The Danish physicist Neils Bohr proposed the following postulates for revising the Rutherford’s model.

• Atom has central nucleus surrounded by electrons.
• An atom consists of small heavy positively charged nucleus in the centre and the electrons revolve around it, in circular paths called orbits or shells.
• Each orbit has fixed energy, so these orbits are called energy levels or energy shells.
• The order of the energy of these energy shells will be
  K < L < M < N < O <…………. or, 1 < 2 < 3 < 4 < 5 <…………..
• As long as an electron remains in a particular orbit, it does not lose or gain energy.
• Energy is neither absorbed nor emitted when electron is moving in an orbit. But energy is absorbed when it jumps from lower orbit to higher orbit. Whereas energy is emitted when it jumps from higher orbit to lower orbit.