Question

Write two limitations of Bohr’s model.

Answer 1

Hint: Bohr’s atomic model is considered as the improved version of Rutherford’s model. Although it explains many significant things but fails to explain theories like Zeeman and Stark effect. It also contradicts the Heisenberg’s uncertainty principle.

Complete step-by-step answer:
Niels Bohr considered the structure of an atom as that of a solar system. His model described an atom as a small and positively charged centre called nucleus with electrons orbiting around it like the planets orbit around the Sun under the influence of electrostatic force of attraction. Bohr’s atomic model was considered as the improved version of the atomic model proposed by Rutherford.
Some of the salient features of this model are,
1. The electrons revolve around the nucleus without radiating any energy in orbits having definite energy and are called energy level or energy shell.
2. He designated different energy levels as K, L, M, N shells and its lowest energy level is called the ground state.
3. Emittance or absorption of energy takes place by an electron when they jump from one energy level to another.
4. The energy absorbed or emitted is the difference in the two energy levels and is given by $\mathrm{\Delta }E=hv$, where $\mathrm{\Delta }E$ is the emitted or absorbed energy h is the Planck’s constant and v is the frequency of electromagnetic radiation emitted or absorbed.
Although, several limitations were also present with this model
i. This model considers that electrons have a both known position and momentum i.e. known orbit and the radius which violates the Heisenberg Uncertainty Principle.
ii. Unlike small sized atoms like hydrogen, spectral predictions were poor for large atoms.
iii. It failed to explain the Zeeman and Stark effect which states the splitting of spectral lines in presence of magnetic and electric fields respectively.

Note: Many scientists like Dalton. J.J, Rutherford, Einstein, Bohr etc. proposed different atomic models with slight to big differences which may cause confusion among different theories. Every theory had some significance that laid the foundation for other scientists.