Question

Briefly explain why is sigma bond stronger than pi bond?

Answer 1

Sigma$\left(\mathrm{\sigma }\right)$ bond:

• This type of covalent bond is formed by the end-to-end (head-on) overlap of bonding orbitals along the internuclear axis.
• This is called head-on overlap or axial overlap.
• The sigma bond can be formed by the combination of atomic orbitals such as $\mathrm{s}-\mathrm{s}$ overlapping, $\mathrm{s}-\mathrm{p}$ overlapping as well as $\mathrm{p}-\mathrm{p}$ overlapping.
• The $\mathrm{s}-\mathrm{s}$ overlapping is shown below:

Pi $\left(\mathrm{\pi }\right)$ bond:

• In the formation of $\mathrm{\pi }$ bond, the atomic orbitals overlap in such a way that their axes remain parallel to each other and perpendicular to the internuclear axis.
• The orbitals formed due to sidewise overlapping consist of two saucer-type charged clouds above and below the plane of the participating atoms.

Strength of sigma and pi bond:

• The strength of a bond is dependent on the extent of overlapping.
• In the case of the sigma bond, the overlapping of orbitals takes place to a larger extent.
• Hence, the sigma bond is stronger in comparison to the pi bond because, in $\mathrm{\pi }$ bond, the extent of overlapping occurs to a smaller extent.