Thomsons Model of the Atom


 
 
Concept Explanation
 

Thomsons Model of the Atom

Structure of an Atom: According to Dalton’s atomic theory, atom was indivisible and indestructible. Now, the discovery of two fundamental particles (electrons and protons) inside the atom, led to the failure of this aspect of in Dalton’s theory. To know the arrangement of electrons and protons within an atom, many scientist proposed various atomic models.

Thomson’s Model of an Atom: J.J. Thomson was the first scientist to propose a model for the structure of an atom. Thomson’s model of an atom was similar to Christmas pudding. The electrons in a sphere of positive charge were like currants (dry fruits) in a spherical Christmas pudding.  It can also be compared to a watermelon, in which, the positive charge in an atom is spread all over like the red edible part, while the electrons studded in the positively charged sphere, like the seeds in the watermelon.

Following are the postulates of this model:

  • Electrons are embedded in the sphere of positive charge.
  • The negative and positive charges are equal in magnitude. Therefore, the atom as a whole is electrically neutral.
  • The mass of an atom is assumed to be uniformly distributed throughout the atom.
  • Limitations of Thomson’s Model of an Atom:

  • J.J. Thomson’s model could not explain the experimental results of other scientists such as Rutherford, as there is no nucleus in the atomic model proposed by Thomson.
  • It could not explain the stability of an atom, i.e. how positive and negative charges could remain, so close together.
  • Sample Questions
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    Question : 1

    Which of the following are the limitations of Thomson model :

    (a) It could not explain the stability of the atom ,i.e. how positive and negative charges could remain, so close together.

    (b) It could not explain the distribution of electrons in the extra nuclear portion of the atom.

    Right Option : A
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    Question : 2

    Electrons are embedded in the sphere of _____________charge.

    Right Option : A
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    Question : 3

    Which of the following are the postulates of Thomson Model :

    (a) Electrons are embedded in the sphere of the positive charge.

    (b) Most of the fast moving alpha particles passed straight through the gold foil.

    (c) The negative and positive particle are equal in magnitude.Therefore, the atom as whole is electrically neutral.

    Right Option : D
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