Carbon is one of the most abundant elements found on earth. It occurs freely in crystalline forms such as diamond and graphite.The diamond crystal is cubic, with the atoms arranged in a tetrahedral configuration. This arrangement of carbon atoms produces a solid that is the hardest known substance. Consequently, it is used as an industrial abrasive. In addition, diamond has a very high refractive index, hence it produces brilliant cut gems. Graphite, on the other hand, is soft, has a hexagonal structure, with the carbon atoms arranged in layer planes. The spacing between the layer planes in graphite is 0.3354 nm (nm = billionth of a meter). This layer structure facilitates easy cleavage along the planes, which makes it desirable as a solid lubricant. There are variations of the graphite structure. When the dimensions of the layer planes are small and the separation between the layer planes becomes large, the carbon is referred to as amorphous carbon (for example, charcoal, coke, and soot). Because of their difference in structures, diamond is an electrical insulator, whereas graphite is a good electrical conductor. The high conductivity of graphite and its good chemical stability are attractive features for its use in electrochemistry.
Read More :- http://electrochem.cwru.edu/ed/encycl/art-c01-carbon.htm
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