Electrons in a hydrogen molecule

Have you ever thought of what forces hold a molecule of matter from decay into atoms? Today it is known that these forces are called chemical, and they are of an electromagnetic nature. In general, the chemical bond can be explained as the result of the collectivization of external - valence electrons of the connecting atoms. At certain distances between the nuclei, collectivized, for example, electrons in the hydrogen molecule, passing between the nuclei, reduce the repulsion of the latter. At large distances, collectivization does not arise.

Electrons in a hydrogen molecule behave as if each electron spent part of the time near one nucleus, and a part near the other

Consider the simplest hydrogen molecule H2. Electrons in a hydrogen molecule behave as if each electron spent part of the time near one nucleus, and a part near the other. That is why the forces that arise in this case are often called exchange forces. That is, the electrons in the hydrogen molecule already belong to two nuclei simultaneously. At the same time, the individuality of hydrogen atoms dissolved when they merged into a new system - a molecule of hydrogen, in which there are now two protons and two electrons.

For table salt, for example, 8 valence electrons are common. One of them is taken from sodium, and 7 from chlorine. Since the residual charge of chlorine is greater than that of sodium, all collectivized electrons are strongly shifted to the core of chlorine and socialization looks quicker as the capture of an electron by a stronger atom in a weaker one. The latter becomes, roughly speaking, a positive ion, and the former becomes negative, and the chemical bond reduces to the attraction of unlike charges.

Then what determines the valence of the atom? To explain this, consider what will happen if, for example, the shooter shoots a rifle from a rifle into a target that can freely rotate around a nail driven into the "top ten". Once in the target, the bullet will cause it to rotate: the rotational moment of the bullet is distributed between the bullet and the target.

Now let the target be fired by electrons or other elementary particles. If they are all "twisted" in one direction, then, after absorbing them, the target will turn. The rotation will be the more intensive the more the spin of the particles. An electron, for example, can be "twisted" in only two ways: the "rotation" of an electron forms either a right or a left screw with the direction of its motion. Therefore, if the spin of one electron is directed in a certain way, then the spin of the other is either parallel to it or antiparallel.

When molecules are formed, everything depends on the direction of the spins. Thus, a chemical bond in a hydrogen molecule arises only when the collectivized electrons in the hydrogen molecule have oppositely directed spins. All because for antiparallel spins electrons spend a relatively long time between the nuclei, so that the average density of the negative charge is sufficient to balance the repulsion of the nuclei. For parallel spins, this density is small, and the nuclei are repulsed!

But why do not three electrons connect three nuclei at once? It turns out that quantum mechanics imposes a special ban on the movement of electrons. It is called the Pauli principle. Two electrons, according to this principle, can not be in the same state. Electrons in a hydrogen molecule can differ only in the orientation of the spins. And only two orientations are possible. And the third electron here is superfluous.