Solid state Chemistry class 12 NCERT

Chemistry notes class 12

Definition: A solid state may be defined as a form of matter in which the constituting particles are closely packed.

1. Interparticle forces: Solid is that form of matter which has maximum interparticle forces.

2. Kinetic Energy: The kinetic energy of solids’ constituent particle is zero

    Interparticle forces decreases: Solid→Liquid→Gas

    Kinetic energy increases: Gas →Liquid → Solid

    Characteristics of solid state:
     i. Rigid
     ii. Definite shape and volume
     iii. High density
     iv. They don’t show diffusion (indiffusible)
     v. Incompressible

Types of solid
  1. Crystalline solids: these are the solids in which constituent particles (atoms, ions) have a regular arrangement for example: - Atoms, ions or molecules etc
  2. Amorphous solids: these are the solids in which the constituent particles do not posses the regular arrangement. For example: - Plastic, rubber etc
Ques: What are the differences between crystalline solids and amorphous solids?
Ans: The differences between crystalline solids and amorphous solids are as follows:

             Crystalline solids

            Amorphous solids

They have sharp melting point

They are of long-range order as well as short-range order.

They are anisotropic.

They have definite cleavage plane.,


Example: all metals, diamond, graphite etc.

They don’t have sharp melting point.

They are of short-range order.


They are isotropic.


They don’t have definite cleavage plane.

Example: glass, plastic etc.

Anisotropy: - When the solid particles have different physical properties in different directions then they are known as anisotropic solids and the phenomena is known as anisotropy
Isotropy: - Solid particles having same properties in all directions.

    Classification of crystalline solids
1. Ionic solid: When the constituent particles are ions i.e., Na+, Cl-, etc

i. They have high melting and boiling point.
ii. They have high electrostatic forces of attraction.
iii. They are generally insulators. In molten and aqueous form, they can conduct since ions are free. 
iv. They are generally hard for example: NaCl, CaCO3 etc.

2. Atomic solids: When the constituent particles are atoms they are also known as covalent solids.

i. They have generally strong covalent forces of attraction.
ii. They are solid at room temperature.
iii. They are generally bad conductors e.g.: AlNO3

3. Molecular solids: - When the constituent particles are molecules.
i. They have weak Vandar Waal forces of attraction.
ii. They are soft.
iii. Their physical state varies according to room temperature i.e. they may be liquid, gaseous and volatile.
iv. They act as insulators.

They (molecular solids) are further classified:
A. Non-polar molecules: - the constituent present in the solids which are the independent molecules in which atoms are linked by covalent bond for example: I2

B.  Polar molecules: - The constituent particles are polar in nature (since dipole forces of attraction). They have low melting and boiling point.

C. Hydrogen bonded molecule solid: - In it highly electronegative elements are bonded with hydrogen atoms by covalent bonds.
i. They are liquid at room temperature.
ii. They are also bad conductors.

4. Metallic solids: - When the constituent particles are metal ions. These are linked by metallic bonds. Mobile valence electrons and the positively charged residues called kernels are bind together. The simultaneous attraction between these leads metallic bonds.
I. They are good conductors of heat as well as electricity. E.g.: all metals. Strength of metallic bond depends upon kernels and mobile electrons.
  • Space lattice: it is 3-D (dimensional) arrangement of constituent particles (atoms, ions or molecules) of solids.
  • Lattice point: Position of atoms, ions or molecules is known as lattice point
  • Unit cell: it is the smallest unit which when repeated form space lattice.

                       Unit cell





In which atoms, molecules or ions are present at the corners of the structure.


When atoms are present in corners as well as in other points

Non-primitive is further classified: -
1. Body centred unit cell (bcc): - When atoms are present at corners as well as in body of unit cell.

2. Face centred unit cell (fcc): - When atoms are present in face as well as in corners.

3. End centred unit cell: - when atoms are present in corners as well as in two opposite faces.
                             Seven crystal system
On the basis of edges length and angles we have 7 crystal system:
1. Cubic
2. Tetragonal
3. Orthorhombic
4. Hexagonal
5. Rhombohedral
6. Triclinic
7. Monoclinic


 Axial distance


     1.  Cubic

     2.  Tetragonal

     3.  Orthorhombic

     4.  Hexagonal

     5.  Rhombohedral

     6.  Triclinic

     7.  Monoclinic










    α=β=γ=90˚  α=β=90˚ γ=120˚



    α=γ=90˚ β≠90˚

Ques: How many Bravais lattice are there? 
Ans: Bravais lattice: A lattice is a framework resembling a three-dimensional periodic array of points on which a crystal is built Bravais showed that identical points can be arranged spatially to produce 14 types of regular pattern. These 14 space lattices are known as Bravais lattices and they are

Few ques related to finding unit cells and making compound formula;
Ques: A compound is made up of A and B elements. Atom A are present at corners and atom B are present at face centres. Find out the formula od compound.
Ans: Number of A atoms= 1/8 *8= 1
        Number of B atoms= 1+3=4
Therefore, formula of compound= A1B4

Ques: A compound is made up of A and B element. Atom of A are present at corners but 1 atom is not present and atom of B are present at face. Find out the formula of compound.

Ques: Potassium crystallizes in a body centre cubic lattice. Calculate approximate number of unit cells in 2g of K (atomic mass=39)
   39g of K contains= 6.022×10^23 atoms
     1g of K will contain=  6.022×10^23÷39 atoms
     2g of K will contain= (6.022×10^23÷39)×2atoms
                                       = (12.044 ×10^23)/39 atoms
                                       = 0.30×10^23 atoms.

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