Bohr model of atom Postulates and problems
Bohr model of atom postulates and problems are discussed in this topic below :
Before we begin to review the details of the topic Bohr model of atom we can summarize it in one paragraph including Bohr’s view of the atomic structure, which is that the electrons revolve around the nucleus in a group of orbits,which are far from the nucleus of the atom a great distance, when an electron changes its orbit
It does so in A sudden qualitative movement, where the energy difference between the primary and final orbits of the atom is emitted in the form of beams of electromagnetic radiation called photons.
The Bohr model of atom was based on his observations on the spectrum resulting from heating the simplest atom, which is the hydrogen atom.
When heating this atom it emits radiation, then we expose it to a triple prism, so the triple prism makes the white light deviate, and produces all the colors of the visible spectrum.
Each color corresponds to a specific amount of energy; but when the light emitted by the hydrogen atom is passed through a triple prism, only certain colors of light are seen.
These colors are consistent with the amount of energy that the electron produced when it moved from orbit to orbit.
This prompted Bohr to say that the electrons have quantities of energy specified in the atom, and by the colors that were emitted from the hydrogen atom.
Bohr was able to use these energies of these colors to find out the quantities of energy that the only electron in the hydrogen atom could possess.
Here, Bohr learned that the electron must release, or absorb, an amount of energy in order to change its orbit, since the differences between the energies of visible light in the atomic spectrum must correspond to the difference between the energies of the orbits in which the electron rotates.
Bohr’s model of the atom suggests that electrons orbit the nucleus at predetermined distances.
Bohr thought that each orbit had a certain energy, so he said that if an electron is at a level of energy in a stable atom, the electron is at the lowest energy level but when adding energy to the atom the electron jumps to a higher level because it now has more energy.
When an electron returns to an idle state (or more stable state, with less energy), it must emit energy, and it does so in the form of “photons” light.
The Bohr model of atom was successfully applied to the hydrogen atom, but failed when applied to other more complex atoms, and although it contained some errors.
It was important because it describes most of the accepted features of atomic theory without using the high-level mathematics present in the modern version.
Unlike previous models, the Bohr model explains the Rydberg formula for the spectral emission lines of atomic hydrogen.
The main points of the Bohr model of atom :
1. Electrons take certain orbits around the nucleus. These orbits are stable and are called “fixed” orbits.
2. Each orbit has its associated energy. For example the orbit closest to the nucleus has E1 energy, which is followed by E2 and so on.
3. Light is emitted when an electron jumps from a higher orbit to a lower orbit and absorbs light when it jumps from a lower orbit to the top.
4. The energy and frequency of the emitted or absorbed light are given in terms of the difference between the energies of the orbits.
Bohr model problems:
* It conflicts with Heisenberg Uncertainty Principle because he considers that the electron orbitals have a known radius and orbit.
* Gives an incorrect value for the orbital angular momentum of the inactivity state.
His outlook is poor for spectra of large atoms.
* Does not expect the relative density of the spectral lines.
* Does not explain the precise structure and super-fine structure of spectral lines.
* Zeeman Effect is not explained.
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