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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