Oxidation Number (Oxidation State) Guide

Determine the oxidation state of elements in common ionic and covalent compounds.

How It Works

Select a common compound or ion from the list to see the oxidation number of each element. The rules-based approach applies standard oxidation state rules: free elements = 0, oxygen = -2 (except peroxides), hydrogen = +1 (except metal hydrides), and the algebraic sum equals the compound charge.

Formula

Sum of oxidation numbers in neutral compound = 0 | In polyatomic ion = charge

Examples

H2O: H = +1, O = -2 | NaCl: Na = +1, Cl = -1 | Fe2O3: Fe = +3 | KMnO4: Mn = +7

Frequently Asked Questions

What are oxidation numbers?

Oxidation numbers (oxidation states) are assigned charges that track electron transfer in redox reactions. They help identify which atoms are oxidized (lose electrons) and which are reduced (gain electrons).

What are the rules for assigning oxidation numbers?

Key rules: (1) Free elements = 0. (2) Monoatomic ions = their charge. (3) O = -2 (except -1 in peroxides). (4) H = +1 (except -1 in metal hydrides). (5) Sum = compound charge.

What is the oxidation number of Mn in KMnO4?

K = +1, each O = -2 (4 O = -8). Sum = 0: +1 + Mn + (-8) = 0, so Mn = +7.