What is "oxidation state"

n. (context chemistry English) the state of an atom having a particular oxidation number

n. the degree of oxidation of an atom or ion or molecule; for simple atoms or ions the oxidation number is equal to the ionic charge; "the oxidation number of hydrogen is +1 and of oxygen is -2" [syn: oxidation number]

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 hypothetical charge 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 for iron in magnetite . The highest known oxidation state is reported to be +9 in the iridium tetroxide cation , while the lowest known oxidation state is −5 for boron, gallium, indium, and thallium in various Zintl phases, a type of intermetallic compound. It is predicted that even a +10 oxidation state may be achieveable by platinum in the platinum tetroxide dication .

The increase in oxidation state of an atom, through a chemical reaction, is known as an oxidation; a decrease in oxidation state is known as a reduction. Such reactions involve the formal transfer of electrons: a net gain in electrons being a reduction, and a net loss of electrons being an oxidation. For pure elements, the oxidation state is zero.

There are various methods for determining oxidation states.

In inorganic nomenclature, the oxidation state is determined and expressed as an oxidation number, and is represented by a Roman numeral placed after the element name.

In coordination chemistry, "oxidation number" is defined differently from "oxidation state".