Rutherford's experiments

Scientists did not immediately come to a correct understanding of the structure of the atom. The first model of the atom was proposed by the English physicist JJ Thomson, who discovered the electron. But his model collided with E. Rutherford's experiments on the distribution of a positive charge in a microparticle. These experiments of Rutherford played a major role in understanding the structure of the atom.

It was already known that the mass of an electron is thousands of times smaller than the mass of the particle itself. Rutherford made the assumption: since in general the atom is neutral, its main mass must fall on the positively charged part. To confirm this hypothesis, Rutherford's experiments were reduced to the following.

He proposed to probe the atom using alpha particles. The electron mass is approximately 8000 times smaller than the mass of α particles, and their speed is very high - it can reach twenty thousand kilometers per second. These were Rutherford's experiments on scattering of alpha particles.

Atoms of heavy elements were bombarded with these particles. Because of the small mass, the electrons could not change the trajectory of α-particles. This could only be done by part of the atom, positively charged. Consequently, by the nature of the scattering of alpha particles, it will be possible to know the distribution of the mass inside the microparticle of matter and the positive charge.

Rutherford's experiments had the following scheme. Any radioactive substance was placed inside the cylinder from the lead. In this cylinder, a narrow canal was drilled longitudinally. The flow of α-particles from this channel fell on a thin foil from the studied material (copper, gold, etc.). Then the alpha particles fell on a translucent screen, which was coated with zinc sulfide. Each particle, facing the screen, gave a flash of light (scintillation), it could be seen in a microscope.

Further experiments by Rutherford showed that a small number of alpha particles (approximately one in two thousand) was deflected by an angle greater than 90 °. This fact greatly puzzled Rutherford. He said it was as incredible as shooting a shell in a piece of thin paper and he would come back to you and hit you. Indeed, it is impossible to predict such a result based on the Thomson model, and Rutherford suggested that the α particle can be dropped back only if the bulk of the atom is in a very small space. So Rutherford's experiments helped him come to the core model. This body is small in size, where almost the entire positive charge and the entire mass of microparticles are concentrated.

The atomic model follows directly from the experiments conducted by Rutherford. The structure of the atom according to Rutherford's concept is as follows. Positively charged nucleus is in the center. Since the atom is neutral, the number of electrons is equal to the ordinal number of the element in the Mendeleev periodic system. They move in a circle above the core, as the planets revolve around the Sun in their orbits. The motion of electrons is due to Coulomb forces. The hydrogen atom contains only one electron that revolves around its nucleus. Its atomic nucleus carries a positive charge and mass, approximately 1836 times the mass of the electron.

This model of the atom had an experimental justification, but on the basis of this model one can not explain the stability of its existence.

Electrons moving in orbit must, according to the laws of classical mechanics, approach the nucleus because of energy losses and, eventually, fall on it. In fact, the electron does not fall on the nucleus. Microparticles of chemical elements are very stable and can exist for a very long time. The conclusion about the imminent destruction of the atom due to energy losses, which does not agree with Rutherford's experiments, is the result of applying the laws of classical mechanics to microscale phenomena. Consequently, the laws of classical physics are inapplicable to phenomena of the microworld.