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Group (periodic table)

Column of elements in the periodic table of the chemical elements

Science Chemistry Basics Principles Periodic table

In chemistry, a group or family is a vertical column in the periodic table of the chemical elements, consisting of elements with similar outermost electron shell configurations and chemical properties. There are 18 numbered groups, as defined by the IUPAC, based on electron arrangements beyond noble gases. Although older naming systems by the Chemical Abstract Service differ, the modern 1–18 system is widely accepted. Groups may be named after their top element or common traits; for example, group 16 is the “oxygen group” or chalcogens. The “iron group” typically refers to group 8 elements like iron, cobalt, and nickel. Some debates remain about elements like hydrogen and helium.

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Group names

Modern group names are numbers 1–18, with the 14 f-block columns remaining unnumbered (together making the 32 columns in the periodic table). Also, trivial names (like halogens) are common. In history, several sets of group names have been used, based on Roman numberings I–VIII, and "A" and "B" suffixes.² ³

Groups in the periodic table

IUPAC group	1a	2	—b	3c	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	d
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 namer	H and alkali metals	alkaline earth metals												triels	tetrels	pnictogens	chalcogens	halogens	noble gases
Name by elementr	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 is not a metal, though it is more analogous to them than any other group. This makes the group somewhat exceptional.b The 14 f-block groups (columns) do not have a group number.c The correct composition of group 3 is scandium (Sc), yttrium (Y), lutetium (Lu), and lawrencium (Lr), as shown here: this is endorsed by 1988⁴ and 2021⁵ IUPAC reports on the question. General inorganic chemistry texts often put scandium (Sc), yttrium (Y), lanthanum (La), and actinium (Ac) in group 3, so that Ce–Lu and Th–Lr become the f-block between groups 3 and 4; this was based on incorrectly measured electron configurations from history,⁶ and Lev Landau and Evgeny Lifshitz already considered it incorrect in 1948.⁷ Arguments can still occasionally be encountered in the contemporary literature purporting to defend it, but most authors consider them logically inconsistent.⁸ ⁹ ¹⁰ Some sources follow a compromise that puts La–Lu and Ac–Lr as the f-block rows (despite that giving 15 f-block elements in each row, which contradicts quantum mechanics), leaving the heavier members of group 3 ambiguous.¹¹ See also Group 3 element#Composition.d 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.

List of group names

IUPACname	OldIUPAC(Europe)	Old CASname(U.S.)	Nameby element('group' or 'family')	IUPACrecommendedtrivial name	Other names
Group 1	IA	IA	lithium group	hydrogen and alkali metals	"lithium group" excludes hydrogen
Group 2	IIA	IIA	beryllium group	alkaline earth metals
Group 3	IIIA	IIIB	scandium group
Group 4	IVA	IVB	titanium group
Group 5	VA	VB	vanadium group
Group 6	VIA	VIB	chromium group
Group 7	VIIA	VIIB	manganese group
Group 8	VIII	VIIIB	iron group
Group 9	VIII	VIIIB	cobalt group
Group 10	VIII	VIIIB	nickel group
Group 11	IB	IB	copper group		Sometimes called coinage metals,but the set is arbitraryf
Group 12	IIB	IIB	zinc group		volatile metals¹²
Group 13	IIIB	IIIA	boron group	trielsb	icosagens¹³earth metals
Group 14	IVB	IVA	carbon group	tetrelsc	crystallogens¹⁴adamantogens¹⁵merylides¹⁶
Group 15	VB	VA	nitrogen group	pnictogenspentelsn
Group 16	VIB	VIA	oxygen group	chalcogens
Group 17	VIIB	VIIA	fluorine group	halogens
Group 18	0	VIIIA	helium groupor neon group	noble gases	aerogens¹⁷

^f Coinage metals: authors differ on whether roentgenium (Rg) is considered a coinage metal. It is in group 11, like the other coinage metals, and is expected to be chemically similar to gold.¹⁸ On the other hand, being extremely radioactive and short-lived, it cannot actually be used for coinage as the name suggests, and on that basis it is sometimes excluded.¹⁹ ^b triels (group 13), from Greek tri: three, III²⁰ ²¹ ^c tetrels (group 14), from Greek tetra: four, IV²² ²³ ^n pentel (group 15), from Greek penta: five, V²⁴

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,²⁵ and was later included as part of the 1990 edition of the Nomenclature of Inorganic Chemistry.²⁶

Non-columnwise groups

While groups are defined to be columns in the periodic table, as described above, there are also sets of elements named "group" that are not a column:

Group names

List of group names

CAS and old IUPAC numbering (A/B)

Non-columnwise groups

Further reading

References