How can the formation of sigma and pi bonds be explained?
1 Answer
By the overlap of atomic orbitals to form molecular orbitals
Explanation:
A sigma bond lies along the axis between the nuclei of the two bonded atoms. It can be thought of as being formed when an orbital from each of the atoms overlaps as the atoms come together. s-orbitals or p-orbitals oriented along the axis of the bond would be suitable.
When the sigma bond is formed, the bonding pair of electrons from these atomic orbitals are now found in a new molecular orbital - a sigma orbital - located between the two nuclei. In this way the electrostatic attraction between the positively charged nuclei and the localised bonding pair of electrons in the sigma orbital results in a strong single covalent bond to be formed.
When a double bond is formed, the first bonding pair occupies a sigma molecular orbital as above. Sideways overlap of two p-orbitals on the bonded atoms results in an additional molecular orbital being formed either side of the sigma-orbital. This is a pi-orbital and in it the second bonding pair are localised.
