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Periodic table group

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Periodic table group

In chemistry, a group (also known as a family) is a column of elements in the periodic table of the chemical elements. There are 18 numbered groups in the standard periodic table, including the d-block elements, but excluding the f-block elements. The elements in a group have similar physical or chemical characteristic of the outermost electron shells of their atoms (i.e., the same core charge), as most chemical properties are dominated by the orbital location of the outermost electron. There are three systems of group numbering. The modern numbering group 1 to group 18 is recommended by the International Union of Pure and Applied Chemistry (IUPAC). It replaces two older naming schemes that were mutually confusing. Also, groups may be identified by their topmost element, like oxygen group (group 16) and some groups have a specific name, like chalcogen (group 16).

CAS and old IUPAC numbering

Two earlier group number systems exist: CAS and old IUPAC. Both use numerals (Arabic or 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. The rules apply differently for transition metals.

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,[1] and was later included as part of the 1990 edition of the Nomenclature of Inorganic Chemistry.[2]

Group names

The periodic table groups are as follows:[1][3] Template:Periodic table (group names)

New IUPAC numbering CAS (American) Old IUPAC (European) Name by element Specific name note
Group 1 IA IA lithium family alkali metals Hydrogen is in this column, but not considered to be an alkali metal
Group 2 IIA IIA beryllium family alkaline earth metals
Group 3 IIIB IIIA scandium family Consisting of rare earth elements plus actinides
Group 4 IVB IVA titanium family
Group 5 VB VA vanadium family
Group 6 VIB VIA chromium family
Group 7 VIIB VIIA manganese family
Group 8 VIIIB VIII iron family
Group 9 VIIIB VIII cobalt family
Group 10 VIIIB VIII nickel family
Group 11 IB IB copper family coinage metals The name coinage metals is not IUPAC-recommended
Group 12 IIB IIB zinc family volatile metals The name volatile metals is not IUPAC-recommended
Group 13 IIIA IIIB boron family triels, icosagens triels from Greek tri (three, III), the name icosagens is not IUPAC-recommended
Group 14 IVA IVB carbon family tetrels, crystallogens tetrels from Greek tetra (four, IV), the name crystallogens is not IUPAC-recommended
Group 15 VA VB nitrogen family pnictogens
Group 16 VIA VIB oxygen family chalcogens
Group 17 VIIA VIIB fluorine family halogens
Group 18 VIIIA Group 0 helium family or neon family noble gases, aerogens

References

Further reading

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