Comprehensive Guide to Polyatomic Ions and Nomenclature Rules

Polyatomic Ion Nomenclature Rules

  • Prefix and suffix naming conventions for oxyanions/oxoanions depend systematically on the number of oxygen atoms bound to the central atom:
    • PER-: Indicates MORE OXYGEN atoms relative to the standard -ate ion (specifically one additional oxygen atom).
    • -ate: Represents the standard or base oxoanion form.
    • -ite: Indicates LESS OXYGEN relative to the -ate ion (specifically one fewer oxygen atom).
    • Hypo-: Indicates even LESS OXYGEN (specifically one fewer oxygen atom than the -ite ion, or two fewer oxygen atoms than the -ate ion).

Positive Polyatomic Ions (Cations)

  • Polyatomic cations carry a net positive formal charge:
    • Ammonium: NH4+NH_4^{+} (Charge: 1+1+)
    • Hydronium: H3O+H_3O^{+} (Charge: 1+1+)

Monovalent Polyatomic Anions (1- Charge)

  • Polyatomic anions possessing a net charge of 1−1-:

    • Hydroxide: OH−OH^{-}
    • Thiocyanate: SCN−SCN^{-}
    • Cyanide: CN−CN^{-}
    • Permanganate: MnO4−MnO_4^{-}
    • Acetate: C2H3O2−C_2H_3O_2^{-}

  • Halogen Oxoanion Series (Charge: 1−1-):

    • Chlorine Series:
    • Perchlorate: ClO4−ClO_4^{-}
    • Chlorate: ClO3−ClO_3^{-}
    • Chlorite: ClO2−ClO_2^{-}
    • Hypochlorite: ClO−ClO^{-}
    • Fluorine Series:
    • Perfluorate: FO4−FO_4^{-}
    • Fluorate: FO3−FO_3^{-}
    • Fluorite: FO2−FO_2^{-}
    • Hypofluorite: FO−FO^{-}
    • Bromine Series:
    • Perbromate: BrO4−BrO_4^{-}
    • Bromate: BrO3−BrO_3^{-}
    • Bromite: BrO2−BrO_2^{-}
    • Hypobromite: BrO−BrO^{-}
    • Iodine Series:
    • Periodate: IO4−IO_4^{-}
    • Iodate: IO3−IO_3^{-}
    • Iodite: IO2−IO_2^{-}
    • Hypoiodite: IO−IO^{-}

  • Nitrogen Oxoanions (Charge: 1−1-):

    • Nitrate: NO3−NO_3^{-}
    • Nitrite: NO2−NO_2^{-}

  • Hydrogen-Containing Oxoanions (Charge: 1−1-):

    • Hydrogen sulfate: HSO4−HSO_4^{-}
    • Hydrogen sulfite (also named bisulfite): HSO3−HSO_3^{-}
    • Hydrogen carbonate: HCO3−HCO_3^{-}
    • Dihydrogen phosphate: H2PO4−H_2PO_4^{-}

Divalent Polyatomic Anions (2- Charge)

  • Polyatomic anions possessing a net charge of 2−2-:
    • Carbonate: CO32−CO_3^{2-}
    • Sulfate: SO42−SO_4^{2-}
    • Sulfite: SO32−SO_3^{2-}
    • Chromate: CrO42−CrO_4^{2-}
    • Dichromate: Cr2O72−Cr_2O_7^{2-}
    • Peroxide: O22−O_2^{2-}
    • Oxalate: C2O42−C_2O_4^{2-}
    • Tartrate: C4H4O62−C_4H_4O_6^{2-}
    • Hydrogen phosphate (also named biphosphate): HPO42−HPO_4^{2-}

Trivalent Polyatomic Anions (3- Charge)

  • Polyatomic anions possessing a net charge of 3−3-:
    • Phosphate: PO43−PO_4^{3-}
    • Phosphite: PO33−PO_3^{3-}