Question

Why was J J Thomson wrong?

Answer 1

Hint: Rutherford overturned Thomson's model in $ 1911 $ with his well-known gold foil experiment, in which he demonstrated that the atom has a tiny, high- mass nucleus. In his experiment, Rutherford observed that many alpha particles were deflected at small angles while others were reflected back to the alpha source.

Complete Step By Step Answer:
According to Thomson's model of the atom, electrons were embedded in a sphere of positive charge and negative and positive charges are equal in magnitude. But after performing Rutherford's gold foil experiment, it was concluded that most of the space inside an atom is empty because most of the alpha particles passed straight through without getting deflected which was contrary to what has been predicted by Thomson's model. Hence, Thomson's model of an atom was rejected.
J J Experiments with cathode ray tubes by Thomson showed that all the atoms contain tiny subatomic particles or electrons that are negatively charged. Thomson suggested the atom's plum pudding model, which had negatively charged electrons trapped in a "soup" filled with positive effects. Thomson was "wrong" because he assumed that the positive charge of an atom was all one uniform blob of matter with the electrons moving in orbits inside the nucleus.

Note:
If Thomson's model were correct, the alpha particles would pass through the atomic structure of the foil unimpeded. Scattering on the electrons embedded in JJ Thompson's atom would not have produced enough large angle scattering, since the electrons were light. Thompson's model would have produced small angle scattering almost all of which was forward.