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 14 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 1988. It replaces two older incompatible naming schemes, used by the Chemical Abstract Service (CAS, more popular in the United States), and by IUPAC before 1988 (more popular in Europe). The system of eighteen groups is generally accepted by the chemistry community, but some dissent exists about membership of elements number 1 and 2 (hydrogen and helium). Similar variation on the inner transition metals continues to exist in textbooks, although the correct positioning has been known since 1948 and was twice endorsed by IUPAC in 1988 (together with the 1–18 numbering) and 2021.

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

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 1988[4] and 2021[5] 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.[5] 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
IUPAC
name		 Old
IUPAC
(Europe)		 Old CAS
name
(U.S.)		 Name
by element
('group' or 'family')		 IUPAC
recommended
trivial name		 Other names
Group 1IAIAlithium group hydrogen and alkali metals "lithium group" excludes hydrogen
Group 2IIAIIAberyllium group alkaline earth metals
Group 3IIIAIIIBscandium group
Group 4IVAIVBtitanium group
Group 5VAVBvanadium group
Group 6VIAVIBchromium group
Group 7VIIAVIIBmanganese group
Group 8VIIIVIIIBiron group
Group 9VIIIVIIIBcobalt group
Group 10VIIIVIIIBnickel group
Group 11IBIBcopper group Sometimes called coinage metals,
but the set is arbitraryf
Group 12IIBIIBzinc group volatile metals[11]
Group 13IIIBIIIAboron group trielsb icosagens[12]
earth metals
Group 14IVBIVAcarbon group tetrelsc crystallogens[13]
adamantogens[14]
merylides[15]
Group 15VBVAnitrogen group pnictogens
pentelsn
Group 16VIBVIAoxygen group chalcogens
Group 17VIIBVIIAfluorine group halogens
Group 180VIIIA helium group
or neon group		 noble gases aerogens[16]
^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.[17] 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.[18]
^b triels (group 13), from Greek tri: three, III[13][16]
^c tetrels (group 14), from Greek tetra: four, IV[13][16]
^n pentel (group 15), from Greek penta: five, V[16]

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.[19]

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:

Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson

Similar sets: noble metals, coinage metals, precious metals, refractory metals.

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. 60 (3). IUPAC: 431–436. doi:10.1351/pac198860030431. S2CID 96704008. Retrieved 24 March 2012.
  3. IUPAC (2005). "Nomenclature of inorganic chemistry" (PDF).
  4. Fluck, E. (1988). "New Notations in the Periodic Table" (PDF). Pure Appl. Chem. 60 (3): 431–436. doi:10.1351/pac198860030431. S2CID 96704008. Archived (PDF) from the original on 25 March 2012. Retrieved 24 March 2012.
  5. Scerri, Eric (18 January 2021). "Provisional Report on Discussions on Group 3 of the Periodic Table" (PDF). Chemistry International. 43 (1): 31–34. doi:10.1515/ci-2021-0115. S2CID 231694898. Archived (PDF) from the original on 13 April 2021. Retrieved 9 April 2021.
  6. William B. Jensen (1982). "The Positions of Lanthanum (Actinium) and Lutetium (Lawrencium) in the Periodic Table". J. Chem. Educ. 59 (8): 634–636. Bibcode:1982JChEd..59..634J. doi:10.1021/ed059p634.
  7. L. D. Landau, E. M. Lifshitz (1958). Quantum Mechanics: Non-Relativistic Theory. Vol. 3 (1st ed.). Pergamon Press. pp. 256–7.
  8. Jensen, William B. (2015). "The positions of lanthanum (actinium) and lutetium (lawrencium) in the periodic table: an update". Foundations of Chemistry. 17: 23–31. doi:10.1007/s10698-015-9216-1. S2CID 98624395. Archived from the original on 30 January 2021. Retrieved 28 January 2021.
  9. Scerri, Eric (2009). "Which Elements Belong in Group 3?". Journal of Chemical Education. 86 (10): 1188. doi:10.1021/ed086p1188. Retrieved 1 January 2023.
  10. Chemey, Alexander T.; Albrecht-Schmitt, Thomas E. (2019). "Evolution of the periodic table through the synthesis of new elements". Radiochimica Acta. 107 (9–11): 1–31. doi:10.1515/ract-2018-3082.
  11. Simmons, L. M. (1947). "A modification of the periodic table". Journal of Chemical Education. 24 (12): 588–591. doi:10.1021/ed024p588.
  12. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 227. ISBN 978-0-08-037941-8.
  13. 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.
  14. Jensen, William B. (2000). "The Periodic Law and Table" (PDF). Archived from the original (PDF) on 2020-11-10. Retrieved 10 December 2022.
  15. Fernelius, W. C.; Loening, Kurt; Adams, Roy M. (1971). "Names of groups and elements". Journal of Chemical Education. 48 (11): 730–731. doi:10.1021/ed048p730.
  16. Rich, Ronald (2007). Inorganic Reactions in Water. Springer. pp. 307, 327, 363, 475. doi:10.1007/978-3-540-73962-3. ISBN 9783540739616.
  17. 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. PMID 31203606. S2CID 189944098.
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  19. Leigh, G. J. Nomenclature of Inorganic Chemistry: Recommendations 1990. Blackwell Science, 1990. ISBN 0-632-02494-1.

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