J. J. Thompson

Thompson contribution to the atom was very significant, he was the first person to suggest that atoms contained negatively and positively charged particles. Thompson discovered this during his experiment that used a cathode ray tube. A cathode ray tube shows an invisible beam emitted from an atom that is attracted to the electrode, a solid electric conductor where an electric current enters at one end and leaves out the other. The beam is represented when a bright dot appears on a fluorescent screen attached at the end of the device. Thompson suggested that the cathode ray was a stream of electrons being emitted from the atom. Thompson first believed that atoms were made up of thousands of electrons to make up for their mass. If this was true then atoms would have a high negative charge, but most atoms have no charge. Thompson suggested that atoms had electrons roughly equal to the atomic number. Thompson came up with the idea that in order to make an atom neutral it had to have the same number of positively charged particles as negative ones. Thompson then created the “Plum Pudding” model to express his idea. The model turned out not to be a correct representation of an atom because electrons are not stationary, they orbit around the nucleus, and protons do not surround electrons, they are located in the nucleus, the model also did not include neutrons.
Rutherford

Rutherford contributed to the atomic theory by discovering that there was a positively charged center of an atom, he named it the nucleus. Rutherford made this discovery during an experiment in which he beamed alpha particles (consists of two protons and two neutrons; identical to a helium nucleus) through a slit in a lead sheet that surrounded at a sheet of gold foil. Most of the particles went through the sheet