Chemistry Classification of Crystalline Solids
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### Topic to be covered

• Classification of Crystalline Solids :
• Molecular Solids :
• Ionic Solids :
• Metallic Solids :
• Covalent or Network Solids :
• Table Classification :

### Classification of Crystalline Solids :

color{green}("On the basis of nature of intermolecular forces :")

(i) Molecular Solids

(ii) Ionic Solids

(iii) Metallic Solids

(iv) Covalent Solids

### Molecular Solids :

color{green}("Molecules are the constituent") color{green}(" particles of molecular solids. Types of molecular solids :")

(a) color{green}("Non- polar molecular solids :")

(i) These solids comprise of either atoms or the non-polar molecules.

(ii) e.g. color{red}(Ar, He, H_2, Cl_2, I_2) etc.

(iii) The atoms or molecules are held by weak dispersion forces or London forces.

(iv) Have low melting points.

(v) Exists in liquid or gaseous state at room temperature and pressure.

(b) color{green}("Polar Molecular Solids :")

(i) Polar molecules are the constituent of solids.

(ii) e.g. color{red}(HCl, SO_2, NH_3) etc.

(iii) Molecules are held together by dipole-dipole interactions.

(iv) Soft and non-conductors of electricity.

(v) Melting point is higher than non-polar molecular solids.

(vi) Gaseous and liquids under room temperature and pressure.

(c) color{green}("Hydrogen Bonded Molecular Solids :")

(i) In such solids there is covalent bond between color{red}(H) and color{red}(F, O) or color{red}(N) atoms e.g. color{red}(H_2O)

(ii) They are non-conductors of electricity.

(iii) Volatile liquids or soft solids at room temperature and pressure.

### Ionic Solids :

(i) Ions are the constituent particles of ionic solids.

(ii) Formed by three dimensional (color{red}(3D)) arrangements of cations and anions bounded by strong coulombic (electrostatic) forces.

(iii) Hard and brittle in nature.

(iv) Have high melting and boiling points.

(v) Electrical insulators in the solid state because ions are not free to move.

(vi) Good conductor of electricity in molten state or when dissolved in water.

### Metallic Solids :

(i) In metallic solids, positive ions are surrounded by and held together by a sea of free electrons.

(ii) Electrons are mobile and evenly spread out throughout the crystal.

(iii) Each metal atom gives one or more electrons.

(iv) Thermal and electrical conductivity of metals is due to the mobile electrons.

(v) They have lustre and colour in certain cases(due to the presence of free electrons).

(vi) Highly malleable and ductile.

### Covalent or Network Solids :

(i) These solids are formed by the formation of covalent bonds between adjacent atoms. These atoms are non-metal.

(ii) Also called giant molecules.

(iii) Covalent bonds are strong and directional in nature.

(iv) Very hard and brittle.

(v) High melting point and may even decompose before melting.

(vi) Insulator and don't conduct electricity.

(vii) e.g. Diamond and silicon carbide.

color{green}("Graphite :")

(i) It is soft and conductor of electricity.

(ii) In graphite each carbon atom is covalently bonded to three of its neighbouring atoms in the same layer.

(iii) The fourth electron is free to move about and is present in between the different layers.

(iv) Due to this free electron, graphite is conductor of electricity.

(v) Different layers slide one over other and makes it a soft solid and a good solid lubricant.

See Table 1.2.