(a) Describe briefly allotropism in p - block elements with specific reference to carbon.

Explanation

Some elements exist in more than one crystalline or molecular forms in the same physical state.
This phenomenon is called allotropism. Most common allotropes of carbon are
(i) Graphite, (ii) Diamond (iii) Fullerenes (iv) Carbon nanotubes, (v) Graphene.
(i) Graphite:
a. It is the most stable allotrophic form of carbon at normal termperature and pressure.
b. It is soft and conducts electricity.
c. It is composed of flat two dimensional sheets of carbon atoms.
d. Each sheet is a hexagonal net of `sp^(2)` hybridised carbon atoms with a C-C bond length of `1.41Å`.
e. Structure of graphite.

(ii) Diamond:
a. It is very hard.
b. The carbon atoms in diamond are `sp^(3)` hybridised with a C-C bond length of `1.54Å`.
c. In the diamond, carbon atoms are arranged in tetrahedral manner.
d. Structure of Diamond.

(iii) Fullerenes:
a. It is newly synthesised allotropes of carbon.
b. The `C_(60)` molecules have a soccer ball like structure and is called buckminster fullerene or buckyballs.
c. It has fused ring structure consists of 20 six membered rings and 12 five membered rings.
d. Each carbon atoms is `sp^(2)` hybridised.
e. The C-C bond distance is `1.44Å` and C=C distance is `1.38Å`.
f. Structure of fullerence,

(iv) Carbon nanotubes:
a. It is recently discovered allotropes, have graphite like tubes fullerene ends.
b. These nanotubes are stronger than steel and conduct electricity.
c. Structure of Carbon nanotubes.

(v) Graphene:
(a) It has a single planar sheet of `sp^(2)` hybridised carbon atoms that are densely packed in a honey caomb crystals lattice.
d. Structure of Graphene,