polyatomic ions

Hydronium: H3O+

Ammonium: NH4+

Acetate: C2H3O2-

Azide: N3-

Bromate: BrO3-

Chlorate: ClO3-

Cyanate: OCN-

Cyanide: CN-

Hydroxide: OH-

Iodate: IO3-

Nitrate: NO3-

Permanganate: MnO4-

Carbonate: CO3-2

Chromate: CrO4-3

Dichromate: Cr2O7-2

Peroxide: O2-2

Sulfate: SO42-

Phosphate: PO4-3