Page 200 - ICSE Chemistry 8

Graphite Thirst for Knowledge

Graphite is a greyish-black opaque substance. It is lighter than
The lead used in our pencils is
diamond. Graphite derives its name from the Greek word
prepared by mixing graphite with
graphein which means to write.
clay.
Occurrence of Graphite

Graphite occurs naturally in both Sri Lanka and Siberia. It also occurs in Russia, Southern Hemisphere in
New Zealand, Northern Hemisphere in California, United States of America and India.

Preparation of Graphite

Graphite can also be prepared ar fi cially when powdered coke is heated with a li le sand and iron(III)
oxide in an electric furnace at a temperature about 3000°C.
SiO 2 + 3C 3000°C SiC + 2CO
Sand Coke Ferric oxide Silicon carbide Carbon monoxide
heat
SiC Si + C
Silicon carbide Silicon Graphite
Structure of Graphite

A graphite crystal consists of layers of carbon atoms or sheets of carbon
atoms. Each carbon atom in every layer is joined to three other carbon
atoms by strong covalent bonds to form fl at hexagonal rings. The various
layers of carbon atoms in graphite are quite far apart so that no covalent
bonds can exist between them and are held together by weak forces.
Since the various layers are joined by weak forces, they can slide over
one another.
Fig. 9.4: Arrangement of carbon
Due to this sheet-like structure, graphite is a compara vely so substance.
atoms in graphite
In a graphite crystal, each carbon atom is joined to only three other
carbon atoms by covalent bonds. Thus, only the three valence electrons of each carbon atom in graphite
are used in bond forma on. The fourth valence electron of each carbon atom is free to move. Due to the
presence of free electrons in a graphite crystal, it conducts electricity.
Properties of Graphite Thirst for Knowledge

• Graphite is a greyish-black, opaque
• Since graphite is non-vola le, it can be used for
substance with metallic lustre.
lubrica ng those machine parts, which operate
• Graphite is so and slippery to touch. at a very high temperature (where ordinary oil

• It is a good conductor of heat and lubricants cannot be used).
electricity. • Graphite is used as a dry lubricant in the form of
• The density of graphite ranges between graphite powder or mixed with petroleum jelly
to form graphite grease.
-3
1.9 to 2.3 g cm .
• Graphite has a very high mel ng point of 3700°C.

• It leaves a greyish-black mark on the paper.

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