To write a net ionic equation , you strip a reaction down to only the species that actually change during the reaction and remove everything that just “watches” (spectator ions).

Big picture: what a net ionic equation is

A net ionic equation shows only the ions and molecules that participate in the chemical change.
Ions that appear unchanged on both sides are called spectator ions and are left out. Example idea: if you mix two clear salt solutions and a solid forms, the net ionic equation shows only the ions that combine to make that solid.

Step‑by‑step method (general recipe)

Use this 5‑step routine for almost any aqueous reaction:

  1. Start with a balanced molecular equation
    • Make sure atoms are balanced (same number of each element on both sides).
    • Include physical states: (s)(s)(s), (l)(l)(l), (g)(g)(g), (aq)(aq)(aq).
  2. Identify strong electrolytes and write the complete ionic equation
    • Break strong electrolytes in aqueous solution into ions:
      • Soluble ionic compounds (e.g., NaCl(aq)(aq)(aq) → Na+^++(aq) + Cl−^-−(aq))
      • Strong acids (e.g., HCl(aq)(aq)(aq) → H+^++(aq) + Cl−^-−(aq))
      • Strong bases (e.g., NaOH(aq)(aq)(aq) → Na+^++(aq) + OH−^-−(aq))
    • Do not split:
      • Solids (s)(s)(s)
      • Liquids (l)(l)(l), like H2_22​O(l)(l)(l)
      • Gases (g)(g)(g)
      • Weak acids/bases (often left as whole molecules, like HF, CH3_33​COOH)
  3. Identify spectator ions
    • These ions appear on both sides of the complete ionic equation with the same charge and same state.
    • They are not involved in the actual chemical change.
  4. Cancel spectators
    • Cross out the spectator ions from both sides.
    • What remains are only the reacting particles.
  5. Write the net ionic equation
    • Write what’s left after cancellation.
    • Check that it is balanced both by atoms and by charge.

Worked example: precipitation reaction

Let’s use a classic one: aqueous sodium chloride and aqueous silver nitrate.

1. Molecular equation (balanced)

NaCl(aq)+AgNO3(aq)→NaNO3(aq)+AgCl(s)\text{NaCl}(aq)+\text{AgNO}_3(aq)\rightarrow \text{NaNO}_3(aq)+\text{AgCl}(s)NaCl(aq)+AgNO3​(aq)→NaNO3​(aq)+AgCl(s)

Everything is already balanced: 1 Na, 1 Cl, 1 Ag, 1 N, 3 O on each side.

2. Complete ionic equation

Split all aqueous strong electrolytes into ions, but keep the solid together:

Na+(aq)+Cl−(aq)+Ag+(aq)+NO3−(aq)→Na+(aq)+NO3−(aq)+AgCl(s)\text{Na}^+(aq)+\text{Cl}^-(aq)+\text{Ag}^+(aq)+\text{NO}_3^-(aq)\rightarrow \text{Na}^+(aq)+\text{NO}_3^-(aq)+\text{AgCl}(s)Na+(aq)+Cl−(aq)+Ag+(aq)+NO3−​(aq)→Na+(aq)+NO3−​(aq)+AgCl(s)

3. Identify spectator ions

  • Na+^++(aq) appears on both sides, unchanged → spectator
  • NO3−_3^-3−​(aq) appears on both sides, unchanged → spectator

4. Cancel spectators

Remove Na+^++ and NO3−_3^-3−​ from both sides:

Cl−(aq)+Ag+(aq)→AgCl(s)\text{Cl}^-(aq)+\text{Ag}^+(aq)\rightarrow \text{AgCl}(s)Cl−(aq)+Ag+(aq)→AgCl(s)

5. Net ionic equation

Ag+(aq)+Cl−(aq)→AgCl(s)\text{Ag}^+(aq)+\text{Cl}^-(aq)\rightarrow \text{AgCl}(s)Ag+(aq)+Cl−(aq)→AgCl(s)

That is the net ionic equation : only the ions that actually create the precipitate.

Another pattern: acid–base neutralization

Example: hydrochloric acid + sodium hydroxide.

1. Molecular equation

HCl(aq)+NaOH(aq)→NaCl(aq)+H2O(l)\text{HCl}(aq)+\text{NaOH}(aq)\rightarrow \text{NaCl}(aq)+\text{H}_2\text{O}(l)HCl(aq)+NaOH(aq)→NaCl(aq)+H2​O(l)

2. Complete ionic equation

H+(aq)+Cl−(aq)+Na+(aq)+OH−(aq)→Na+(aq)+Cl−(aq)+H2O(l)\text{H}^+(aq)+\text{Cl}^-(aq)+\text{Na}^+(aq)+\text{OH}^-(aq)\rightarrow \text{Na}^+(aq)+\text{Cl}^-(aq)+\text{H}_2\text{O}(l)H+(aq)+Cl−(aq)+Na+(aq)+OH−(aq)→Na+(aq)+Cl−(aq)+H2​O(l)

3–4. Spectators and cancellation

  • Spectators: Na+^++(aq), Cl−^-−(aq)
  • Cancel them:

H+(aq)+OH−(aq)→H2O(l)\text{H}^+(aq)+\text{OH}^-(aq)\rightarrow \text{H}_2\text{O}(l)H+(aq)+OH−(aq)→H2​O(l)

5. Net ionic equation

H+(aq)+OH−(aq)→H2O(l)\text{H}^+(aq)+\text{OH}^-(aq)\rightarrow \text{H}_2\text{O}(l)H+(aq)+OH−(aq)→H2​O(l)

For strong acid + strong base in water, this is almost always the net ionic equation.

Common reaction types that use net ionic equations

You most often write net ionic equations for:

  • Precipitation reactions
    • Two aqueous salt solutions form an insoluble solid.
    • Net ionic equation shows the ions that form the precipitate.
  • Acid–base neutralizations
    • Acid + base → water + a salt.
    • Net ionic often shows H+^++ + OH−^-− → H2_22​O.
  • Some redox reactions in solution
    • Where electrons are transferred and ions change oxidation states.

Reactions with only gases and pure liquids (like H2_22​ + O2_22​ → H2_22​O) generally do not give a useful net ionic equation because there are no free ions in solution.

Quick checklist you can memorize

When you’re in an exam or doing homework, run through this:

  1. Is the molecular equation balanced?
  2. Did I label states correctly (especially what is aqueous vs. solid)?
  3. Did I split only aqueous strong electrolytes into ions?
  4. Did I identify and cancel all spectator ions?
  5. Is my final net ionic equation balanced for atoms and charge?

If you want, send a specific equation you’re working on, and I can walk you through turning that exact one into a net ionic equation step by step.