Class 11 Chemistry - Chapter Chemical Bonding and Molecular Structure NCERT Solutions | Apart from tetrahedral geometry, another

Welcome to the NCERT Solutions for Class 11th Chemistry - Chapter Chemical Bonding and Molecular Structure. This page offers a step-by-step solution to the specific question from Exercise 1, Question 21: apart from tetrahedral geometry another possible....
Question 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?

Answer

The phenomenon of mixing of orbitals of the same atom with slight difference in energies so as to redistribute their energies and give new orbitals of equivalent energy and shape. The new orbitals formed are known as hybrid orbitals, it is called as hybridization.

Now, Electronic configuration of carbon atom:

C: 1s2 2s2 2p2

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

Here 1 s orbital & 3 p orbitals under goes 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, 3 p orbitals & 1 d orbitals has 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.

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