Oxidation Number Rules

General Rules

1. For an atom in its elemental form, oxidation number = 0.

2. For a monoatomic ion, oxidation number = ion charge

3. The sum of the oxidation numbers for all atoms in a neutral compound equals zero.

4. The sum of the oxidation numbers for all atoms in a polyatomic ion equals the charge on the ion.

Rules for specific atoms in compounds:

Atom or Group Oxidation Number

Group 1A cation +1

Group 2A cation +2

Hydrogen +1 in combination with nonmetals

-1 in combination with metals or boron

Fluorine -1

Oxygen -1 in peroxides

-2 in all other compounds