Question

how did J.J. Thomson discover the electron?Explain his ''plum pudding'' model of the atom.

Answer 1

Dear Student

Thomson model:

According to this model, an atom can be considered as a sphere of uniformly distributed positive charge in which there are electrons distributed symmetrically.

The electrons must be held by the positive charges by electrostatic forces. The mutual repulsions between the electrons are balanced by the force of attraction towards the centre of the sphere.

In an atom with a single electron like the hydrogen atom, the electron must be situated at the centre of the positive sphere.

In an atom with two electrons, like the helium atom, the two electrons must be symmetrically situated on opposite sides of the centre at a distance equal to half the radius of the positive sphere.

In the three-electron system, the electrons should be at the corners of a symmetrically placed equilateral triangle, the side of which is equal to the radius of the sphere.

Proceeding in this manner, Thomson could explain the arrangement of electrons ranging from 1 to 100 inside the positive sphere.

This model was also called 'the plum pudding model'. The electrons are like plums in a pudding (negative charge). The seeds in a watermelon fruit can be given as a parallel comparison.

Regards