Thomson’s Model of Atom:
After the discovery of electron and proton, the scientists started thinking of arranging these particles in an atom. Different models were proposed to explain the distribution of subatomic particles in an atom. The first simple model was proposed by J.J Thomson known as Thomson’s atomic model.
J.J. Thomson proposed that an atom consists of a uniform sphere in which positive charge is uniformly distributed. The electrons are embeded into it in such a way as to give the most stable electrostatic arrangement .The radius of the sphere is of the order of 10-10 m, which is equal to the size of the atom. This model was much like pudding or cake (of positive charge) with raisins (electrons) embeded into it. Therefore, this model is also known as raisin pudding model. This model was also given names such as plum pudding or water melon. An important feature of this model is that the mass of the atom is considered to be evenly spread over the atom.
This model explains some of the known properties and electrical neutrality of atom. However, it was soon discarded, when Rutherford and his co-workers observed unusual scattering of α-particles by the thin metal foils. Since this model could not explain the experimental results, it was therefore, rejected.