Editing Oxidation state (section)

{{short description|Hypothetical charge of an atom if all its bonds to different atoms were fully ionic}}

In [[chemistry]], the '''oxidation state''', or '''oxidation number''', is the hypothetical [[Electrical charge|charge]] of an atom if all of its [[Chemical bond|bonds]] to other atoms are fully [[Ionic bond|ionic]]. It describes the degree of [[oxidation]] (loss of [[electron]]s) of an [[atom]] in a [[chemical compound]]. Conceptually, the oxidation state may be positive, negative or zero. Beside nearly-pure [[ionic bonding]], many [[covalent bond]]s 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 [[ionization energy]] 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 [[Electronegativities of the elements (data page)|the choice]] of [[electronegativity]] 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 [[inorganic compound]]s. Also, several observations regarding chemical reactions may be explained at a basic level in terms of oxidation states.

Oxidation states are typically represented by [[integer]]s which may be positive, zero, or negative. In some cases, the average oxidation state of an element is a fraction, such as {{sfrac|8|3}} for [[iron]] in [[magnetite]] {{chem2|Fe3O4}} ([[#Fractional oxidation states|see below]]). The highest known oxidation state is reported to be +9, displayed by [[iridium]] in the [[iridium tetroxide|tetroxoiridium(IX)]] cation ({{chem2|IrO4+}}).<ref>{{cite journal|first1=G.|last1=Wang|first2=M.|last2=Zhou|first3=G. T.|last3=Goettel|first4=G. J.|last4=Schrobilgen|first5=J.|last5=Su|first6=J.|last6=Li|first7=T.|last7=Schlöder|first8=S.|last8=Riedel|title=Identification of an iridium-containing compound with a formal oxidation state of IX|journal=Nature|volume=514|issue=7523|date=2014|pages=475–477|doi=10.1038/nature13795|pmid=25341786|bibcode=2014Natur.514..475W|s2cid=4463905}}</ref> It is predicted that even a +10 oxidation state may be achieved by [[platinum]] in tetroxoplatinum(X), {{chem2|PtO4(2+)}}.<ref>{{cite journal |last1=Yu |first1=Haoyu S. |last2=Truhlar |first2=Donald G. |date=2016 |title=Oxidation State 10 Exists |url= |journal=Angewandte Chemie International Edition |volume=55 |issue=31 |pages=9004–9006 |doi=10.1002/anie.201604670 |pmid=27273799 |access-date=|doi-access=free }}</ref> The lowest oxidation state is −5, as for [[boron]] in {{chem2|Al3BC}}<ref>{{citation |last=Schroeder |first=Melanie |title=Eigenschaften von borreichen Boriden und Scandium-Aluminium-Oxid-Carbiden |url=https://d-nb.info/995006210/34 |page=139 |access-date=2020-02-24 |archive-url=https://web.archive.org/web/20200806021428/https://d-nb.info/995006210/34 |url-status=live |language=de |archive-date=2020-08-06}}</ref> and [[gallium]] in [[pentamagnesium digallide]] ({{chem2|Mg5Ga2}}).

In [[Stock nomenclature]], which is commonly used for inorganic compounds, the oxidation state is represented by a [[Roman numeral]] placed after the element name inside parentheses or as a superscript after the element symbol, e.g. [[Iron(III) oxide]]. The term ''oxidation'' was first used by [[Antoine Lavoisier]] to signify the reaction of a substance with [[oxygen]]. Much later, it was realized that the substance, upon being oxidized, loses electrons, and the meaning was extended to include other [[Chemical reaction|reactions]] 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 [[redox|reduction]]. 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.