Which is the correct Lewis structure for CO32-?
The Correct Answer and Explanation is :
The carbonate ion (CO₃²⁻) consists of a central carbon atom bonded to three oxygen atoms, forming a trigonal planar structure. Each oxygen atom carries a negative charge, and the carbon atom has no formal charge. This configuration results from the delocalization of electrons across the three C–O bonds, a phenomenon known as resonance.
Steps to Draw the Lewis Structure:
- Determine the Total Number of Valence Electrons:
- Carbon (C) is in group 14, contributing 4 valence electrons.
- Each oxygen (O) is in group 16, contributing 6 valence electrons.
- The 2⁻ charge adds 2 extra electrons.
- Total valence electrons = 4 (C) + 3 × 6 (O) + 2 (charge) = 24 electrons.
- Arrange the Atoms:
- Place the carbon atom at the center, as it is less electronegative than oxygen.
- Arrange the three oxygen atoms symmetrically around the carbon atom.
- Distribute the Electrons:
- Form single bonds between the carbon and each oxygen atom, using 6 electrons (3 bonds × 2 electrons per bond).
- Distribute the remaining 18 electrons as lone pairs on the oxygen atoms.
- Assign Formal Charges:
- Each oxygen atom has 7 electrons (6 from lone pairs and 1 from the bond), resulting in a formal charge of -1 per oxygen.
- The carbon atom has 4 electrons from the bonds, resulting in no formal charge.
- Indicate Resonance:
- The actual structure is a resonance hybrid, with the negative charges and double bonds delocalized over the three oxygen atoms.
This delocalization explains why all C–O bond lengths are equal and intermediate between single and double bonds. The trigonal planar geometry and the absence of lone pairs on the central atom contribute to the ion’s stability.
For a visual demonstration of drawing the Lewis structure of the carbonate ion, you may find the following video helpful:
videoHow to Draw the Lewis Structure of CO₃²⁻ (Carbonate Ion)turn0search0