Ions in Solution

Many solids are made of ions. When one dissolves, water pulls the ions apart and each moves on its own. The dissolution equation:

NaCl(s) → Na⁺(aq) + Cl⁻(aq)

(s) is solid; (aq) is dissolved in water.

The small numbers in the formula become numbers of ions:

CaCl₂(s) → Ca²⁺(aq) + 2Cl⁻(aq)

Dissolved CaCl₂

A group of atoms with one charge, like NH₄⁺ or SO₄²⁻, stays whole:

(NH₄)₂SO₄(s) → 2NH₄⁺(aq) + SO₄²⁻(aq)

The charges on the right add up to zero.