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ES 3.1 PPT
 

ES 3.1 PPT

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    ES 3.1 PPT ES 3.1 PPT Presentation Transcript

    •  Matter is anything taking up space and having mass.  The amount of matter in an object is its mass. 3 main states of matter include:  SOLID: definite mass, definite volume, definite shape  LIQUID: definite mass, definite volume, indefinite shape  GAS: indefinite mass, indefinite volume, indefinite shape The amountof disorder in atoms or molecules is known as entropy.  Example: SOLID  LIQUID = Entropy increasing  Example: GAS  SOLID = Entropy decreasing
    •  All matter has 2 types of distinguishing characteristics:  Physical properties  Chemical properties Physical properties can be observed without changing the composition of the substance.  Examples: density, color, hardness, freezing point, boiling point, and the ability to conduct electricity. Chemical properties describe how a substance reacts with other substances.  Examples: oxidation (iron reacting with oxygen to form rust).
    •  An element is a substance that cannot be broken down into simpler, stable substances by ordinary chemical means.  About 90 elements occur naturally on Earth.  8 of those make up more than 98% of Earth’s crust. Elements consist of atoms, which are the smallest units of an element having the chemical properties of that element.  A single atom is so small, its size is difficult to imagine.  Look at the thickness of a sheet of notebook paper  about 1,000,000 atoms lined up side by side would be equal to that thickness.
    •  Atoms are made up of even smaller parts called subatomic particles.  3 major kinds include:  Protons – subatomic particle having a positive charge located in the nucleus of an atom.  Neutrons – subatomic particle having no charge located in the nucleus of an atom.  Electrons – subatomic particle having a negative charge located in energy levels surrounding the nucleus of an atom.
    •  The maximum number of electrons an energy level can occupy is expressed by the formula 2n2, where n= the energy level.
    • Oxygen (O) Magneisum (Mg)8 protons, 8 neutrons, 8 electrons 12 protons, 12 neutrons, 12 electrons
    •  The number of protons in the nucleus of an atom is called the atomic number.  All atoms of any given element have the same atomic number  thus the same number of protons.  Since an uncharged atom has an equal number of protons and electrons, the atomic umber is also equal to the number of electrons.
    •  The Periodic Table of Elements is a system for classifying elements and was first devised by the Russian chemist, Dmitri Mendeleev, in 1869. Elements onthe Periodic Table are ordered according to their atomic numbers.  Rows are called periods.  Columns are called groups.  Elements in the same column have similar arrangements of electrons around their atom, therefore having similar chemical Mendeleev properties.
    •  The sum of the number of protons and neutrons in an atom is the mass number.  This is the atomic mass rounded to the nearest whole number.  The mass of a subatomic particle is too small to be expressed in grams.  So, we use a special unit called the atomic mass unit (amu).  Protons and neutrons each have an atomic mass close to 1 amu.  In contrast, electrons have much less.  The mass of 1 proton is equal to the combined mass of about 1840 electrons!
    •  Although atoms of a given element contain the same number of protons, the number of neutrons may differ. An atom of the same element having the same number of protons (atomic number), but a different number of neutrons (different mass number) is called an isotope.
    •  A Carbon-14 atom having 8 neutrons is more massive than a Carbon- 11 atom having only 5 neutrons.  Different isotopes of the same element have slightly different properties.  Unstable isotopes are subject to radioactive decay, where they will emit energy and change into another element. Since isotopes of an element have different masses, the Periodic Table uses an average atomic mass, which is the weighted average of the atomic masses of the naturally occurring isotopes.  Isotopes of Hydrogen (H): 1H, 2H (Deuterium), and 3H (Tritium).  On the Periodic Table, the average atomic mass of Hydrogen (H) is 1.00794 u.
