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Polyatomic ion
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<h2 id="nomenclature-of-polyatomic-anions">Nomenclature of polyatomic anions</h2> <p>There are several patterns that can be used for learning the nomenclature of polyatomic anions. First, when the prefix <i>bi</i> 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 <i>bi-</i> prefix is to use the word hydrogen in its place: the anion derived from H+. For example, let us consider the carbonate(<a href="/facts/Carbonate/FES1QHkN">CO2−3</a>) ion: </p> H+ + <a href="/facts/Carbonate/FES1QHkN">CO2−3</a> → <a href="/facts/Bicarbonate/zzSVVAl1">HCO−3</a>, <p>which is called either bicarbonate or hydrogen carbonate. The process that forms these ions is called <a href="/facts/Protonation/q5Gf9z0M">protonation</a>. </p><p>Most of the common polyatomic anions are <a href="/facts/Oxyanion/0GuWXr6D">oxyanions</a>, conjugate bases of <a href="/facts/Oxyacid/p0bMdwSx">oxyacids</a> (acids derived from the <a href="/facts/Oxide/DXtoVe1C">oxides</a> of <a href="/facts/Nonmetal_(chemistry)/0oejKuzK">non-metallic elements</a>). For example, the <a href="/facts/Sulfate/yuWVxsUf">sulfate</a> anion, <a href="/facts/Sulfur/IK0amTfM">S</a><a href="/facts/Oxygen/acyn6o8r">O</a>2−4, is derived from <a href="/facts/Sulfuric_acid/Wom6fymJ">H2SO4</a>, which can be regarded as <a href="/facts/Sulfur_trioxide/Ijvm08Lq">SO3</a> + <a href="/facts/Water/0lkXnJPK">H2O</a>. </p><p>The second rule is based on the <a href="/facts/Oxidation_state/W53W6s6V">oxidation state</a> 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 <a href="/facts/Chlorine/y27UwYBM">chlorine</a> <a href="/facts/Oxyanion/0GuWXr6D">oxyanion</a> family: </p> <table><tbody><tr><th>Oxidation state</th><td>−1</td><td>+1</td><td>+3</td><td>+5</td><td>+7</td></tr><tr><th>Anion name</th><td><a href="/facts/Chloride/m9NUaUDR">chloride</a></td><td><a href="/facts/Hypochlorite/XMJdjAEM">hypochlorite</a></td><td><a href="/facts/Chlorite/EYtQI4wC">chlorite</a></td><td><a href="/facts/Chlorate/Ypne0mrY">chlorate</a></td><td><a href="/facts/Perchlorate/WCC53zS2">perchlorate</a></td></tr><tr><th>Formula</th><td>Cl−</td><td>ClO−</td><td>ClO−2</td><td>ClO−3</td><td>ClO−4</td></tr><tr><th>Structure</th><td></td><td></td><td></td><td></td><td></td></tr></tbody></table> <p>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 <i>-ate</i> ion is considered to be the base name; adding a <i>per-</i> prefix adds an oxygen, while changing the <i>-ate</i> suffix to <i>-ite</i> will reduce the oxygens by one, and keeping the suffix <i>-ite</i> and adding the prefix <i>hypo-</i> 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 <i>-ite</i> has one less oxygen than the <i>-ate</i>, but different <i>-ate</i> anions might have different numbers of oxygen atoms. </p><p>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. </p> <table><tbody><tr><td><a href="/facts/Bromide/bHSfxGk1">bromide</a></td><td><a href="/facts/Hypobromite/A7SJv8j3">hypobromite</a></td><td><a href="/facts/Bromite/6XxKSAaA">bromite</a></td><td><a href="/facts/Bromate/UH4DoPFT">bromate</a></td><td><a href="/facts/Perbromate/0sKLy0t5">perbromate</a></td></tr><tr><td>Br−</td><td>BrO−</td><td>BrO−2</td><td>BrO−3</td><td>BrO−4</td></tr><tr><td><a href="/facts/Iodide/JyVRGWMX">iodide</a></td><td><a href="/facts/Hypoiodite/XBDsmBKr">hypoiodite</a></td><td><a href="/facts/Iodite/1LBRGCfm">iodite</a></td><td><a