Polyatomic ions or compounds

Positive polyatomic ions: 

Ammonium: NH4(+)

Negative polyatomic ions: 

Nitrate: NO3(-)

Nitrite: NO2(-)

Sulfate: SO4(2-)

Sulfite: SO3(2-)

Carbonate: CO3(2-)

Phosphate: PO4(3-)

Hydroxide: OH(-)