Apart from tetrahedral geometry, another possible geometry for CH4 is square planar with four H atoms at the corners of the square and the C atom at its centre. Explain why CH4 is not square planar?
Here 1 s orbital & 3 p orbitals undergo hybridization to form sp3 hybrid orbitals .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, ie, 1 s orbital, 3p orbitals & 1 d orbitals have to undergo hybridization .However, an atom of carbon does not have d-orbitals to 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.
