Oxidation

Oxidation is defined as the interaction between [|oxygen] molecules and all the different substances they may contact, from metal to living tissue. Technically, however, with the discovery of electrons, oxidation came to be more precisely defined as the loss of at least one electron when two or more substances interact. Those substances may or may not include oxygen. The opposite of oxidation is reduction — the addition of at least one electron when substances come into contact with each other. Sometimes oxidation is not such a bad thing, as in the formation of super-durable anodized [|aluminum]. Other times, oxidation can be destructive, such as the [|rusting] of an automobile or the spoiling of fresh fruit. When you bite into an apple and let it sit for a little while the inside will begin turning a darker and darker brownish color. This is the result of the apples' tissue oxidizing.

The **oxidation state** is an indicator of the degree of [|oxidation] of an [|atom] in a [|chemical compound] .It is defined as the charge an atom might be imagined to have when electrons are counted according to an agreed-upon set of rules:
 * Oxidation** is the //loss// of [|electrons] or an //increase// in oxidation state by a [|molecule], [|atom] , or [|ion].
 * (1) the oxidation state of a free element (uncombined element) is zero
 * (2) for a simple (monoatomic) ion, the oxidation state is equal to the net charge on the ion (For example, Cl- has an oxidation state of -1)
 * (3) hydrogen has an oxidation state of 1 and oxygen has an oxidation state of −2 when they are present in most compounds. (Exceptions to this are that hydrogen has an oxidation state of −1 in hydrides of active metals, e.g. LiH, and oxygen has an oxidation state of −1 in peroxides, e.g. H 2 O 2 or −1/2 in superoxides, e.g. **KO2**)
 * (4) the algebraic sum of oxidation states of all atoms in a neutral molecule must be zero, while in ions the algebraic sum of the oxidation states of the constituent atoms must be equal to the charge on the ion.

The formal oxidation state is the //hypothetical// [|charge] that an atom would have if all bonds to atoms of different elements were 100% [|ionic]. Oxidation states are typically represented by [|integers], which can be positive, negative, or zero. In some cases, the average oxidation state of an element is a fraction, such as 8/3 for iron in [|magnetite] ( Fe3O 4 ). The highest known oxidation state is +8 in the tetroxides of [|xenon], [|iron] , [|ruthenium] , [|osmium] and [|hassium] , while the lowest known oxidation state is −4 for some elements in the [|carbon group]. 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.