The plum pudding model of atoms as proposed by J.J. Thomson postulated the atom to be composed of electrons that lie in a positively charged entity. This model of the atom is represented in figure X.
In 1909, an experiment was conducted by Hans Geiger and Ernest Marsden, known as the gold foil experiment, in which they passed alpha particles through a gold foil. A photographic film was placed behind the foil and an image was created by the particles that were able to pass through the foil. This revealed that the rays created by the particles were not able to pass through the foil uniformly, some of the particles were strongly deflected from their original direction and some bounced back to the source. An alpha particle is positively charged. The observations from the experiment could be explained by by an atomic model consisting of a small, dense positively charged center called the nucleus around which negatively charged electrons revolved.
The cathode ray experiments, performed by J.J. Thomson, involved an air-tight glass tube with a cathode (negative electrode) and an anode (positive electrode). A ray traveling from the cathode to the anode bent in the opposite direction when a negatively charged plate was placed near it and bent towards a positively charged plate. This proved that the ray was negatively charged.
His series of cathode ray experiments proved that negatively charged particles called electrons exist, while the gold foil experiment proved the existence of a nucleus.