Question

Which bond length is the longest?

$\mathrm{C}-\mathrm{C}$, $\mathrm{C}=\mathrm{C}$and $\mathrm{C}\equiv \mathrm{C}$.

Answer 1

1. Bond length is defined the as average distance between the centres of two bonded atoms' nuclei.
2. The bond length depends on bond order.
3. Bond order is the multiplicity of bonds eg for $\mathrm{C}\equiv \mathrm{C}$bond order is three and for $\mathrm{C}=\mathrm{C}$bond order is two.
4. Higher the bond order, higher will be the bond strength and lower the bond length.
5. Applying the above concept we get to know that $\mathrm{C}-\mathrm{C}$will have the greatest bond length among $\mathrm{C}-\mathrm{C}$, $\mathrm{C}=\mathrm{C}$and $\mathrm{C}\equiv \mathrm{C}$.
6. The order of bond length in a decreasing order being:$\mathrm{C}-\mathrm{C}$> $\mathrm{C}=\mathrm{C}$>$\mathrm{C}\equiv \mathrm{C}$.
7. Therefore, $\mathrm{C}-\mathrm{C}$ bond length is longest.