Parentheses rule:

Use parentheses ONLY if: it’s polyatomic AND you need more than 1 of it

Polyatomic ions (you must memorize these):

• NO₃⁻ → nitrate

• SO₄²⁻ → sulfate

• C₂H₃O₂⁻ → acetate

👉 Notice: more than one element = polyatomic

NOT polyatomic (single atoms):

• Mg²⁺

• Ba²⁺

• Ag⁺

👉 Just one element → NOT polyatomic

SO₄²⁻ has:

• S (sulfur)

• O₄ (oxygen)

👉 More than one atom → polyatomic

🧠 How to recognize a polyatomic ion

x🔑 Rule:

A polyatomic ion = more than 1 atom + has a charge

👉 So if you see:

• multiple capital letters OR

• a known group of atoms

…it’s polyatomic.