Thomson's model of an atom says
Before the discovery of subatomic particles, John Dalton came up with Dalton’s atomic theory where he suggested that atoms are indivisible particles. It explained atoms cannot be broken down into further smaller particles. However, the discovery of subatomic particles disapproved the postulates proposed in Dalton Atomic Theory. The discovery of subatomic particles led to the search how the subatomic particles are arranged in an atom. J.J. Thomson was the first and one of the many scientists who proposed models for the structure of an atom. J.J. Thomson discovered negatively charged particles by cathode ray tube experiment in the year 1897. The particles were named electrons. J.J Thomson believed electrons to be two thousand times lighter than a proton. He assumed that an atom is composed of a cloud of negative charge in a sphere of positive charges. J.J Thomson and Rutherford first demonstrated the ionization of air in x rays.