Question

What was the drawback of Rutherford's model of atom? Describe Bohr’s model of atom and explain its usefulness over Rutherford’s model.

Answer 1

Hint: The Bohr’s model does not dismiss all the postulates and observations of Rutherford's atomic model, but only develops further on its limitations. Bohr's model could successfully explain the various spectral lines of the hydrogen atom and provided many important formulas for atomic calculations.

Complete answer:
Rutherford's model of an atom was based on the assumption that the electrons revolve around the nucleus in specific orbits. The drawbacks of this model were:
1.This model could not explain the cause of stability of an atom. The assumption regarding the revolution of electrons in their orbits around the nucleus was a major limitation as the electrons would accelerate and dissipate or radiate energy in some form due to their charge. This loss of energy by the electrons would ultimately result in a spiral motion where their velocities go on decreasing and they sink into the nucleus. If a phenomenon like this happens then the entire structure of an atom would collapse and the matter won’t exist in its stable form.
2.Another major drawback of this model was the inability to explain the distinct and specific electron emission lines of a hydrogen atom.
Bohr’s model of an atom was based on the following postulates:
1.The most important postulate was that electrons move in fixed energy paths called the orbits and the electron is incapable of changing its energy with time. The electrons can jump from lower to higher energy levels by absorbing fixed amounts of energy and emitting back the same amount of energy as they fall back to the lower energy levels.
This postulate overcomes the major limitations posed by Rutherford's model of atoms.
2.A particular frequency will be absorbed or released in between two energy states that is given by the relation:
\[v = \dfrac{{\Delta E}}{h} = \dfrac{{{E_2} - {E_1}}}{h}\]
Where \[\Delta E\] stands for the energy difference between two levels.
3.Only those energy levels will be allowed in an atom that have the values of their angular momentum as the integral multiples of a fixed factor \[\left( {\dfrac{h}{{2\pi }}} \right)\] :
\[{\text{Angular momentum}} = mvr = n\left( {\dfrac{h}{{2\pi }}} \right)\]
Bohr's model is useful in calculating the frequency and wavelengths of all the spectral lines associated with the hydrogen atom. It gives a clear picture of the structure of an atom by giving insights into the allowed energy levels, the distribution of electrons and is useful in determining the radius of orbits and velocities of electrons in each level. This model is also applicable for other single electron species.
Thus the Bohr’s model is more useful and effective in determining the structure of an atom than Rutherford’s model.

Note:
Even though Bohr's model of an atom is very accurate in determining a lot of factors about the structure of an atom, it is only limited to single electron species. For multi electron species, the quantum mechanical model of an atom is used.