List of Common Polyatomic Ions

Names, Formulas and Charges of Polyatomic Ions

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.

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-