Oxidation state

In <a href="/facts/Chemistry/SrNqkGVm">chemistry</a>, the oxidation state, or oxidation number, is the hypothetical <a href="/facts/Electrical_charge/xxsBfmlB">charge</a> of an atom if all of its <a href="/facts/Chemical_bond/ArNUMnIB">bonds</a> to other atoms are fully <a href="/facts/Ionic_bond/R6nUJI5u">ionic</a>. It describes the degree of <a href="/facts/Oxidation/Pyd5RVcj">oxidation</a> (loss of <a href="/facts/Electron/L0KBo5cW">electrons</a>) of an <a href="/facts/Atom/FoQ4kGN5">atom</a> in a <a href="/facts/Chemical_compound/37FXqqtv">chemical compound</a>. Conceptually, the oxidation state may be positive, negative or zero. Beside nearly-pure <a href="/facts/Ionic_bonding/R6nUJI5u">ionic bonding</a>, many <a href="/facts/Covalent_bond/EzMLf3Pz">covalent bonds</a> exhibit a strong ionicity, making oxidation state a useful predictor of charge.
The oxidation state of an atom does not represent the "real" charge on that atom, or any other actual atomic property. This is particularly true of high oxidation states, where the <a href="/facts/Ionization_energy/lezUajfA">ionization energy</a> required to produce a multiply positive ion is far greater than the energies available in chemical reactions. Additionally, the oxidation states of atoms in a given compound may vary depending on <a href="/facts/Electronegativities_of_the_elements_(data_page)/BBURTWVu">the choice</a> of <a href="/facts/Electronegativity/H7Vq7Uah">electronegativity</a> scale used in their calculation. Thus, the oxidation state of an atom in a compound is purely a formalism. It is nevertheless important in understanding the nomenclature conventions of <a href="/facts/Inorganic_compound/TfFfzxSz">inorganic compounds</a>. Also, several observations regarding chemical reactions may be explained at a basic level in terms of oxidation states.
Oxidation states are typically represented by <a href="/facts/Integer/PUwwrawx">integers</a> which may be positive, zero, or negative. In some cases, the average oxidation state of an element is a fraction, such as ⁠8/3⁠ for <a href="/facts/Iron/QK1JYy8E">iron</a> in <a href="/facts/Magnetite/SVxoGUs2">magnetite</a> Fe3O4 (see below). The highest known oxidation state is reported to be +9, displayed by <a href="/facts/Iridium/TFQutoj1">iridium</a> in the <a href="/facts/Iridium_tetroxide/MhF4I3y0">tetroxoiridium(IX)</a> cation (IrO+4). It is predicted that even a +10 oxidation state may be achieved by <a href="/facts/Platinum/qJC6lQf7">platinum</a> in tetroxoplatinum(X), PtO2+4. The lowest oxidation state is −5, as for <a href="/facts/Boron/Pmwgd7Mf">boron</a> in Al3BC and <a href="/facts/Gallium/EucevDs9">gallium</a> in <a href="/facts/Pentamagnesium_digallide/E6GbV4nw">pentamagnesium digallide</a> (Mg5Ga2).
In <a href="/facts/Stock_nomenclature/FbrV1lmQ">Stock nomenclature</a>, which is commonly used for inorganic compounds, the oxidation state is represented by a <a href="/facts/Roman_numeral/7BA8nn78">Roman numeral</a> placed after the element name inside parentheses or as a superscript after the element symbol, e.g. <a href="/facts/Iron(III)_oxide/vam0XoC5">Iron(III) oxide</a>.
The term oxidation was first used by <a href="/facts/Antoine_Lavoisier/UheVQrhu">Antoine Lavoisier</a> to signify the reaction of a substance with <a href="/facts/Oxygen/acyn6o8r">oxygen</a>. Much later, it was realized that the substance, upon being oxidized, loses electrons, and the meaning was extended to include other <a href="/facts/Chemical_reaction/GpqWlKrz">reactions</a> in which electrons are lost, regardless of whether oxygen was involved.
The increase in the oxidation state of an atom, through a chemical reaction, is known as oxidation; a decrease in oxidation state is known as a <a href="/facts/Redox/Pyd5RVcj">reduction</a>. Such reactions involve the formal transfer of electrons: a net gain in electrons being a reduction, and a net loss of electrons being oxidation. For pure elements, the oxidation state is zero.

Oxidation state open-in-new

Oxidation state