Class 9 Chemistry Structure of The Atom Rutherford’s Experiment-Discovery of Nucleus

Rutherford’s Experiment-Discovery of Nucleus

Alpha particle

  • Alpha particle is a positively charged particle having 2 units of positive charge and 4 units of mass.
  • It is actually helium ion, He2+.
  • Rutherford’s alpha particles scattering experiment led to the discovery of small positively charged nucleus in the atom which contained protons and neutrons.


  • When fast moving alpha particles are allowed to strike a thin gold foil of about thousand atoms thick in vacuum, it is found that:-
  1. Most of the fast moving alpha particles passed straight through gold foil.
  2. Some of the alpha particles were deflected by small angles.
  3. About 1 out of every 12000 particles appeared to rebound.
  • Conclusion:-
  1. Most of the space in the atom is empty.
  2. The positive charge of the atom occupies very little space.
  3. The electrons revolve around the nucleus in circular paths.
  4. All the positive charges and the mass of the atom were concentrated in a very small volume at the centre.
  5. It shows the presence of a nucleus in the atom.
    1. Nucleus of an atom is positively charged.
    2. Nucleus of an atom is very dense and hard.
    3. The size of the nucleus is very small compared to the size of the atom.
  • Drawbacks:-
  1. The major drawback of this model is that it did not explain the stability of the atom.
  2. According to the electromagnetic theory if a charged particle undergoes acceleration then it must radiate energy continuously.
  3. Thus, the revolving electron loses energy and falls into the nucleus.
  4. Then the atom would be highly unstable and hence matter could not exist in a form that is known now but it is known that atoms are stable.



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