Chemistry:Group (periodic table)

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Short description: Column of elements in the periodic table of the chemical elements
In the periodic table of the elements, each numbered column is a group.

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.

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 1a 2 3b n/a b 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Trivial name H and Alkali metalsr Alkaline earth metalsr Coin­age metals Triels Tetrels Pnicto­gensr Chal­co­gensr Halo­gensr Noble gasesr
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 Ce–Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Period 7 Fr Ra Ac Th–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 3 has scandium (Sc) and yttrium (Y). For the rest of the group, sources differ as either being (1) lutetium (Lu) and lawrencium (Lr), or (2) lanthanum (La) and actinium (Ac), or (3) the whole set of 15+15 lanthanides and actinides. IUPAC has initiated a project to standardize the definition as either (1) Sc, Y, Lu and Lr, or (2) Sc, Y, La and Ac.[4]
c 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.
by element
trivial name
Other trivial name
01 Group 1 1A IA 1A IA  
lithium family
alkali metals*
02 Group 2 2A IIA 2A IIA beryllium family alkaline earth metals*
03 Group 3 3A IIIA 3B IIIB scandium family
04 Group 4 4A IVA 4B IVB titanium family
05 Group 5 5A VA 5A VB vanadium family
06 Group 6 6A VIA 6B VIB chromium family
07 Group 7 7A VIIA 7B VIIB manganese family
08 Group 8 80 VIII 8B1 VIIIB iron family
09 Group 9 81 VIII 8B2 VIIIB cobalt family
10 Group 10 82 VIII 8B3 VIIIB nickel family
11 Group 11 1B IB 1B IB copper family coinage metals
12 Group 12 2B IIB 2B IIB zinc family
13 Group 13 3B IIIB 3B IIIA boron family triels from Greek tri (three, III)[5][6]
14 Group 14 4B IVB 4A IVA carbon family tetrels from Greek tetra (four, IV)[5][6]
15 Group 15 5B VB 5A VA nitrogen family pnictogens* pentels from Greek penta (five, V)[6]
16 Group 16 6B VIB 6A VIA oxygen family chalcogens*
17 Group 17 7B VIIB 7A VIIA fluorine family halogens*
18 Group 18 00 0 8A 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;[7]
  • "icosagens" for group 13;[8]
  • "crystallogens",[5] "adamantogens",[9] and "merylides" for group 14;
  • "aerogens" for group 18.[6]

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.[10]

See also


  1. "The Periodic Table Terms" (in en). 
  2. 2.0 2.1 Fluck, E. (1988). "New Notations in the Periodic Table". Pure Appl. Chem. (IUPAC) 60 (3): 431–436. doi:10.1351/pac198860030431. Retrieved 24 March 2012. 
  3. IUPAC (2005). "Nomenclature of inorganic chemistry". 
  4. "The constitution of group 3 of the periodic table". IUPAC. 2015-12-18. 
  5. 5.0 5.1 5.2 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. 
  6. 6.0 6.1 6.2 6.3 Rich, Ronald (2007). Inorganic Reactions in Water. Springer. pp. 307, 327, 363, 475. doi:10.1007/978-3-540-73962-3. ISBN 9783540739616. 
  7. "volatile metal". 
  8. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 227. ISBN 978-0-08-037941-8. 
  9. William B. Jensen, The Periodic Law and Table
  10. Leigh, G. J. Nomenclature of Inorganic Chemistry: Recommendations 1990. Blackwell Science, 1990. ISBN:0-632-02494-1.

Further reading