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Everything exists around us in either of the three states i.e. solid, liquid or gas.

Solid state is that wherein the chemical substances are characterised by a definite shape and volume, rigidity, high density, low compressibility. Solids are very important in our day to day life.

Characteristics of solid state

  • definite shape due to strong Intermolecular forces of attraction.
  • distinct boundaries.
  • fixed volume.
  • cannot flow.
  • They have negligible compressibility
  • possess a tendency to uphold their shape when exposed to external force.
  • break under force but it is difficult to change their shape so they are rigid.
  • have high density and do not diffuse at all.

There are solids which are crystalline and then there are solids that are amorphous.

 Crystalline Solid

Crystalline solid contains a regular arrangement. they have short range & as well as long-range order and have definite geometric shape. They have a high melting point and definite heat fusion. They undergo clean cleavage, they are truly solid.

 Image Credit – Exam Fear.

Amorphous Solid

  • containing irregular arrangement
  • has short range order only
  • irregular shape
  • melting over a range of temperature
  • they do not have a definite heat of fusion
  • they are pseudo solid or supercooled solid.

Classification of crystalline solid

Image Credits- Exam Fear

The unit cell is the smallest three-dimensional portion that constitutes a complete space lattice which as and when repeated over and again in different directions tends to produce the complete space lattice. There is the simple or primitive unit cell where the particles are present only in the corners.The face centred unit cell is where the particles are present at the corners and also at the centre of the six faces.The body centred unit cell is one where the particles are present at the corners of the cell as well as the centre of the unit cell. The end centred unit cell is the one where the particles are present at the corners and as well as the centre of the two opposite faces.

 Packing efficiency:

The percentage of the total space filled by the particles is called packing efficiency.

Packing fraction:

The fraction of the total space filled is called packing fraction.

Calculation of spaces occupied

In a simple cubic unit cell:-

Suppose radius of the sphere is = r

The edge length of unit cell       = a

As sphere are touching each other


No. of sphere per unit cell= 8*1/8=1

Image Source- Blogspot


Volume of sphere = 4/3πr3

Volume of cube =a3= (2r)3 = 8r3

Packing fraction

% occupied = 52.4%


In face-centred cubic structure (Cubic close packing):-spheres of the face centre touching the sphere of the corner,

Then, AC = 4r

in ∆ ABC

Image Source- Blogspot


In body centred cubic structure: – Sphere at the body centred touching the sphere of the corner.

Body diagonal, AD = 4r

Further, face diagonal,

Source- Blogspot

% occupied = 68%


Radius (r) of the octahedral void =0.414R

Radius (r) of the tetrahedral void = 0.225R

In CCP or HCC. If there are N spheres in t

No. of octahedral voids = N

No. of Tetrahedral voids = 2N


Magnetic properties of solids.

Diamagnetic Substances:

Substances which are weakly repelled by the external magnetic field are called diamagnetic substances.

Ex: TiO2, H2O, NaCl

Paramagnetic Substances:

Substances which are attracted by the external magnetic field are called paramagnetic substances.

Ex: O2, Cu2+, Fe3+

Ferromagnetic Substances: 

Substances which show permanent magnetism even in the absence of magnetic field are called ferromagnetic substances.

Ex: Fe, Ni

Anti- Ferromagnetic Substances: 

Substances which are expected to possess’ paramagnetism and ferromagnetism on the basis of magnetic moments of the domains but actually they posses Zero magnetic moment are called antiferromagnetic substances.

Ex: MnO

Ferromagnetic Substances: 

Substances that possess large magnetism on the basis of magnetic moments of the domains but actually have small net magnetic moment are called ferromagnetic substances.

Ex: Fe3O4

Learn more about how to study chemistry for class 12. Click here.


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