Neils Bohr proposed a model of atom in 1912 to remove the drawbacks of Rutherford's atomic model and to explain the structure of an atom in detail. The features of Bohr's model of atom are given below:-
i) An electron revolves in the orbit of atom with well-defined energy.
ii) Energy of orbits increases from the inner shell to the outer shells i.e. energy of orbit nearest to the nucleus is the lowest.
iii) If energy is supplied to an electron, it moves from a lower orbit to a higher orbit. When an electron moves from a higher orbit (energy level) to a lower orbit (energy level), energy is radiated as electromagnetic waves.
iv) Each orbit or shell represents an energy level. Such orbits are represented as K,L,M,N,O (named starting from the centre of an atom).
v) The shell or orbits are associated with a certain amount of energy and energy of orbits/shells increases from the nucleus towards the valence shell.