Free elements have an oxidation number of 0

Diatomic Ions have an oxidation number of 0

Ions of one atom have an oxidation number equal to its charge

The sum of oxidation numbers in a neutral compound is 0

The sum of oxidation numbers in a polyatomic ion is equal to the charge of the ion

Metals always have a positive oxidation number

Nonmetals can be positive and negative depending on the compound they are forming

• Hydrogen tends to have oxidation number of +1