Strip out the ions that do not react
A net ionic equation shows only the species that actually change. You take the full reaction, break the dissolved compounds into ions, then delete the ions that sit unchanged on both sides. What remains is the real chemistry.
Cancelling the struck-through spectator ions leaves the net ionic equation: Ag+(aq) + Cl−(aq) → AgCl(s). Sodium and nitrate were dissolved before and after, so they are dropped.
The four steps
- Balance and label. Write the balanced molecular equation with a state (s, l, g, aq) on every compound.
- Dissociate. Split every aqueous strong electrolyte — soluble salts, strong acids, strong bases — into its ions.
- Cancel spectators. Remove any ion that is identical on both sides.
- Check charge. The total charge on the left must equal the total charge on the right, and atoms must still balance.
Which compounds split into ions
Solubility decides what dissociates. Soluble aqueous compounds become ions; insoluble products become the precipitate that drives the reaction.
| Rule | Soluble? | Exceptions |
|---|---|---|
| Group 1 & ammonium salts | Yes | none |
| Nitrates, acetates | Yes | none |
| Chlorides, bromides, iodides | Yes | Ag, Pb, Hg |
| Sulfates | Yes | Ba, Pb, Ca, Sr |
| Carbonates, phosphates | No | Group 1, ammonium |
| Hydroxides | No | Group 1, Ba, Sr |
Strong acids (HCl, HNO₃, H₂SO₄) and strong bases (NaOH, KOH) dissociate fully. Weak acids and bases stay written as molecules.
Common questions
What is a spectator ion?
A spectator ion appears in the same form, with the same charge, on both sides of the complete ionic equation. It is dissolved before and after the reaction and takes no part in it, so it is cancelled out. In silver chloride precipitation, sodium and nitrate ions are the spectators.
How do I derive the net ionic equation?
Balance the molecular equation and mark every state, split all aqueous strong electrolytes into their ions, then cross out any ion that is identical on both sides. What is left is the net ionic equation. Solids, liquids, gases and weak electrolytes stay written as whole formulas.
Why do solids and gases stay as full formulas?
Only substances that actually dissolve and dissociate in water are written as separate ions. A precipitate (s), a gas (g), pure water (l) and weak acids or bases are not free-floating ions in solution, so they keep their molecular form.
What if every ion cancels?
If nothing is left, no reaction occurred, or your solubility calls were wrong. A valid net ionic equation must still have reactants and products and must balance for both atoms and charge.
