Editing Main-group element (section)

{{Short description|Chemical elements in groups 1, 2, 13–18}}
{{Use dmy dates|date=September 2022}}
[[File:Simple Periodic Table Chart-blocks.svg|450px|thumb|right|The [[periodic table]] of the [[chemical element]]s. The columns represent the [[group (periodic table)|groups]]. Groups 1, 2 and 13 to 18 constitute the main group. Sometimes groups 3 and 12, as well as the [[lanthanide]]s and [[actinide]]s (the two rows at the bottom), are also included in the main group.]]

In [[chemistry]] and atomic [[physics]], the '''main group''' is the [[group (periodic table)|group]] of [[chemical element|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{{cn|date=January 2024}}) 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 metal]]s) are the most [[abundance of the chemical elements|abundant]] elements on [[Earth]], in the [[Solar System]], and in the [[universe]]. [[Group 12 element]]s are often considered to be transition metals; however, [[zinc]] (Zn), [[cadmium]] (Cd), and [[mercury (element)|mercury]] (Hg) share some properties of both groups, and some scientists believe they should be included in the main group.<ref>{{cite web |title=Nomenclature of Inorganic Chemistry |url=http://old.iupac.org/reports/provisional/abstract04/connelly_310804.html |publisher=[[International Union of Pure and Applied Chemistry]] |access-date=2011-09-27}}</ref><ref>{{cite journal |journal=[[Journal of Chemical Education]] |volume=80 |issue=8 |year=2003 |url=http://www.uv.es/~borrasj/ingenieria_web/temas/tema_1/lecturas_comp/p952.pdf |title=The Place of Zinc, Cadmium, and Mercury in the Periodic Table |author1-link=William B. Jensen |first=William B.|last=Jensen |page=952 |doi=10.1021/ed080p952 |bibcode=2003JChEd..80..952J}}</ref>

Occasionally, even the [[group 3 element]]s as well as the [[lanthanide]]s and [[actinide]]s have been included, because especially the group 3 elements and many lanthanides are [[electronegativity|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).<ref name=King>{{cite book |last=King|first=R. Bruce |date=1995 |title=Inorganic Chemistry of Main Group Elements |publisher=[[Wiley-VCH]] |isbn=0-471-18602-3}}</ref>

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).