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 1a 2 n/a 3b 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 c
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 metalsr alkaline earth metalsr coin­age metalsd 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–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.
n/a Do not have a group number
b The composition of group 3 is not agreed among sources: see Periodic table#Group 3 and Group 3 element#Dispute on composition. General inorganic chemistry texts usually 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. However, sources that study the matter usually put scandium, yttrium, lutetium (Lu), and lawrencium (Lr) in group 3, as shown here. Some sources, including IUPAC, currently follow a compromise that puts La–Lu and Ac–Lr as the f-block rows, leaving the heavier members of group 3 ambiguous. The arrangement with Sc, Y, Lu, and Lr in group 3 has been recommended by a 2021 IUPAC preliminary report on this question.
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.
d 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.[4] 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.[5]
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 1IAIA 
lithium family		hydrogen
and
alkali metals*
Group 2IIAIIAberyllium familyalkaline earth metals*
Group 3IIIAIIIBscandium family
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 familytriels from Greek tri (three, III)[6][7]
Group 14IVBIVAcarbon familytetrels from Greek tetra (four, IV)[6][7]
Group 15VBVAnitrogen familypnictogens*pentels from Greek penta (five, V)[7]
Group 16VIBVIAoxygen familychalcogens*
Group 17VIIBVIIAfluorine familyhalogens*
Group 180VIIIAhelium family
or neon family		noble gases*

Some other names have been proposed and used without gaining wide acceptance:

  • "volatile metals" for group 12;[8]
  • "icosagens" for group 13;[9]
  • "crystallogens",[6] "adamantogens",[10] and "merylides" for group 14;
  • "aerogens" for group 18.[7]

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.[11]

See also

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. Conradie, Jeanet; Ghosh, Abhik (2019). "Theoretical Search for the Highest Valence States of the Coinage Metals: Roentgenium Heptafluoride May Exist". Inorganic Chemistry. 58 (13): 8735–8738. doi:10.1021/acs.inorgchem.9b01139.
  5. Grochala, Wojciech; Mazej, Zoran (2015). "Chemistry of silver(II): a cornucopia of peculiarities". Philosophical Transactions of the Royal Society A. 373. doi:10.1098/rsta.2014.0179. Retrieved 23 December 2021.
  6. 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. S2CID 104746665. Retrieved 17 August 2019.
  7. Rich, Ronald (2007). Inorganic Reactions in Water. Springer. pp. 307, 327, 363, 475. doi:10.1007/978-3-540-73962-3. ISBN 9783540739616.
  8. "volatile metal". Glosbe. Retrieved 14 January 2021.{{cite web}}: CS1 maint: url-status (link)
  9. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 227. ISBN 978-0-08-037941-8.
  10. William B. Jensen, The Periodic Law and Table
  11. Leigh, G. J. Nomenclature of Inorganic Chemistry: Recommendations 1990. Blackwell Science, 1990. ISBN 0-632-02494-1.

Further reading
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