Rutherford's Atom

I. Video on Rutherford's Gold Foil Experiment

II. Notes on Gold Foil Experiment

Upon the discovery of positive and negative subatomic particles from J.J. Thomson's Cathode Ray Experiment, scientists began to wonder how these subatomic particles arranged themselves within an atom.

William Thomson (also known as Lord Kelvin) hypothesized that the subatomic particles arranged themselves within the atom much like raisins in plum pudding where the raisin could be thought of as the negative particles the the pudding itself represented a positive cloud. He aptly described his idea of the atom as the "Plum Pudding Model," as illustrated below.

PLUM PUDDING MODEL

However, Ernest Rutherford's famous Gold Foil Experiment ultimately proved that that the subatomic particles arranged themselves in a nuclear manner where atom is mostly empty space with a small positive nuclear core, with the negative particles located away from the nucleus.

Positively charged alpha particles where shot from a device through a thin gold foil. The detector surrounding the foil recorded that the majority of the particles went straight through. However, every once in a while, the particles would ricochet into different directions. To Rutherford, this observation stunned him. As recorded in his notes, "It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you." Rutherford concluded that the results indicated that the atom was mostly empty space with a small positive core.