hapetusnumeron

The hapetusnumeron is a term used in chemistry to refer to the oxidation number of an atom within a chemical species. It is a formal bookkeeping value assigned to atoms to describe the degree of oxidation or reduction during chemical reactions.

Definition and rules: The hapetusnumeron is an integer assigned to each atom according to conventional rules: in a neutral compound, the sum of all hapetusnumeron values is zero; in a polyatomic ion, the sum equals the ion’s charge. An atom in its elemental form has hapetusnumeron zero. In bonds between atoms of different electronegativity, electrons are assigned to the more electronegative atom. Hydrogen is usually +1 (−1 in metal hydrides), oxygen normally −2 (−1 in peroxides, +2 in OF2). The hapetusnumeron values depend on the chosen reference and do not imply full formal charge or actual electron ownership.

Examples: In NaCl, sodium has hapetusnumeron +1 and chlorine −1. In H2O, hydrogen is +1 and oxygen −2. In the permanganate ion, MnO4−, manganese has +7 and each oxygen −2.

Use and limitations: Hapetusnumeron are used for balancing redox reactions, determining electron transfer, and analyzing reaction mechanisms. It is a useful abstraction, and while the hapetusnumeron is typically an integer, fractional values can arise in systems with delocalized electrons or mixed valence.

History: The concept developed in the 19th and early 20th centuries as chemists established a standardized method to describe oxidation and reduction.

See also: oxidation number, oxidation state, redox reaction, formal charge.