    •  An atom’s chemical properties are largely determined by the number of the outermost electrons, valence electrons, in an atom’s electron cloud.  Within each group (column), the atoms of each element generally have the same number of valence electrons.  For Groups 1 and 2, the number of valence electrons in each atom is the same as that atom’s group number.  Atoms of elements in Groups 3-12 (Transition Metals) have 2 or more valence electrons.  For Groups 13-18, the number of valence electrons in each atom is the same as that atom’s group number minus 10, except for Helium (He), which only has 2 valence electrons.
    •  Elements whose atoms have only 1, 2, or 3 valence electrons tend to lose electrons rather easily.  These elements have metallic properties and are generally classified as metals. Elements whose atoms have from 4-7 valence electrons are more likely to gain electrons.  Many of these elements are classified as nonmetals. When an atom has 8 valence electrons, it is considered stable, or chemically un-reactive.  It’s outer shell is full … Octet Rule
    •  Elements rarely occur in pure form in Earth’s crust, but rather as a combination with other elements  we discussed Quartz, SiO2  A substance made of two or more elements chemically combined is called a compound.  A group of atoms held together by chemical forces is called a molecule.  All compounds are molecules, but not all molecules are compounds!  Some elements occur as diatomic molecules, which are molecules made up of only two atoms.  Mnemonic: I Have No Bright Or Clever Friends  Iodine (I2), Hydrogen (H2), Nitrogen (N2), Bromine (Br2), Oxygen (02), Chlorine (Cl2), and Fluorine (F2).
    •  A chemical formula is a combination of letters and numbers showing which elements make up a compound.  Also shows the number of atoms of each element that are required to make a molecule of a compound. The chemical formulafor water is H20, indicating each water molecule consists of 2 atoms of Hydrogen and 1 atom of Oxygen, shown by the subscript. x2 x2 Superscript Subscript
    •  Another example of a chemical formula is sodium chloride, NaCl, halite, or table salt … they all mean the same thing!  Sodium (Na) is a silvery metal and Chlorine (Cl) is a poisonous greenish-yellow gas.  They both make up table salt, which you can eat. + =
    •  A chemical reaction showing the combination of elements and compounds is called a chemical equation.  The reactants are on the left-hand side of the arrow, combining to form the products, on the right-hand side of the arrow.  The arrow means “yields” or “gives”.
    •  Chemical equations mustbe balanced to show accurate chemical information.  An equation is balanced when the number of atoms of each element on the right side equal the number of atoms of the same element on the left side. You cannot change the chemical formulas, but rather put numbers called coefficients in front of chemical formulas.  A coefficient multiplies the subscript in a formula; 4 Hydrogen (H) atoms are in the formula 2H20.
    •  Try balancing the following equations: ___ Hg + ___ O2  ___ HgO ___ KNO2 + ___ O2  ___ KNO3 ___ Al + ___ HCl  ___ AlCl3 + ___ H2
    •  The forces holding the atoms in molecules together are called chemical bonds.  They form due to the attraction between positive and negative charges. Atoms form chemical bonds by either transferring or sharing valence electrons from one atom to another.  When this happens, the atoms become charged.  A particle, such as an atom or molecule, carrying a charge is called an ion.
    •  An attraction between oppositely charged ions resulting in the transfer of electrons from one atom to another is called an ionic bond.
    •  Let’s look again at NaCl, or sodium chloride:
    •  The Sodium (Na) atom transfers 1 electron, becoming positively charged (Na+1). The Chlorine (Cl) atom accepts the 1 electron, becoming negatively charged (Cl-1).  This chemical reaction results in table salt, NaCl.
    •  An attraction between atoms sharing electrons is called a covalent bond.  The positive nucleus of each atom is attracted to the shared negative electrons.
    •  On Earth, elements and compounds are generally mixed together.  A mixture is a combination of 2 or more substances not chemically combined. Mixtures in which 2 or more substances are not uniformly distributed are called heterogeneous mixtures.  Examples include: igneous rock, granite (contains the minerals quartz, feldspar, hornblende, and biotite mica). Mixtures in which 2 or more substances are uniformly dispersed throughout are called homogeneous mixtures.  Examples include: Sea water (NaCl is dissolved in H2O).