In a sigma bond, orbital overlap is always along the internuclear axis so the bond is centered directly between the two nuclei. In contrast, a pi bond forms from sideways overlap of orbitals. The electron density associated with a pi bond lies above and below the internuclear axis rather than along it. As a result, a pi bond is weaker than a s-type bond. Also, sigma bonds are stronger because they possess less energy than pi bonds. This can be depicted on a typical energy level diagram for the molecular orbitals. The hybridized atomic orbitals will be at a lower energy level than the remaining p-orbital, which is perpendicular to the molecule's plane.Hence the pi bonds are weaker.