Group (periodic table)

The periodic table of the chemical elements. The columns represent the groups

In chemistry, a group (also known as a family) is a vertical column in the periodic table of the chemical elements. There are 18 groups in the standard periodic table, including the d-block elements, but excluding the f-block elements.

The explanation of the pattern of the table is that 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 conventional ways of numbering: One using Arabic numerals, and two using Roman numerals. The Roman numeral names are the original traditional names of the groups; the Arabic numeral names are those recommended by the International Union of Pure and Applied Chemistry (IUPAC) to replace the old names in an attempt to reduce the confusion generated by the two older, but mutually confusing, schemes.

There is considerable confusion surrounding the two old systems in use (old IUPAC and CAS) that combined the use of Roman numerals with letters. Both systems agree on the Roman numerals, which indicate (approximately) the highest oxidation number of the elements in that group (and therefore indicates similar chemistry with other elements with the same Roman numeral), which 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 1 valence electron. Therefore, it is located in group 1. Calcium (Ca) is in group 2, for it contains 2 valence electrons. The rules apply differently for groups 3-12.

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 were designated to main group elements (A) and transition elements (B). The old IUPAC system was frequently used in Europe while the CAS was 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, and was later included as part of the 1990 edition of the Nomenclature of Inorganic Chemistry.

Groups

The periodic table groups are as follows:

New IUPAC numbering	Old IUPAC (European)	CAS (American)	Name
Group 1	IA	IA	the alkali metals or lithium family
Group 2	IIA	IIA	the alkaline earth metals or beryllium family
Group 3	IIIA	IIIB	the scandium family (consisting of the rare earth elements plus the actinides)
Group 4	IVA	IVB	the titanium family
Group 5	VA	VB	the vanadium family
Group 6	VIA	VIB	the chromium family
Group 7	VIIA	VIIB	the manganese family
Group 8	VIII	VIIIB	the iron family
Group 9	VIII	VIIIB	the cobalt family
Group 10	VIII	VIIIB	the nickel family
Group 11	IB	IB	the coinage metals (not an IUPAC-recommended name) or copper family
Group 12	IIB	IIB	the zinc family
Group 13	IIIB	IIIA	the triels, boron group or boron family
Group 14	IVB	IVA	the tetrels, carbon group or carbon family
Group 15	VB	VA	the pnictogens or nitrogen family
Group 16	VIB	VIA	the chalcogens or oxygen family
Group 17	VIIB	VIIA	the halogens or fluorine family
Group 18	Group 0	VIIIA	the noble gases or helium family or neon family

References

Background

• Scerri, E. R. The Periodic Table, Its Story and Its Significance, Oxford University Press, 2007. ISBN 978-0-19-530573-9.