Question

Postulates of Bohr's atomic theory, limitations of Bohr's

Answer 1

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.
• 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.
• 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,

• 1^st orbit (energy level) is represented as K shell and it can hold up to 2 electrons.
• 2^nd orbit (energy level) is represented as L shell and it can hold up to 8 electrons.
• 3^rd orbit (energy level) is represented as M shell and it can contain up to 18 electrons.
• 4^th orbit (energy level) is represented as N Shell and it can contain maximum 32 electrons.

Limitations of Bohr’s Model of an Atom:

Bohr atomic model had few limitations. They are:

• Failure to explain Zeeman Effect (how atomic spectra are affected by magnetic fields).
• It contradicts Heisenberg Uncertainty Principle.
• Unable to explain how to determine the spectra of larger atoms.