Group (periodic table)

In the periodic table of the elements, each numbered column is a 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 periodic table, but the f-block columns (between groups 2 and 3) are not numbered. The elements in a group have similar physical or chemical characteristics 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 or have a specific name. For example, group 16 is variously described as oxygen group and chalcogen.

CAS and old IUPAC numbering

Two earlier group number systems exist: CAS (Chemical Abstracts Service) 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.

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

In history, several sets of group names have been used:^[1][3]

Group names in the Periodic table
Group number^a		1	2		3^d	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18
Mendeleev (I–VIII)		IA	IIA		IIIB	IVB	VB	VIB	VIIB	VIIIB			IB	IIB	IIIB	IVB	VB	VIB	VIIB	^b
CAS (US, pattern A-B-A)		IA	IIA		IIIB	IVB	VB	VIB	VIIB	VIIIB			IB	IIB	IIIA	IVA	VA	VIA	VIIA	VIIIA
old IUPAC (Europe, pattern A-B)		IA	IIA		IIIA	IVA	VA	VIA	VIIA	VIIIB			IB	IIB	IIIB	IVB	VB	VIB	VIIB	0
Trivial name		Alkali metals	Alkaline earth metals										Coin­age metals^e	Vola­tile metals^e	Icosa­gens^e	Crys­tallo­gens^e	Pnicto­gens	Chal­co­gens	Halo­gens	Noble gases
Name by element		Lith­ium group	Beryl­lium group		Scan­dium group	Titan­ium group	Vana­dium group	Chro­mium group	Man­ga­nese group	Iron group	Co­balt group	Nickel group	Cop­per group	Zinc group	Boron group	Car­bon group	Nitro­gen group	Oxy­gen group	Fluor­ine group	Helium or Neon group
Period 1		H^c																		He
Period 2		Li	Be												B	C	N	O	F	Ne
Period 3		Na	Mg												Al	Si	P	S	Cl	Ar
Period 4		K	Ca		Sc	Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn	Ga	Ge	As	Se	Br	Kr
Period 5		Rb	Sr	^d	Y	Zr	Nb	Mo	Tc	Ru	Rh	Pd	Ag	Cd	In	Sn	Sb	Te	I	Xe
Period 6		Cs	Ba	La–Yb	Lu^d	Hf	Ta	W	Re	Os	Ir	Pt	Au	Hg	Tl	Pb	Bi	Po	At	Rn
Period 7		Fr	Ra	Ac–No	Lr^d	Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg	Cn	Nh	Fl	Mc	Lv	Ts	Og
^a Current, modern IUPAC group number.
^b The noble gases had not yet been discovered at the time of Mendeleev's original table. Later (1902), Mendeleev accepted the evidence for the existence of the noble gases, and placed them in a separate "group 0".
^c Hydrogen (H), while placed in column 1, is not considered to be in the group alkali metals.
^d Group 3: Depending on the source, the entries below scandium and yttrium in this group include lutetium (Lu) and lawrencium (Lr), or lanthanum (La) and actinium (Ac), or the whole set of 15 lanthanides and 15 actinides. IUPAC has initiated a project to choose between the first two possibilities, so that the recommended definition of Group 3 will be either (1) the elements Sc, Y, Lu and Lr, or (2) the elements Sc, Y, La and Ac.The constitution of group 3 of the periodic table:
^e This group name is not recommended by IUPAC.

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

References

1. Fluck, E. (1988). "New Notations in the Periodic Table" (PDF). Pure Appl. Chem. IUPAC. 60 (3): 431–436. doi:10.1351/pac198860030431. Retrieved 24 March 2012.
2. Leigh, G. J. Nomenclature of Inorganic Chemistry: Recommendations 1990. Blackwell Science, 1990. ISBN 0-632-02494-1.
3. IUPAC (2005). "Nomenclature of inorganic chemistry" (PDF).

Further reading

• Scerri, E. R. (2007). The periodic table, its story and its significance. Oxford University Press. ISBN 978-0-19-530573-9.