Chemical Formulas and Chemical Compounds

Oxidation Numbers

Oxidation number• A number assigned to an element in a

compound that indicates the general distribution of electrons in the compound.

Rules for Assigning Oxidation Numbers1. Atoms in a pure element (Na or O2) 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 (H2O2) 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

Sample Problems

a. KClO4

b. SO32-

c. NF3

d. CO2

e. NO3-

f. NH4Cl