Polyatomic Ions

Polyatomic ions are tightly bound groups composed of multiple elements that possess an overall charge. The positively charged ions are called cations, while the negatively charged ions are called anions. 

The charts below show some of the most common polyatomic ions grouped by their respective charges. Unfortunately when it comes to learn them all you will have to seat down and memorize. 

The one major +1 charge polyatomic ion is the ammonium ion. 

NH4-Ion-AmmoniumAmmonium Ion

The +2 charge cation is the mercury (I) ion, which is composed of two mercury ions that are bonded together to form a dimer.  

Mercury-I-Ion-Hg2+-cationMercury (I) Ion

There are many - 1 charge anions and these are the most commonly recognized. 

Acetate-CH3CO3-C2H3O2-CN-OH-NO3-NO2-HCO3-HSO3-HSO4-H2PO4-SCN-OCN-MnO4-H2PO3-1 Charge Polyatomic Anions

Polyatomic ions containing halogens are referred to as oxyhalogens or halogen oxyanions. 

Perchlorate-chlorate-chlorite-hypochlorite-HClO-HClO2-HClO3-HClO4Halogen Oxyanions

The most common – 2 charge polyatomic ions are: 

C2O4-CO3-CrO4-Cr2O7-HPO4-O2-SO3-SO4-SiO3-S2O3-2 Charge Polyatomic Anions

The most common – 3 charge polyatomic ions are: 

PO4-PO3-AsO4-Phosphate-phosphite-arsenite-3 Charge Polyatomic Anions

Memorizing these polyatomic ions will be essential later on when dealing with naming binary molecular compounds, ionic compounds, and oxyacids. In addition our review on the various charges will be further discussed when calculating oxidation states and oxidation numbers,