What is the molecular geometry of CO32-?
The Correct Answer and Explanation is:
The molecular geometry of the carbonate ion (CO₃²⁻) is trigonal planar.
Explanation:
- Electron Configuration: In the carbonate ion, the central carbon atom is bonded to three oxygen atoms. The carbon atom has a formal charge of 0, while the oxygen atoms carry a -1 charge each, leading to a total charge of -2 for the ion.
- VSEPR Theory: According to the Valence Shell Electron Pair Repulsion (VSEPR) theory, the geometry of a molecule or ion is determined by the repulsion between electron pairs around the central atom. In CO₃²⁻, the carbon atom is surrounded by three bonding regions corresponding to the three oxygen atoms, and there are no lone pairs of electrons on the carbon. This arrangement minimizes electron repulsion and places the three bonding regions as far apart as possible, resulting in a trigonal planar shape.
- Bond Angles: In this trigonal planar geometry, the bond angles between the oxygen atoms are approximately 120°. This is characteristic of molecules with three regions of electron density around a central atom.
- Resonance: One key feature of the carbonate ion is resonance. The actual bonding in CO₃²⁻ is a hybrid of three equivalent structures, where the double bond to one oxygen atom alternates among the three oxygens. This means that the bond order between carbon and each oxygen is not an integer but is effectively 1⅓, which helps distribute the negative charge equally over the three oxygen atoms.
- Polarity: Despite the trigonal planar geometry and the symmetry, the carbonate ion is nonpolar because the distribution of charge is uniform across the ion due to the resonance structures.
In summary, the molecular geometry of CO₃²⁻ is trigonal planar with bond angles of about 120°, and it exhibits resonance to stabilize the overall structure.
