Oxidation Number 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
Oxygen -1 in peroxides
-2 in all other compounds