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ALLOTROPES OF CARBON:

A characteristic property of the elements of carbon family is that these show allotropy. Example: carbon has two important allotropic forms i.e.  Crystalline and amorphous

(1) DIAMOND:

(1) Each carbon is linked to another atom and there is very closed packing in structure of Diamond.

(2) Density and hardness is very much greater for diamond because of closed packing in diamond due to sp3 hybrid and are tetrahedrally arranged around it. And C-C distance is 154 pm
(3) Diamond has sharp cutting edges that's why it is employed in cutting of glass.
(4) Diamond crystals are bad conductor of electricity because of absence of mobile electron.
(5) 1 carat of diamond = 200 mg.
(6) Diamond powder if consumed is fatal and causes death in minutes.
(2) GRAPHITE: 
(1) In Graphite Carbons are sp2 hybridised out of the four valence electrons, three   involved in (sp2-sigma) covalent bonds form hexagonal layers and fourth unhybridised p– electron of each carbon forms an extended delocalized p-bonding with carbon atoms of adjacent layers
 (2) Each carbon is linked with 3 carbons and one carbon will be left and form a two dimensional shed like structure.
(3) Distance between two layers is very large so no regular bond is formed between two layers. The layers are attached with weak vander waal force of attraction.

(4) The carbon have unpaired electron so graphite is a good conductor of current.

(5) The C-C bond length within a layer is 141.5 pm while the inter layer distance is 335.4 pm shorter than that of Diamond (1.54 Å).
(6) Due to wide separation and weak interlayer bonds, graphite is sift , greasy and a lubricant character and low density.
(7) Graphite marks the paper black so it is called black lead or plumbago and so it is used in pencil lead.
(8) Composition of pencil lead is graphite plus clay .the percentage of lead in pencil is zero .
 (9) Graphite has high melting point so it is employed in manufacture of crucible.
(10) Graphite when heated with oxidizing agents like alkaline KMnO4 forms mellatic acid (Benzene hexa carboxylic acid).
(11) Graphite on oxidation with HNO3 gives acid i.e. known as Graphite acid C12H6O12

(3) FULLERENCES:
(1) A fascinating discovery was the synthesis of spherical carbon-cage molecules called fullerences. The discovery of fullerene was awarded the noble prize in chemistry (1996). Fullerenes   were first prepared by evaporation of graphite using laser.
(2) Fullerences are sooty material so formed consists of C60 with small amount of C70 and other fullerences containing an even number of carbon up to 350
(3) Fullerences have a smooth structure and unlike diamond and graphite, dissolved in organic solvent like toluene.
(4)  C60 is the most stable fullerene. It has the shape of a football and called buckminsterfullerene
(5) C60 consists of fused five and six membered carbon rings
(6) Six membered rings surrounded by alternatively by hexagons and pentagons of carbon.

(7) Five membered rings are surrounded by five hexagons carbon rings.

(8) There are 12 five –membered rings
(9) There are 20 Six –membered rings
(10) In fullerenes all the carbon sp2 hybridised each carbon formed three sigma bond and the fourth electron delocalized to formed pi bond .
(11) All the carbon atom are equivalent but all C-C bond are not equivalent.
(12)  In the structure C-C bonds of two different bond length occur at the fusion of two six membered rings the bond length is  C-C = 135.5 pm and at the fusion of  five and six membered rings C-C bond length is 146.7 pm.
(13) There are both single and double bonds
(14) The smallest fullerenes are C20.
(15) Thermodynamically the most stable allotrope of carbon is considered to be graphite. This is due standard enthalpy of formation of graphite is taken zero .while enthalpy of formation of diamond and fullerenes are 1.90 KJ/Mole and 38.1 KJ/Mole respectively.      

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