Question

Explain the following:

Why does the element silicon, not form a graphite like structure whereas carbon does.

Answer 1

In graphite, carbon is sp²-hybridised and each carbon is linked to three other carbon atoms by forming hexagonal rings. Each carbon is now left with one unhybridised p-orbital which undergoes sideways overlap to form three p-p double bonds. Thus, graphite has two-dimensional sheet like (layered) structure consisting of a number of benzene rings fused together. Silicon, on the other hand, does not form an analogue of carbon because of the following reason:

Due to bigger size and smaller electronegativity of Si than C, it does not undergo sp²-hybridisation and hence it does not form p-p double bonds needed for graphite like structure. Instead, it prefers to undergo only sp³-hybridisation and hence silicon has diamond like three­dimensional network