Elements → have an oxidation number of 0

Certain elements, when present in compounds, have common oxidation numbers. Group one metals are always +1, group 2 metals are always +2.

Hydrogen has an oxidation number of +1, except in metal hydrides where it becomes -1, eg. LiH

Oxygen has an oxidation number of -2, except when in peroxide (H2O2), where it is -1.

For monoatomic ions, the oxidation number is equal to the charge of the ion

For polyatomic ions, the sum of oxidation numbers is equivalent to the total charge of the ion

In a neutral compound, the sum of oxidation numbers is equal to 0

The most electronegative element has a negative oxidation number.