What are allotropes? Sketch the structure of two allotropes of carbon namely diamond and graphite. What is the impact of structure on physical properties of two allotropes?

(N/A) Allotropy is the existence of an element in more than one form,having the same chemical properties but different physical properties. The various forms of an element are called allotropes.
Diamond:
In diamond,each carbon atom is $sp^{3}$ hybridized and bonded to four other carbon atoms in a rigid $3-D$ tetrahedral network. This structure makes it a very hard substance. In fact,diamond is one of the hardest naturally-occurring substances. It is used as an abrasive and for cutting tools.
Graphite:
It has $sp^{2}$ hybridized carbon atoms,arranged in the form of hexagonal layers. These layers are held together by weak van der Waals' forces. These layers can slide over each other,making graphite soft and slippery. Therefore,it is used as a lubricant.