OxidationsstufenErhöhung

Oxidationsstufe, known in English as oxidation state, is a formal bookkeeping tool used in chemistry to describe the oxidation level of an atom within a molecule or ion. The oxidation number assigned to each atom is a notional charge the atom would have if all bonds were completely ionic and the overall structure were ionically composed. The sum of oxidation numbers in a neutral substance is zero; in a polyatomic ion it equals the ion’s charge.

Assignments follow general rules with common exceptions. An element in its free, elemental form has oxidation number zero. A monoatomic ion carries the charge of the ion. Oxygen is typically −2, with exceptions such as peroxides (−1) and OF2 (oxygen +2). Hydrogen is usually +1 when bonded to nonmetals; in metal hydrides it is −1. Fluorine is always −1 in compounds; other halogens are often −1 unless bonded to more electronegative elements. The oxidation numbers of all atoms in a molecule or ion must sum to the molecule’s or ion’s overall charge.

Oxidation states are a useful accounting device for redox chemistry, helping to balance redox equations, identify electron transfer, and describe trends in oxidation behavior, especially for transition metals that exhibit variable oxidation states. It is important to remember that oxidation numbers are formal charges and do not necessarily correspond to actual charges on atoms in covalent bonds.

In German-language chemistry, the term Oxidationsstufe is used synonymously with oxidation state or oxidation number.