Question

Which statement about graphite and diamond is correct ?
(a) Diamond has a high melting point but graphite does not.
(b) Graphite and diamond both conduct electricity.
(c) Graphite and diamond both have giant structures.
(d) Graphite is ionic and diamond is covalent.

Answer 1

Hint: To solve this question, we need to look into the properties and structure of both diamond and graphite. Both are composed of carbon atoms that are linked together through covalent bonds that extend in three dimensions.

Complete answer:
Both diamond and graphite are covalent network solids.
Let us look into their properties one by one.
In diamond, each carbon forms four covalent bonds with other carbon atoms in a three dimensional structure and these bonds are very strong. Due to the very strong covalent bonds, the melting point of diamond is very high ($4000\quad^{o}{ C }$) since melting requires the breaking of the lattice structure which in turn leads to the breaking of the covalent bonds. Due to the same reason diamond is very hard. Diamond is an insulator i.e. it does not conduct electricity due to the lack of free electrons. It is also not soluble in water or any organic solvent because of its very high lattice enthalpy which cannot be overcome by its solvation enthalpy.
While diamond has a three dimensional network structure, graphite has a layered structure extending in three dimensions. Each carbon atom in a layer uses three of its valence electrons to form covalent bonds with three other carbon atoms. This leaves one valence electron from each carbon atom in a layer which becomes delocalised over the entire sheet of atoms in the layer. These electrons move freely within the layer to which they belong but not in the other neighbouring layers. The bonds existing between the carbon atoms in a particular layer are stronger than the bonds in diamond because of the presence of free electrons in graphite that provides additional bonding. Like diamond, graphite has a high melting point and is insoluble in water or organic solvents. Due to the presence of delocalised electrons, graphite conducts electricity.

Hence, the correct answer to the above question is (c) Graphite and diamond both have giant structures.

So, the correct answer is “Option (C) Graphite and diamond both have giant structures.”

Note: Always remember that both diamond and graphite are allotropic forms of carbon. Graphite is thermodynamically the most stable form of carbon while diamond is the kinetically most stable form of carbon.