Discuss in brief sp³ hybridisation. Explain the formation of methane and ethane.

 hybridisation: Electronic configuration of carbon (Z = 6) in the excited state is 1s² 2s¹

This type of hybridization involves the mixing of all four filled orbitals i.e. 1s and 3p orbitals to form four new orbitals called sp³ hybrid orbitals of equivalent enthalpies and identical shapes. 


Fig. Representation of sp³ hybridization:
A single sp³ hybrid orbital.
The four sp³ hybrid orbitals are directed towards the four corners of a tetrahedral. The angle between two adjacent sp³ hybrid orbitals. Each sp³ hybrid orbital has 1/4 s-character and 3/4 p-character. sp³ hybridization is also known as tetrahedral hybridisation.

(i) The molecular orbital structure of methane: In methane molecule, carbon atom undergoes sp³ hybridisation. Each sp³ hybrid orbital overlaps with 1s orbital of hydrogen atom along the internuclear axis to form four 

 bond.

Molecular orbital structure of methane

The four C – H bonds are directed towards the four corners of a regular tetrahedron. So methane has a tetrahedral structure. Each H – C – H bond angle is of 109°.28’. Each C – H bond length is 109 pm (1.09 Å).

(ii) Molecular orbital picture of ethane: In ethane molecule, both carbon atoms are in the sp³ hybrid state. In its formation, one hybrid orbital of one carbon atom overlaps with one sp³ hybrid orbital of a second carbon atom along the internuclear axis to form a sigma (σ) C – C bond. The remaining three sp³ hybrid orbitals of each carbon atom overlap with 1 s orbital of hydrogen atom axially to form six sigma C – H bonds.

     

The length of C-C bond in ethane is 154 pm (or 1- 54 Å) and that of each C - H bond is 109 pm (or 1-09 Å).