Bohr Atomic Model
The Bohr Atomic model is a description of the structure of atoms, particularly hydrogen, proposed by Danish physicist Niels Bohr in 1913. The Bohr Atomic model of the atom was the first to incorporate quantum theory and was the forerunner of entirely quantum-mechanical models. It represented a significant break from earlier, classical representations. The properties of atomic electrons are described by the Bohr model and all of its successors in terms of a set of permissible (possible) values. Only when electrons abruptly leap between permissible, or stationary, states do atoms absorb or release radiation. The German-born physicists James Franck and Gustav Hertz obtained direct experimental evidence for the existence of such discrete states in 1914.
Bohr changed his mind about the planetary electrons’ mobility to align the model with the regular patterns (spectral series) of light emitted by real hydrogen atoms. Bohr was able to explain the series of discrete wavelengths in the hydrogen emission spectrum by restricting the orbiting electrons to a series of circular orbits with discrete radii. He argued that light only emitted from hydrogen atoms when an electron moved from an outer orbit to one closer to the nucleus. The energy lost by the electron during the sudden transition is identical to the energy of the emitted light quantum.
Bohr Atomic Model- Diagram
Below is the Bohr atomic Model of a Nitrogen atom.
Bohr Atomic Model- Formula
Bohr’s Formula is:
where l is the angular momentum, n is the Principle Quantum number, h is Planck’s constant.
Also, The energy and radii of electron orbits in atoms are quantized, according to Bohr, with energy for transitions between orbits given by ∆E = hf = Ei − Ef, where ∆E is the difference in energy between the beginning and final orbits and hf is the energy of an absorbed or emitted photon.
Bohr Atomic Model- Postulates and Limitations
Bohr Atomic Model- Postulates
The postulates of Bohr’s atomic model are:
- Orbits, shells, and energy levels are the set circular paths electrons take around the nucleus. Stationary orbit describes the orbits.
- Each round orbit has a predetermined amount of energy, and these circular orbits are referred to as orbital shells. As long as the electrons in the fixed orbital shells continue to rotate around the nucleus, they will not emit energy.
- Integers such as n=1 or n=2 or n=3 and so on are used to represent the various energy levels. Quantum numbers are what they’re called. Quantum numbers can have a wide range of values, ranging from the lowest energy level (nucleus side n=1) to the greatest energy level.
- When electrons jump from one energy level to another, they change their energy. In an atom, electrons get the requisite energy to go from a lower to a higher energy level. When an electron loses energy, however, it shifts from a higher to a lower energy level.
- The various energy levels or orbits are represented in two ways: 1, 2, 3, 4… and K, L, M, N….. shells. The ground state of an electron is its lowest energy level.
Bohr Atomic Model- Limitation
Following are the limitations of Bohr’s atomic model:
- The Heisenberg Uncertainty Principle is violated in Bohr’s atomic model. According to the Bohr atomic model theory, electrons have both a known radius and orbit, i.e., known position and momentum at the same time, which Heisenberg claims is impossible.
- When it comes to smaller atoms like hydrogen, the Bohr atomic model theory makes accurate forecasts, but when it comes to larger atoms, it makes poor spectral predictions.
- When the spectral line is divided up into fine lines in the presence of an electric field, Bohr’s atomic model fails to describe the Stark effect.
- When the spectral line is broken into numerous components in the applied magnetic field, Bohr’s atomic Model likewise fails to explain the Zeeman phenomenon.
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Bohr Atomic Model- FAQs
What does Bohr’s model explain?
According to the Bohr model, electrons orbit the nucleus at constant energy levels. At greater energy levels, orbits further from the nucleus exist. Electrons emit energy in the form of light when they return to a lower energy level.
What are the main points of Bohr’s atomic model?
Electrons orbit the nucleus in fixed-size and-energy orbits. The size of the orbit affects its energy. The smallest orbit contains the lowest energy. When an electron moves from one orbit to another, it absorbs or emits radiation.
How does Bohr’s model explain atomic spectra?
According to Bohr’s theory, atomic spectra are created when electrons absorb energy from a source, jump to a higher energy level, then descend back to a lower energy level, releasing the energy contrast between the different energy levels.
What are the merits and demerits of Bohr’s atomic model?
The ground state orbital angular momentum provided by the Bohr Model is erroneous. It has a hard time predicting the spectra of bigger atoms. It does not forecast spectral line relative intensities. Fine and hyperfine structure in spectral lines are not explained by the Bohr Model.
What are the disadvantages of the Bohr Model?
It is incapable of explaining the spectrum of atoms other than hydrogen, such as the helium atom, which has only two electrons. It also fails to explain spectral line splitting in the existence of a magnetic or electric field.