During the time of the experiment by Ernest Rutherford in 1909 at the University of Manchester, the popular model of the atom was the 'Plum Pudding Model'. - Through his experiment, he noticed that the alpha rays were getting deflected by the center mass, and hence concluded the presence of positively charged particles in the nucleus and let to the discovery of the nucleus. - Plum Pudding Model had propounded that there were floating negatively charged electrons. - Further ahead, Rutherford's experiment replaced the Plum Pudding Model. - Electron was discovered by JJ Thomson. - Neutron was discovered by James Chadwick.