Question

Compare the structure of the crystal of diamond & graphite with special reference to the reason for diamond being the hardest natural substance while graphite one of the softest. Compare the electrical & thermal conductivity of the two crystalline allotropes of carbon.

Answer 1

• Structure of crystal of diamond : Hardest natural substance is due to – strength and uniformity of the carbon – carbon covalent bond [tetrahadron structure].
  It is bad conductor of electricity and heat due to abscence of free electrons in the crystal, i.e. no electron is free to move.
• Structure of graphite : “Is soft and greasy due to parallel layers of C-atoms held together by weak VANDER WAAL – forces which slide over one another, i.e. hexagonal structure.
  It is good conductor of heat and electricity due to – presence of mobile electrons in the crystal.