Oxidation States

Oxidation states show how oxidised or reduced an element is within a compound or ion.

If the oxidation state increases the substance is oxidised If the oxidation state decreases the substance is reduced.

Rules for oxidation numbers:

1. The oxidation number of an atom is zero in a neutral substance that contains atoms of only one element.

2. The oxidation number of simple ions is equal to the charge on the ion.

3. The oxidation number of hydrogen is +1 when it is combined with a nonmetal.

4. The oxidation number of hydrogen is -1 when it is combined with a metal.

5. The metals in Group IA form compounds in which the metal atom has an oxidation number of +1.

6. The elements in Group IIA form compounds in which the metal has an oxidation number of +2.

7. The oxidation number of oxygen in a compound is usually -2. If, however, the oxygen is in a class of compounds called peroxides then the oxygen has an oxidation number of -1. If the oxygen is bonded to flourine, the number is +1.

8. The elements in Group VIIA often form compounds in which the nonmetal has a -1 oxidation number.