Bohr model of the atom was proposed by Neil Bohr in 1915. It came into existence with the modification of Rutherford’s model of an atom. Rutherford’s model introduced the nuclear model of an atom, in which he explained that a nucleus (positively charged) is surrounded by negatively charged electrons.
Bohr modified this atomic structure model by explaining that electrons move in fixed orbital’s (shells) and not anywhere in between and he also explained that each orbit (shell) has a fixed energy level. Rutherford basically explained the nucleus of an atom and Bohr modified that model into electrons and their energy levels.
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Postulates of Bohr Atom
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 quantum numbers. The range of quantum numbers may vary and begin from the lowest energy level (nucleus side n=1) to the 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. The lowest energy level of the electron is called the ground state. Learn the concept of Valency here in detail here.
The change in energy occurs when the electrons jump from one energy level to another. In an atom, the electrons move from lower to higher energy levels by acquiring the required energy. However, when an electron loses energy it moves from higher to lower energy level.
Limitations of Bohr’s Model of an Atom
Bohr atomic model had few limitations. They are:
Failure to explain the Zeeman Effect (how atomic spectra are affected by magnetic fields).
It contradicts the Heisenberg Uncertainty Principle.
Unable to explain how to determine the spectra of larger atoms.
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