In 1924, Niels Bohr proposed a model of the hydrogen atom. It was based on certain postulates which were experimentally proved to be correct but still had some limitations. We will discuss these limitations in this article:
Limitations Of Bohr’s Model
Bohr’s theory is based on some postulates which are not experimentally proved.
- The first postulate is that the hydrogen atom is a spherically symmetric system, and its total angular momentum is a constant. This is not true as there are different levels of energy in an atom.
- The second postulate says that the electron in orbit around nucleus has discrete energy states. This too is not correct because we have seen many instances where an electron can jump between two states with no intermediate state. This shows that the electrons can exist at any point in space-time (the region between two events). It does not follow that there are definite orbits for them to move around their nuclei.*
The third postulate says that only one orbital exists for each principal quantum number.*
The postulate of stationary orbits is not correct.
- The postulate that stationary orbits are possible is not correct. According to Bohr’s model, electrons can only occupy certain discrete energy levels. But these discrete energy levels are just an approximation; in reality, the electron is continuously absorbing and emitting photons (light particles) as it moves about its atom. When an electron absorbs a photon, it moves from a lower energy level to a higher one; when it emits a photon, the opposite happens—the electron returns to its original state. This movement of the electron between different energy states explains why we see light in all colors: each color corresponds to one specific set of frequencies (or energies).*
The postulate of stationary orbits is not correct.*
Bohr’s theory does not give correct value for the velocity of the electron in different orbits.
Bohr’s model was based on the assumption that electrons are spherical particles. But according to quantum mechanics, electrons are not stationary, they move through space in orbits around the nucleus. This means that there is no such thing as a fixed radius or energy level; instead, these properties depend on what orbit an electron is in.
The velocity of an electron depends on its energy and radius: it decreases as you go up in energy and increases as you go down. It also increases with increasing distance from the atomic nucleus (see Figure 1).
It cannot explain the splitting of spectral lines in magnetic field and electric field.
Bohr’s model is a great way to explain the spectra of hydrogen atoms in their ground states, but it fails to explain why there should be any splitting at all. The Bohr model can predict the wavelengths of spectral lines in an electric field or magnetic field, but not both at once. This means that while we have a theory that explains how electrons move through space and time (quantum mechanics), we still don’t have any good way of predicting how they interact with other particles or fields.
It does not give correct expression for the intensity of spectral lines emitted by hydrogen atom.
Bohr’s model has a few limitations. It cannot explain the splitting of spectral lines in magnetic field and electric field. Bohr’s model is a fairly good model, but still has some limitations.
Bohr’s model is a fairly good model, but still has some limitations.
Bohr’s model is a good start, but it needs to be improved. The Bohr model has some limitations. For example, the Bohr model does not explain why electrons are found in specific orbits around the nucleus of an atom.
The Bohr model also cannot explain why electrons do not radiate energy when moving from one orbit to another due to their acceleration as they move through space and time (this is known as “quantum leap”).
Closing
Bohr’s model is a fairly good model, but still has some limitations. It cannot explain the splitting of spectral lines in magnetic field and electric field. It does not give correct expression for the intensity of spectral lines emitted by hydrogen atom. It does not give correct value for the velocity of the electron in different orbits. These are some limitations of Bohr’s theory which we have discussed in this article.