href="/facts/Iodate/n60p0YSa">iodate</a></td><td><a href="/facts/Periodate/y9IRt4t6">periodate</a></td></tr><tr><td>I−</td><td>IO−</td><td>IO−2</td><td>IO−3</td><td>IO−4 or IO5−6</td></tr><tr><td><a href="/facts/Sulfide/d8YMjLeu">sulfide</a></td><td><a href="/facts/Hyposulfite/Q17KV63L">hyposulfite</a></td><td><a href="/facts/Sulfite/xdppUlKA">sulfite</a></td><td><a href="/facts/Sulfate/yuWVxsUf">sulfate</a></td><td><a href="/facts/Persulfate/IlAYjLH8">persulfate</a></td></tr><tr><td>S2−</td><td>S2O2−2</td><td>SO2−3</td><td>SO2−4</td><td>SO2−5 or S2O2−8</td></tr><tr><td><a href="/facts/Selenide/vA9Ls4xH">selenide</a></td><td>hyposelenite</td><td><a href="/facts/Selenite_(ion)/wJvsRY2r">selenite</a></td><td><a href="/facts/Selenate/drzesLxu">selenate</a></td><td></td></tr><tr><td>Se−2</td><td>Se2O2−2</td><td>SeO2−3</td><td>SeO2−4</td><td></td></tr><tr><td><a href="/facts/Telluride_(chemistry)/r8gVazKR">telluride</a></td><td>hypotellurite</td><td><a href="/facts/Tellurite_(ion)/lD5UQzRb">tellurite</a></td><td><a href="/facts/Tellurate/jnAvMCss">tellurate</a></td><td></td></tr><tr><td>Te−2</td><td>TeO2−2</td><td>TeO2−3</td><td>TeO2−4</td><td></td></tr><tr><td><a href="/facts/Nitride/9vkrCbJ4">nitride</a></td><td><a href="/facts/Hyponitrite/apQuyU2C">hyponitrite</a></td><td><a href="/facts/Nitrite/qkz2XScK">nitrite</a></td><td><a href="/facts/Nitrate/5AnVlYnL">nitrate</a></td><td><a href="/facts/Peroxynitrate/bnl1lT4k">pernitrate</a></td></tr><tr><td>N−3</td><td>N2O2−2</td><td>NO−2</td><td>NO−3</td><td>NO−4</td></tr><tr><td><a href="/facts/Phosphide/u5J5Apjs">phosphide</a></td><td><a href="/facts/Hypophosphite/Je5Gckyh">hypophosphite</a></td><td><a href="/facts/Phosphite/Uq54qjld">phosphite</a></td><td><a href="/facts/Phosphate/FDGVCxUG">phosphate</a></td><td>perphosphate</td></tr><tr><td>P−3</td><td>H2PO−2</td><td>PO3−3</td><td>PO3−4</td><td>PO3−5</td></tr><tr><td><a href="/facts/Arsenide/UpkRk4uf">arsenide</a></td><td>hypoarsenite</td><td><a href="/facts/Arsenite/SfFCftGH">arsenite</a></td><td><a href="/facts/Arsenate/IWco5TAH">arsenate</a></td><td></td></tr><tr><td>As3−</td><td>AsO3−2</td><td>AsO3−3</td><td>AsO3−4</td><td></td></tr></tbody></table> <p>Some oxo-anions can <a href="/facts/Dimer_(chemistry)/mU64PnEq">dimerize</a> with loss of an oxygen atom. The prefix <i>pyro</i> is used, as the reaction that forms these types of chemicals often involves heating to form these types of structures.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> The prefix <i>pyro</i> is also denoted by the prefix <i>di-</i> . For example, dichromate ion is a dimer. </p> <table><tbody><tr><td><a href="/facts/Sulfite/xdppUlKA">sulfite</a></td><td><a href="/facts/Pyrosulfite/QoXW01ua">pyrosulfite</a></td></tr><tr><td>SO2−3</td><td>S2O2−5</td></tr><tr><td><a href="/facts/Sulfate/yuWVxsUf">sulfate</a></td><td><a href="/facts/Pyrosulfate/PoR7hg9y">pyrosulfate</a></td></tr><tr><td>SO2−4</td><td>S2O2−7</td></tr><tr><td><a href="/facts/Phosphite_anion/D3ao0j17">phosphite</a></td><td><a href="/facts/Pyrophosphite/D3ao0j17">pyrophosphite</a></td></tr><tr><td>PO3−3</td><td>P2O4−5</td></tr><tr><td><a href="/facts/Phosphate/FDGVCxUG">phosphate</a></td><td><a href="/facts/Pyrophosphate/L9FPEkhF">pyrophosphate</a></td></tr><tr><td>PO3−4</td><td>P2O4−7</td></tr><tr><td><a href="/facts/Arsenate/IWco5TAH">arsenate</a></td><td>pyroarsenate</td></tr><tr><td>AsO3−4</td><td>As2O4−7</td></tr><tr><td><a