He proposed that
(a) Electrons revolve
round the nucleus in a fixed orbit.
(b) He called these
orbits as ‘stationary orbit’.
(c) Each stationary
orbit is associated with fixed amount of energy, thus electrons do not radiate
energy as long as they keep on revolving around the nucleus in fixed orbit.
The circular path around
the nucleus is called orbit, energy level or shell. Energy level are
represented by letter – K, L, M, N, …. and so on.