Group (periodic table)

The periodic table of the chemical elements. Columns represent groups

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 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 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]

Groups in the periodic table
Group numbera 1 2 3c 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Mendeleev (I–VIII) I II III IV V VI VII VIII I II III IV V VI VII 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 VIII IB IIB IIIB IVB VB VIB VIIB 0
Trivial name Alkali metals Alkaline earth metals Coin­age metalse Vola­tile metalse Icosa­gense Crys­tallo­gense 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 Hc 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 Lud Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Period 7 Fr Ra Ac–No Lrd Rf Db Sg Bh Hs Mt Ds Rg Cn Uut Fl Uup Lv Uus Uuo
a Current, modern IUPAC group number.
b While not included in Mendeleev's original table, Mendeleev later (1902) 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, lutetium (Lu) and lawrencium (Lr) may be included; lanthanum (La) and actinium (Ac) may be included; the f-block (with 14 lanthanides and 14 actinides) may be included.
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 is in this column, but 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 pnictogens*
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. ↑ 1.0 1.1 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