Question

(a) What is graphite? Of what substance is graphite made?
(b) Describe the structure of graphite with the help of a labelled diagram.
(c) Why is graphite a good conductor of electricity but diamond is a non-conductor of electricity?
(d) State any two uses of graphite.

Answer 1

(a) Graphite is an allotrope of carbon, and is a soft, greyish black and opaque substance. The graphite is made up of carbon atoms. On burning graphite in the presence of oxygen, only carbon dioxide gas is evolved proving that graphite is only made of carbon.

(b) The structure of graphite consists of layers or sheets of carbon atoms which form flat hexagonal rings. In a graphite layer or sheet, each carbon atom is connected to three other carbon atoms by covalent bonds. Each layer of carbon atoms is at a distance with no covalent bonds existing between them. As the various layers of carbon atoms in a graphite crystal are held by weak Van der Waals forces, the layers can slide over each other smoothly.
The following diagram represents the structure of a graphite crystal:



(c) Graphite is a good conductor of electricity because of the presence of free electrons in its crystal. As we know that an atom of carbon has 4 valence electrons, in a graphite crystal, each carbon atom is connected to only three other carbon atoms by covalent bonds. This means that the fourth valence electron of each carbon atom is free. These free moving electrons are responsible for the conduction of electricity in a graphite crystal. But in the case of diamond these free electrons are not available due to its structure. Hence, diamond is a non-conductor.

(d) Uses of graphite:
(i) As graphite is a good conductor of electricity, it is used in making carbon electrodes in dry cells.
(ii) Graphite is used in making pencil leads and black paints.