Polyatomic ion
A polyatomic ion is an ion consisting of a molecule with covalently bonded atoms or of a metal complex that can be considered as acting as a single unit in the context of acid/base chemistry or in the formation of salts. Note, a polyatomic ion is also referred to in older works as a radical. In current usage the term radical refers to free radicals which are uncharged species with an unpaired electron.
A large polyatomic ion will often be considered as the conjugate acid or conjugate base of a neutral molecule, for example the conjugate acid of adrenaline at the amine group.
Note that many of the common negatively-charged anionic polyatomic ions are conjugate bases of acids derived from the oxides of non-metallic elements. For example the sulfate or SO42- ion is derived from H2SO4 which can be regarded as SO3 + H2O.
Common polyatomic ions
| Common polyatomic ions | |
|---|---|
| acetate | CH3COO- |
| aluminate | AlO2-, Al2O42- |
| ammonium | NH4+ |
| arsenate | AsO43- |
| arsenite | AsO33- |
| azide | N3- |
| bicarbonate (hydrogen carbonate) | HCO3- |
| tetraborate | B4O72- |
| bromate | BrO3- |
| bromite | BrO2- |
| carbide | C22- |
| carbonate | CO32- |
| chlorate | ClO3- |
| chlorite | ClO2- |
| chromate | CrO42- |
| chromite | CrO2- |
| cyanate | CNO- |
| cyanide | CN- |
| dichromate | Cr2O72- |
| dihydrogen phosphate | H2PO4- |
| dihydrogen phosphite | H2PO3- |
| disulfide | S22- |
| formate (formiate) | HCO2- |
| hydrogen carbonate (bicarbonate) | HCO3- |
| hydrogen phosphate | HPO42- |
| hydrogen phosphite | HPO32- |
| hydrogen sulfate | HSO4- |
| hydrogen sulfite | HSO3- |
| hydronium | H3O+ |
| hydroxide | OH- |
| hypobromite | BrO- |
| hypochlorite | ClO- |
| hypoiodite | IO- |
| hypophosphite | PO23- |
| iodate | IO3- |
| iodite | IO2- |
| mercury(I) | Hg22+ |
| molybdate | MoO42- |
| nitrate | NO3- |
| nitrite | NO2- |
| oxalate | (COO)22- |
| perbromate | BrO4- |
| perchlorate | ClO4- |
| periodate | IO4- |
| permanganate | MnO4- |
| peroxide | O22- |
| phosphate | PO43- |
| phosphite | PO33- |
| pyridinium | C5H5NH+ |
| pyrophosphate | P2O74- |
| quaternary ammonium | NR4+ |
| silicate | SixOy |
| sulfate | SO42- |
| sulfide | S2- |
| sulfite | SO32- |
| superoxide | O2- |
| tartrate | (CH(OH)COO)22- |
| thiocyanate | CNS- |
| thiosulfate | S2O32- |
| tosylate (toluenesulfonate) | CH3C6H4SO3- |
| triflate (trifluoromethanesulfonate) | CF3SO3- |
| tungstate | WO42- |