Polyatomic ion

There are several patterns that can be used for learning the nomenclature of polyatomic anions. First, when the prefix bi is added to a name, a hydrogen is added to the ion's formula and its charge is increased by 1, the latter being a consequence of the hydrogen ion's +1 charge. An alternative to the bi- prefix is to use the word hydrogen in its place: the anion derived from {{chem2|H+}}. For example, let us consider the carbonate({{chem2|link=carbonate|CO3(2-)}}) ion:

:{{chem2|H+}} + {{chem2|link=carbonate|CO3(2-)}} → {{chem2|link=bicarbonate|HCO3-}},

which is called either bicarbonate or hydrogen carbonate. The process that forms these ions is called protonation.

Most of the common polyatomic anions are oxyanions, conjugate bases of oxyacids (acids derived from the oxides of non-metallic elements). For example, the sulfate anion, {{chem2|auto=yes|SO4(2-)}}, is derived from {{chem2|link=sulfuric acid|H2SO4}}, which can be regarded as {{chem2|link=sulfur trioxide|SO3}} + {{chem2|link=water|H2O}}.

The second rule is based on the oxidation state of the central atom in the ion, which in practice is often (but not always) directly related to the number of oxygen atoms in the ion, following the pattern shown below. The following table shows the chlorine oxyanion family:

As the number of oxygen atoms bound to chlorine increases, the chlorine's oxidation number becomes more positive. This gives rise to the following common pattern: first, the -ate ion is considered to be the base name; adding a per- prefix adds an oxygen, while changing the -ate suffix to -ite will reduce the oxygens by one, and keeping the suffix -ite and adding the prefix hypo- reduces the number of oxygens by one more, all without changing the charge. The naming pattern follows within many different oxyanion series based on a standard root for that particular series. The -ite has one less oxygen than the -ate, but different -ate anions might have different numbers of oxygen atoms.

These rules do not work with all polyatomic anions, but they do apply to several of the more common ones. The following table shows how these prefixes are used for some of these common anion groups.

Some oxo-anions can dimerize with loss of an oxygen atom. The prefix pyro is used, as the reaction that forms these types of chemicals often involves heating to form these types of structures.{{GoldBookRef|file=P04959|title=pyro}} The prefix pyro is also denoted by the prefix di- . For example, dichromate ion is a dimer.

The following tables give additional examples of commonly encountered polyatomic ions. Only a few representatives are given, as the number of polyatomic ions encountered in practice is very large.

Many polyatomic molecules can carry spatially separated charges, forming zwitterions or, in general, polycharged polyatomic ions. A typical example are amino acids, which carry both charged amino and carboxyl groups. These charges can influence the chemical{{Cite journal |last=Pizzi |first=Andrea |last2=Dhaka |first2=Arun |last3=Beccaria |first3=Roberta |last4=Resnati |first4=Giuseppe |date=2024-07-01 |title=Anion⋯anion self-assembly under the control of σ- and π-hole bonds |url=https://pubs.rsc.org/en/content/articlelanding/2024/cs/d3cs00479a |journal=Chemical Society Reviews |language=en |volume=53 |issue=13 |pages=6654–6674 |doi=10.1039/D3CS00479A |issn=1460-4744|doi-access=free }} and physical properties of substances.{{Cite journal |last=Novikov |first=Anton P. |last2=Safonov |first2=Alexey V. |last3=German |first3=Konstantin E. |last4=Grigoriev |first4=Mikhail S. |date=2023-12-18 |title=What kind of interactions we may get moving from zwitter to “dritter” ions: C–O⋯Re(O4) and Re–O⋯Re(O4) anion⋯anion interactions make structural difference between L-histidinium perrhenate and pertechnetate |url=https://pubs.rsc.org/en/content/articlelanding/2024/ce/d3ce01164j |journal=CrystEngComm |language=en |volume=26 |issue=1 |pages=61–69 |doi=10.1039/D3CE01164J |issn=1466-8033|url-access=subscription }}

Polyatomic ion structure may influence thin film growth.{{Cite journal |last=Wijesundara |first=Muthu B. J. |last2=Ji |first2=Yuan |last3=Ni |first3=Boris |last4=Sinnott |first4=Susan B. |last5=Hanley |first5=Luke |date=2000-11-01 |title=Effect of polyatomic ion structure on thin-film growth: Experiments and molecular dynamics simulations |url=https://pubs.aip.org/aip/jap/article-abstract/88/9/5004/486174/Effect-of-polyatomic-ion-structure-on-thin-film?redirectedFrom=fulltext |journal=Journal of Applied Physics |volume=88 |issue=9 |pages=5004–5016 |doi=10.1063/1.1315329 |issn=0021-8979|url-access=subscription }} Analyses of polyatomic ion composition is key point in mass-spectrometry.{{Cite journal |last=Boulicault |first=Jean E. |last2=Alves |first2=Sandra |last3=Cole |first3=Richard B. |date=2016-08-01 |title=Negative Ion MALDI Mass Spectrometry of Polyoxometalates (POMs): Mechanism of Singly Charged Anion Formation and Chemical Properties Evaluation |url=https://pubs.acs.org/doi/abs/10.1007/s13361-016-1400-6 |journal=Journal of the American Society for Mass Spectrometry |volume=27 |issue=8 |pages=1301–1313 |doi=10.1007/s13361-016-1400-6|url-access=subscription }}{{Cite journal |last=Ehlers |first=A. W. |last2=de Koster |first2=C. G. |last3=Meier |first3=Robert J. |last4=Lammertsma |first4=K. |date=2001-09-01 |title=MALDI-TOF-MS of Saturated Polyolefins by Coordination of Metal Cations: A Theoretical Study |url=https://pubs.acs.org/doi/abs/10.1021/jp010627j |journal=The Journal of Physical Chemistry A |volume=105 |issue=38 |pages=8691–8695 |doi=10.1021/jp010627j |issn=1089-5639|url-access=subscription }}{{Cite journal |last=Roithová |first=Jana |last2=Schröder |first2=Detlef |date=2010-02-10 |title=Selective Activation of Alkanes by Gas-Phase Metal Ions |url=https://pubs.acs.org/doi/10.1021/cr900183p |journal=Chemical Reviews |volume=110 |issue=2 |pages=1170–1211 |doi=10.1021/cr900183p |issn=0009-2665|url-access=subscription }}

• Monatomic ion
• Protonation
• Onium ion

{{Reflist}}

• [https://antoine.frostburg.edu/chem/senese/101/compounds/polyatomic.shtml General Chemistry Online: Companion Notes: Compounds: Polyatomic ions]
• [https://web.archive.org/web/20121227231645/http://www2.pvc.maricopa.edu/tutor/chem/chem130/nomenclature/polyatomicion.html List of polyatomic ions]
• [http://www.chemistry.wustl.edu/~edudev/LabTutorials/PeriodicProperties/Ions/ions.html Tables of Common Polyatomic Ions], including PDB files

Category:Ions