href="/facts/Chromate_and_dichromate/6xkFLIJw">chromate</a></td><td><a href="/facts/Dichromate/6xkFLIJw">dichromate</a></td></tr><tr><td>CrO2−4</td><td>Cr2O2−7</td></tr><tr><td><a href="/facts/Carbonate/FES1QHkN">carbonate</a></td><td><a href="/facts/Dicarbonate/NAAe892M">dicarbonate</a></td></tr><tr><td>CO2−3</td><td>C2O2−5</td></tr><tr><td>selenite</td><td>pyroselenite</td></tr><tr><td>SeO2−3</td><td>Se2O2−5</td></tr></tbody></table> <h2 id="other-examples-of-common-polyatomic-ions">Other examples of common polyatomic ions</h2> <p>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. </p> <a href="/facts/Anion/wrbwhF3z">Anions</a><table><tbody><tr><td><a href="/facts/Tetrahydroxyborate/VjSKKVgC">Tetrahydroxyborate</a></td><td>B(OH)−4</td></tr><tr><td><a href="/facts/Acetylide/3u0EMxz3">Acetylide</a></td><td>C2−2</td></tr><tr><td><a href="/facts/Ethoxide/RqG0rm1v">Ethoxide</a> or ethanolate</td><td>C2H5O−</td></tr><tr><td><a href="/facts/Acetate/U90VVczy">Acetate</a> or ethanoate</td><td>CH3COO− or C2H3O−2</td></tr><tr><td><a href="/facts/Benzoate/7HrmrBYS">Benzoate</a></td><td>C6H5COO− or C7H5O−2</td></tr><tr><td><a href="/facts/Citrate/EgKGQBdl">Citrate</a></td><td>C6H5O3−7</td></tr><tr><td><a href="/facts/Formate/Py3GhI7L">Formate</a></td><td>HCOO−</td></tr><tr><td><a href="/facts/Carbonate/FES1QHkN">Carbonate</a></td><td>CO2−3</td></tr><tr><td><a href="/facts/Oxalate/u0Gdem0A">Oxalate</a></td><td>C2O2−4</td></tr><tr><td><a href="/facts/Cyanide/t0o8FMKI">Cyanide</a></td><td>CN−</td></tr><tr><td><a href="/facts/Chromate_and_dichromate/6xkFLIJw">Chromate</a></td><td>CrO2−4</td></tr><tr><td><a href="/facts/Chromate_and_dichromate/6xkFLIJw">Dichromate</a></td><td>Cr2O2−7</td></tr><tr><td><a href="/facts/Bicarbonate/zzSVVAl1">Bicarbonate</a> or hydrogencarbonate</td><td>HCO−3</td></tr><tr><td><a href="/facts/Phosphate/FDGVCxUG">Hydrogen phosphate</a></td><td>HPO2−4</td></tr><tr><td><a href="/facts/Phosphate/FDGVCxUG">Dihydrogen phosphate</a></td><td>H2PO−4</td></tr><tr><td><a href="/facts/Hydrogen_sulfate/yuWVxsUf">Hydrogen sulfate</a> or bisulfate</td><td>HSO−4</td></tr><tr><td><a href="/facts/Manganate/3Kr1qk0S">Manganate</a></td><td>MnO2−4</td></tr><tr><td><a href="/facts/Permanganate/nJa04jVh">Permanganate</a></td><td>MnO−4</td></tr><tr><td><a href="/facts/Zincate/GazR5fbW">Zincate</a></td><td>ZnO2−2</td></tr><tr><td><a href="/facts/Aluminate/dRaFaNlM">Aluminate</a></td><td>AlO−2</td></tr><tr><td><a href="/facts/Tungstate/ek9P92Tz">Tungstate</a></td><td>WO2−4</td></tr><tr><td><a href="/facts/Azanide/5rnJAKEp">Azanide</a> or amide</td><td>NH−2</td></tr><tr><td><a href="/facts/Peroxide/VMU8y4xB">Peroxide</a></td><td>O2−2</td></tr><tr><td><a href="/facts/Superoxide/2X2sQocn">Superoxide</a></td><td>O−2</td></tr><tr><td><a href="/facts/Hydroxide/zW0wxpWD">Hydroxide</a></td><td>OH−</td></tr><tr><td><a href="/facts/Bisulfide/xIwK8as1">Bisulfide</a></td><td>SH−</td></tr><tr><td><a href="/facts/Cyanate/EcDWGQQh">Cyanate</a></td><td>OCN−</td></tr><tr><td><a href="/facts/Thiocyanate/S438CJp8">Thiocyanate</a></td><td>SCN−</td></tr><tr><td><a href="/facts/Orthosilicate/CKXheWm5">Orthosilicate</a></td><td>SiO4−4</td></tr><tr><td><a href="/facts/Thiosulfate/LYu0KhDu">Thiosulfate</a></td><td>S2O2−3</td></tr><tr><td><a href="/facts/Azide/AaJwyv1z">Azide</a></td><td>N−3</td></tr><tr><td><a href="/facts/Tetraperoxochromate/qaucNwQt">Tetraperoxochromate</a></td><td>Cr(O2)3−4</td></tr></tbody></table> <a