Overview of the Experiment
Rutherford's Gold Foil Experiment, conducted by Ernest Rutherford and his students Hans Geiger and Ernest Marsden in 1909, involved firing positively charged alpha particles at a thin sheet of gold foil. The experiment aimed to test J.J. Thomson's "plum pudding" model of the atom, which predicted that alpha particles would pass straight through with minimal deflection.
Experimental Setup and Observations
A beam of alpha particles was directed at a very thin gold foil, with a fluorescent screen placed around the foil to detect where the particles landed. While most alpha particles passed directly through the foil, some were deflected at large angles, and a very small fraction (about 1 in 8,000) were scattered backward, as if they had hit something dense.
Disproving the Plum Pudding Model
These unexpected results contradicted the plum pudding model, which proposed that an atom's mass and positive charge were uniformly distributed. If the plum pudding model were correct, the alpha particles should have experienced only minor deflections, not large-angle scattering or backward bounces.
The Nuclear Model of the Atom
Based on these observations, Rutherford proposed the nuclear model of the atom. This model suggested that atoms consist of a tiny, dense, positively charged nucleus at the center, surrounded by mostly empty space where electrons orbit. The small, dense nucleus was responsible for the large deflections and backward scattering of the alpha particles.