Question

Write a note on: 

i. Diamond 

ii. Graphite 

iii. Fullerene

Answer 1

i. Diamond:

a. Diamond is an allotrope of carbon. It is used in jewellery and is the most precious crystal.

b. Covalent bonds between sp³ hybridized carbon atoms continue in all directions to form a giant network.

c. Diamond is very strong and hard due to presence of strong covalent bonds.

d. It is the hardest material and has very high melting point (3550^oC).

ii. Graphite:

a. Graphite is an allotrope of carbon in which each carbon atom is sp² hybridized and forms covalent bonds with three other sp² hybridised carbon atoms. This results in formation of interlinked six membered rings.

b. \(\pi \) bonds are formed between carbon atoms by utilizing half filled unhybridised 2p_z orbital on each carbon atom. Layers of carbon atoms are formed.

c. Electrons present in delocalized molecular orbitals can move freely and conduct electricity. Hence graphite is a good conductor of electricity.

d. Graphite is sufficiently hard due to presence of relatively stronger covalent bonds. The adjacent layers of carbon atoms are held together by weak van der Waal’s forces of attraction.

e. The layers of carbon atoms in graphite can slide over other layers. Hence, graphite is used as lubricant for reducing friction.

f. It is used in ribbons used for printing in computers and typewriters. It is also used in lead pencils.

iii. Fullerene:

a. Fullerene is an allotrope of carbon. It is also called Buckball or Buckminster fullerene.

b. When a high power laser was focused on carbon, fullerene was formed. It has formula C₆₀ and shape of a soccer ball (hollow sphere).

c. sp² hybridized carbon atoms occupy sixty equidistant places on this sphere. They form hexagons and pentagons.

d. Fullerenes are present in carbon soot.

e. Fullerene reacts with potassium to form K₃₅C₆₀. This compound is a superconductor of electricity at 18 K. It reacts with transition metal to form a catalyst.

f. Tubes made from fullerene and graphite are called nanotubes. These are used as high strength materials, electric conductors, molecular sensors and semiconductors.

Answer 2

Diamond is a well-known allotrope of carbon. The hardness and high dispersion of light of diamond make it useful for both industrial applications and jewelry. Diamond is the hardest known natural mineral. This makes it an excellent abrasive and makes it hold polish and luster extremely well. No known naturally occurring substance can cut (or even scratch) a diamond, except another diamond. It is also one of the costliest elements in the world.

Graphite, named by Abraham Gottlob Werner in 1789, from the Greek  for its use in pencils) is one of the most common allotropes of carbon. Unlike diamond, graphite is an electrical conductor. Thus, it can be used in, for instance, electrical arc lamp electrodes. Likewise, under standard conditions, graphite is the most stable form of carbon. Therefore, it is used in thermochemistry as the standard state for defining the heat of formation of carbon compounds.