Bohr’s atomic model is modified form of Rutherford atomic model. To overcome several limitation in Rutherford model, Niels Bohrs proposed this theory in 1913. This theory is based on quantum theory of radiation. It has 3-main postulates.
First postulate of Bohr’s atomic model
Electrons revolves around the nucleus in circular path. There is a type of attractive force which holds electron and nucleus together. This attractive force is equal to centripetal or electrostatic force(i.e.Columb’s force).
Second postulate of Bohr’s atomic model
Electrons can only revolve in certain discrete orbit & orbits with non-radiating energy. Non-radiating energy orbits are also called as stationary orbits. The angular momentum of orbits should be equal to an integral multiple of h/2π.
Third postulates of Bohr’s atomic model
When electron jumps from higher level energy to lower energy level, there is a certain difference in energy level. This difference in energy is radiated in the form of electromagnetic radiation with frequency 'v'.
i.e E2-E1= hv
h = Planck's constant
v = frequency
This is called quantization of energy.
Success of Bohr's theory
- It explains the stability of atom.
- It explains the line spectrum of Hydrogen.
- Energy of electrons in nth orbit can be numerically calculated.
- Radius & velocity of electrons in nth orbit can also be numerically calculated.
Read also: Rutherford atomic model
Limitation of Bohr’s theory
- It is only applicable to mono- electronic elements. i.e. It is only applicable to elements containing only one electron such as Hydrogen atom. It is also applicable to He+, li2+, Na10+ etc. as they also contains only one electron.
- It is unable to explain the splitting of lines in the magnetic field. In magnetic field Zeeman effect is seen while in electric field Stark effect is seen. This theory is unable to explain these splitting lines.
- It is unable to explain the 3-dimensional model of atom.
- It is also unable to explain the shape of molecules.
- It does not obey the de-Broglie and Heisenberg uncertainty principle.
Do you know ?
►Bohr’s atomic model is also called as planetary model. In Bohr’s model, nucleus is at center and electrons moves around it. In Solar system, Sun is at center and planet moves around it.
►It is based on quantum theory of radiation.
►The main drawback of this theory is that it is unable to obey de-Broglie and Heisenberg uncertainty principle.
a) Bohr’s atomic model is based on?
Ans: It is based on quantum theory of radiation which is also called as electromagnetic theory. Quantum theory of radiation was given by Maxwell.
b) Bohr’s atomic model resembles with?
Ans: It resembles with planetary model of our solar system. In Bohr’s model, nucleus is at center and electrons revolves around it. In our solar system, sun is at the center and planets moving around it.
c) What are the successes of Bohr’s model?
Ans: It explains the stability of atom by introducing non-radiating energy orbits called as stationary orbits. It explains the line spectrum of Hydrogen. It is also success in predicting the numerical value of radius, energy & velocity of electron revolving in nth orbits of an atom.
d) What are the main limitation of Bohr’s model?
Ans: The main drawback of this theory is that it is unable to obey de-Broglie and Heisenberg uncertainty principle.