<u>Answer:</u>
Dalton thought that atoms are indivisible. During Dalton’s period subatomic particles like protons, electrons and neutrons were not discovered. So, Dalton’s atomic model was just a sphere that is atom is the smallest particle of all matter.
J.J. Thomson is the scientist who discovered the electron. His experiments were called as Cathode ray tube experiments. His model was a sphere in which the negatively charged particles were embedded like the plums present in a pudding.
Hence his model was called as plum pudding model. Goldstein discovered a positively charged particle which was called as protons. Rutherford gold foil experiment predicted that nucleus is in the centre and the electrons were present around the nucleus.
He predicted that the mass of the atom is due to the nucleus and the electrons have negligible mass. The nucleus mass is due to the presence of positive protons present in the centre of the atom. His model was called as planetary model. As the planets move around the sun, the electrons are moving around the nucleus.
Bohr’s model refined certain elements of the Rutherford model that were problematic.This model of an atom shows nucleus contains protons and neutrons that make up the mass of the atom.
