Main-group element

In chemistry and atomic physics, the main group is the group of elements (sometimes called the representative elements) whose lightest members are represented by helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, and fluorine as arranged in the periodic table of the elements. The main group includes the elements (except hydrogen, which is sometimes not included^{[citation needed]}) in groups 1 and 2 (s-block), and groups 13 to 18 (p-block). The s-block elements are primarily characterised by one main oxidation state, and the p-block elements, when they have multiple oxidation states, often have common oxidation states separated by two units.

Main-group elements (with some of the lighter transition metals) are the most abundant elements on Earth, in the Solar System, and in the universe. Group 12 elements are often considered to be transition metals; however, zinc (Zn), cadmium (Cd), and mercury (Hg) share some properties of both groups, and some scientists believe they should be included in the main group.^[1]^[2]

Occasionally, even the group 3 elements as well as the lanthanides and actinides have been included, because especially the group 3 elements and many lanthanides are electropositive elements with only one main oxidation state like the group 1 and 2 elements. The position of the actinides is more questionable, but the most common and stable of them, thorium (Th) and uranium (U), are similar to main-group elements as thorium is an electropositive element with only one main oxidation state (+4), and uranium has two main ones separated by two oxidation units (+4 and +6).^[3]

In older nomenclature, the main-group elements are groups IA and IIA, and groups IIIB to 0 (CAS groups IIIA to VIIIA). Group 12 is labelled as group IIB in both systems. Group 3 is labelled as group IIIA in the older nomenclature (CAS group IIIB).

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References

^ "Nomenclature of Inorganic Chemistry". International Union of Pure and Applied Chemistry. Retrieved 27 September 2011.
^ Jensen, William B. (2003). "The Place of Zinc, Cadmium, and Mercury in the Periodic Table" (PDF). Journal of Chemical Education. 80 (8): 952. Bibcode:2003JChEd..80..952J. doi:10.1021/ed080p952.
^ King, R. Bruce (1995). Inorganic Chemistry of Main Group Elements. Wiley-VCH. ISBN 0-471-18602-3.

Ralf Steudel, "Chemie der Nichtmetalle" (Chemistry of the nonmetals), 2nd Edition. Walter deGruyter, Berlin 1998. ISBN 3-11-012322-3

Periodic table

Periodic table forms

Standard	18-column 32-column
Alternative	Alternatives Janet's left step table
Extended	Extension beyond the 7th period Aufbau Fricke Pyykkö

Sets of elements

By periodic table structure

Groups	1 (Hydrogen and alkali metals) 2 (Alkaline earth metals) f-block groups 3 4 5 6 7 8 9 10 11 12 13 (Triels) 14 (Tetrels) 15 (Pnictogens) 16 (Chalcogens) 17 (Halogens) 18 (Noble gases)
Periods	1 2 3 4 5 6 7 8+ Aufbau Fricke Pyykkö
Blocks	s-block p-block d-block f-block g-block Aufbau principle

By metallicity

Metals	Alkali metals Alkaline earth metals Lanthanides Actinides Transition metals Post-transition metals
Metalloids	Lists of metalloids by source Dividing line
Nonmetals	Reactive nonmetals Noble gases

Other sets

Elements

Lists	By: Abundance (in humans) Atomic properties Nuclear stability Symbol
Properties	Aqueous chemistry Crystal structure Electron configuration Electronegativity Goldschmidt classification Term symbol
Data pages	Abundance Atomic radius Boiling point Critical point Density Elasticity Electrical resistivity Electron affinity Electron configuration Electronegativity Hardness Heat capacity Heat of fusion Heat of vaporization Ionization energy Melting point Oxidation state Speed of sound Thermal conductivity Thermal expansion coefficient Vapor pressure

History

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See also

References