What is an oxidation state?

An oxidation state is the hypothetical charge an atom would have if all its bonds were fully ionic. It tracks how many electrons an atom has gained or lost in a compound, which is essential for balancing redox reactions and naming compounds.

Why do transition metals have many oxidation states?

Transition metals have closely spaced d and s electrons that can be removed in varying numbers without much energy difference. This lets elements like iron, manganese, and chromium form stable compounds across several oxidation states, giving rich, colorful chemistry.

What oxidation state does oxygen usually have?

Oxygen is almost always minus 2, the value to assume unless told otherwise. Exceptions include peroxides such as hydrogen peroxide where it is minus 1, superoxides at minus one half, and the rare compound OF2 where oxygen is plus 2.

How do I find an unknown oxidation state in a compound?

Assign known states (group 1 is plus 1, group 2 is plus 2, oxygen minus 2, hydrogen plus 1) and set the algebraic sum equal to the overall charge. Solve for the unknown. For example in SO4 two-minus, sulfur works out to plus 6.

Are oxidation states the same as ionic charge?

Not always. For simple ions like Na plus they match, but oxidation state is a bookkeeping device that applies even to covalent bonds where no real ions exist. It is a formalism for counting electrons, not a literal measured charge.

Common Oxidation States Reference

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Oxidation states track how many electrons an atom has effectively gained or lost in a compound. This reference lists the common and notable oxidation states for elements across the periodic table, with the principal state highlighted and an example compound for each.

How it works

The oxidation state is assigned by treating every bond as if it were fully ionic — the more electronegative atom “takes” the shared electrons. A few rules make most assignments quick:

Free elements are 0 (e.g. O₂, Fe metal).
Group 1 metals are always +1; group 2 are +2.
Oxygen is usually −2; hydrogen is usually +1.
The sum of oxidation states equals the overall charge of the species.

For an unknown element in a compound, apply the known states and solve. In SO₄²⁻, oxygen contributes 4 × (−2) = −8, so sulfur must be +6 for the ion to total −2.

Tips and example

Transition metals show several states; the highlighted one is the most common.
The maximum oxidation state of a main-group element often equals its group number (e.g. sulfur reaches +6).
Use the example compound shown to anchor each element in its typical state.