Discovery of Atomic Nucleus




In 1911, Rutherford and his associates set an experiment to explore the structure of atoms. They bombarded a beam of alpha particles from a radioactive materials, on a thin film gold foil, as shown in the figure. To detect the scattered alpha particles from the gold foil, a fluorescent screen was used. When an Alpha-Particles strikes the screen, a tiny flash of light is given off.

Rutherford and his associates placed the screen at various angles in the path of scattered Alpha-Particles. They counted the number of Alpha-Particles striking the screen at various angles. 



Observations:
From the above experiment, Rutherford and his fellows got the following observations.

1) Most of the Alpha-Particles were scattered through small angles.
2) A few Alpha-Particles were deflected through more than 90 degrees.
3) Some Alpha-Particles were reflected nearly backward indicating that they had elastic head on collision with massive objects.

Conclusion: 
On the basis of their experimental observations, Rutherford and his associates introduced the nuclear model of atom.

1)  In this model of atom consists of a tiny positively charges hard core called Nucleus.
2) The diameter of the nucleus is of the order of 10^-15 m.
3) The nucleus contains the maximum mass of the atom and its charge '1' is  q= z e
     here Z is the atomic number of the element and e = 1.6* 10^-19 C ( charge on proton )
4) The atomic radius is of the order of 10^-10 m . So the ratio of the nucleus radius to the radius of atom.

                           Ratio =       10^-15 m / 10^-10 m 

5) According to equation concept, the electron's cloud is there around the nucleus.

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