According to the Bohr’s atomic model, the electrons revolve around the nucleus in certain orbits. These electrons are distributed in various orbits according to a scheme proposed by Bohr and Bury. The Bohr and Bury scheme gives the following rules for the distribution of electrons in various orbits.

(i) The maximum number of electrons which can be accommodated in a given orbit is given by the formula 2n2, where not is the quantum number of the orbit. Thus and so on.

(ii) The outermost orbit can have at the most 8 electrons, and the next inner to the outermost (penultimate) can have at the most 18 electrons, (if permissible in accordance with rule i).

(iii) It is not always necessary to fill up an orbit completely before starting the next higher orbit.