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Rules for Oxidation State

Rules for oxidation number:

The oxidation number for uncombined elements is zero and for an ion is the charge of the ion.

The sum of the oxidation numbers is equal to the total charge which is zero in neutral compounds.

The more electronegative element is given a negative oxidation number.

Fluorine is always -1, hydrogen +1 except with a less electronegative element.

Oxygen is -2 except in peroxides where it is -1 and with fluorine where it is positive.

Roman numerals are used for ions with different charges e.g. iron(II) Fe²⁺ and iron (III) Fe³⁺.

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Specification: AQA Chemistry (7404), AS-level, 3.1.7 Oxidation, reduction and redox equations. Topic: Oxidation and Reduction.

Oxidation: The addition of oxygen, the removal of hydrogen, the loss of electrons, or an increase in oxidation number.
Oxidation number: A number that represents the number of electrons an atom has lost or gained, or would do if the compound were fully ionic.