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Question

Which of the following are the crystalline forms of carbon?

A
Diamond
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B
Graphite
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C
Coke
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D
Fullerene
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Solution

The explanation for the correct options:

A Diamond

B Graphite

D Fullerene

Crystalline forms of carbon:

  • The crystalline forms have definite geometrical shapes and regular arrangements of atoms in their structure.
  • Among the allotropes of carbon, diamond, graphite, and fullerenes are crystalline.

A) Diamond

  • Carbon has an electronic arrangement of 2,4. In a diamond, each carbon shares electrons with four other carbon atoms by forming four single bonds.
  • It has a very high melting point (almost 4000°C). Very strong carbon-carbon covalent bonds have to be broken throughout the structure before melting occurs.
  • It is very hard. This is again due to the need to break very strong covalent bonds operating in 3-dimensions.
  • It doesn't conduct electricity. All the electrons are held tightly between the atoms and aren't free to move.
  • It is insoluble in water and organic solvents. There are no possible attractions that could occur between solvent molecules and carbon atoms that could outweigh the attractions between the covalently bound carbon atoms.

B) Graphite

  • Graphite has a layer structure.
  • Graphite has a high melting point.
  • Graphite is insoluble in water and organic solvents​.
  • Each carbon atom uses three of its electrons to form simple bonds with its three close neighbors. That leaves the fourth electron in the bonding level, hence, the free electron causes the graphite to conduct electricity. and makes the layers of the graphite slide together.

D) Fullerene

  • ​A fullerene is an allotrope of carbon whose molecule consists of carbon atoms connected by single and double bonds so as to form a closed or partially closed mesh, with fused rings of five to seven atoms.
  • The molecule may be a hollow sphere, ellipsoid, tube, or many other shapes and sizes.

The explanation for the incorrect options:

C) Coke

  • Coke is an amorphous allotropic form of Carbon.
  • Coke is obtained by destructive distillation of coal and contains about 80 to 95 Carbon.​
  • However, coke neither has a definite geometrical shape nor a regular arrangement of atoms in its structure and hence is an amorphous form of carbon.

Hence, Options A Diamond, B Graphite, and D Fullerene are the crystalline allotropes of carbon.


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