Question

The correct order of $C-O $ bond length among $CO,CO_3^{2-}$, $CO_2$ is

• A. $CO_2 < CO_3^{2-} < CO$
• B. $CO < CO_3^{2-} < CO_2$
• C. $CO_3^{2-} < CO_2 < CO$
• D. $CO < CO_2 < CO_3^{2-}$

Answer 1

The Correct Option is D

To determine the correct order of C-O bond lengths for CO, CO_2, and CO_3^{2-}, let's consider the factors affecting these bond lengths: bond order and resonance structures.

1. Carbon Monoxide (CO):
   • CO has a triple bond between carbon and oxygen in the form of C \equiv O. The bond order is 3.
   • Higher bond order implies a shorter bond length.
2. Carbon Dioxide (CO₂):
   • CO_2 has a linear structure with two double bonds between carbon and oxygen, written as O = C = O. The bond order is 2 for each C-O bond.
   • Double bonds are longer than triple bonds but shorter than single bonds.
3. Carbonate Ion (CO₃^2-):
   • CO_3^{2-} is an example of resonance; it has three contributing structures with an average bond order of 1.33 for each C-O bond.
   • Resonance leads to bond lengths that are intermediate between a single bond and a double bond; this results in longer bond lengths than both CO and CO_2.

Based on the bond orders and structural considerations, the correct order of C-O bond lengths from shortest to longest is:

• CO - shortest, due to the triple bond
• CO_2 - intermediate, due to the double bond
• CO_3^{2-} - longest, due to resonance and shared bonds

This analysis matches the given correct answer: CO < CO_2 < CO_3^{2-}.