Allotropes of Carbon

Formed due to catenation and pπ-pπ bond formation of carbon.

1. Diamond:

• Has crystalline lattice
• Carbon atom undergoes sp³ hybridisation
• Shape: tetrahedral
• C-C bond length =  154 pm
• Hardest substance
  
  

Uses:

• Diamond paste is used in polishing
• Used as abrasive in sharpening hard tools which are used for cutting, grinding etc.
• Used as a gemstone

2. Graphite:

• Has layered structure which are held by van der Waals forces
• Distance between two layers is 340pm
• Each layer has planar hexagonal rings of carbon atoms
• c-c bond length within a layer is 141.5pm
• carbon undergoes sp² hybridisation
• The electrons are delocalized over the whole sheet and are mobile. Therefore, graphite conducts electricity along the sheet.
• It is soft and slippery
• Thermodynamically most stable form of carbon
  
  

Uses:

• Used as a dry lubricant in machine parts.
• In making lead pencils
• Being resistant to chemicals and having a high melting point and also because it is a good conductor of heat, graphite is used to make crucibles.
• The presence of free electrons makes graphite a good conductor of electricity and it is used to make electrodes.
• Graphite has the ability to absorb fast-moving neutrons, thus, it is used in nuclear reactors to control the speed of the nuclear fission reaction.

3. Fullerene:

• Made by heating graphite in an electric arc in presence of inert gases.
• Fullerenes consist of 20 hexagonal and 12 pentagonal rings as the basis of an icosahedral (polyhedron with 20 faces) symmetry closed cage structure.
• Each carbon atom is bonded to three others and is sp² hybridized. The C60 molecule has two bond lengths - the 6:6 ring bonds can be considered "double bonds" and are shorter than the 6:5 bonds.
• C60 is not "super aromatic" as it tends to avoid double bonds in the pentagonal rings, resulting in poor electron delocalization. As a result, C60 behaves like an electron deficient alkene, and reacts readily with electron rich species.
• The geodesic and electronic bonding factors in the structure account for the stability of the molecule. In theory, an infinite number of fullerenes can exist, their structure based on pentagonal and hexagonal rings, constructed according to rules for making icosahedra.
• Buckminster fullerenes are also known as buck balls
  
  

Uses:

• Used to trap free radicals generated during an allergic reaction and block the inflammation that results from an allergic reaction.
• The antioxidant properties of buckyballs may be able to fight the deterioration of motor function due to multiple sclerosis.
• Combining buckyballs, nanotubes and polymers to produce inexpensive solar cells that can be formed by simply painting a surface.
• Used to store hydrogen, possibly as a fuel tank for fuel cell powered cars.
• Buckyballs may be able to reduce the growth of bacteria in pipes and membranes in water systems.