i. Electrons revolve around the nucleus in certain circular paths called orbits or energy levels which are named as K, L, M, N etc.
ii. Only those orbits are possible in which angular momentum is an integral multiple of h/2πwhere h is Planck‟s constant.
iii. As long as electrons revolve in a particular orbit, it does not emit or absorb energy
iv. If an electron jumps from higher to lower energy level, energy is emitted and when electron jumps from lower to higher energy level energy is absorbed.