Group (periodic table)

{{Use Oxford spelling|date = March 2019}}

{{Use Oxford spelling|date = March 2019}}

[[File:Simple Periodic Table Chart-blocks.svg|upright=1.75|thumb|right|In the [[periodic table]] of the elements, each column is a ''group''.]]

[[File:Simple Periodic Table Chart-blocks.svg|upright=1.75|thumb|right|In the [[periodic table]] of the elements, each column is a ''group''.]]

In [[chemistry]], a '''group'''

In [[chemistry]], a '''group''' (also known as a '''family'''){{Cite web|url=https://www.shmoop.com/periodic-table/terms.html|title=The Periodic Table Terms|website=www.shmoop.com|language=en|access-date=2018-09-15|archive-date=2019-04-06|archive-url=https://web.archive.org/web/20190406105358/https://www.shmoop.com/periodic-table/terms.html|url-status=dead}} is a column of elements in the [[Periodic table|periodic table of the chemical elements]]. There are 18 numbered groups in the periodic table; the 14 [[Block (periodic table)#f-block|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 shell]]s of their atoms (i.e., the same [[core charge]]), because most chemical properties are dominated by the orbital location of the outermost electron.

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.{{Citation needed|date=June 2025}} The 1-18 system is based on each atom's s, p and d electrons beyond those in atoms of the preceding [[noble gas]]. Two older incompatible naming schemes can assign the same number to different groups depending on the system being used. The older schemes were 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 [[Period 1 element#Position of period 1 elements in the periodic table|elements number 1 and 2]] ([[hydrogen]] and [[helium]]). Similar variation on the [[inner transition metal]]s 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 "[[chalcogen]]s". An exception is the "[[iron group]]", which usually refers to [[group 8 element|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.{{cite web|title=Nomenclature of inorganic chemistry|url=http://old.iupac.org/publications/books/rbook/Red_Book_2005.pdf|author=IUPAC|year=2005}}

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.{{cite web|title=Nomenclature of inorganic chemistry|url=http://old.iupac.org/publications/books/rbook/Red_Book_2005.pdf|author=IUPAC|year=2005}}