Two inequivalent Lewis structures (Structure A and Structure B) are proposed for the carbonate ion, CO32−. In Structure A the central carbon is double-bonded to one oxygen atom and single-bonded to the other two; in Structure B the double bond is placed between carbon and a different oxygen atom, leaving the other two single-bonded.
Answer the following questions to assess the relative contribution of each structure to the resonance hybrid.
(1) For Structure A, compute the formal charge on the carbon atom and on each of the three oxygen atoms.
(2) Repeat the formal-charge calculation for Structure B.
(3) Identify which of the two structures (A or B) is a more significant contributor to the resonance hybrid, or whether they contribute equally. Support your conclusion quantitatively with the formal-charge data.
(4) Using the concept of resonance, predict the average C–O bond order expected experimentally in CO32− and explain how your formal-charge analysis supports this prediction.