Bohr’s model of the atom Niels Bohr proposed the following postulates regarding the model of the atom.

**(i) **Only certain orbits known as discrete orbits of electrons are allowed inside the atom.

**(ii) **While revolving in these discrete orbits, the electrons do not radiate energy. These discrete orbits or shells are shown in the following diagram.

The first orbit (i.e., for n = 1) is represented by letter K. Similarly, for n = 2, it is L − shell, for n = 3, it is M − shell and for n = 4, it is N − shell. These orbits or shells are also called energy levels.