An ion is an atom or molecule that has acquired an electric charge due to loss or gain of electrons. Thus, a polyatomic ion is an ion that is composed of 2 or more atoms. ScienceStruck lists down some common polyatomic ions with their charges and oxidation numbers.
Did You Know?
A negatively charged polyatomic ion that has one or more oxygen atoms bonded to another element is known as an oxyanion; for e.g. the sulphate, nitrate, and carbonate ions.
A polyatomic ion is composed of two or more atoms, and it carries a charge that is positive or negative.
When a polyatomic ion takes part in a chemical reaction, its oxidation number plays a significant role. The oxidation number is also known as Oxidation State. It is a number that is either positive, negative, or zero. The oxidation number of an ion indicates the number of electrons that an ion can gain, lose, or share when chemically reacting with another ion (monatomic or polyatomic), atom, compound, or molecule.
The oxidation number of a polyatomic ion is the sum of oxidation numbers of its constituent atoms. It is equal to the charge on the ion.
Common Polyatomic Ions
| Polyatomic Ion | Chemical Symbol | Charge | Oxidation Number |
| Ammonium | NH4+ | +1 | +1 |
| Phosphonium | PH4+ | +1 | +1 |
| Hydronium | H3O+ | +1 | +1 |
| Fluoronium | H2F+ | +1 | +1 |
| Tropylium | C7H7+ | +1 | +1 |
| Guanidine | C(NH2)3+ | +1 | +1 |
| Mercury | Hg22+ | +2 | +2 |
| Acetate | C2H3O2– | -1 | -1 |
| Bicarbonate | HCO3– | -1 | -1 |
| Bisulphate | HSO4– | -1 | -1 |
| Bisulfite | HSO3– | -1 | -1 |
| Bromate | BrO3– | -1 | -1 |
| Bromite | BrO2– | -1 | -1 |
| Chlorate | ClO3– | -1 | -1 |
| Chlorite | ClO2– | -1 | -1 |
| Cyanide | CN– | -1 | -1 |
| Hydroxide | OH– | -1 | -1 |
| Hypobromite | BrO– | -1 | -1 |
| Hypochlorite | ClO– | -1 | -1 |
| Hypoiodite | IO– | -1 | -1 |
| Iodate | IO3– | -1 | -1 |
| Iodite | IO2– | -1 | -1 |
| Nitrate | NO2– | -1 | -1 |
| Nitrite | NO2– | -1 | -1 |
| Perbromate | HBrO3– | -1 | -1 |
| Perchlorate | ClO4– | -1 | -1 |
| Permanganate | MnO4– | -1 | -1 |
| Dihydrogen phosphate | H2PO4– | -1 | -1 |
| Carbonate | CO32- | -2 | -2 |
| Chromate | CrO42- | -2 | -2 |
| Dichromate | Cr2O72- | -2 | -2 |
| Oxalate | C2O42- | -2 | -2 |
| Peroxide | O22- | -2 | -2 |
| Sulfate | SO42- | -2 | -2 |
| Sulfite | SO32- | -2 | -2 |
| Thiosulfite | S2O32- | -2 | -2 |
| Hydrogen phosphate | HPO42- | -2 | -2 |
| Ferricyanide | Fe(CN)63- | -3 | -3 |
| Phosphate | PO43- | -3 | -3 |
| Ferrocyanide | Fe(CN)64- | -4 | -4 |