General characterstics of solid state

  • Solids have definite mass,volume and shape due to the fixed position of their constituent particles.
  • Solids have short intermolecular distances and strong intermolecular forces.
  • The constituent particles of solids (atoms, molecules or ions ) have fixed positions and can only oscillate about their mean positions.
  • Solids are incompressible and rigid.

Types of solid states– Based on the arrangement of constituent particles,

  1. Crystalline Solids
  2. Amorphous solids


Crystalline Solids

Amorphous Solid


  • Definite characteric geometrical shape
  • Irregular shape

Melting point

  • Melt at a sharp and characteristic temperature
  • Gradually soften over a range of temperature

Cleavage property

  • When cut with a sharp edged tool , they split into two pieces and the newly generated surfaces are plain and smooth
  • When cut with a sharp edged tool, they cut into two pieces with irregular pieces


  • Anisotropic (physical properties have different value in different directions) in nature

  • Isotropic (physical properties have same value in different directions) in nature


  • True solids
  • Pseudo solids or supercooled liquids

Order in arrangement of constituent particles

  • Long range order
  • Only short range order

Heat of fusion

  • They have a definite and characteristic heat of fusion
  • They don’t have definite heat of fusion
  • Classification of crystalline solids on the basis of nature of intermolecular forces

Types of solids

Type of forces

Properties and examples

Ionic solids

  • Lattice points are occupied by +ve and -ve ions held together by strong coulombic (Electrostatic) forces
  • High lattice energies,
  • Hard but brittle,
  • High meting and boilong point,
  • Insulator in solid state but good condcutors in molten state and in aqueous solutions
  • E.g. NaCl,MgO,ZnS

Covalent or network solids

  • Lattice point are occupied by atoms held by a network of covalent bonds
  • Extremely high mp
  • Very hard and brittle,
  • insulator expect graphite,
  • E.g-Diamond,quartz,SiC,graphite

Metallic solids

  • In metals, the array of lattice points is occupied by +ve ions. The outer electrons are loosely held
  • Hard but malleable and ductile,
  • Fairly high melting point
  • Good conductor of electricity in solid state as well as in molten state
  • E.g-All metals and alloys

Molecular solids (polar, non polar and hydrogen bonded)

  • Lattice positions are occupied by molecules and are held together by weak van der waals forces
  • Soft
  • Low melting points
  • Insulators
  • E.g.Solid CO2,HCl,Ice

-Crystal lattice

  • A regular three dimensional arrangement of the constituent particles of a crystal in space is called crystal lattice

-Unit cell

  • It is a smallest portion of a crystal lattice which when repeated in different directions, generated the entire lattice
  • A unit cell in characterised by six parameters-three edges a,b and c and angles b\w the edges, α,β and γ.

Types of unit cells

  • Primitive unit cells

Constituent particles are present only on the corner positions of a unit cell.

  • Centred unit cell

Unit cell contains constituent particles at corners as well as at some other positions

There are a 3 type of centred unit cell.

  • Body-centred

One Constituent particles at body centre besides the ones that are at its corners.

  • Face-centred

One constituent particle present at the centre of each face besides the ones that are at its corners.

  • End-centred

One constituent particles present at the centre of ant two opposite faces besides the ones that are at its corners.