Rules for Assigning Oxidation Numbers:

1) The oxidation number for an atom of any free (uncombined) element is ZERO.Examples: Na, Ca have zero oxidation number.

2) The oxidation number of an element in self-combination is always ZERO.Examples: H2, O2, P4 have zero oxidation number.

3) In most hydrogen containing compounds, oxidation number of hydrogen is + 1.(Exception is when H combines with alkali metals or alkaline earth to form hydrides of metals such as: NaH, LiH, CaH2. Then, the oxidation number of H is -1).

4) In compounds involving the alkali metals, the elements are assigned oxidation number of +1.

5) In compounds involving the alkaline earth metals, the elements are asasigned oxidation number of +2.

6) Oxygen is usually assigned an oxidation number of -2 for oxides. It has an oxidation number of -1 in peroxides (H2O2).

7) Fluorine always has oxidation number of -1 in compounds. The other elements in that group is usually -1 in compounds with elements of low electronegativity.

8) The sum of oxidation numbers of all the atoms in the formula for a neutral compound is ZERO.

9) The sum of oxidation numbers of an ion or complex ion is the same as the charge on that ion.