This radiation also seemed to be unaffected by electric and magnetic fields. In 1930, Walther Bothe and Herbert Becker fired alpha particles at beryllium and found that a highly penetrating radiation resulted. Rutherford and Chadwick continued to make observations and see if any of there results suggested the existence of the neutron, but failed to confirm its existence. Rutherford proposed that a neutral particle similar in size to a proton must exist in the nucleus and he called this theoretical particle the neutron.

However, there were problems that arose as a result of this assumption. Electrons occupied the large amounts of empty space that surrounded the nucleus of the atom.Īfter Rutherford discovered that the atom consisted of a nucleus, it was logical to assume that the nucleus consisted of protons and electrons.The nucleus contained all of the positive charge of the atom.The vast majority of the mass of an atom occupied an extremely small and dense area in the middle of the atom.Thomson had been successful in isolating the electron, however, the positive pudding from his model was rejected following Rutherford’s interpretation of the Gieger-Marsden experiment, as discussed previously.Ĭonsequently, Rutherford suggested a nuclear model of the atom that obeyed the following principles: This led Rutherford to develop his model of the atom.Įrnest Rutherford had described a new model of the atom, building upon the plum pudding model which had earlier been suggested by JJ Thomson. He concluded that the charge throughout the atom was not uniform at all and that the atom must consist of a small, dense, positively charged nucleus surrounded by smaller negatively charged electrons. Rutherford knew that the small negatively charged electrons would not create a large enough electrostatic force to deflect the large positive alpha particle as observed. Marsden and Geiger found that most of the alpha particles passed through undeflected but to the surprise of Rutherford, they found that about 1/8000 deflected at angles greater than 90°. In trying to confirm Thomson’s model of the atom, Rutherford expected all of the alpha particles to pass through undeflected, or at most, very small angles. Under the guidance of Ernest Rutherford, Geiger and Marsden were directed to investigate the scattering of alpha particles by firing them at a thin foil made of gold.

J.J Thomson’s investigation of cathode rays led him to develop the ‘plum pudding’ model of the atom which consisted of very small negatively charged electrons spread throughout a positive charge of very low density.

Nuclear model of the atom