The Solid State | Chemistry Notes, Class 12 | Note For Science

Definition Of Solid

The substance which have definite mass, volume and shape are called solid.

Characteristics Of Solids

1. Solid has definite mass, volume & shape.

2. Internuclear distance is very short.

3. The Intermolecular force in solid is very strong.

4. Solids are incompressible and rigid.

Solids are classified into two types:-

1. Amorphous Solids.

2. Crystalline Solids.

1. Amorphous Solids

Amorphous solids are the solids in which the constituent particles are not arranged in a regular manner are called Amorphous Solids.

2. Crystalline Solids

Crystalline solids are the solids in which the constituent particles are arranged in a regular manner are called Crystalline Solids.

Differences between Crystalline Solids and Amorphous Solids:-

Crystalline Solids

1. It has regular shape.

2. It has definite heat of fusion.

3. True Solid. 

4. Long range order (Which means there is a regular pattern of the arrangement of particles which repeats itself over the entire crystal).  

Example: Diamond, $NaCl$, $KCl$, $NH_3$, $H_2$, $H_2O$(ice).

5. Crystalline solids are anisotropic in nature (which means some of the physical like resistant, refractive index gives different values which its measures in different direction for the same crystal).

Amorphous Solids

1. It has irregular shape.

2. It has indefinite heat of fusion.

3. Pseudo Solids or super cooled liquids. 

4. Short range order.  

Example: Glass, Plastics, Rubber etc.

5. Amorphous solids are isotropic in nature.

Glasses are called super cooled liquid because they have a tendency to flow though very slowly.

Crystalline Solids are Further Classified Into Four Types:-

1. Molecular Solids

2. Ionic Solids

1. Molecular Solids

Molecules are the constituent particles in molecular solids.

It is further classified into three types:-

a) Non-Polar Molecular Solids:-

It is composed of either non-polar molecules or mono-atomic molecules ($He$, $Ne$) which are held together by weak dispersion force or london force.

Non-Polar Molecular Solids are usually liquids or gases at room temperature and pressure.

b) Polar Molecular Solids:-

It is composed or polar molecules ($HCl$, $SO_2$, $NH_3$) which are held together by dipole-dipole force.

Polar Molecular Solids usually liquids or gases at room temperature and pressure.

c) H-Bonded Molecular Solids:-

It is composed of polar molecules and they are held together by stronger hydrogen bonding. Example: Ice etc.

2. Ionic Solids

It is composed of ion and they are held together by stronger electrostatic or coulombic force of attraction. In pure form ionic solida are insulator because the ions cannot move but in molten state or when dissolve in water the ions become free to move and thus they conduct electricity.

Problems: 

Question 1: Why ionic solids are insulator?

Question 2: In which state ionic solids are good conductor of electricity? Why?

3. Metallic Solids:-

Metals are orderly collection of positive ions which are surrounding by held together by a sea of free electron. These electrons are mobile (movable) and therefore metals are good conductor of heat and electricity.

Example: Iron ($Fe$), Silver($Ag$), Gold($Au$) etc.

4. Covalent and Network Solid:-

These are the solid of non-metals in which they form covalent bond with the adjacent atoms throughout the crystal.

Example: Diamond, Graphite, Silicon, Carbide etc.