The most significant achievements of physicists of the past who worked in the field of the structure of matter at the level of electron-nuclear representations date back to the beginning of the last century. One of such breakthroughs in the knowledge of the microworld is known in the history of science under the name “Pauli principle ” . By that time, it became clear that the quantum nature of the phenomena occurring within the atom, dramatically changes many concepts about the realities of the microworld. And what is this - a quantum? This is a certain unit of measurement of a physical quantity in the form of its minimum “portion”, which cannot be less. For example, the radius of the first electron orbit cannot be less than 5.29 · 10–11 m. It is incorrect to speak of distances shorter than this value - they do not seem to exist.
The quantum essence of well-known physical concepts, such as mass, force, energy, expands the idea of the nature of electrons and other particles that make up an atom. And, of course, in order to speak objectively about the "bricks of the universe", tools were created to describe them. Since then, the state of the electron is characterized by four numbers, which are called quantum. Various combinations of these numbers determine the only full and unique appearance of any electron. As soon as it became possible to describe the energy, spatial and internal state of the electron, the following question arose on the agenda: how are the electrons, which can be many in each atom, located around the nucleus? How are they “packed” there? The study of this issue led to the formulation of the law, now known as the Pauli principle. What is its essence?
A little self-education
1. The atom in its simplest form has the main components - the nucleus and electrons located, respectively, in the center and in orbits around the nucleus. The radii of the orbits (denoted by n) take the values of integers, starting with one quantum - the minimum possible “portion” of distance. For the case when n = 1, we have a minimally “low” orbit along which the electron with the lowest energy rotates. The energy level of an electron is determined by the quantum number n, which is also called the principal. Note that for a given radius n, we can calculate the number of electrons in this orbit using the formula N = 2 (n • n). From here, the limiting number of electrons in any orbit with number n is easily calculated: in the first - two, in the second - eight, in the third - eighteen, etc. This conclusion about filling the shells with electrons in an amount not exceeding N is an essential point that contains the Pauli principle.
2. An electron can have energy sublevels of each main level. They are denoted by the symbol l, are called a secondary (or orbital) quantum number and can have a value l from 0 to 4. The value of the number l determines the spatial shape of the electron cloud: spherical, dumbbell-shaped, etc.
3. The motion of the electron, in other words, the flow of current, leads to the creation of a circular magnetic field. But in this case, the electron has an orbital magnetic moment, which is characterized by the next, third in a row, quantum number ml. It is called the magnetic quantum number and is the projection of the orbital angular momentum of the electron on the direction of the magnetic field. The values that ml can take lie in the range from –l to + l, taking into account the zero value, and in total there can be (2l + 1).
4. And finally, the last quantum characteristic of an electron is spin. It contains only 2 attributes ms = + 1/2 and ms = -1 / 2. The physical essence of the spin is the moment of the mechanical momentum of the electron, which has no connection with its motion in space.
The relationship of the Pauli principle and the periodic system Mendeleev
In 1925, the discovery of the fundamental properties of the microworld was made in physics, comparable in significance only to the table of D.I. Mendeleev. It received the name of its "godfather" and has since been known as the Pauli principle. Chemistry as a science of substances and their interactions within the framework of a periodic system could not explain many of the mechanisms of processes that occur when atoms combine, form molecules, etc. The main reason was that the level of detail of the atom, from the point of view of chemistry, began on the concepts of atom, electron, nucleus. These atomic-molecular representations arose and established about 150 years ago - in the century before last. A little later A.M. Butlerov developed the theory of chemical compounds, and then a periodic law was discovered . This allowed us to imagine the birth of a molecule from atoms and gave an understanding of the structure of atomic "economy".
Understanding the essence of the quantum characteristics of the electron model became possible after the Pauli principle was formulated. With its help, the picture of the location of the shells and the order of their filling with electrons was explained. The essence of the principle is that electrons can have any set of the above four quantum features, but an atom cannot have two electrons in its composition that are identical in all quantum characteristics.
The main result of the discovery of the laws of the structure of the atom, which contains the Pauli principle, is physics, i.e. the nature of the phenomenon of filling the shells with electrons. And this, in turn, provided the prerequisites for the justification of the periodic law. Thus, the “chemical” content of the laws of the general structure of the atom and molecule has received its fundamental confirmation in physics by building the internal “architecture” of the atom.