Oxidation Number Rules & FORMULAS

IONS Cations: positively charged atoms (Ca ++ ) All Metals will become cations Anions: negatively charged atoms (O -2 ) Non metals become anions, names end in ide, Root + ide (oxide) Polyatomic Ions: group of atoms with a electrostatic charge. (S )

Polyatomic Ions Acetate C 2 H 3 O 2 - Cyanide CN - Chlorate ClO 3 - Chlorite ClO 2 - Hydrogen Carbonate or bicarbonate HCO 3 - Hydrogen Sulfate HSO 4 - Hydrogen Sulfite HSO 3 - Hydroxide OH - Nitrate NO 3 - Nitrite NO 2 - Permanganate MnO 4 - Manganate MnO 4 -2 Carbonate CO 3 -2 Chromate CrO 4 -2 Dichromate Cr 2 O 7 -2 Sulfate SO 4 -2 Sulfite SO 3 -2 Oxalate C 2 O 4 -2 Phosphate PO 4 -3 Phosphite PO 3 -3 Silicate SiO 3 -2 Ammonium NH 4 +

Formulas Chemical Formula: chemical symbols representing the composition of a substance. Molecular Formula: shows the number and kinds of atoms present in a molecule of a compound. Empirical Formula: shows the number and kinds of atoms with simplest whole number ratio of the atoms in the compound. (formulas for ionic compounds are empirical)

Oxidation/Reduction Oxidation: loss of 1 or more e - Na – e - = Na + The atom is a electron donor with oxidation number of +1. Reduction: gaining of 1 or more e - Cl + e - = Cl - Electron acceptor ox # of -1 Oxidation #: an assigned # representing the oxidation state of the element. May be a positive or negative number, depending on if atom lost or gained electrons.

Oxidation # Rules 1.The oxidation number of an atom of a free element is zero. 2.The oxidation number of a monatomic (one-atomed) ion is equal to its charge. 3.The algebraic sum of the oxidized #’s of the 2 different atoms in the formula of a compound must be equal to zero. Ex: Na + + Cl - = = NaCl Mg +2 + Cl - =

Molecules, Compounds & Bonding Molecule: 2 or more atoms bonded together. Compound: 2 or more substance chemically bonded together. Bonding Ionic Bonding: transfer of electrons, occurring between a metal & nonmetal.

Free atoms are rarely found in nature. Many atoms combine at ordinary temperature. Exceptions are the noble gases. Therefore: 1 molecule of, for example, Helium is monatomic and is written He. All noble gases are monatomic molecules. There are some gases that are diatomic when by themselves. (H 2,F 2,O 2,N 2,Cl 2,Br 2,I 2 )

O 2 – two atoms of oxygen bonded chemically together to form 1 molecule. 2O – two separate unbonded atoms of oxygen 3O 2 – three molecules of oxygen, each which consists of two O atoms bonded together. (6 atoms) 2H 2 O – two molecules of water, each containing two atoms of H & one atom of O.

Covalent Bonding: sharing of electrons, occurring between molecules or nonmetals. 1.Pure, nonpolar covalent bonding: there is an equal attraction for the shared electrons and a resulting balance distribution of charge. 2.Polar covalent bonding: there is an unequal attraction for the shared electrons & a resulting unbalanced distribution of charge. (H 3 O + )

Electronegativity: atoms ability to attract an electron. **The difference between electronegativity of each atom determines the type of bond or the % ionic character of the bond. That is, is it a ionic bond, covalent, pure covalent, polar covalent or non-polar covalent. When an atom of one element combines chemically with an atom of another element, both atoms usually attain a stable outer shell (OCTET) Electron transfer is always exothermic. Electron sharing is usually exothermic, sometimes endothermic.

4.In compounds, the oxidation number of H is +1. Except when a metallic hydride (combines with a metal). (-1) 5.In compounds, the oxidation number of O is -2, unless it’s a peroxide where it is a -1 or when combined with F it is a In combinations involving nonmetals, the oxidation # of the less electronegative element is +, and that of the more electronegative element is negative. (except H and active metals, H is -1, forming a metallic hydride)

7.The algebraic sum of the oxidation #’s of the atoms in the formula of a polyatomic ion is equal to the ions charge. Ex: N O 3 - x + 3(-2)= -1 X – 6 = - 1 N = = +6 O = - 2 X = +5