Bohr’s Model of the Atom:
Niels Bohr in 1913 gave a model of atom which was a modification of Rutherford’s model. The main points of this model are:
(i) Electrons revolve around the nucleus in circular orbits.
(ii) The electrons revolve only in certain permissible orbits and not in other orbits. These special orbits are also known as discrete orbits.
(iii) The energies of permissible orbits are fixed and therefore these orbits are called stationary states or energy level or shells. Energy levels or shells are designated by K, L, M, N, etc. The K orbit is nearest to the nucleus and therefore it is the first orbit (n = 1); L is the second orbit (n = 2); M is the third orbit (n= 3) and so on.
(iv) As long as the revolves in its discrete fixed energy level (or shell) it does not lose energy. Thus, the energy of an electron remains constant in a fixed orbit. Electrons in different orbits have different energies.
(v) Energy is emitted or absorbed by an atom only when an electron moves from one orbit to another.
(vi) An Atom is made up of three kinds of particles: Electrons, protons and nuetrons.
(vii) Electrons are negatively charged, protons are positively charged and neutrons are neutral, i.e, they have no electric charge.