Imperfections in Solids

  • Constituent particles in crystalline solids are arranged in a short range as well as long range
    order yet crystals are not perfect.
  • They possess small crystals have defects that are irregularities in the arrangement of constituent
    particles in them when crystallization process occurs at fast or moderate rate.
  • These defects are of two types- point defects and line defects.
  • The irregularities or deviations from ideal arrangement around a point or an atom in a
    crystalline substance.
  • The irregularities or deviations from ideal arrangement in entire rows of lattice points are known as line defects.
  • These irregularities are called crystal defects.
  • Point defects can be classified into three types: (i) stoichiometric defects
    (ii) impurity defects and (iii) non-stoichiometric defects

Defects in Solid

The Solid State Notes Class 12
Solid Defects
Chemistry Class 12 Chapter 1 The Solid State Notes
Chemistry Class 12 Chapter 1 The Solid State Notes
The Solid State Notes

Electrical Properties of soilds

Solids exhibit electrical conductivities that extend from 27 orders of magnitude ranging from 10–20 to 107 ohm–1 m–1.


  • Solids with conductivities ranging between 104 to 107 ohm–1m–1 are conductors.
  • Metals have conductivities in the order of 107 ohm–1m–1 are good conductors.
  • For example, Iron, Copper, Aluminum.

A man touching the electric pole with a metal rod will get an electric shock because metal rod is a conductor whereas a man touching the same with a wooden plank will be safe because wood is an insulator.

  • Semiconductors:
  • Solids with conductivities in the intermediate range from 10–6 to 104 ohm–1 m–1.
  • For example, Gallium, Germanium, Silicon
  • Metals conduct electricity both in solid state as well as molten state.
  • The conductivity of metals depends upon the number of valence electrons available per atom.
  • The atomic orbitals of metal atoms form molecular orbitals that are close in energy to each other as to form a band.
  • Partial filling or overlapping with a higher energy unoccupied conduction band enables the electrons to flow easily under an applied electric field.
  • This results in conductivity of metals.

If the gap between valence band and the conduction band is large, electrons cannot jump to it and such a substance has very low conductivity that makes it behave like an insulator

Number of cation vacancies in lattice of NaCl = Number of divalent Sr2+ ions added.

Concentration of cation vacancy on doping with 10-3 mol% of SrCl2. = 10-3 mol% = 10-3 / 100 = 10-5 mol.

Number of Sr2+ ion in 10-5 mol = 10-5 x 6.023 x 1023 = 6.023 x 1018

Hence number of cationic vacancies = 6.023 x 1018

Electron – rich impurities

In a periodic table Silicon and germanium belongs to group 14 with four valence electrons each.  In their crystals each atom forms four covalent bonds with surrounding atom.

When doped with a group 15 element like P or As, which contains five valence electrons,

Applications of n-type and p-type semiconductors

  • n-type and p-type semiconductors finds a great use in manufacturing electronic components.
  • Diode is a combination of n-type and p-type semiconductors extensively used as a rectifier.
  • Transistors are manufactured by keeping a layer of one type of semiconductor between two layers of another type of semiconductor.
  • npn and pnp type of transistors are used to detect or amplify radio or audio signals.
  • The solar cell is an efficient photo-diode used for conversion of light energy into electrical energy.
  • Gallium arsenide (GaAs) semiconductors have very fast response and have transformed the design of semiconductor devices.
  • Transition metal oxides show marked differences in electrical properties.
  • TiO, CrO2 and ReO3 behave like metals.
  • Rhenium oxide, ReO3 resembles metallic copper in terms of its conductivity and appearance.
  • Certain other oxides like VO, VO2, VO3 and TiO3 exhibit metallic or insulating properties depending on temperature.
  • its spin around its own axis.
  • Electron being a charged particle undergoes these motions and can be considered as a small loop of current possessing a magnetic moment.
  • Therefore, each electron has a permanent spin and an orbital magnetic moment associated with it.
  • Magnitude of this magnetic moment is very small and is measured in the unit called Bohr magneton, μ B and is equal to 9.27 × 10–24A m2.

On the basis of their magnetic properties, substances can be classified into five categories:

  • Paramagnetic
  • Diamagnetic
  • Ferromagnetic
  • Antiferromagnetic
  • Ferrimagnetic.


  • Ferromagnetic substances get strongly attracted towards magnetic field.
  • They can be permanently magnetized.
  • In solid state, the metal ions of ferromagnetic substances are grouped together into small regions and are known as domains that act as a tiny magnet.
  • In an unmagnetised ferromagnetic substance the domains are randomly oriented that cancels out their magnetic moments.
  • When placed in a magnetic field all the domains of the substance get oriented in the direction of the magnetic field producing a strong magnetic effect which persists even on removal of the magnetic field and the ferromagnetic substance becomes a permanent magnet.
  • For example, iron, cobalt, nickel, gadolinium and CrO2 are ferromagnetic substances.

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