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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 on 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 (). 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. The possibility of +9 and +10 oxidation states in platinum group elements, especially iridium(IX) and platinum(X), has been discussed by Kiselev and Tretiyakov.〔Kiselev, Yurii M. and Tretiyakov, Yurii D. (1999), ''Russian Chemical Reviews'', 68, 365-379 "The problem of oxidation state stabilisation and some regularities of a Periodic system of the elements" ()〕 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/numbers. In inorganic nomenclature the oxidation state is determined and expressed as an oxidation number represented by a Roman numeral placed after the element name. In coordination chemistry, oxidation number is defined differently from oxidation state. ==IUPAC definitions of oxidation state and oxidation number== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Oxidation state」の詳細全文を読む スポンサード リンク
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