Group (periodic table)

In chemistry, a group (also known as a family[1]) is a column of elements in the periodic table of the chemical elements. There are 18 numbered groups in the periodic table; 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), because most chemical properties are dominated by the orbital location of the outermost electron.

In the periodic table of the elements, each numbered column is a group.

There are three systems of group numbering for the groups; the same number may be assigned to different groups depending on the system being used. The modern numbering system of "group 1" to "group 18" has been recommended by the International Union of Pure and Applied Chemistry (IUPAC) since about 1990. It replaces two older incompatible naming schemes, used by the Chemical Abstract Service (CAS, more popular in the US), and by IUPAC before 1990 (more popular in Europe). The system of eighteen groups is generally accepted by the chemistry community, but some dissent exists about membership of several elements. Disagreements mostly involve elements number 1 and 2 (hydrogen and helium), as well as inner transition metals.

Groups may also be identified using their topmost element, or have a specific name. For example, group 16 is also described as the "oxygen group" and as the "chalcogens". An exception is the "iron group", which usually refers to "group 8", but in chemistry may also mean iron, cobalt, and nickel, or some other set of elements with similar chemical properties. In astrophysics and nuclear physics, it usually refers to iron, cobalt, nickel, chromium, and manganese.

Group names

In history, several sets of group names have been used:[2][3]

Groups in the Periodic table

IUPAC group	1^a	2	n/a	3	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, A-B-A)	IA	IIA		IIIB	IVB	VB	VIB	VIIB	VIIIB			IB	IIB	IIIA	IVA	VA	VIA	VIIA	VIIIA
old IUPAC (Europe, A-B)	IA	IIA		IIIA	IVA	VA	VIA	VIIA	VIIIB			IB	IIB	IIIB	IVB	VB	VIB	VIIB	0
Trivial name	H and Alkali metals^r	Alkaline earth metals^r										Coin­age metals		Triels	Tetrels	Pnicto­gens^r	Chal­co­gens^r	Halo­gens^r	Noble gases^r
Name by element^r	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																		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		Y	Zr	Nb	Mo	Tc	Ru	Rh	Pd	Ag	Cd	In	Sn	Sb	Te	I	Xe
Period 6	Cs	Ba	La–Yb	Lu	Hf	Ta	W	Re	Os	Ir	Pt	Au	Hg	Tl	Pb	Bi	Po	At	Rn
Period 7	Fr	Ra	Ac–No	Lr	Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg	Cn	Nh	Fl	Mc	Lv	Ts	Og

^a Group 1 is composed of hydrogen (H) and the alkali metals. Elements of the group have one s-electron in the outer electron shell. Hydrogen is not considered to be an alkali metal as it rarely exhibits behaviour comparable to theirs, though it is more analogous to them than any other group. This makes the group somewhat exceptional.
^n/a Do not have a group number
^b Group 18, the noble gases, were not discovered at the time of Mendeleev's original table. Later (1902), Mendeleev accepted the evidence for their existence, and they could be placed in a new "group 0", consistently and without breaking the periodic table principle.
^r Group name as recommended by IUPAC.

New IUPAC name	Old IUPAC (Europe)	CAS name (U.S.)	Name by element	IUPAC recommended trivial name	Other trivial name
Group 1	IA	IA	lithium family	hydrogen and alkali metals*
Group 2	IIA	IIA	beryllium family	alkaline earth metals*
Group 3	IIIA	IIIB	scandium family
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
Group 13	IIIB	IIIA	boron family		triels from Greek tri (three, III)[4][5]
Group 14	IVB	IVA	carbon family		tetrels from Greek tetra (four, IV)[4][5]
Group 15	VB	VA	nitrogen family	pnictogens*	pentels from Greek penta (five, V)[5]
Group 16	VIB	VIA	oxygen family	chalcogens*
Group 17	VIIB	VIIA	fluorine family	halogens*
Group 18	0	VIIIA	helium family or neon family	noble gases*

Some other names have been proposed and used without gaining wide acceptance: "volatile metals" for group 12;[6] "icosagens" for group 13;[7] "crystallogens",[4] "adamantogens",[8] and "merylides" for group 14; and "aerogens" for group 18.[5]

CAS and old IUPAC numbering (A/B)

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,[2] and was later included as part of the 1990 edition of the Nomenclature of Inorganic Chemistry.[9]

See also

• Period (periodic table)

References

1. "The Periodic Table Terms". www.shmoop.com. Retrieved 2018-09-15.
2. Fluck, E. (1988). "New Notations in the Periodic Table" (PDF). Pure Appl. Chem. IUPAC. 60 (3): 431–436. doi:10.1351/pac198860030431. S2CID 96704008. Retrieved 24 March 2012.
3. IUPAC (2005). "Nomenclature of inorganic chemistry" (PDF).
4. Liu, Ning; Lu, Na; Su, Yan; Wang, Pu; Quan, Xie (2019). "Fabrication of g-C₃N₄/Ti₃C₂ composite and its visible-light photocatalytic capability for ciprofloxacin degradation". Separation and Purification Technology. 211: 782–789. doi:10.1016/j.seppur.2018.10.027. Retrieved 17 August 2019.
5. Rich, Ronald (2007). Inorganic Reactions in Water. Springer. pp. 307, 327, 363, 475. doi:10.1007/978-3-540-73962-3. ISBN 9783540739616.
6. https://glosbe.com/en/en/volatile%20metal
7. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 227. ISBN 978-0-08-037941-8.
8. W. B. Jensen, The Periodic Law and Table
9. Leigh, G. J. Nomenclature of Inorganic Chemistry: Recommendations 1990. Blackwell Science, 1990. ISBN 0-632-02494-1.

Further reading

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

See also