Editing Group (periodic table) (section)

==CAS and old IUPAC numbering (A/B)==
<span id="CAS and old IUPAC"></span>Two earlier group number systems exist: ''CAS'' ([[Chemical Abstracts Service]]) and ''old IUPAC''. Both use [[Numerical digit|numeral]]s ([[Arabic numerals|Arabic]] or [[Roman numbers|Roman]]) and letters ''A'' and ''B''. Both systems agree on the numbers. The numbers indicate approximately the highest oxidation number of the elements in that group, and so indicate similar chemistry with other elements with the same numeral. The number proceeds in a linearly increasing fashion for the most part, once on the left of the table, and once on the right (see [[List of oxidation states of the elements]]), with some irregularities in the transition metals. However, the two systems use the letters differently. For example, potassium (K) has one [[valence electron]]. Therefore, it is located in group 1. Calcium (Ca) is in group 2, for it contains two valence electrons.

In the old IUPAC system the letters A and B were designated to the left (A) and right (B) part of the table, while in the CAS system the letters A and B are designated to [[main group]] elements (A) and transition elements (B). The old IUPAC system was frequently used in Europe, while the CAS is most common in America. The new IUPAC scheme was developed to replace both systems as they confusingly used the same names to mean different things. The new system simply numbers the groups increasingly from left to right on the standard periodic table. The IUPAC proposal was first circulated in 1985 for public comments,<ref name="Fluck 1988">{{cite journal |last1=Fluck |first1=E. |year=1988 |title=New Notations in the Periodic Table |journal=[[Pure and Applied Chemistry|Pure Appl. Chem.]] |volume=60 |pages=431–436 |publisher=[[International Union of Pure and Applied Chemistry|IUPAC]] |doi=10.1351/pac198860030431 |url=http://www.iupac.org/publications/pac/1988/pdf/6003x0431.pdf |access-date=24 March 2012 |issue=3 |s2cid=96704008 }}</ref> and was later included as part of the 1990 edition of the ''Nomenclature of Inorganic Chemistry''.<ref>Leigh, G. J. ''Nomenclature of Inorganic Chemistry: Recommendations 1990''. Blackwell Science, '''1990'''. {{ISBN|0-632-02494-1}}.</ref>