Oxidation Number Rules

The oxidation number will equal the total charge of the compound. Here are the list of rules to remember to figure out the oxidation numbers of certain compounds to discover how they react.

Free Elements (O₂, H₂, S₈, etc.₎

Have an oxidation number of zero. No exceptions.

Monatomic ion (Cu²⁺, Br^-, etc.)

Has an oxidation number equal to its charge, e.g., +2 for Cu2+ and -1 for Br-. No exceptions.

Group 1 alkali metals (Na, K, Fr, etc.)

Have an oxidation number of +1 in all compounds. No exceptions.

Group 2 alkali earth metals (Be, Ca, Ba, etc.)

Have an oxidation number of +2 in all compounds. No exceptions.

Fluorine (F)

Has an oxidation number of -1 in all compounds. No exceptions

Oxygen (O)

Has an oxidation number of -2. Exception: Peroxides e.g.,H₂O₂ where it has an oxidation number of -1.

Hydrogen (H)

Has an oxidation number of +1 in most compounds. Exception: Metal hydrides where it has an oxidation number of -1.

Halogens, group 17 (F, Cl, Br, etc.)

Typically have an oxidation number of -1 in compounds, except when combined with oxygen or another halogen.