Question

Apart from tetrahedral geometry, another possible geometry for CH4 is square planar with the four H atoms at the corners of the square and the C atom at its centre. Explain why CH4 is not square planar? 

Answer 1

Electronic configuration of carbon atom: 

_⁶C:1s² 2s² 2p²

In the excited state, the orbital picture of carbon can be represented as:

Hence, carbon atom undergoes sp₃ hybridization in CH₄ molecule and takes a tetrahedral 

shape. 

For a square planar shape, the hybridization of the central atom has to be dsp₂ . However, an atom of carbon does not have d-orbitalsto undergo dsp₂ hybridization. Hence, the structure of CH₄ cannot be square planar. Moreover, with a bond angle of 90° in square planar, the stability of CH₄ will be very less because of the repulsion existing between the bond pairs. Hence, VSEPR theory also supports a tetrahedral structure for CH₄.