Answer:
On
the basis of nature ofintermolecular forces crystalline solids have been
classified into four categories.
(i) Ionic (ii) Metallic
(iii) Covalent (iv) Molecular.
(i) Ionic solids : Solids in which constituent particles
are held by ionic bonds are .called ionic solids. Ionic solids are made of ions
(cations and anions). In ionic solids cations and anions are bound by strong
electrostatic forces of attraction (coulombic force). Ionic solids are formed
by three dimensional arrangement of cations and anions. e.g., NaCI, ZnS,
etc.
(ii) Metallic solids : Solids in which constituent
particles are held by metallic bond are called metallic solids.
Examples : Iron, copper, silver, sodium, magnesium, aluminium,
etc.
Metallic solids are made of metal ions and electrons.
These are formed by three dimensional arrangement of metal ions surrounded by
electrons.
(iii) Covalent solids : Solids in which constituent
particles are held together by a network of covalent bonds throughout the
crystal are called covalent solids.
Examples: Diamond, graphite, silica (quartz), carborundum (silicon
carbide).
These are also called network solids. Covalent solids are made
of non-metallic atoms. These atoms are bound by forming covalent bonds between
adjacent atoms throughout the crystals. These solids have giant structures.
(iv) Molecular solids: Solids in which constituent
particles are held together by weak van der Waals forces are called molecular
solids.
Molecular solids are made of discrete covalent molecules. Examples;
Iodine, naphthalene, phosphorus, sulphur, camphor, etc.
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