Oxidation State Calculator

What Is an Oxidation State? An oxidation state (oxidation number) is a hypothetical charge assigned to an atom in a molecule or ion, assuming all bonds are ionic (electrons assigned to the more electronegative atom). Oxidation states are a bookkeeping tool — not the actual charge.

Rules for Assigning Oxidation States (in priority order)

1. Pure element: always 0 (Na, O₂, Cu, Fe)
2. Monatomic ion: equals the ionic charge (Na⁺ = +1, Cl⁻ = −1, Fe²⁺ = +2)
3. Fluorine: always −1 in compounds
4. Oxygen: almost always −2 (except in peroxides like H₂O₂ where it is −1; and OF₂ where it is +2)
5. Hydrogen: +1 when bonded to nonmetals; −1 when bonded to metals (metal hydrides)
6. Group 1 metals: always +1 in compounds
7. Group 2 metals: always +2 in compounds
8. The sum of all oxidation states = overall charge of the species (0 for molecules, ±n for ions)

Common Oxidation States Transition metals often have multiple: Fe (+2, +3), Cu (+1, +2), Mn (+2, +4, +7) Sulfur: −2, 0, +4, +6 (H₂S, S₈, SO₂, SO₄²⁻) Nitrogen: −3, 0, +1, +2, +3, +4, +5 (NH₃, N₂, N₂O, NO, HNO₂, NO₂, HNO₃) Chlorine: −1, +1, +3, +5, +7

Redox Reactions Oxidation = loss of electrons = increase in oxidation state Reduction = gain of electrons = decrease in oxidation state OIL RIG: Oxidation Is Loss, Reduction Is Gain The species that is oxidized is the reducing agent; the one reduced is the oxidizing agent.

Common Compound Examples H₂O: H = +1, O = −2 | CO₂: C = +4, O = −2 | H₂SO₄: S = +6 KMnO₄: Mn = +7, K = +1, O = −2 | K₂Cr₂O₇: Cr = +6 Na₂O₂ (sodium peroxide): O = −1 | NaH: H = −1