Allotropy- Allotropic Forms OF Carbon- Structure OF Diamond PDF

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Allotropy- Allotropic Forms OF Carbon- Structure OF Diamond Chemistry...

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ALLOTROPY-ALLOTROPIC FORMS OF CARBON-STRUCTURE OF DIAMOND DEFINITION Existence of an element in more than one physical forms in the same physical state is called ALLOTROPY and different physical forms are referred to as ALLOTROPES. Allotropes of an element are differing in physical properties but they have same chemical properties. Carbon exists in two allotropic forms: Crystalline form Amorphous form CRYSTALLINE FORMS There are two crystalline forms of carbon. Diamond Graphite AMORPHOUS FORMS There are a number of amorphous forms of carbon such as: coal coke lampblack animal charcoal carbon black etc . DIAMOND

STRUCTURE OF DIAMOND Figs In diamond, each carbon atom is covalently bonded to four other carbon atoms to give a tetrahedral unit. In diamond each carbon atom is sp3 hybridized. Therefore each carbon atom forms four sigma bonds with neighboring carbon atoms. In diamond C-C-C bond angle is 109.5o. These basic tetrahedral units unite with one another and produce a cubic unit cell. C-C bond length is 1.54Ao. C-C bond energy is 347 kJ/mole. In diamond crystal, basic units joined to form octahedral shape of diamond crystal. In diamond each C-atom utilizes its four unpaired electrons in bond formation. These bonding electrons are localized. Due to this reason diamond is a bad conductor of electricity. PROPERTIES Diamond is the hardest substance ever known. Pure diamond is colorless. Its melting point is 3500oC Pure diamond is transparent to X-rays. It has high refractive index 2.45. Due to impurities it may be coloured.

Its density is 3.51 gm/cm3. At 2000oC, it readily changes to graphite....