Chemistry - Summer symposium 2011 will be held during August 9–11, 2011, in Bogota, Colombia, at the campus of the Universidad de los Andes. The conference is being sponsored by the Universidad de los Andes (Colombia). This event is the continuation of the International Society for the Philosophy of Chemistry - Summer symposium 2010, organised in Oxford at the University College during August 9–11, 2010. References [1] Weisberg, M. (2001). Why not a philosophy of chemistry? American Scientist. Retrieved April 10, 2009 from (http:/ / www. americanscientist. org/ bookshelf/ pub/ why-not-a-philosophy-of-chemistry|http:/ / www. americanscientist. org/ bookshelf/ pub/ why-not-a-philosophy-of-chemistry) [2] Scerri, E.R., & McIntyre, L. (1997). The case for the philosophy of chemistry. Synthese, 111: 213–232. Retrieved April 10, 2009 from http:/ / philsci-archive. pitt. edu/ archive/ 00000254/ .pdf here (http:/ / www. chem. ucla. edu/ dept/ Faculty/ scerri/ pdf/ Case_for_poc. pdf) [3] Schummer, Joachim. (2006). Philosophy of science. In Encyclopedia of philosophy, second edition. New York, NY: Macmillan. [4] Ebbing, D., & Gammon, S. (2005). General chemistry. Boston, MA: Houghton Mifflin. [5] Pavia, D., Lampman, G., & Kriz, G. (2004). Organic chemistry, volume 1. Mason, OH: Cenage Learning. [6] Scerri, Eric R. (2008). Collected Papers on Philosophy of Chemistry. London: Imperial College Press. ISBN 978-1-84816-137-5. [7] http:/ / plato. stanford. edu/ entries/ chemistry/ [8] http:/ / www. springeronline. com/ sgw/ cda/ frontpage/ 0,11855,4-0-70-35545882-0,00. html?referer=www. wkap. nl [9] http:/ / www. hyle. org/ journal/ concept. htm [10] http:/ / www. americanscientist. org/ template/ BookReviewTypeDetail/ assetid/ 14418;jsessionid=aaaeI64wZUcz2T External links • Philosophy of Chemistry ( entry by Michael Weisberg, Paul Needham, and Robin Hendry in the Stanford Encyclopedia of Philosophy • International Society for the Philosophy of Chemistry ( • International Society for the Philosophy of Chemistry Summer symposium 2011 ( intsocphilchem2011/)
  • 181. Article Sources and Contributors 179 Article Sources and Contributors Chemistry  Source:  Contributors: .mdk., 08walta,,, 64squares, 94chauj, A Doon, AGK, APH, Acegikmo1, Acerperi, Adam Bishop, Adashiel, AdjustShift, Adminsr, Adqam, Adventurer, Aeluwas, Ahoerstemeier, Aiowe ;nhg8ohegpo8haeog, Ajrocke, Akanemoto, Alan Liefting, Alex S, Alhutch, Alison, Amcfreely, AmiDaniel, Amire80, Ams80, Anaraug, Ancheta Wis, Andrew Gray, Andrewpmk, Andris, Andy85719, Andycjp, Andyso, Angela, Anger22, Ann Stouter, Anonymous anonymous, Antandrus, Apha, ArglebargleIV, Arjun01, Arkuat, Arnon Chaffin, Art Carlson, Astrochemist, Astrovega, Atepnurdjaman, Atomician, AuGold, AustinZ, AxelBoldt, Azareal7, BRG, Bact, Ballista, Ban Bridges, Barakta, Barticus88, Basharh, Basketballcooliog, Bduke, Beetstra, Ben D., Ben-Zin, Ben.c.roberts, Bender235, Benjah-bmm27, Bensaccount, Bfesser, Bidgee, Bill Nye the wheelin guy, Bjf, Blackpower, Bluemask, Bmeguru, Bmicomp, Bob, Bob the ducq, Bobblewik, Bobby1011, Bobo192, Bongwarrior, Bonnerman, BookSquirrel, Boothy443, BorgQueen, Borislav, Bornhj, Braddodson, Bradeos Graphon, Braindrain0000, Brandon5485, Brent45801, Brian Pearson, Brian0918, Brianga, Brion VIBBER, Brockert, BrokenSegue, Bruce1ee, Burntsauce, Bwithh, CDN99, Cacycle, Cadiomals, Caesura, Cafzal, Caltas, Camembert, Cant sleep, clown will eat me, CanDo, Car Henkel, Cdogsimmons, Cenarium, Centrx, Century0, Charles