Even in ancient Greece, philosophersguessed about the internal structure of matter. And the first models of the structure of atoms appeared already at the beginning of the 20th century. The hypothesis of J. Thomson was not perceived by the scientific community of that time to be critical, because before it various theories about what was inside the smallest particles of matter had already been put forward.
Until the XIX century, scientists assumed that the atomis indivisible. However, everything changed after Joseph Thomson discovered the electron in 1897 - it became clear that the scientists were wrong. Both models of the atom of Thomson and Rutherford were put forward at the beginning of the last century. The first was the model of W. Thomson, who suggested that the atom is a bunch of matter that has a positive electric charge. Inside this bunch are uniformly distributed electrons - that's why this model was called "cake". After all, according to it, the electrons in matter are arranged like raisins in a cake. Another unofficial name for the model is "Pudding with raisins".
This model was developed even more in detailJJ Thomson. Unlike W. Thomson, he assumed that the electrons in the atom are located strictly on one plane, which are concentric rings. Despite the equal importance of the models of the atom of Thomson and Rutherford for the science of the time, it should be noted that J. Thomson, among other things, first proposed a method for determining the number of electrons inside an atom. His method was based on the scattering of X-rays. J. Thomson suggested that it is the electrons that are the particles that should be in the center of the scattering of the rays. In addition, it was Thomson who was the scientist who discovered the electrons. In modern schools, it is with the study of its discoveries that the study of the course of quantum mechanics begins.
However, in comparison with the Rutherford model, the modelThomson's atom had one significant drawback. She could not explain the discrete nature of atomic radiation. It was impossible with her help and say something about the reasons for the stability of the atom. Finally, it was disproved when the famous experiments of Rutherford were made. The model of the Thomson atom was of no less value to the science of that time than other hypotheses. It should be borne in mind that all these models, available at that time, were purely hypothetical.
In 1906-1909, G. Geiger, E. Mardsen and E.E.Rutherford conducted experiments in which alpha particles were scattered on the surface of gold foil. Briefly, the models of the Thomson and Rutherford atoms are described as follows. In the Thomson model, electrons are distributed unevenly in the atom, and in Rutherford's theory they rotate in concentric planes. A distinctive factor in Rutherford's experiment was the use of alpha particles instead of electrons. Alpha particles, unlike electrons, had a much larger mass, and did not undergo significant deviations when they collided with electrons. Therefore, scientists had the opportunity to register only those collisions that occurred with a positively charged part of the atom.
This experience was crucial for science.With its help, scientists were able to get answers to those questions that remained a mystery to the authors of various atomic models. Thomson, Rutherford and Bohr, although they had the same base, nevertheless made a somewhat different contribution to science-and the results of Rutherford's experiments in this case were striking. Their results were exactly the opposite of what the scientists expected to see.
Most of the alpha particles passed through a leaffoil along straight (or practically straight) trajectories. However, the trajectories of some alpha particles deviated to significant angles. And this was evidence that in the atom there was a formation with a very high density, and had a positive charge. In 1911, based on experimental data, a model of the structure of the Rutherford atom was put forward. Thomson, whose theory was previously considered dominant, at this time continued to work in the laboratory of Cavendish University. Until the end of his life the scientist continued to believe in the existence of a mechanical ether, despite all the advances in scientific research of that time.
Summarizing the results of the experiments, ErnestRutherford put forward the basic theses of his theory: according to it, the atom consists of a heavy and dense nucleus of very small dimensions; around this nucleus are located electrons that are in continuous motion. The radii of the orbits of these electrons are also small: they are 10-9 m. This model was called "planetary" because of its similarity to the model of the solar system. In it, the planets move in elliptical orbits around a huge and massive center, which has an attraction - the Sun.
Electrons rotate in an atom with such a giantspeed that form around the surface of the atom something like a cloud. According to Rutherford's theory, atoms are spaced from each other at some distance, which allows them not to stick together. After all, around each of them there is a negatively charged electron shell.
What are the main differences between the twothe most important theories of the structure of the atom? Rutherford assumed that in the center of the atom there is a nucleus with a positive electric charge, and whose volume, in comparison with the dimensions of the atom, is negligible. Thomson also assumed that the entire atom is a formation with a high density. The second major difference was understanding the position of the electrons in the atom. According to Rutherford, they rotate around the nucleus, and their number is approximately equal to ½ of the atomic mass of the chemical element. In Thomson's theory, the electrons inside the atom are unevenly distributed.
However, despite all the advantages, on thatThe Rutherford theory contained one important contradiction. According to the laws of classical electrodynamics, an electron that rotated around the nucleus had to constantly emit portions of electrical energy. Because of this, the radius of the orbit along which the electron moves must continuously emit electromagnetic radiation. According to these ideas, the lifetime of an atom must be negligible.
Most often, when they say about the opening of the internalstructure of the atom, mention the names of Thomson and Rutherford. Rutherford's experiments, whose atomic model is now known to every student of physics and mathematics in higher education, is now part of the history of science. When Rutherford made his discovery, he exclaimed: "Now I know what the atom looks like!" However, in reality he was wrong, because the true picture became known to scientists much later. Although the Rutherford model was subjected to significant adjustments over time, its meaning remained unchanged.
However, in addition to the models of the Thomson atom andRutherford, there was another theory explaining the inner structure of these tiny particles of matter. It belongs to Niels Bohr - the Danish physicist, who offered his explanation in 1913. According to his model, an electron in an atom does not obey the standard physical laws. It was Bohr who was the scientist who introduced into science the concept of the relationship between the radius of the electron's orbit and its speed.
In the process of creating his theory Bohr tookthe basis of the model of Rutherford, but subjected it to considerable refinement. The models of the atoms of Bohr, Rutherford, and Thomson can now seem somewhat simple, but they formed the basis for modern ideas about the internal structure of the atom. Today, the quantum model of an atom is generally accepted. Despite the fact that quantum mechanics can not describe the motion of the planets of the solar system, the concept of orbit has so far remained in theories describing the internal structure of the atom.
