In his experiments,
Rutherford studied the scattering of \(\alpha\)-particles on a thin gold foil. He and his colleagues found that in addition to particles that scatter at a small angle, there are also those that drastically (at an angle greater than \(90^\circ\)) change the direction of their original trajectory. Some particles "bounce off" the film by nearly \(180^\circ\).
Based on the results of the measurement and calculation, in 1911, Rutherford proposed a new atomic model: the atom consists of a small positively charged nucleus of \(~10^{-14} {m}\) in its center and electrons, which are distributed around it in a relatively large space \(10^{-10} {m}\). Because the mass of the electrons is very small, virtually the entire mass of the atom is concentrated in the nucleus. According to Rutherford, the centripetal force required for the circulation of electrons around the nucleus comes from the Coulomb force between the positive nucleus and the electrons. The idea is similar to the planets orbiting the Sun, so it was named "solar system model". However, such an atom would be flat and also cannot be stable. Due to the repulsion between the electrons, the tiny particles would have to push each other off their orbits. In addition, according to the laws of electrodynamics, every accelerating charge (including the circular electron) necessarily radiates off some of its energy. As a result, the energy of the system decreases; the electrons gradually approach the nucleus, and eventually fall into it. During this process, the orbital period of the electrons changes and the frequency of the radiation emitted by the atom must also change. Because electrons do not fall into the nucleus and thus atoms are "long-lived", the solar system model does not accurately describe reality either.