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

( mr^{2} )
ω = nh / 2π

( mr^{2} )
( v / r ) = nh / 2π

mvr = nh / 2π

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

= 1, 2, 3 etc

- Momentum of
revolving electron = mv

- Moment of electron
about nucleus = mvr

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