Matthews, ChemGardener, Chemistrypal, Chillum, Chris the speller, Chrislk02, Christian List, Christopher Parham, Chun-hian, Ck lostsword, Clackmannanshireman, Clemwang, CobraWiki, Codex Sinaiticus, Coinpeice, Colonies Chris, Computerjoe, Conversion script, Cronullasoutherland, Crystallina, Curps, Cyktsui, Cyw90, DARTH SIDIOUS 2, DMacks, DVD R W, Daniel5127, Danny, Danski14, Dantecat, Darenshan54, DarkCatalyst, Darrien, Darthgriz98, Daven200520, David Little, David Stapleton, DavidLevinson, DavidRader, Dawn1234, Dazedbythebell, Dcoetzee, Delirium, Deltabeignet, Demophon, Denali134, Depressio, DerHexer, Derek.cashman, Deryck Chan, Desertsky85451, Deviator13, Devnull17, Dick slicky, DigitalGhost, Dinosaur puppy, Djcozmik, Doctormatt, Docu, Dodger67, Dodgerdave, Dogposter, Doug Alford, DrBob, Dreg743, Dren55, Dtgm, Dustimagic, Dylan Lake, ESkog, EamonnPKeane, Eaolson, EarthPerson, EdChem, Edgar181, Edonovan, Edwy, Egil, El C, ElinorD, EllaRess, Emojones, Emperorbma, Enormousdude, Eric Forste, EscapingLife, Eugenedakin, Evercat, Evil saltine, Explicit, Extra999, Ezeu, F2020, FF2010, Facklere, Fahlmanb, Falcorian, Fatdemon, Fdevilbis, Feezo, Feydakin, Fiestabowl 2003, Figure, Filefire, Fireyair, Flockmeal, Flubeca, Francs2000, Frecklefoot, FreplySpang, Fte, Fuzheado, Fuzzywallaby, Fys, GDonato, Gadfium, Galoubet, Gamewizard71, Gareth Owen, Gashead 12, Gentgeen, Ghutchis, Giftlite, Gilligan mark, Girdi, Glass Sword, Glossary, Gmhisham, Gnangarra, GnuDoyng, Go for it!, Goatberg, Gossip14, Graham87, GregorB, Greyhood, Grstain, Gryphn, Guanaco, Gunmetal, Gurch, Gwernol, HJ Mitchell, Hadal, Hajhouse, Hallenrm, HansHermans, Happenstancial, HappyApple, HappyCamper, Hattar393, Hdt83, Headbomb, Henry W. 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  • 183. 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  • 184. Article Sources and Contributors 182 Useight, User A1, User27091, V8rik, Vanished User 1004, VasilievVV, Vatic7, Versus22, Vsmith, Vulcan Hephaestus, WODUP, WRK, Walrus heart, Wavelength, WeißNix, Welsh, West.andrew.g, Whoop whoop pull up, Wiki13, WikiLaurent, WikipedianMarlith, William Avery, Winchelsea, Wizardist, Wj32, Wsvlqc, Xaosflux, Xkfusionxk, Yamamoto Ichiro, Yougi, Zhanghia, Zntrip, Zythe, Ásgeir IV., Александър, రవిచంద్ర, 852 anonymous edits Chemical reaction  Source:  Contributors:, 2D, 4lex, 4twenty42o, 9258fahsflkh917fas, A3r0, A876, A8UDI, Abeg92, Acroterion, Adi4094, Ahoerstemeier, Ainlina, Aion, Airconswitch, Aitias, Alansohn, Albertshilling28, Ale jrb, Allstarecho, Alperen, Amanafu, Amberbrown842, Amcfreely, Amplitude101, Anbu121, Andre Engels, Andy M. 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Iswikinumber2, IvanLanin, Jeff G., Mark Yen, Mets501, Mhym, Nosferatütr, Raublexxion, Sadi Carnot, V8rik, Wayne Riddock, 6 anonymous edits Outline of chemistry  Source:  Contributors:,,, Alistair b, Andre Engels, Auroranorth, Bduke, Beland, Burn, Centrx, ChemGardener, Christian75, Conversion script, Coppertwig, Cybercobra, David Kernow, Docu, Dp462090, Dwmyers, Emesee, Eu.stefan, Fibonacci, Fluffernutter, Fplay, Gamewizard71, Go for it!, GorillaWarfare, Graham87, Gurch, Hankwang, Itub, Jack Merridew, Jcwf, JeffW, JohnBlackburne, Karol Langner, Magioladitis, Malcolm Farmer, Marj Tiefert, Mav, MyNameIsNotBob, Narayanese, Nexus Seven, Nho, OldakQuill, Oxymoron83, Pegship, Philip Trueman, Quiddity, RDBury, Rifleman 82, Robert Skyhawk, Seattle