Milestones of scientific discoveries - the Pauli principle

The most significant achievements of physicists of the past, working 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 of the "Pauli principle " . By that time, it became clear that the quantum nature of the phenomena occurring within the atom dramatically changed many concepts about the realities of the microworld. And what is this quantum? This is a certain unit of measurement of physical quantity in the form of its minimum "portion", less of which can not be. For example, the radius of the first electron orbit can not be less than 5.29 × 10-11 m. It is incorrect to speak about distances less than this amount - they do not exist, as it were.

Quantum is the essence of well-known physical concepts, such as mass, force, energy, expands ideas about the nature of electrons and other particles that make up the atom. And, naturally, in order to talk about the "bricks of the universe" in detail, tools were created for their description. Since then, the state of an electron is characterized by four numbers, which are called quantum numbers. Different 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 do electrons, which in each atom can be a lot, settle around the nucleus? How are they "packed"? The study of this question led to the formulation of a 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 the 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, beginning with one quantum - the minimum possible "portion" of the 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 the electron is determined by the quantum number n, which is also called the principal number. Note that for a given radius n, it is possible to calculate the number of electrons in this orbit by the formula N = 2 (n • n). From here, it is easy to calculate the limiting number of electrons in any orbit with the number n: the first - two, the second - eight, the third - eighteen, etc. This conclusion about the filling of shells with electrons in an amount not exceeding N is an important point that contains the Pauli principle.

2. An electron can have energy sublevels of each main level. They are denoted by the symbol l, called the spin-off (or orbital) quantum number, and can have the value l from 0 to 4. The value of the number l determines the spatial shape of the electron cloud: spherical, dumbbell, etc.

3. The motion of an 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 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 the number ml can take are in the range from -l to + l, taking into account the zero value, and all of them can be (2l + 1).

4. Finally, the last quantum characteristic of an electron is spin. It contains only 2 signs ms = + 1/2 and ms = -1 / 2. The physical essence of spin is the moment of the mechanical impulse of the electron, which has no connection with its motion in space.

The connection between the Pauli principle and the periodic system Mendeleyev's

In 1925 in physics, the discovery of the fundamental property of the microworld was made, comparable only to the table of DI Mendeleyev. It received the name of its "godfather" and has since been known as the Pauli principle. Chemistry as a science about substances and their interactions within the framework of the periodic system could not explain many of the mechanisms of the processes that take place in the unification of atoms, the formation of 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 became established about 150 years ago - the century before last. A little later, A.M. Butlerov developed a theory of chemical compounds, and then a periodic law was discovered . This allowed to represent the birth of a molecule from atoms and gave an understanding of the structure of the 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 arrangement of the shells and the order of their filling by electrons were explained. The essence of the principle is that electrons can have any set of the above four quantum features, but the atom can not have in its composition two electrons, 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, that is, The nature of the phenomenon, which consists in filling the shells with electrons. And this, in turn, gave 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 constructing the internal "architecture" of the atom.