In order to overcome the objections raised against Rutherford’s model of the atom,
Neils Bohr put forward the following postulates about the model of an atom:
(i) Only certain special orbits known as discrete orbits of electrons, are allowed inside the atom.
(ii) While revolving in discrete orbits the electrons do not radiate energy.
These orbits or shells are called energy levels. Energy levels in an atom are shown in
These orbits or shells are represented by the letters K,L,M,N,… or the numbers, n=1,2,3,4,….