Why are pi (#pi#) bonds weaker than sigma (#sigma#) bonds?
In a σ bond, the electrons are in orbitals between the nuclei of the bonding atoms.
Electron density is greatest between the nuclei.
The electrons attract the nuclei and form a σ bond — the strongest type of covalent bond.
In a π bond, the p orbitals overlap side-on.
The overlap is less efficient, because the electron density is off to the sides of the σ bond.
The electrons are not as effective in attracting the two nuclei. Thus, a π bond is weaker than a σ bond.