1. Chemical Formulas and Chemical Compounds Oxidation Numbers

2. Oxidation number A number assigned to an element in a compound that indicates the general distribution of electrons in the compound.

3. Rules for Assigning Oxidation Numbers 1.Atoms in a pure element (Na or O 2 ) have an oxidation number equal to zero 2.In a binary compound the more electronegative element gets a negative charge and the other gets a positive charge. 3.Fluorine always has an oxidation # = -1 4.Oxygen usually has an oxidation # = -2 Peroxides are an exception (H 2 O 2 ) where oxidation # = -1 5.Hydrogen has an oxidation # = +1 when bonded to more electronegative elements or -1 when bonded to metals 6.The sum of oxidation numbers is 0 for a neutral compound 7.The sum of oxidation numbers for a polyatomic ion is equal to the charge of the ion

4. Sample Problems a.KClO 4 b.SO 3 2- c.NF 3 d.CO 2 e. NO 3 - f.NH 4 Cl