Oxidation States: A Complete Guide

What is an oxidation state?

An oxidation state (or oxidation number) is a hypothetical charge that an atom acquires when all its bonds are considered ionic. It's a bookkeeping tool that allows us to track electron transfer in oxidation-reduction (redox) reactions.

Rules for assigning oxidation states

1. The oxidation state of an element in its elemental form is 0.
   Examples: Fe, O₂, Cl₂ → all have state = 0.

2. For monatomic ions, the oxidation state equals the charge of the ion.
   Example: Na⁺ → +1, Cl⁻ → −1.

3. Oxygen almost always has state −2, except:

   • In peroxides (H₂O₂): −1
   • In OF₂: +2

4. Hydrogen has state +1 in compounds with non-metals and −1 in metal hydrides.

5. The sum of oxidation states in a neutral molecule equals 0.

Example: potassium permanganate (KMnO₄)

We know:

• K = +1 (rule 2)
• O = −2 × 4 = −8 (rule 3)

Therefore: +1 + Mn + (−8) = 0 → Mn = +7

Importance in chemistry

Oxidation states are fundamental for:

• Balancing redox reactions using the ion-electron method.
• Identifying oxidizing and reducing agents.
• Systematic nomenclature of compounds (e.g., FeCl₂ = iron(II) chloride).

Explore molecules and their oxidation states in our ChemModel Studio.