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PLANETRY MODEL OF AN ATOM

RUTHERFORD’S ATOMIC MODEL OR PLANETRY MODEL OF AN ATOM OR GOLD FOIL EXPERIMENT OR DISCOVERY OF NUCLEUS: In order to determine the structure of an atom, Rutherford carried out Gold Foil experiment in year 1911.He bombarded alpha-particles on 0.00004cm thick gold foil. Alpha-particles are emitted from radioactive elements like Radium and Polonium.

Alpha particles are helium nuclei which can penetrate through matter to some extent. Rutherford observed the effect of alpha particles on the photographic plate or a screen coated with zinc sulphide. He proved that the Plum Pudding Model of the atom was not correct.

OBSERVATIONS: Observations made by Rutherford are as follow: 1)Almost all the particles passed through the foil un-deflected. 2)Out of 20,000 particles, only a few were deflected at fairly large angles and very few bounced back on hitting the gold foil.

RESULTS OF EXPERIMENT: After carrying out an experiment, Rutherford proposed PLANETRY MODEL for an atom and concluded following results. 1)Since most of the particles passed through the foil un-deflected , therefore most of the volume occupied by an atom is empty.

  • The deflection of a few particles proved that there is a “center of positive charges” in an atom, which is called “nucleus” of an atom.
  • The complete renounce of a few particles show that the nucleus is very dense and hard.
  • Nucleus is located at the center of an atom.
  • The whole mass of an atom is concentrated in the nucleus.
  • Since a few particles were deflected it shows that the size of the nucleus is very small as compared to the total volume of an atom.
  • An atom as a whole is neutral, therefore the number of electrons in an atom is equal to the number of protons.
  • Except electrons, all other fundamental particles that lie within the nucleus , are known as Nucleons.
  • The electrons revolve around the nucleus.

 

DEFECTS IN RUTHERFORD’S MODEL: Following are the main defects found in Rutherford’s atomic model.

  • According to classical theory of radiations, electrons being the charged particles should release or emit energy continuously and they should ultimately fall into the nucleus.
  • If electrons emit energy continuously, they should form a continuous spectrum, but in fact line spectrum was observed.

For your information: Rutherford was a British Newzeland chemist. He performed a series of experiments using α particles. He won the 1908 Noble Prize in Chemistry. In 1911, he proposed the nuclear model of the atom and performed the first experiment to split atom. Because of his great contributions, he is considered the father of nuclear science.

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