Bohr model of an atom

Bohr model of an atom .

To overcome the drawbacks of Rutherford’s model, in 1913 Neil Bohr proposed a new model of the atom.

This can be stated as:

(i)Atom is spherical.

(ii)Most part of the atom is empty.

(iii)Protons and neutrons are located in the nucleus.

(iv)Electrons move around the nucleus in an atom in orbits known as energy levels having fixed energy.

(v)The energy levels are either designated as K, L, M, N etc. or numbered as n = 1, 2, 3, 4, etc.

(vi)The absorption or emission of energy can occur only by transition of electrons from lower to the higher energy level, or vice-versa.

Thus, as long as electrons continue to revolve in the same energy level, they neither lose nor gain energy and the atom remains stable.

Distribution of Electrons in Different Energy Levels

According to the Bohr the maximum number of electrons in any energy level is 2n^2 where n is the number of that energy level. The energy levels are also known as shells.

K - Shell (n = 1) = 2n^2 = 2 x 1^2  = 2 electrons

L - Shell (n = 2 ) = 2n^2 = 2 x 2^2  = 8 electrons

M - Shell (n = 3 ) = 2n^2 = 2 x 3^2  = 18 electrons

N - Shell (n = 4 ) = 2n^2 = 2 x 4^2   = 32 electrons

The electrons firstly occupy the lowest energy shell. This systematic distribution of electrons is called electron configuration of the atom.