oksüdatsiooniastme

Oksüdatsiooniastme (oxidation state) is a concept in chemistry used to track the hypothetical charge an atom would have if all its bonds to different atoms were purely ionic. It is a bookkeeping tool that helps chemists understand redox reactions, where electrons are transferred between species. The oxidation state of an atom in a molecule or ion is assigned based on a set of rules, though some exceptions exist.

Elemental substances, like O2 or Fe, have an oxidation state of 0 for each atom. In compounds, oxygen usually has an oxidation state of -2, except in peroxides where it is -1 and when bonded to fluorine where it is positive. Hydrogen typically has an oxidation state of +1 when bonded to nonmetals and -1 when bonded to metals. Fluorine always has an oxidation state of -1 in compounds. The sum of the oxidation states of all atoms in a neutral compound equals zero. For a polyatomic ion, the sum of the oxidation states equals the charge of the ion. Changes in oxidation states during a reaction indicate that a redox process has occurred. An increase in oxidation state signifies oxidation, while a decrease signifies reduction.