Provincial chemistry teacher John Dalton in 1803the Law of Multiple Relationships. This theory says that if a particular chemical element can form compounds with other elements, then each part of the mass will have a part of the mass of another substance, and the relationships between them will be the same as between small integers. This was the first attempt to explain the complex structure of matter. In 1808, the same scientist, trying to explain the law discovered by him, suggested that in different elements atoms can have different masses.
The first model of the atom was created in 1904.The electronic structure of the atom in this model scientists called "pudding with raisins." It was believed that an atom is a body with a positive charge, in which its components are evenly mixed. Such a theory could not answer the question of whether the constituents of the atom are in motion or at rest. Therefore, almost simultaneously with the theory of "pudding", the Japanese Nagaoka proposed a theory in which the structure of the electron shell of an atom was likened to the solar system. However, referring to the fact that when rotating around an atom its components must lose energy, and this does not correspond to the laws of electrodynamics, Vin rejected the planetary theory.
However, after the discovery of the electron, it became clear that the structure of the atom is more complex than it was imagined. Questions arose: what is an electron? How is it arranged? Are there other subatomic particles?
By the beginning of the twentieth century, the planetary theory was finally adopted. It became clear that each electron, moving along the orbit of the nucleus as a planet around the Sun, has its own trajectory.
But further experiments and researchrefuted this opinion. It turned out that electrons do not have their own trajectory, however, it is possible to predict the region in which this particle turns out most often. Rotating around the nucleus, the electrons form an orbital, which was called the electron shell. Now it was necessary to investigate the structure of the electron shells of atoms. The physicists were interested in the questions: how exactly do the electrons move? Is there orderliness in this movement? Maybe the movement is chaotic?
Progenitor of atomic physics N.Bohr and a number of the same large scientists have proved: electrons rotate shell-layers, and their movement meets certain laws. It was necessary to study the structure of the electron shells of atoms densely and in detail.
It is especially important to know this structure for chemistry,because the properties of matter, this was already clear, depend on the device and the behavior of the electrons. From this point of view, the behavior of the electron-orbitals is the most important characteristic of this particle. It was found that the closer to the nucleus of the atom are the electrons, the more effort it takes to break the electron-nucleus bond. Electrons located near the nucleus have the maximum connection with it, but the minimum energy reserve. In external electrons, on the other hand, the connection with the nucleus weakens, and the energy reserve increases. Thus, around the atom, electronic layers are formed. The structure of the electron shells of atoms became clearer. It turned out that the energy levels (layers) form particles close to the energy reserve.
Today it is known that the energy leveldepends on n (this quantum number) and corresponds to integers from 1 to 7. The structure of the electron shells of atoms and the largest number of electrons at each level is determined by the formula N = 2n2.
The large letter in this formula denotes the largest number of electrons in each level, and the small one indicates the ordinal number of that level.
The structure of the electron shell of atomsestablishes that in the first shell there can be no more than two atoms, and in the fourth - no more than 32. The outer, completed level contains no more than 8 electrons. Layers, where electrons are smaller, are considered incomplete.
