a) List at least three crystal allotropes (or structures) of carbon. b) What is

Question

a) List at least three crystal allotropes (or structures) of carbon.

b) What is the nature of the bonding in thesethreedifferent carbon materials? Include a description of bond hybridization.

c) If C60 buckey balls assemble to form a face centered cubic lattice would you expect the melting temperature to be high or low? Explain your answer.

d)Describe the conductivity of graphite along its planar structure versus perpendicular to its planar structure. Is there a difference? If so, please explain

Explanation / Answer

a) Three crystal allotropes of carbon are Diamond, graphite and fullerene.

b) Diamond: Each carbon in a diamond crystal is bonded to four other carbon atoms making a lattice. As each carbon has four single bonds it is sp3 hybridised

Graphite: Carbon atoms are bonded together to make a giant structure but in this case all of the carbons are bonded to only three neighbour. So it is sp2 hybridised. As the sp2 hybridisation results in planar structures, there are 2 dimensional layers of carbon atoms and each layer is linked to the next layer by weak Van der Waal's forces.

Fullerene: These are small molecules of carbon in which the structure is closed over into spheres of atoms like a football. The bonding has delocalised pi molecular orbitals throughout the structure and the carbon atoms are a mixture of sp2 and sp3 hybridised systems.

c) C60 buckey balls sublimes at 6000 C. It has high melting point due to it's giant molecular structure.

d) The electrical conductivity of graphite is direction-dependent: the -system of delocalized electrons allows metallic conduction parallel to the planes, while much lower conductivity in case of perpendicular to the planes.

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