Q. 17. State the postulates of Bohr's model of atom.
What is the maximum number of electrons that can be
accommodated in a shell?
Answers
Answer:
Quantum mechanics, Quantum physics, the theory of relativity, etc are the modern subjects that interests, astound, and confuse almost everybody. These topics form the basis of modern physics. However, the very first-time quantum theory was incorporated in Bohr’s Model of an atom or Bohr atomic model. Later this model became the predecessor of complete quantum mechanical models.
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The physicist Niels Bohr said, “Anyone who is not shocked by quantum theory has not understood it.” He also said, “We must be clear that when it comes to atoms, language can only be used as in poetry.”
Bohr atomic model and the models after that explain the properties of atomic electrons on the basis of certain allowed possible values. The model explained how an atom absorb or emit radiation when electrons on subatomic level jump between the allowed and stationary states. German-born physicists James Franck and Gustav Hertz obtained the experimental evidence of the presence of these states.
Bohr Atomic Model
A Danish physicist named Neil Bohr in 1913 proposed the Bohr atomic model. He modified the problems and limitations associated with Rutherford’s model of an atom. Earlier in Rutherford Model, Rutherford explained in an atom a nucleus is positively charged and is surrounded by electrons (negatively charged particles).
The electrons move around in a predictable path called orbits. Bohr modified Rutherford’s model where he explained that electrons move around in fixed orbital shells. Furthermore, he explained that each orbital shell has fixed energy levels. Therefore, Rutherford basically explained a nucleus of an atom whereas Bohr took the model one step ahead. He explained about electrons and the different energy levels associated with it.
According to Bohr Atomic model, a small positively charged nucleus is surrounded by revolving negatively charged electrons in fixed orbits. He concluded that electron will have more energy if it is located away from the nucleus whereas the electrons will have less energy if it located near the nucleus.
Bohr atomic model
Bohr’s Model of an Atom (Source Credit: Britannica)
Postulates of the Bohr Atomic Model
Electrons revolve around the nucleus in a fixed circular path termed “orbits” or “shells” or “energy level.”
The orbits are termed as “stationary orbit.”
Every circular orbit will have a certain amount of fixed energy and these circular orbits were termed orbital shells. The electrons will not radiate energy as long as they continue to revolve around the nucleus in the fixed orbital shells.
The different energy levels are denoted by integers such as n=1 or n=2 or n=3 and so on. These are called as quantum numbers. The range of quantum number may vary and begin from the lowest energy level (nucleus side n=1) to highest energy level. Learn the concept of an Atomic number here.
The different energy levels or orbits are represented in two ways such as 1, 2, 3, 4… or K, L, M, N….. shells.