Question

Describe the Bohr model of the Hydrogen atom in detail. Take into account the following points:

(a) Explain its significance and prediction.

(b) How does the Bohr model explain the spectrum of the Hydrogen atom.

(c) Explain the shortcomings of this model.

Answer 1

Bohr overcome the shortcoming of rutherford model as rutherford model could not explain decay of atom over time by radiating energy as electromagnetic theory tells that an accelerating charged particle emits radiation in the form of electromagnetic waves. Therefore, the energy of such an electron should constantly decrease and the electron should collapse into the nucleus. This would make the atom unstable.

The classical electromagnetic theory also states that the frequency of the electromagnetic waves emitted by an accelerating electron is equal to the frequency of revolution. This would mean that, as the electron spirals inwards, it would emit electromagnetic waves of changing frequencies. In other words, it would emit a continuous spectrum. However, actual observation tells us that the electron emits a line spectrum.

Bohr tells postulates which explain line spectrum

Bohr defined these stable orbits in his second postulate. According to this postulate:

• An electron revolves around the nucleus in orbits
• The angular momentum of revolution is an integral multiple of h/2p – where Planck’s constant [h = 6.6 x 10-34 J-s
• Hence, the angular momentum (L) of the orbiting electron is: L = nh/2p