Question

Which of the following is not correct?

• A. All are incorrect
• B. $\sigma$ bond is stronger than $\pi$-bond
• C. Double bond is shorter and stronger than a single bond
• D. $\sigma$ bond is weaker than $\pi$-bond

Answer 1

The correct option is D $\sigma$ bond is weaker than $\pi$-bond

$\sigma$ bond is stronger than $\pi$ bond. It is because of the fact that the overlapping of atomic orbitals can take place to a greater extent (head on) during the formation of $\sigma$ bond whereas, the overlapping of orbitals occurs to a smaller extent (lateral) during the formation of $\pi$ bond.

Double bonds have more electrons being shared between the bonded atoms. More the bonding electrons stronger is the bond. So, the bond length reduces and the energy required to break a double bond is more than that of a single bond. Therefore, double bonds are stronger.
For example,
The bond lengths of $C-C$ $\left(\sigma bond\right)$, $C=C$ (one $\sigma$ and one $\pi$ bond) and $C\equiv C$ (one $\sigma$ and two $\pi$ bonds) are 154 pm, 134 pm and 120 pm respectively. Their respective average bond energies are approximately 347, 614 and 839 kJ/mol.