Lewis Structure Generator
Bicarbonate ion · HCO3−

HCO3− Lewis Structure

Bicarbonate is commonly drawn as HO–C(=O)–O⁻. The double bond and negative charge resonate between the two non-protonated oxygens; the O–H bond does not move between contributors.

Open HCO3− in the generatorSee drawing steps
HCO₃⁻
[ HO—C(=O)—O⁻ ]
Two equivalent contributors for the non-protonated oxygens
Total valence electrons24
Resonance forms2 equivalent
Central atomCarbon
Geometry at carbonTrigonal planar

HCO3− overview

Hydrogen contributes one electron, carbon four, three oxygens eighteen and the charge adds one. Hydrogen must bond to oxygen, not carbon, giving an HO–C–O framework with a third oxygen attached to carbon.

How to draw HCO3−

  1. Count 24 valence electrons.
  2. Use carbon as the central atom and attach three oxygens.
  3. Attach hydrogen to one oxygen.
    This oxygen remains the hydroxyl oxygen in the resonance set.
  4. Form one C=O double bond.
  5. Place −1 on the other non-protonated single-bonded oxygen and draw the second resonance contributor.

What moves in resonance?

Only electrons move. The C=O bond and the negative charge switch between the two oxygens that are not bonded to hydrogen. Moving the hydrogen would create a different proton-transfer structure, not a resonance contributor.

Formal charges

Carbon, the hydroxyl oxygen and the double-bonded oxygen are zero in the displayed contributor. The non-protonated single-bonded oxygen is −1.

Common mistakes

  • Bonding hydrogen directly to carbon.
  • Moving hydrogen between resonance contributors.
  • Drawing three equivalent C–O bonds without explaining resonance.
  • Forgetting the overall brackets and charge.

Last reviewed: July 16, 2026. Educational reference only.