Sigma Bond and Pi Bond

Sigma(σ) bond: A covalent bond which is formed by head on overlapping or end to end overlapping of one atomic orbital with the another along the inter nuclear axis is known as sigma bond.

Properties of sigma bond:

  • These bonds determine the shape of the molecule.
  • Sigma bond is stronger than pi bond.
  • Free rotation of atoms or groups is possible around this bond.
  • It is less reactive than pi bond.
  • Electrons involved in sigma bond are localized.
  • Sigma bonds can have independent existence.

It can be further classified into several types:

  1. S-S overlapping: A bond which is formed by the overlapping of 1s orbital of one atom with 1s orbital of another atom along the inter nuclear axis is called S-S overlapping.
  2. S-P overlapping: A bond which is formed by the overlapping of 1s orbital of one atom and 1p orbital of another atom along the inter nuclear axis is called S-P overlapping.
  3. P-P overlapping: A bond which is formed by overlapping of 1p orbital of one atom and 1 p orbital of another atom along the internuclear axis is called P-P overlapping.

Pi(σ) bond: A covalent bond formed by the sideways and lateral overlapping of one atom with the another atom along the inter nuclear axis is called Pi- bond. During the formation of pi-bond the overlapping takes place above and below the internuclear axis.

Properties of pi bond:

  • Pi bonds are weaker than sigma bonds.
  • Free rotation of atoms is not possible around sigma bond.
  • Pi bonds are more reactive than sigma bonds.
  • Pi bonds is formed only when the sigma bonds is already formed.
  • Pi-bond does not determine the shape of molecule, however it may affect the bond angle.
  • Pi electrons are mobile in nature.
Note: If the compound has single bond, there is one sigma bond. It the compound has double bond, there is sigma and pi bond each. If the compound has triple bond, there is one sigma bond and two pi bonds.

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