Sigma and pi bonds-definition, differences and detail explanation with examples

 Sigma and pi bond differences

    In this article, I will discuss the sigma and pi bonds in detail.

Sigma bond (σ)

       A bond that is formed by the linear or head-to-head overlap of atomic orbitals is known as a sigma bond. Thus a single bond, which is formed between two s atomic orbitals or one s and one p orbitals or two p orbitals by head to head overlap is known as a sigma bond. This overlap occurs along the same axis. The bond which is formed by this process possesses axial symmetry. All single bonds are called sigma bonds.

       In the sigma bond, electron distribution is concentrated along the internuclear axis.  

sigma bonds

Examples:

       The bond between two hydrogen atoms is formed by the head-to-head overlap of two s atomic orbitals.

sigma bond in the hydrogen molecule

       The bond between ammonia and boron trifluoride is formed by head to head overlap of px orbital of ammonia which has a lone pair and 2px vacant orbital of boron trifluoride.

sigma bond between ammonia and boron trifluoride

Pi bond (π)

       The bond which is formed by the parallel, sideways, or lateral overlap of two p_y, p_x, or Pz atomic orbitals is known as the pi bond.

pi bond

       In this bond electronic distribution lies above and below the molecular axis. The orbitals which form this bond must be coplanar.

pi-bond

Examples:

       The first bond between two oxygen atoms is a sigma bond and 2^nd bond is a pi bond which is formed by the sideways overlap of two p_y orbitals.

pi bond in an oxygen molecule