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[1]) is a column of elements in the periodic table of the chemical elements. There are 18 numbered groups in the periodic table, and the f-block columns (between groups 3 and 4) 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 the oxygen group and as the chalcogens.

Group names

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

Groups in the Periodic table
IUPAC group 1 2 3a a 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 Alkali metals 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 H 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 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]
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.
h Hydrogen (H), while placed in group 1, is not considered to be part of the alkali metals.
New
IUPAC
names		Old
IUPAC
(Europe)		CAS
(U.S.)		Name by elementTrivial name
(*=IUPAC recommended name)		note
Group 1IAIAlithium familyalkali metals*
Group 2IIAIIAberyllium familyalkaline earth metals*
Group 3IIIAIIIBscandium familyConsisting of rare earth elements plus actinides
Group 4IVAIVBtitanium family
Group 5VAVBvanadium family
Group 6VIAVIBchromium family
Group 7VIIAVIIBmanganese family
Group 8VIIIVIIIBiron family
Group 9VIIIVIIIBcobalt family
Group 10VIIIVIIIBnickel family
Group 11IBIBcopper familycoinage metals
Group 12IIBIIBzinc family
Group 13IIIBIIIAboron familytrielstriels from Greek tri (three, III)
Group 14IVBIVAcarbon familytetrelstetrels from Greek tetra (four, IV)
Group 15VBVAnitrogen familypentels, pnictogens*pentels from Greek penta (five, V)
Group 16VIBVIAoxygen familychalcogens*
Group 17VIIBVIIAfluorine familyhalogens*
Group 18Group 0VIIIAhelium family or neon familynoble gases*

Some other names have been proposed and used without gaining wide acceptance: volatile metals for group 12; icosagens for group 13; crystallogens, adamantogens, and merylides for group 14; and aerogens for group 18.

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.[5]

References

  1. ↑ "The Periodic Table Terms". www.shmoop.com. Retrieved 2018-09-15.
  2. 1 2 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.
  3. ↑ IUPAC (2005). "Nomenclature of inorganic chemistry" (PDF).
  4. ↑ "The constitution of group 3 of the periodic table". IUPAC. 2015-12-18.
  5. ↑ 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.
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