Neil Bohr put forward the following postulates about the model of an atom:
(i) Atoms has nucleus that is present in the centre.
(ii) There are only certain special orbits known as discrete orbits in which the electrons revolve around the nucleus,
are known to be present inside the atom.
(iii) While revolving in discrete orbits the electrons do not radiate energy.
(iv) These orbits or shells are called energy levels. These orbits or shells are represented by the letters K, L, M, N, … or the numbers, n = 1, 2, 3, 4, ….