Lewis Structure Generator
Carbonate ion · CO3²− · Reviewed guide

CO3²− Lewis Structure

Carbonate has 24 valence electrons. One contributor contains one C=O bond and two C–O⁻ bonds, and three equivalent contributors describe the delocalized bonding.

Open CO3²− in the generatorSee drawing steps
CO₃²⁻
[ O⁻–C(=O)–O⁻ ]²⁻
One of three equivalent resonance contributors
Valence electrons24
Central atomCarbon
GeometryTrigonal planar
Bond angle120°

CO3²− structure overview

Carbon contributes 4 electrons, the three oxygens contribute 18, and the −2 charge adds 2 electrons. Carbon is central because it can connect all three oxygens.

How to draw carbonate

  1. Count 24 electrons.
    4 + 18 + 2 = 24.
  2. Connect carbon to three oxygens.
    Begin with three single bonds.
  3. Complete oxygen octets.
    Carbon remains short of an octet.
  4. Form one C=O bond.
    Move one oxygen lone pair into a bond.
  5. Show charges and resonance.
    The two single-bonded oxygens are −1; move the double bond to produce three contributors.

Formal charges

Carbon and the double-bonded oxygen have formal charge 0. Each single-bonded oxygen has −1, giving the required −2 total.

Geometry

Three bonding domains around carbon give trigonal planar geometry. Resonance does not move atoms, so every contributor has the same arrangement.

Common mistakes

  • Forgetting to add two electrons for the −2 charge.
  • Drawing three C=O bonds while also forcing an octet-only carbon model.
  • Leaving off ion brackets and the overall charge.
  • Treating one oxygen as permanently double bonded.

Reviewed July 16, 2026. Educational reference only.