Bohr’s Theory of Hydrogen Atom

The model at first presents the planetary model but later assumes about electrons. The premise was that the structure of the atoms could be synced. As Bohr’s theory states, electrons orbit the nucleus in defined shells with a definite radius.

Hydrogen Spectrum

A spectrum is created when electrons move between various energy levels. In the visible light spectrum, Balmer’s equation can be used to describe the four wavelengths of hydrogen. The wavelengths are 656, 486, 434, and 410nm, respectively. As an electron in an excited state when it goes downwards to energy level n=2, they correlate to photon emission. For all energy level transitions, the Rydberg formula generalises the Balmer series. The Rydberg formula is applied with an nf of 2 to obtain the Balmer lines.

The energy obtained is always negative, with the stated ground a being, n = 1 having the highest negative value. Because the energy of the electrons in the orbit is directly proportional to the energy of an electron completely detached from its nucleus, n = ∞.

The energy of an electron in orbit is always negative due to an electron in a given or fixed orbit outside the nucleus being much more stable than the electron that is extraordinarily far from its nucleus.

Absorption and emission

According to Bohr’s hypothesis, electrons would absorb energy in the form of photons to reach a higher energy level. Because the mentioned electron is less stable after the transition process to a very higher level of energy and is known as an excited state. For a given transition, the emitted photon’s energy is equal to the difference in energy between the two energy levels.

Bohr model postulates:

Postulate I:

Bohr proposed that electrons in an atom may rotate in stable orbits without producing radiant energy, which was a significant departure from recognised assumptions of classical mechanics and electromagnetic. He also argued that each atom can exist in one of several stable states. Each state mentioned has distinct total energy. These are known as atoms, stationary states.

Postulate II:

In his second postulate, Bohr defined these stable orbits.

• An electron orbits the nucleus in orbits, according to this hypothesis.
• The angular momentum of revolution is an integral multiple of h – where h = 6.6 x 10-34 J-s is Planck’s constant.
• As a result, the circling electron’s angular momentum (L) is L = nh.

Postulate III

Bohr introduced early quantum notions into the atomic theory with this postulate. An electron can migrate from a non-radiating orbit to one with a lower energy level, according to this theory. A photon with the same energy as the energy difference between the two states is emitted. As a result, the emitted photon’s frequency is:

hv = E_i – E_f

Rydberg formula

The Rydberg formula calculates the wavelengths of a spectral line in many calculations and the wavelengths of a spectral line in many chemical elements.

Limitations

The Bohr Model was a significant stride forward in atomic theory development. It does, however, have some drawbacks.

• For complicated atoms, Bohr’s model fails miserably.
• It goes against Heisenberg’s Principle. Bohr’s model assumes that electrons have a defined orbit, which Heisenberg states are impossible.
• It was unable to explain why some spectral lines are brighter than others.
• The size of the Bohr model is extremely constrained. When dealing with bigger atoms, undefined spectral predictions are produced.
• It couldn’t explain why, in the presence of the magnetic field, some spectral lines split into multiple lines.
• It is unable to estimate spectral line relative intensities.
• Bohr’s theory of electrons living in defined radius with known radius and velocity is contradicted by Heisenberg’s uncertainty principle.
• This doesn’t account for the Zeeman Effect, which occurs when a spectral line splits into many parts in the presence of an electric or magnetic field.
• We can recognise it as a fact that speeding electrons do not emit electromagnetic radiation and are ignored by the Bohr model.

The essential idea in both the contemporary quantum mechanical model and the Bohr model of the hydrogen atom may appear to be significantly different. Traditional physics is unable to explain all of the phenomena that occur at the atomic level. By merging the idea of quantization into the electronic structure of the hydrogen atom, Bohr was the first to realise the quantization of electronic hells and was able to successfully explain the emission spectra of hydrogen as well as other one-electron systems.

Conclusion

In this section, we learned about the hydrogen atom model that was theorised by the scientist Neils Bohr in the year 1913. The article explained the atomic model, the hydrogen spectrum that is formed, and the various energy levels of the spectra. Also, the 3 postulates of the model are well-defined above; everything has limitations and so does this model.