He postulated that the electrons can only move in certain orbits around the atomic nucleus, comparable to the planetary motion around the sun. Therefore, he expanded the atom model of Rutherford especially with regard to the atomic shell. The physicist Niels Bohr suspected that this behavior must have something to do with the electron shell.
If the energy is only slightly lower, suddenly there is no illumination (for example Franck-Hertz experiment). For example, some atoms can only be excited to glow when bombarded with particles of specific energy. However, some phenomena can not be explained with this atomic model. The Rutherford model in many cases provides a very good explanation of physical processes in matter. According to the Bohr’s atomic model, electrons move on discrete shells around the nucleus (discrete energy levels).
