Question

Carbon and silicon belong to (IV) group. The maximum coordination number of carbon in commonly occurring compounds is 4, whereas that of silicon is 6. This is due to

• A. Large size of silicon
• B. More electropositive nature of silicon
• C. Availability of low lying d-orbitals in silicon
• D. Both (a) and (b)

Answer 1

The correct option is C

Availability of low lying d-orbitals in silicon

The electronic configuration of carbon is $1s^2,2s^2,2p^2$
Clearly, n = 2 and there are no suitable vacant d-orbitals that
could accommodate enough electrons to extend its octet.

Silicon does have low-energy $3d$ orbitals and can thus extend its octet.