The oxidation state, often called the oxidation number, is an indicator of the degree of oxidation (loss of electrons) of an atom in a chemical compound. Conceptually, the oxidation state, which may be positive, negative or zero, is the hypotheticalcharge that an atom would have if all bonds to atoms of different elements were 100% ionic, with no covalent component. This is never exactly true for real bonds.
The term "oxidation" was first used by Lavoisier to mean reaction of a substance with oxygen. Much later, it was realized that the substance, upon being oxidized, loses electrons, and the use of the term "oxidation" was extended to include other reactions in which electrons are lost.
Oxidation states are typically represented by integers. In some cases, the average oxidation state of an element is a fraction, such as 8/3 for iron in magnetite (Fe 3O 4). The highest known oxidation state is reported to be +9 in the iridium tetroxide cation (IrO+ 4), while the lowest known oxidation state is −5 for boron, gallium, indium, and thallium in various intermetallic compounds. The possibility of +10 oxidation states in platinum group elements, especially platinum(X), has been discussed by Kiselev and Tretiyakov.