Question

Apart from tetrahedral geometry, another possible geometry for $CH_{4}$ is square planar with the four H atoms at the corners of the square and the C atom at its centre. Explain why $CH_{4}$ is not square planar?

Answer 1

The mixing of orbitals with the difference in energy to form new orbitals of equal energy is called "hybridization" and new orbitals are called hybrid orbitals. The Carbon's atomic number is 6 and its electronic configuration is ${ 1s }^{ 2 }2s^{ 2 }2{ p }^{ 2 }$. In the excited state, 1 s-orbital and 3 p-orbitals are involved in hybridization and gives rise to tetrahedral shape for methane.

Whereas in the square planar structure of methane molecule, the hybridization involves d-orbital. For square planar structure 1 s, 3 p, and 1 d orbitals have to undergo hybridization. Since, carbon does not contain d-orbitals the square planar structure is not possible. Only tetrahedral structure is possible for methane molecule.