Page 198 - ICSE Chemistry 8

Carbon exists in two allotropic forms—crystalline and amorphous. The crystalline forms of carbon are
diamond, graphite and fullerenes. The amorphous forms are charcoals (namely wood charcoal, bone or
animal charcoal and sugar charcoal), coke, gas carbon, lampblack and coal.
All forms of carbon diff er in their physical proper es, but they all produce carbon dioxide with release of
heat when burnt in the presence of oxygen.

Crystalline Forms of Carbon

Diamond
Thirst for Knowledge
Diamond is the purest form of carbon. It is the hardest known
naturally occurring substance. It can therefore be cut only by Diamond-bearing rocks
another diamond. Some diamonds have diff erent colours such are called kimberlite
as grey, brown, black, pink. These colours are due to impuri es rocks, a er the town
present in these diamonds. A pure diamonds is colourless in of Kimberley in South
Africa.
nature.
Occurrence of Diamond

Diamonds are found in many parts of the world such as South Africa, Brazil, Namibia, the Democra c
Republic of Congo, Botswana, Belgium, Russia, Australia, USA and India. South Africa produces and supplies
nearly 70% of the world’s demand for diamonds. In India, diamonds are found in Golconda (Karnataka)
and Panna (Madhya Pradesh).

Natural Diamonds Thirst for Knowledge

Diamonds are formed when carbon is trapped in molten lava. India was once famous for
Natural diamonds are formed by the ac on of high pressure and ‘Kohinoor’ diamond that was
temperature on carbon present in the earth, at a depth of about found in Wajrakarur (Andhra
150 km. Diamonds are brought to the surface, mostly by volcanic Pradesh). It now adorns the crown
of the Bri sh queen.
erup ons along with kimberlite rocks.

These rocks are named a er the kimberly mines in South Africa.
Artificial or Synthetic Diamonds

A er many years of research, scien sts have been able to prepare ar fi cial or synthe c diamonds from
pure carbon. When pure carbon is subjected to a very high pressure and temperature (about 3000°C), it
compresses to give small diamonds. Ar fi cial diamonds are widely used for making cu ng and grinding
tools. The chemical proper es of natural and ar fi cial diamonds are the same.

Structure of Diamond

Each carbon atom in diamond is linked to four other carbon atoms by
strong covalent bonds. The four surrounding carbon atoms are at the
four ver ces (four corners) of a regular tetrahedron. The carbon atoms
are thus held fi rmly in place. As a result, a diamond crystal appears to be
a closely-packed three-dimensional rigid structure. Fig. 9.2: Arrangement of carbon
atoms in diamond

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