Neil Bohr proposed the Bohr model of atom in 1915 with the modification of Rutherford’s model of atom.
Rutherford’s model had introduced nuclear model of atom, in which he explained that a nucleus (positively charged) is surrounded by negatively charged electrons.
Bohr modified this atomic structure model. He explained that electrons move in fixed orbital’s (shells) and not anywhere in between and he also explained that each orbit (shell) has a fixed energy level.
Rutherford basically explained nucleus of an atom which Bohr modified by explaining that model into electrons and their energy levels.
Postulates of Bohr’s Model of an Atom:
The atom-consists of a small (positively charges) nucleus at its centre.
The whole mass of the atom is concentrated at the nucleus and the volume of nucleus is smaller than the volume of the atom by a ratio of about 1:105.
All the protons and neutrons of the atom are contained in the nucleus.
The electrons of the atom revolve round the nucleus in definite circular paths known as orbits or shells which are designed as K, L, M, N etc. numbered as (n)=1, 2, 3, 4 etc. outward from the nucleus.
Each orbit is associated with a fixed amount of energy. Therefore, these orbits are also known as energy levels or energy shells.
The energy of the atom changes when an electron jumps from state (energy level) to another state (energy level).
As long as an electron remains in a particular orbit, it does not lose or gain energy.
Limitations of Bohr’s Model of an Atom
Bohr’s Atomic model violates the Heisenberg Uncertainty Principle.
It could not explain the spectra obtained from larger atoms.
Bohr’s model of an atom failed to explain Zeeman Effect (effect of magnetic field on the spectra of atoms).
It also failed to explain the Stark effect (effect of electric field on the spectra of atoms).