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Bohr’s atomic model

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 around the nucleus. He applied Planck’s Quantum theory for revolving electron.

The main postulates are:

Electrons revolve around the nucleus with high velocity in circular paths called orbits or shells.

As long as the electron is in a particular orbit, its energy is constant. Therefore, these orbits are called stationary orbits.

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.

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

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

where   energy of first orbit

 energy of second orbit

h = Planck’s constant 

 frequency of radiation

The angular momentum of the electron revolving in a stationary orbit is equal to integral multiples of .

Angular momentum, 

where

n = integer (1,2,3,4…)

h = Planck’s constant

m = mass of the electron

v = velocity of electron

r = radius of the circular orbit

Therefore, the angular momentum of the electron in various orbits is equal to  etc.

Thus, the momentum is said to be quantized.

Merits of Bohr’s atomic model:

Limitations of Bohr’s atomic model :

 

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