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Nuclear Atomic Model

The Nucleus

New Zealand born, Ernest Rutherford was J.J. Thomson's student and decide to prove that the Plum-Pudding model was correct and Phillip Lenard was wrong.

So, Rutherford had his assistants Hans Geiger and Ernest Marsden put the Plum-Pudding model to the test. In 1909, Geiger and Marsden performed the famous Gold Foil experiment that led to the discoveries of the atomic nucleus and that the atom was mostly space.

Geiger and Marsden set up an experiment to determine the effect of bombarding a thin sheet of gold foil with rays from a radioactive source such as radium. They cut a small hole in a lead plate so that the stream of rays could be focused. Then they placed a thin sheet of gold foil and a viewing screen on the other side of the hole as shown in the diagram.

The flashes of light produced when alpha particles strike the zinc sulfide screen can be observed through a movable microscope. Most of the alpha particles passed through the gold foil undeflected, but a few were deflected back toward the source.

The Gold Foil experiment demonstrated that the mass of the atom was the same as predicted by Thompson's model, but the volume of the mass was much smaller and seemed to be located in the center of the atom. This massive center, known today as the atomic nucleus, has a volume one trillionth the volume of the whole atom.

The nucleus is a very small, very dense, centrally located, positivley charged region in the atom.

Thompson's Plum Pudding model was no longer workable. So, in 1911, Rutherford proposed the Nuclear Atomic Model.

Rutherford's new model stated that the atom was mostly empty space with a small, very dense positively charged nucleus surrounded by negatively charged electrons located in the atomic space.