Chemistry · Reference Sheet

Common Polyatomic Ions

Grouped by charge. The charge belongs to the whole ion — it does not change when you build a formula. When you need more than one, wrap it in parentheses: Ca(NO₃)₂.

Charge 1−1−

Acetate	C₂H₃O₂⁻
Hydrogen carbonatebicarbonate	HCO₃⁻
Hydrogen sulfatebisulfate	HSO₄⁻
Bromate	BrO₃⁻
Chlorate	ClO₃⁻
Chlorite	ClO₂⁻
Cyanide	CN⁻
Dihydrogen phosphate	H₂PO₄⁻
Hydroxide	OH⁻
Hypochlorite	ClO⁻
Iodate	IO₃⁻
Nitrate	NO₃⁻
Nitrite	NO₂⁻
Perchlorate	ClO₄⁻
Permanganate	MnO₄⁻
Thiocyanate	SCN⁻

Charge 1+1+

Ammonium	NH₄⁺
Hydronium	H₃O⁺

Charge 2−2−

Carbonate	CO₃²⁻
Chromate	CrO₄²⁻
Dichromate	Cr₂O₇²⁻
Hydrogen phosphate	HPO₄²⁻
Oxalate	C₂O₄²⁻
Peroxide	O₂²⁻
Silicate	SiO₃²⁻
Sulfate	SO₄²⁻
Sulfite	SO₃²⁻
Thiosulfate	S₂O₃²⁻

Charge 3−3−

Borate	BO₃³⁻
Phosphate	PO₄³⁻
Phosphite	PO₃³⁻

The −ate / −ite pattern. When one element pairs with oxygen, the everyday version ends in −ate. One fewer oxygen → −ite. Add the prefix per− for one more oxygen than −ate, and hypo− for one fewer than −ite. The charge stays the same across the whole ladder:

hypochlorite ClO⁻ → chlorite ClO₂⁻ → chlorate ClO₃⁻ → perchlorate ClO₄⁻