The C=C double bond consists of one σ and one π bond. The sigma bond is formed from the direct (head-on) overlap of two atomic orbitals, one from each carbon atom. The pi bond is formed from the sideways overlap of two p orbitals. The double bond is shorter than a single bond, and the bond strength is greater than but less than double the bond strength of a single bond.The pi bond prevents the two carbon atoms from rotating about the double bond.