Bohr model of atom – (Based upon Planck’s Quantum theory)

Main postulates – (1) Electron in a atom revolve around the nucleus only in a certain selected circular path called orbits. These orbits having definite energy. Hence called as Energy Shells. They are designated as K L M N shells.

1. The revolving electron can emit or absorb energy only in fixed amount or packets called Quanta.
2. Under suitable conditions, when energy is supplied to an atom, electron jump from lower to lighter energy state. The lighter state of electron is called existed state.
3. Electron in existed state has a tendency to jump back to the lower energy state it radiates the same amount of energy absorbed.
4. The energy emitted or absorbed in quanta is equal to the difference between energies of two energy levels.

ΔE = E₂-E₁

E1 & E2

1. Only those orbits are permitted in which the regular momentum of electron is a whole no. multiple of h/2π .

If n = 1 then = h/2π

If n = 2 then = h/π

if n = 3 then = 3h/2π

if n = 4 then = 2h/π

This postulate constitute energy is the key concept of Bohr’s theory. Quantization mean that a quantity can’t change gradually and continuously to have any arbitrary valve but changes only abruptly and discontinuously to have certain definite or discrete value.