Question

Question 4.21 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?

Class XI Chemical Bonding and Molecular Structure Page 130

Answer 1

electronic configuration of carbon
in Ground state ,
₆C : 1s², 2s², 2px¹, 2py¹

in excited state
₆C : 1s², 2s², 2px¹, 2py¹,2pz¹

In CH4 molecule , carbon is sp³ Hybridized , so it is tetrahedral in shape . for square planar , dsp² Hybridisation is required which is not possible in Carbon due to absence of d - orbitals. also we know, according to VSEPR theory , four bonded electron pairs around carbon atom arranged themselves in regular tetrahedral geometry , which bond angle is 109°28' while in square planer structure ,the bond angle 90° . therefore CH4 can't be square planar .
hence, CH4 is tetrahedral in shape.

Answer 2

CH4 cant be a square planner because it has not any lone pair so we have to make sure that bond pair- bond pair repulsion should minimum

 In square planner it is 90°

And

In Tetrahedral geometry it is 109°28'