Alchemy - pseudoscience based upon the belief that cheap metal could be turned into gold Greek philosopher Aristotle proposed that all matter is made up of a combination of four basic elements: Air, water, fire, earth
There are 115 known elements, of those 92 occur naturally in the universe. The rest are man-made.
Each element has a chemical symbol. The symbols come from:
the first letter of the name of the element
the first letter and one other letter in the
-the Greek or Latin name for the element.
Only the first letter of the symbol is capitalized.
3.3 Dalton’s Atomic Theory Law of Constant Composition A given compound always contains the same proportions by mass of the elements.
John Dalton - English scientist who proposed that matter is made up of atoms Dalton’s Atomic Theory
All matter is made up of tiny particles called
2. All atoms of a given element are identical in mass and properties. 4. When elements react, their atoms combine in simple, whole-number ratios. 3. Atoms of a given element are different from those of any other element.
5. Atoms are indivisible and indestructible in chemical processes.
chemical formula - shows the types of atoms and the number of each type in a molecule of a given compound * Rules for Writing Formulas, p. 54.
History of the Atom J.J. Thomson - showed that atoms of any element can be made to emit negative particles. He concluded that all atoms must contain the negative particles we now call electrons . He also concluded that atoms must contain positively charged particles to balance out the negative charges of the electrons.
William Thomson (aka Lord Kelvin )
proposed that an atom might be like a plum
believed the electrons were randomly scattered
throughout a uniform “pudding” of positive
Ernest Rutherford’s Gold Foil Experiment Rutherford aimed a beam of alpha particles at a sheet of gold foil. Most of the particles went straight through the foil, but some were deflected at large angles or even backward.
Atoms contain a dense center or nucleus of
positive charge around which electrons move.
2. Atoms are mostly empty space.
He later concluded that the nucleus must contain protons or positively charged particles to balance out the negative electrons.
An atom consists of a tiny nucleus and electrons that orbit around the nucleus. The nucleus contains: protons neutrons - positively charged - no charge Electrons have very little mass, so the mass of an atom comes from the protons and neutrons in the nucleus. The properties of an element are due to the number and arrangement of electrons in its atoms.
Atoms have an equal number of electrons and protons. The number of protons in the nucleus of an atom is called the _______________. atomic number The sum of an atom’s protons and neutrons is called the ________________. mass number Atoms of the same element with different numbers of neutrons are called ____________. isotopes
Elements are listed on the periodic table in order of increasing _________________. atomic numbers Dmitri Mendeleev - 1869, arranged the known elements according to increasing atomic mass He found that the elements could be grouped together into vertical families with similar properties. There were some inconsistencies with his arrangement.
Henry Moseley - 1913, arranged the elements according to increasing atomic numbers Prior to Moseley, atomic numbers were thought of as arbitrary numbers. He showed that they were not arbitrary, but had an experimentally measurable basis.
Modern Periodic Law “ The properties of elements are a periodic function of their increasing atomic numbers.” Horizontal rows on the periodic table are called __________. periods Vertical columns are called families or ________. groups Elements in the same family have similar chemical properties. The period number is called the principle quantum number and it represents the number of electron energy levels of the elements in that period.
very reactive metals
Alkaline Earth Metals - Group 2 Halogens
- very reactive nonmetals
Transition Metals - group of metals between Groups 2 and 3 Element Song
Hydrogen - most common element in the universe - behaves like no other element - very reactive with other elements
Very few elements exist in nature in their pure uncombined form. Gold, silver, and platinum are called ___________ because they are relatively unreactive. noble metals Many elements exist in the form of diatomic molecules : molecules made up of two atoms.
Metals are solid at room temperature. Many nonmetals are solid and many are gases at room temperature. Only two elements are liquid at room temperature: mercury (Hg) and bromine (Br 2 ) Different forms of a given element are called ___________. allotropes Carbon has three allotropes: Diamond Graphite Buckminsterfullerene
Ion - an atom or group of atoms that has gained or lost electrons Cation - positively charged ion
formed when an atom loses one or more
- named using the name of the parent atom Example : A sodium atom will lose one electron to become a sodium ion (Na + ).
Anion - negatively charged ion
formed when an atom gains one or more
named by taking the root name of the atom
and changing the ending to - ide .
Example : A chlorine atom will gain one electron to become a chloride ion (Cl - ). All alkali metals (Group 1) form 1 + ions . All alkaline earth metals (Group 2) form 2 + ions . All Group 3 metals form 3 + ions . All Group 6 nonmetals form 2 - ions . All halogens (Group 7) form 1 - ions .
Ionic compounds - compounds formed due to the attraction between metal cations and nonmetal anions Example: sodium chloride, NaCl The Na + and Cl - are attracted to each other and held together by the opposite charges. Ionic compounds can conduct electric current. * Example 3.6, p. 77. Ionic compounds are also called salts .
A chemical compound must have a net charge of zero. For an ionic compound: total positive charge of cations total negative charge of anions + = zero net charge Na + + Cl - NaCl Ionic compounds are also called salts .