Rutherford's Gold Foil: The Pivot to the Modern Nuclear Atom Model

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Rutherford's gold foil experiment :

In 1909, Ernest Rutherford, who had worked under Thomson and subscribed to his plum-pudding model, performed an experiment in an attempt to confirm Thomson’s model. This experiment was determined to find out the structure of an atom. The above figure illustrates the experiment. His experiment, employing \(\alpha \text {-particles }\), proved it wrong instead. In the experiment, Rutherford directed the positively charged \(\alpha\) - particles at an ultrathin sheet of gold foil. These particles were to act as probes of the gold atoms’ structure.

Rutherford explained the results by postulating the nuclear model of the atom, in which most of the mass of each gold atom and all of its positive charge reside in a very small, extremely dense region which he called the nucleus. He postulated further that most of the volume of an atom is empty space in which electrons move around the nucleus. Subsequent experiments led to the discovery of positive particles (protons) and neutral particles (neutrons) in the nucleus. Thus, it was discovered that the atom is composed of electrons, protons, and neutrons.

In the \(\alpha\)- scattering experiment, most of the particles passed through the foil were unscattered because they did not encounter the minute nucleus of any gold atom. Occasionally, however, an \(\alpha \text {-particles }\) came close to a gold nucleus. In such encounters, the repulsion between the highly positive charge of the gold nucleus and the positive charge of the \(\alpha\) - particle was strong enough to deflect the particle, as shown in Figure above.