Thomson Model Of Atom In Chemistry,  Plum-Pudding Model, Important Topics For JEE 2025

Thomson Model Of Atom In Chemistry : J. J. Thomson, proposed that an atom possesses a spherical shape (radius approximately 10 ¹⁰ m) in which the positive charge is uniformly distributed. The electrons are embedded into it in such a manner as to give the most stable electrostatic arrangement. Many different names are given to this model, for example, plum pudding, raisin pudding or watermelon model . This model can be visualized as a pudding or watermelon of positive charge with plums or seeds (electrons) embedded into it. An important feature of this model is that the mass of the atom is assumed to be uniformly distributed over the atom. Although this model was able to explain the overall neutrality of the atom, but was not consistent with the results of later experiments.

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Thomson Model Of Atom

• Sir J. J. Thomson, who discovered the electron, was the first to suggest a model of atomic structure.

• Thomson was the first scientist to propose a detailed model of an atom.
• According to his model, electrons are embedded in positively charged sphere of an atom.
• An atom is electrically neutral because it contains equal number of protons and electrons.
• This model of an atom is also known as
• Plum - Pudding Model
• Raisin Pudding Model
• Water Melon Model

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Thomson visualized all the positive charge of the atom as being spread out uniformly throughout a sphere of atomic dimensions (i.e. approx. 10 ^–10 m in diameter). The electrons were smaller particles together carrying a negative charge, equal to the positive charge in the atom. They were studded in the atom like plums in a pudding.

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Drawbacks of the Thomson Model of Atom

• An important drawback of this model is that the mass of the atoms is considered to be evenly spread over that atom.
• It is a static model. It does not reflect the movement of electrons.
• It could not satisfactorily explain the results of scattering experiments carried out by Rutherford.

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Achievements Of Thomson

Thomson was awarded with Noble Prize for physics in 1906, for his theoretical and experimental investigations on the conduction of electricity by gases.

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