href="/facts/Cation/wrbwhF3z">Cations</a><table><tbody><tr><th colspan="2"><a href="/facts/Onium_ion/92qxuw9q">Onium ions</a></th><th colspan="2"><a href="/facts/Carbenium_ion/vwRVNmxp">Carbenium ions</a></th><th colspan="2">Others</th></tr><tr><td><a href="/facts/Guanidine/lGzDoPuJ">Guanidinium</a></td><td>C(NH2)+3</td><td><a href="/facts/Tropylium_cation/3vAk8fwQ">Tropylium</a></td><td>C7H+7</td><td><a href="/facts/Mercury_(element)/WlxfoHva">Mercury(I)</a></td><td>Hg2+2</td></tr><tr><td><a href="/facts/Ammonium/jYm8wc1n">Ammonium</a></td><td>NH+4</td><td><a href="/facts/Triphenylcarbenium/IQTQz06L">Triphenylcarbenium</a></td><td>(C6H5)3C+</td><td><a href="/facts/Dihydrogen_cation/MWh6WYVG">Dihydrogen</a></td><td>H+2</td></tr><tr><td><a href="/facts/Phosphonium/uS2PCt7X">Phosphonium</a></td><td>PH+4</td><td><a href="/facts/Cyclopropenium_ion/e4Paw0D8">Cyclopropenium</a></td><td>C3H+3</td><td></td><td></td></tr><tr><td><a href="/facts/Hydronium/HzE3BGYJ">Hydronium</a></td><td>H3O+</td><td><a href="/facts/Trifluoromethyl_cation/5tQlaKAa">Trifluoromethyl</a></td><td>CF+3</td><td></td><td></td></tr><tr><td><a href="/facts/Fluoronium/kW03c9rL">Fluoronium</a></td><td>H2F+</td><td></td><td></td><td></td><td></td></tr><tr><td><a href="/facts/Pyrylium_salt/QTplu8Ez">Pyrylium</a></td><td>C5H5O+</td><td></td><td></td><td></td><td></td></tr><tr><td><a href="/facts/Sulfonium/GcF77hXv">Sulfonium </a></td><td>H3S+</td><td></td><td></td><td></td><td></td></tr></tbody></table> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Monatomic_ion/HovBdsqw">Monatomic ion</a></li> <li><a href="/facts/Protonation/q5Gf9z0M">Protonation</a></li> <li><a href="/facts/Onium_ion/92qxuw9q">Onium ion</a></li></ul> <h2 id="external-links">External links</h2> <ul><li><a href="https://antoine.frostburg.edu/chem/senese/101/compounds/polyatomic.shtml">General Chemistry Online: Companion Notes: Compounds: Polyatomic ions</a></li> <li><a href="https://web.archive.org/web/20121227231645/http://www2.pvc.maricopa.edu/tutor/chem/chem130/nomenclature/polyatomicion.html">List of polyatomic ions</a></li> <li><a href="http://www.chemistry.wustl.edu/~edudev/LabTutorials/PeriodicProperties/Ions/ions.html">Tables of Common Polyatomic Ions</a>, including <a href="/facts/Protein_Data_Bank/oUhq4ABD">PDB</a> files</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Petrucci, Ralph H.; Herring, F. Geoffrey; Madura, Jeffry D.; Bissonnette, Carey (2017). General chemistry: principles and modern applications (Eleventh ed.). Toronto: Pearson. p. A50. ISBN 978-0-13-293128-1. <a href="978-0-13-293128-1" target="_blank">978-0-13-293128-1</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>"Ionic Compounds Containing Polyatomic Ions". www.chem.purdue.edu. Retrieved 2022-04-16. <a href="https://www.chem.purdue.edu/gchelp/nomenclature/poly_atom.htm" target="_blank">https://www.chem.purdue.edu/gchelp/nomenclature/poly_atom.htm</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>"IUPAC - radical (free radical) (R05066)". goldbook.iupac.org. Retrieved 25 January 2023. <a href="https://goldbook.iupac.org/terms/view/R05066" target="_blank">https://goldbook.iupac.org/terms/view/R05066</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "pyro". doi:10.1351/goldbook.P04959 <a href="/wiki/International_Union_of_Pure_and_Applied_Chemistry" target="_blank">/wiki/International_Union_of_Pure_and_Applied_Chemistry</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> </ol>