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General Chemistry I · Aqueous Reactions

Net Ionic Equations

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Want it in plain words first? Jump to Eli explains — the same idea, no jargon.
On this page 7 sections
  1. In 30 seconds
  2. Why this matters
  3. The college version
  4. Eli explains
  5. Key takeaway
  6. Study tools
  7. Sources & references

In 30 seconds

A reaction in solution can be written three ways. The molecular equation shows all reactants and products as neutral formulas. The complete ionic equation shows every soluble strong electrolyte as its free ions. The net ionic equation results from canceling spectator ions — ions present on both sides that do not participate — leaving only the species that actually change. The net ionic equation is the truest description of what happens at the particle level, and it must conserve both atoms and electric charge.

Why this matters

The net ionic equation strips away bystanders to reveal the actual chemistry — that lead(II) ions and iodide ions, no matter their original compounds, always make yellow lead(II) iodide. This focus lets chemists predict reactions between families of compounds, understand water-softening and scale formation, and reason about acid–base and redox reactions, which are also best written in net ionic form.

The college version

Key Ideas

Three levels of representation

  • Molecular equation: AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq).
  • Complete ionic equation: Ag⁺(aq) + NO₃⁻(aq) + Na⁺(aq) + Cl⁻(aq) → AgCl(s) + Na⁺(aq) + NO₃⁻(aq).
  • Net ionic equation: Ag⁺(aq) + Cl⁻(aq) → AgCl(s).

Rules for writing each level

  • Only soluble strong electrolytes are written as separated ions.
  • Insoluble solids (s), weak electrolytes, and nonelectrolytes stay as whole formulas.
  • Spectator ions appear unchanged on both sides and are removed.

Charge and mass balance

  • Atoms of each element must be equal on both sides.
  • The total electric charge must also be equal on both sides (a unique check that molecular equations don't require).

Equations and Variables

  • Molecular: AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)
  • Complete ionic: Ag⁺(aq) + NO₃⁻(aq) + Na⁺(aq) + Cl⁻(aq) → AgCl(s) + Na⁺(aq) + NO₃⁻(aq)
  • Net ionic: Ag⁺(aq) + Cl⁻(aq) → AgCl(s)
  • Spectator ions here: Na⁺ and NO₃⁻.

How It Works (Problem-Solving Method)

  1. Write and balance the molecular equation, including (aq)/(s) states from the solubility rules.
  2. Write the complete ionic equation: separate each soluble strong electrolyte into its ions.
  3. Identify spectator ions — identical ions on both sides.
  4. Cancel the spectators.
  5. Write the net ionic equation with the remaining species; check atom balance and charge balance.

Worked Example

Write the net ionic equation for: Pb(NO₃)₂(aq) + 2 KI(aq) → PbI₂(s) + 2 KNO₃(aq).

  1. Molecular equation is already balanced.
  2. Complete ionic: separate soluble strong electrolytes (Pb(NO₃)₂, KI, KNO₃ are all aqueous; PbI₂ is the solid): Pb²⁺(aq) + 2 NO₃⁻(aq) + 2 K⁺(aq) + 2 I⁻(aq) → PbI₂(s) + 2 K⁺(aq) + 2 NO₃⁻(aq)
  3. Spectator ions: K⁺ and NO₃⁻ (appear on both sides).
  4. Cancel them.
  5. Net ionic: Pb²⁺(aq) + 2 I⁻(aq) → PbI₂(s).
    • Charge check: left = (+2) + 2(−1) = 0; right = 0. Balanced.

Common Confusions

  • "Write every substance as ions." — Only soluble strong electrolytes are split; keep (s), (l), (g), weak electrolytes, and nonelectrolytes whole.
  • "Cancel ions that appear on both sides even if their amount differs." — Spectators must appear with the same coefficients; otherwise they participate and stay in the net equation.
  • "Net ionic equations don't need charge balance." — They do; total charge must be equal on both sides (e.g., Pb²⁺ + 2 I⁻ → PbI₂ is charge-neutral on both sides).
  • "The net ionic equation shows the spectator ions." — It shows only the participating species; spectators are removed.
Eli, the EliExplains learning guide

Eli explains

The same idea, in plain words

Explain it like I’m 10

Think of a reaction like a play where some actors change costume and others just stand there. The molecular equation is the playbill with everyone's full name. The complete ionic equation shows every actor separately. The net ionic equation is just the two actors who actually do something on stage — the "spectators" who stood still in the background are edited out. The catch: you can only "edit out" an actor if they truly didn't change — in chemistry, a spectator ion must appear exactly the same on both sides, and the final equation still has to balance both atoms and electric charge.

Key takeaways

  • Molecular → complete ionic → net ionic.
  • Only soluble strong electrolytes split into ions.
  • Spectator ions are unchanged on both sides and are canceled.
  • Net ionic equations must balance atoms and charge.
  • Solids, liquids, gases, weak electrolytes, and nonelectrolytes stay whole.
  • Three forms: molecular, complete ionic, net ionic.
  • Split only soluble strong electrolytes into ions.
  • Cancel spectator ions (identical on both sides).
  • Net ionic equation balances atoms and charge.

Keep learning

Ready to build on this? Continue to the next lesson.

Practice General Chemistry I

This lesson has no separate scored set. Practice draws from the subject’s question bank.

Study tools & related lessonsYou’ll learn to · Related

You’ll learn to

  • Distinguish molecular, complete ionic, and net ionic equations.
  • Identify spectator ions and cancel them correctly.
  • Write a net ionic equation from a molecular equation.
  • Verify that a net ionic equation conserves both atoms and charge.

Sources & references

  1. Chemistry LibreTexts, "7.7: Writing Chemical Equations for Reactions in Solution — Molecular, Complete Ionic, and Net Ionic Equations."
  2. Chemistry LibreTexts, "4.2: Precipitation Reactions."
  3. OpenStax, "4.1 Writing and Balancing Chemical Equations." *Chemistry 2e*.

This lesson was adapted from the open educational references above; their licenses and attributions are preserved. See Copyright & Licensing.

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