Jörg, SebastianHelm, SeventyThree, Smack, Sodium, Stewartadcock, Sunderland06, The Anome, The Transhumanist, The Transhumanist (AWB), TheTito, V8rik, Vsmith, Walkerma, Woohookitty, Zarboki, 45 anonymous edits Common chemicals  Source:  Contributors: ArticCynda, Barhamd, Bmusician, ChemGardener, ChemNerd, Christian75, Colonel Warden, Cool3, Dark Silver Crow, Dream Focus, Dunderbud, Extra999, Flarn2006, Frap, Freestyle-69, Gaius Cornelius, GreatWhiteNortherner, Ipatrol, Itub, Japheth the Warlock, Joeylawn, John H, Morgan, Lmatt, MER-C, Mtking, Northamerica1000, Open2universe, Pipedreamergrey, RHaworth, RedFox581, Rolandog, Russoc4, SB Johnny, Seven of Nine, SiliconDioxide, Skamecrazy123, Smokefoot, SunCreator, Sześćsetsześćdziesiątsześć, Tassedethe, Tide rolls, WOSlinker, Whoop whoop pull up, Witch-King, Xyzzyplugh, Yongrenjie, 87 anonymous edits International Year of Chemistry  Source:  Contributors: Baseball Bugs, Christian75, CorporatecommsUK, Davidm617617, Ebe123, Extremepro, Fetchcomms, Good Olfactory, HenkvD, Janhmoonstone30, Kkumsindia, Lumos3, Marek69, Materialscientist, Mayooranathan, Michaelmas1957, NewEnglandYankee, Petergans, Pjoef, Plastkemiforetagen, Prayerfortheworld, Quest for Truth, SarahStierch, Sreejithk2000, StAnselm, Wurdwiz, 26 anonymous edits List of chemists  Source:  Contributors: A bit iffy, A. 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Article Sources and Contributors 183 Mdebets, Michael Snow, Mkcas, Moormand, Mystique, Nasnema, OA340, Oreckel, Oxymoron83, Pflodo, Philip Trueman, PierreAbbat, Pingveno, PuzzletChung, RadioFan, Robert Foley, Romanm, Ronhjones, Russoc4, Scotorroz, SemperBlotto, Shellreef, Sietse Snel, Snags, Snoyes, SteveMcCluskey, Stewartadcock, Tanthalas39, Tarquin, Techman224, Template namespace initialisation script, TenOfAllTrades, The Anome, The Thing That Should Not Be, The Wordsmith, The chemistds, TheAlmightyEgg, Theresa knott, Thomasgl, Thue, Tide rolls, Tim Starling, Tregoweth, Tsemii, Turbonick, V8rik, Vanderesch, Walkerma, Wang, Wapcaplet, Wayne Slam, Wimvandorst, Wipe, Wtmitchell, Xdenizen, Yawny45, ZeroOne, 201 anonymous edits List of important publications in chemistry  Source:  Contributors: APH, Bduke, Bryan Sanctuary, Cadmium, Cgingold, Chemistbrian, ChrisGualtieri, Curb Chain, Cutler, DGG, Dcljr, Dirac66, Edgar181, Edward, Ekotkie, Eras-mus, Fiona Shortt, Fuhghettaboutit, Gaius 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Nicolazonta, Niko pd, Northamerica1000, P99am, Pemmy, Qgauss, Radiometer, Sekmi, Sellersb, Shadowboy813, Spud Gun, TDF, Thorwald, UnitedStatesian, VQuakr, Vi2, Vizbi, Vriend, WikHead, Williamseanohlinger, Wrpscott, Xebvor, 96 anonymous edits List of unsolved problems in chemistry  Source:  Contributors: AWeishaupt, Altenmann, Andycjp, Aschwole, Bduke, Bogdangiusca, C933103, Chipotle, Cobblet, Coppertwig, David Latapie, Deniska.G, E kwan, Eastlaw, Edgar181, Gareth E Kegg, GeeJo, Gurch, Heliumballoon, Huhnra, Isotope23, JeffW, Jmnbatista, Kwamikagami, Lfh, Makecat, Mgiganteus1, MigueldelosSantos, Northfox, PJTraill, Pheticsax, Physchim62, Piotrek54321, Quietly, RDBrown, Remi0o, Rnaplus, Rune.welsh, Seraphimblade, StAnselm, T-dot, The Earwig, The Transhumanist, Thezookeeper, Tyrant Tim, Uranium grenade, V8rik, Wdfarmer, Welsh, Wikipediatrix, Xoloz, 33 anonymous edits Periodic systems of small molecules  Source:  Contributors: Arthur Rubin, Bearcat, Beeblebrox, Christian75, Cirt, David 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