Consider the bonding properties of the three compounds (CO2, CO, CO32- ). Explain the hybridization of the carbon atom
and pi-bonding in each compound based on valence bond theory,
and determine which one has the weakest carbon-to-oxygen
bond.

CO3^2- has the weakest C-O bond

Explanation:

Hybridization is a valence bond concept that has to do with the mixing of atomic orbitals to give hybrid atomic orbitals suitable for overlapping with orbitals of other atoms to form molecules. The hybridization of the carbon atom in CO, CO2 and CO3^2- are; sp, sp and sp2. This implies that there must be pi bonding in each of the species since sp and sp2 hybridized carbon atoms are known to lead to molecules possessing pi bonds.

In CO2, carbon in sp hybridized state is bonded to two oxygen atoms in sp2 hybridized state leading to a double bond between carbon and each oxygen atom. In CO, the carbon atom is sp hybridized while the oxygen atom is sp2 hybridized. CO3^2- contains an sp2 hybrized carbon atom in a trigonal planar geometry.

The relative bond lengths of the C-O bond in CO2, CO and CO3^2- is 116 pm, 112.8 pm and 136pm. Hence CO3^2- has the longest bond length. Remember that bond length is inversely proportional to the bond order. That is, the shorter the bond length, the greater the bond order. This implies that CO will have the greatest bond order because it shows the shortest bond length. It turns out that CO has a bond order of 3, CO2 has a bond order of 2 and CO3^2- has a bond order of 1.33. This is intermediate between the bond order of single and that of double C-O bond hence CO3^2- is represented using resonance structures.

The species with the longest C-O bond length also has the weakest C-O bond hence CO3^2- has the weakest C-O bond.

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