Oxidation States

General rules

    1. A neutral element that is not part of a compound has an oxidation state of zero.
    2. Monoatomic ions have oxidation states equal to their ionic charges.
    3. The sum of the oxidation states in any formula is equal to the overall charge on that formula.
    4. Oxygen tends to have an oxidation state of –2 in compounds*.
    5. Hydrogen tends to have an oxidation state of +1 in compounds**.

*Oxygen

    1. When bonded to a nonmetal (other than fluorine) oxygen has an oxidation state of –2.
    2. As the oxide ion, O2–, oxygen has an oxidation state of –2.
    3. As the peroxide ion, O22–, oxygen has an oxidation state of –1.
    4. As the superoxide ion, O2–, oxygen has an oxidation state of –1/2.
    5. In elemental form, O2 or O3, oxygen has an oxidation state of 0.
    6. When bonded to fluorine, oxygen will have a positive oxidation state dictated by rule #3 above. Fluorine always has an oxidation state of –1 in compounds.

**Hydrogen

    1. When bonded to a nonmetal, hydrogen has an oxidation state of +1.
    2. When bonded to a metal, hydrogen has an oxidation state of –1.
    3. In elemental form, H2, hydrogen has an oxidation state of 0.