List of Common Polyatomic Ions

Names, Formulas, and Charges

Three atoms

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This is a list of some of the most common polyatomic ions. It is worth committing the polyatomic ions to memory, including their molecular formulas and ionic charge.

Polyatomic Ion Charge = +1

Ammonium ion
This is the structure of an ammonium ion. Todd Helmenstine

Polyatomic ions with a positive 1 charge do occur, but the main one you'll encounter and need to know is the ammonium ion. Remember, because it is a cation, when it reacts and forms a compound, it is cited first in the chemical formula.

  • ammonium - NH4+

Polyatomic Ion Charge = -1

Chlorate anion
This is the one of the resonant structures of the chlorate anion. Ben Mills/PD

Many of the common polyatomic ions have an electrical charge of -1. It's good to know these ions on sight to help balance equations and predict compound formation.

  • acetate - C2H3O2-
  • bicarbonate (or hydrogen carbonate) - HCO3-
  • bisulfate (or hydrogen sulfate) - HSO4-
  • hypochlorite - ClO-
  • chlorate - ClO3-
  • chlorite - ClO2-
  • cyanate - OCN-
  • cyanide - CN-
  • dihydrogen phosphate - H2PO4-
  • hydroxide - OH-
  • nitrate - NO3-
  • nitrite - NO2-
  • perchlorate - ClO4-
  • permanganate - MnO4-
  • thiocyanate - SCN-

Polyatomic Ion Charge = -2

Thiosulfate anion
This is the chemical structure of the thiosulfate anion. Todd Helmenstine

Polyatomic ions with a minus 2 charge are also common.

  • carbonate - CO32-
  • chromate - CrO42-
  • dichromate - Cr2O72-
  • hydrogen phosphate - HPO42-
  • peroxide - O22-
  • sulfate - SO42-
  • sulfite - SO32-
  • thiosulfate - S2O32-

Polyatomic Ion Charge = -3

Phosphate anion
This is the chemical structure of the phosphate anion. Todd Helmenstine

Of course, several other polyatomic ions form with the negative 3 charge, but the borate and phosphate ions are the ones to memorize.

  • borate - BO33-
  • phosphate - PO43-