BOHR'S ATOMIC THEORY :

Neils bohr proposed a model of an atom based on atomic spectra of hydrogen

He retained the basic concepts of Rutherford's model i.e., the atom has a positively charged nucleus at the center and the electrons revolve round the nucleus.He applied Planck's Quantum theory for revolving electron.

The main postulates are:

  1. Electrons revolvearound the nucleus with high velocity in circular paths called Orbit or shells.
  2. As long as the electron is in a particular orbit,its energy is constant.Therefore,these orbits are called stationary orbits
  3. Each stationary orbit is associated with a definite energy and is known as energy level.these energy levels are named as K,L,M,N,.... etc.,or numbered as 1,2,3,4,.... etc.
  4. When an electron jumps from a higher energy level to a lower energy level,the difference in energy is emitted as radiation in quanta.

    5. When an electron jumps from a lower energy level to a higher energy level,the difference in energy is absorbed as radiation in quanta.

    E2 - E1 = hu

    where,

    E1 = energy of first orbit

    E2 = energy of second orbit

    h = Planck's constant (6.625 * 10-34) J.sec

    u = frequency of radiation

  5. The angular momentum of the electron revolving in a stationary orbit is equal to integral multiples of h/(2*pI).

    6. Angular momentum,

    mvr = nh/(2*PI)

    Where,

    m =mass of electron

    v = velocity of electron

    r = radius of orbit

    n = integer (1,2,3,4,....)

    h = Plank's constant

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