The nuclear (or planetary) model was proposed by E. Rutherford. Its appearance in 1911 was preceded by experiments with colleagues in which alpha particles were aimed at a thin foil of gold and other metals. It was found that most of the alpha particles penetrate the target relatively freely. It was difficult to explain the fact that a small part of the particles are deflected at large angles, and sometimes even reflected back. From this, the following conclusions were drawn: – the nucleus has a very small volume in comparison with the atom; – the mass of the nucleus is almost equal to the mass of the atom, electrons account for fractions of a percent; – at a great distance from the nucleus, electrons revolve (like planets around the Sun); – the positive charge of the nucleus is exactly compensated by the total charge of the electrons, that is, the atom is electrically neutral.
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