What is the average bond order of each carbon–oxygen bond in the carbonate ion, CO_3^{2-}?

• A. 1.33
• B. 1.67
• C. 1
• D. 2
• E. 1.33

Answer: (A)

Verified step by step guidance

1. Identify the structure of the carbonate ion, CO_3^{2-}. It consists of one carbon atom bonded to three oxygen atoms, with an overall charge of -2.
2. Recognize that the carbonate ion exhibits resonance, meaning the double bond between carbon and oxygen is delocalized over the three C–O bonds. This means the bonds are equivalent and have the same bond order.
3. Determine the total number of bonding electron pairs between carbon and oxygen atoms. In the resonance structures, there is one C=O double bond and two C–O single bonds, but resonance averages these out.
4. Calculate the average bond order by dividing the total number of bonds between carbon and oxygen by the number of C–O bonds. Since there are 4 bonding pairs (one double bond counts as 2 bonds) distributed over 3 bonds, use the formula: \(\text{Average bond order} = \frac{\text{Total number of bonds}}{\text{Number of bonds}} = \frac{4}{3}\)
5. Express the average bond order as a decimal to understand the bond character, which will be approximately 1.33, indicating partial double bond character in each C–O bond.