Nuclear Model of the Atom – Learn
The Geiger–Marsden Experiment
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.
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. 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. 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°.
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. 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. This led Rutherford to develop his model of the atom.
Rutherford’s Atomic Model
investigate, assess and model the experimental evidence supporting the nuclear model of the atom, including:
– the Geiger–Marsden experiment
– Rutherford’s atomic model
– Chadwick’s discovery of the neutron