Bohr's Atomic Model


The atomic model is proposed by Bohr in 1913. The Bohr has made following assumptions.

  • The atom has massive positive charged nucleus.
  • The electrons revolve round their nucleus in circular orbits. The centrifugal force between electron and nucleus is balanced by electrostatic pull.
  • The electron cannot revolve round the nucleus in any arbitrary orbit but certain definite discrete orbits ( stationary orbits ). 
  • The orbital angular momentum of the electron is equal to an integral multiple of h/2π

      Orbital angular momentum = nh / 2π

     Where n = Integer

                 h = Planck’s constant


  • The electrons does not radiate out any electromagnetic energy while revolving in the stationary orbits. 
  • In other words. the orbits are non-radiating path of the electron.
  • When electrons jump from one orbit to another orbit, the atom radiates out energy. 
  • If E1 and E2 are the energy of the two orbits before and after electron jump, the frequency of the emitted photon is given by

       E1 – E2 = hf

      ΔE = hf

      Where f = Frequency of the emitted radiations

  • If I is moment of inertia of an electron and ω is its angular velocity, then

      ωI = nh / 2π

      ( mr2 ) ω = nh / 2π

      ( mr2 ) ( v / r ) = nh / 2π

      mvr = nh / 

  • The n is called as principal quantum number or Bohr’s circular orbit and it is first, second and third orbits etc…. It fixes the size of allowed orbits

      = 1, 2, 3 etc

  • Momentum of revolving electron = mv
  • Moment of electron about nucleus = mvr

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