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Theory:

Watermelon Model:
  • In \(1904\), J.J.Thomson proposed an atom model after the discovery of electrons.
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  • Thomson suggested that the shape of an atom relates to a sphere (radius1010 m).
  • The positively charged particles are evenly distributed with electrons arranged so that the atom is electrically neutral.
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  • The name of Thomson's atom model is the Plum pudding model or Watermelon model. The settled electrons are related to the seed of the watermelon.
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  • Watermelon’s red mass expressed the positive charge distribution.
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Watermelon modal
  • The Plum pudding theory concluded that 'the mass of an atom is evenly spread all over the atom'.
Note: Thomson’s model successfully explains the electrical neutrality of the atom.
Limitations of Thomson’s Model:
  • Thomson's atomic model could not explain the positive charge on the electrons inside the atom.
  • This model explains only for protons and electrons, not for neutron and nucleus.
  • It did not explain the stability of an atom.
  • It failed to explain Rutherford's scattering experiment.