Bohr’s Model of Atom

Bohr’s Model of

  • The central part of an is called the nucleus.
  • Electrons revolve around the nucleus and have fixed energy levels called shells or orbits.

n=1    K

n=2   L

n=3  M


  • An electron move only in those orbits for which the angular momentum is an integral multiple of h/2π

h= Planck constant

  • While moving in a particular shell on an electron neither absorbs nor loses energy.
  • By absorbing energy an electron jump from one orbit to another orbit. The difference in the energy is given by ∆E= hv

To overcome the defects of the Bohr model of the there are two concepts:

Dual Behaviour of Matter

De-Broglie suggested that small particles have also the property of a wave.

De-Broglie equation : λ = h/mv


λ= wavelength

h= Planck’s constant

m= mass of a particle

v= velocity of the particle

Big particles like moving stone ball etc. do not show the property of a wave because their mass is high hence the wavelength is too short to measure.

Heisenberg Uncertainty Principle

It is impossible to measure simultaneously the position and momentum or velocity of a small moving particle with absolute accuracy.

∆p. ∆x = h/4π


m.∆v. ∆x = h/4π


∆p= uncertainty in the momentum

∆x= uncertainty in the position of the particle

∆v= uncertainty in the velocity

m= mass of the particle.

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