Page 66 - NCERT Science Class 10 English Medium

points of these compounds. Since the electrons are shared between
atoms and no charged particles are formed, such covalent compounds
are generally poor conductors of electricity.

Allotropes of carbon
The element carbon occurs in different forms in nature with
widely varying physical properties. Both diamond and
graphite are formed by carbon atoms, the difference lies in
the manner in which the carbon atoms are bonded to one
Figure 4.5
Figure 4.5
Figure 4.5
Figure 4.5
Figure 4.5
another. In diamond, each carbon atom is bonded to four
Electron dot structure for
other carbon atoms forming a rigid three-dimensional methane
structure. In graphite, each carbon atom is bonded to three
other carbon atoms in the same plane giving a hexagonal array.
One of these bonds is a double-bond, and thus the valency of
carbon is satisfied. Graphite structure is formed by the
hexagonal arrays being placed in layers one above the other.
More to Know!

The structure of diamond
The structure of C-60
The structure of graphite
Buckminsterfullerene
These two different structures result in diamond and graphite having very different
physical properties even though their chemical properties are the same. Diamond is
the hardest substance known while graphite is smooth and slippery. Graphite is also
a very good conductor of electricity unlike other non-metals that you studied in the
previous Chapter.
Diamonds can be synthesised by subjecting pure carbon to very high pressure and
temperature. These synthetic diamonds are small but are otherwise indistinguishable
from natural diamonds.
Fullerenes form another class of carbon allotropes. The first one to be identified was
C-60 which has carbon atoms arranged in the shape of a football. Since this looked
like the geodesic dome designed by the US architect Buckminster Fuller, the molecule
was named fullerene.

Q U E S T I O N S

1. What would be the electron dot structure of carbon dioxide which has
the formula CO ?
2
2. What would be the electron dot structure of a molecule of sulphur which ?
is made up of eight atoms of sulphur? (Hint – The eight atoms of sulphur
are joined together in the form of a ring.)

Carbon and its Compounds 61

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