Rutherford's α-rays Scattering Experiment | Chemistry Class 11

Notes | Chemistry
Rutherford's α-rays  Scattering Experiment - Observation, Nuclear Model of Atom and Limitation.
Class: 11

Rutherford’s model of atom is based on the α-rays scattering experiment which was performed by Ernest Rutherford and his co-workers in 1910 AD. In this experiment α-rays emitted from radioactive substance where bombarded on a thin gold foil around which a movable screen coated with Zns flashes were produced which could be easily observed. By examining the Zns screen in different position, it was possible to determine the proportion of α-rays scattering away from the Gold foil.

The observation made by his experiment are :

1. Most of the α-particles nearly 99% passed through the gold foil without any deflection. 
2. Some of the α-particles were deflected through small angle. 
3. Very few (1 in million) α-particles were deflected through angles more than 90 or even bounce back in 180 degree angle. 

Rutherford’s Nuclear Model of Atom.

From these α-rays scattering experiment Rutherford came into conclusion about model of atom as below:

1. There is empty space in the atom since most of α-particles passes through gold foil without any deflection. 
2. Since, some of α-particles are deflected through small angles there must be a heavy positively charged mass occupying a very small space within the atom. 
3. The large deflection or even bouncing back of α-particles is due to the encounter of α-particles with positively charged mass present in nucleus. 

Limitation ( Drawbacks ) at Rutherford’s atomic model.

The atomic model proposed by Rutherford’s was soon found to be defective. The major defects of his atomic model are:

1. Electron continuously revolving around the nucleus under the influence of attractive force loses energy in the form of electromagnetic radiation due to which the speed of electron will slow down and its orbit becomes smaller and smaller and finally the electron would fall into the nucleus.

2. It could not explain how and where all these electrons were arranged in an atom. 

3. It could not explain the origin of lines of spectra of any atom. 

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