explain about Bohr's atomic model theory and its limitation
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Answer:
Explanation: 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’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. 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 other. In an atom, the electrons move from lower to higher energy level by acquiring the required energy. However, when an electron loses energy it moves from higher to lower energy level. Therefore, • 1st orbit (energy level) is represented as K shell and it can hold up to 2 electrons. • 2nd orbit (energy level) is represented as L shell and it can hold up to 8 electrons. • 3rd orbit (energy level) is represented as M shell and it can contain up to 18 electrons. • 4th orbit (energy level) is represented as N Shell and it can contain maximum 32 electrons.
Distribution of Electrons in Orbits or Shells: Electronic distribution of various orbits or energy levels can be calculated by the formula 2n2. Here, ‘n’ denotes the number of orbits. Limitations of Bohr’s Model of an Atom: Bohr atomic model had few limitations. They are: • Failure to explain how atomic spectra are affected by magnetic fields also called as Zeeman effect. • Unable to explain how to determine the spectra of larger atoms.
Answer:
Thomson’s atomic model and Rutherford’s atomic model failed to answer any questions related to the energy of an atom and its stability. In the year 1913, Niels Bohr proposed an atomic structure model, describing an atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the positively charged nucleus as planets around the sun in our solar system, with attraction provided by electrostatic forces, popularly known as Bohr’s atomic model.
Limitations of Bohr Atomic Model Theory
It violates the Heisenberg Uncertainty Principle. The Bohr atomic model theory considers electrons to have both a known radius and orbit i.e. known position and momentum at the same time, which is impossible according to Heisenberg.
The Bohr atomic model theory made correct predictions for smaller sized atoms like hydrogen, but poor spectral predictions are obtained when larger atoms are considered.
It failed to explain the Zeeman effect when the spectral line is split into several components in the presence of a magnetic field.
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