Postulates of Bohr's theory :

1st postulate: Electrons revolve round the positively charged nucleus in circular orbits called, stationary orbits. Electrons do not radiate energy while revolving in these stationary orbits.

2nd postulate: The angular momentum of electron in a circular orbit is always integral multiplies of   h/2 [pie(symbol)]

mvr=nh/2pie where n=1,2,3,.............

3rd postulate: When electron jumps from higher energy state to lower energy state, the difference of energy appears in the form of a photon of frequency v

The frequency of the emitted photon is given by

E=E2-E1

hv =E2-E1

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Bohr combined classical and early quantum mechanics concepts to propose a three-postulate theory. These postulates are:

1. An electron in an atom revolves in certain stable orbits without emitting radiant energy. Each atom has certain definite stable orbits. Electrons can exist in these orbits. Each possible orbit has definite total energy. These stable orbits are called the stationary states of the atom.

2. An electron can revolve around the nucleus in an atom only in those stable orbits whose angular momentum is the integral multiple of h2πh2π , where h is the Planck’s constant. If the mass of the electron be m and it is revolving with velocity v in an orbit of radius r, then its angular momentum will be mvr.

According to Bohr’s postulate, mvr = nh / 2π, where n=1, 2, 3,.. and is called the ‘principle quantum number’ of the orbit. This equation is called ‘Bohr’s quantisation condition’.

3. An electron can make a transition from its stable orbit to another lower stable orbit. While doing so, a photon is emitted whose energy is equal to the energy difference between the initial and final states.

If the energy of the initial and final states are Ei and Ef respectively, then the frequency v of the photon is given by
v = (Ef−Ei) / hv = (Ef−Ei) / h
This is called ‘Bohr’s frequency condition’.

Hi Aspirants,

The basic postulates of Bohrs Theory of Atomic Spectra states that an electron in an atom revolves in certain stable orbits without emitting radiant energy. Each atom has certain definite stable orbits. Electrons can exist in these orbits. Each possible orbit has definite total energy.

Hope it helps!!