Editing Oxidation state (section)

=== Use in nomenclature ===
When it was realized that some metals form two different binary compounds with the same nonmetal, the two compounds were often distinguished by using the ending ''-ic'' for the higher metal oxidation state and the ending ''-ous'' for the lower. For example, FeCl<sub>3</sub> is [[ferric chloride]] and FeCl<sub>2</sub> is [[ferrous chloride]]. This system is not very satisfactory (although sometimes still used) because different metals have different oxidation states which have to be learned: ferric and ferrous are +3 and +2 respectively, but cupric and cuprous are +2 and +1, and stannic and stannous are +4 and +2. Also, there was no allowance for metals with more than two oxidation states, such as [[vanadium]] with oxidation states +2, +3, +4, and +5.<ref name=Petrucci />{{rp|84}}

This system has been largely replaced by one suggested by [[Alfred Stock]] in 1919<ref>{{cite journal|first=A.|last=Stock|title=Einige Nomenklaturfragen der anorganischen Chemie|trans-title=Some nomenclature issues of inorganic chemistry|journal=Angew. Chem.|volume=32|issue=98|date=1919|pages=373–374|doi=10.1002/ange.19190329802|bibcode=1919AngCh..32..373S|url=https://zenodo.org/record/1424478|access-date=2019-07-01|archive-date=2020-08-06|archive-url=https://web.archive.org/web/20200806044615/https://zenodo.org/record/1424478|url-status=live}}</ref> and adopted<ref name="1940IUPACinorgnom">{{cite journal|first1=W. P.|last1=Jorissen|first2=H.|last2=Bassett|first3=A.|last3=Damiens|first4=F.|last4=Fichter|first5=H.|last5=Rémy|title=Rules for naming inorganic compounds|journal=J. Am. Chem. Soc.|volume=63|date=1941|pages=889–897|doi=10.1021/ja01849a001}}</ref> by [[IUPAC]] in 1940. Thus, FeCl<sub>2</sub> was written as [[iron(II) chloride]] rather than ferrous chloride. The Roman numeral II at the central atom came to be called the "[[Stock nomenclature|Stock number]]" (now an obsolete term), and its value was obtained as a charge at the central atom after removing its ligands along with the [[electron pair]]s they shared with it.<ref name="RedBook2005" />{{rp|147}}