Editing Polyatomic ion (section)

{{Short description|Ion containing two or more atoms}}
{{More citations needed|date=November 2021}}
[[File:Nitrate-ion-elpot.png|thumb|right|200px|An [[electric potential|electrostatic potential]] map of the [[nitrate]] ion ({{chem2|auto=yes|NO3-}}). Areas coloured translucent red, around the outside of the red oxygen atoms themselves, signify the regions of most negative electrostatic potential.]]
      
A '''polyatomic ion''' (also known as a '''molecular ion''') is a [[covalent bond]]ed set of two or more [[atom]]s, or of a [[complex (chemistry)|metal complex]], that can be considered to behave as a single unit and that usually has a net [[electrical charge|charge]] that is not zero,<ref name="PetrucciA50">{{cite book |last1=Petrucci |first1=Ralph H. |last2=Herring |first2=F. Geoffrey |last3=Madura |first3=Jeffry D. |last4=Bissonnette |first4=Carey |title=General chemistry: principles and modern applications |date=2017 |publisher=Pearson |location=Toronto |isbn=978-0-13-293128-1 |page=A50 |edition=Eleventh}}</ref> or in special case of [[zwitterion]] wear spatially separated charges where the net charge may be variable depending on [[Acidity function|acidity]] conditions.  The term [[molecule]] may or may not be used to refer to a polyatomic ion, depending on the definition used. The prefix ''poly-'' carries  the meaning "many" in Greek, but even ions of two atoms are commonly described as polyatomic.<ref>{{Cite web |title=Ionic Compounds Containing Polyatomic Ions |url=https://www.chem.purdue.edu/gchelp/nomenclature/poly_atom.htm |access-date=2022-04-16 |website=www.chem.purdue.edu}}</ref>

In older literature, a polyatomic ion may instead be referred to as a ''[[Radical (chemistry)|radical]]'' (or less commonly, as a ''radical group'').{{Citation needed|date=June 2022}} In contemporary usage, the term ''radical'' refers to various [[Radical (chemistry)|free radical]]s, which are [[species (chemistry)|species]] that have an [[unpaired electron]] and need not be charged.<ref>{{cite web |title=IUPAC - radical (free radical) (R05066) |url=https://goldbook.iupac.org/terms/view/R05066 |website=goldbook.iupac.org |access-date=25 January 2023}}</ref>

A simple example of a polyatomic ion is the [[hydroxide]] ion, which consists of one [[oxygen atom]] and one hydrogen atom, jointly carrying a net charge of [[elementary charge|−1]]; its chemical formula is {{chem2|auto=yes|OH-}}. In contrast, an [[ammonium]] ion consists of one nitrogen atom and four hydrogen atoms, with a charge of +1; its chemical formula is {{chem2|auto=yes|NH4+}}.

Polyatomic ions often are useful in the context of [[acid–base reaction|acid–base chemistry]] and in the formation of [[salt (chemistry)|salts]].

Often, a polyatomic ion can be considered as the [[conjugate acid|conjugate acid or base]] of a neutral [[molecule]]. For example, the [[conjugate base]] of [[sulfuric acid]] (H<sub>2</sub>SO<sub>4</sub>) is the polyatomic [[hydrogen sulfate]] [[anion]] ({{chem2|HSO4-}}). The removal of another [[hydron (chemistry)|hydrogen ion]] produces the [[sulfate]] anion ({{chem2|SO4(2-)}}).