Question 8.7: Predict the shape of the carbonate ion, CO3^2–....

There are three equivalent resonance forms of a CO_{3}^{2–} ion:

The three equivalent resonance forms tell us that all three C–O bonds in a CO_{3}^{2–} ion are equivalent. In each resonance form there are three groups of electrons and no lone pairs around the central carbon atom. Thus, a CO_{3}^{2–} ion is of the class AX_3. We predict that a carbonate ion is trigonal planar with O–C–O bond angles of 120°. This prediction is in agreement with experimental results. The equivalence of the three C–O bonds in a CO_{3}^{2–} ion makes the three O–C–O bond angles equivalent (120°).