1
Parse the ion formula
CO32- -> C, O, O, O
The ion contains one carbon atom and three oxygen atoms.
Lewis Structure
CO32- Lewis Structure
Carbonate ion
CO32- has three equivalent resonance forms. One form is shown with one C=O bond and two C-O- bonds.
Use the diagram and steps below to check the carbonate ion Lewis structure, CO32- Lewis dot structure, valence electrons, formal charges, and molecular shape.
The double bond can be placed on any one of the three oxygens; the real ion is a resonance hybrid.
CO32-
Carbonate ion
Valence electrons24
Central atomC
GeometryTrigonal planar
Bond angleAbout 120 deg
PolarityIon
Electron geometryTrigonal planar
VSEPR Geometry
Molecular geometry
Trigonal planar
Electron geometry
Trigonal planar
Bond angle
About 120 deg
Polarity
Ion
Valence electrons
24
Bonding / lone pairs
3 / 0 around C
Central atom
C
Electron regions
3
How to Draw CO32-: Step-by-Step
2
Count total valence electrons
4 + 18 + 2 = 24
Add 2 electrons for the 2- charge.
3
Choose the central atom
Central atom: C
Carbon is placed in the center with three oxygens around it.
4
Draw one resonance form
One C=O and two C-O bonds
Two single-bonded oxygens carry -1 formal charge in the shown form.
5
Check resonance
3 equivalent forms
The C=O double bond can be placed on any one oxygen.
6
Final answer
The CO32- Lewis structure has three equivalent resonance forms. In one form, carbon has one C=O double bond and two C-O single bonds; the single-bonded oxygen atoms carry -1 formal charge.
Formal Charges
| Atom | Formal charge |
|---|---|
| C | 0 |
| double-bonded O | 0 |
| single-bonded O | -1 each |
Common Mistakes
- Do not draw only one fixed carbonate structure without mentioning resonance.
- The overall ion charge is 2-, not a neutral molecule.
FAQ
What is the Lewis structure for CO32-?
The CO32- Lewis structure has three equivalent resonance forms. In one form, carbon has one C=O double bond and two C-O single bonds; the single-bonded oxygen atoms carry -1 formal charge.
What is the Lewis dot structure for CO32-?
The Lewis dot structure for CO32- is the electron-dot drawing shown above. The CO32- Lewis structure has three equivalent resonance forms. In one form, carbon has one C=O double bond and two C-O single bonds; the single-bonded oxygen atoms carry -1 formal charge.
How many valence electrons does CO32- have?
CO32- has 24 total valence electrons in this Lewis structure.
What is the molecular geometry of CO32-?
CO32- has trigonal planar molecular geometry and trigonal planar electron geometry.
Is CO32- polar or nonpolar?
CO32- is an ion, so the overall charge matters more than a polar or nonpolar label. Its listed VSEPR shape is trigonal planar.
References
Method notes are aligned with standard Lewis structure steps: count valence electrons, draw a skeleton, distribute electrons, form multiple bonds when needed, and check formal charges and resonance.
OpenStax Chemistry 2e: Lewis Symbols and Structures and Formal Charges and Resonance.