But how can we come to this structure? It is worth dwelling on this issue in a little more detail. As you know, all objects are electrified, exchange charges, but where are they located? If all bodies have charges, including dielectrics (albeit small), therefore, charges are present in the structure of matter. Matter, as has already been proven, consists of molecules, and those of atoms, therefore, charges are inside atoms.
And the story of the discovery of the structure of the atom begins in 1897, when Joseph John Thompson discovered electrons while studying electric current in gases. That is, when a current was passed in a tube in which there were two electrodes the cathode and the anode, the cathode emitted some rays, the so-called «cathode rays», the honor of accurately determining the type of these rays belongs to Mr. Thompson, who, by deflecting them in a magnetic field, as well as accelerating them in an electric field, established that this nothing else but some particles emitted by the cathode, with a negative electric charge, which is why they were called electrons.
Figure 2.1. Joseph John Thomson
And subsequent studies have led to the conclusion that electrons are part of an atom and when they fly out under the influence of an electric field, this leads to the transformation of an atom into an ion. But an ordinary atom is electrically neutral, therefore, in order to balance this charge, there must be a part with a positive charge in the atom. That is, an atom consists of charges that interact in some way. How does this interaction appear and is this interaction an explanation of the behavior of atoms in chemical reactions, in reactions with absorption and emission of light with certain wavelengths. After all, atoms may well be light sources, the same discharged gas emits light with certain spectra, at strict wavelengths, and how is this explained with the help of these interactions?
To explain this, in 1902, Mr. William Thompson, better known as Lord Kelvin, proposed his model of the structure of the atom, and already John Thompson studied it in more detail, so this model is known as the Thompson model. This model was popular until 1904 and is better known as the «raisin pudding model». According to this model, the atom consists entirely of positive matter, and electrons are inside it, moving freely. And with the help of this model, it was quite possible to describe some of the results.
Figure 2.2. William Thompson or Lord Kelvin
Figure 2.3. The Thompson model of the hydrogen atom
For example, you can describe a hydrogen atom. If we imagine a hydrogen atom in such a model, then the electron will «float» in a positive charge, but it will be pulled to the center of this positive «drop», due to the force of electrostatic equilibrium. If we assume that the electron departs from the center by a certain radius smaller than the radius of the atom itself, then it will be attracted by the mental sphere formed by this radius. But since it is charged uniformly, it can be concentrated in the center and simply written using the Coulomb formula (2.1).
And to determine the charge of an imaginary sphere formed inside a common large charge, you can use the ratio of this imaginary sphere to the entire sphere, and since the charge of the common sphere is already known and equal to the charge of the electron so that the atom is neutral, then the expression (2.2) is obtained, where the charge of the imaginary sphere is derived.
And if we already substitute this value for the Coulomb force, we get (2.3), a rather interesting expression that is directly proportional to the distance by which the electron moves away from the center.
Also, for further convenience, we can introduce here the notion that the coefficient outside the radius of the imaginary sphere is the vibrational stiffness (2.4), and if we write with this stiffness not the Coulomb force formula itself, but its projection onto the radius of the imaginary sphere, then we get the expression (2.5), and negative, due to the fact that the vector the forces and the distance itself (the direction of the electron) are opposite.
And now, if we assume that the electron oscillates in this way, then it resembles the construction of an oscillator or, more precisely, a mathematical pendulum with its rigidity and frequency determined by (2.6).
And if we substitute the necessary rigidity for (2.6), and take the mass of the electron as the mass, then the frequency will have the order of optical waves. That is, the atom glows in the visible region and even the glow effect can be explained using the Thompson model, but alas, another problem has arisen here. Even if we assume that the hydrogen atom glows, then according to this model it glows only with 1 frequency, when in reality it emits light with 4 frequencies. So it was proved that the Thompson model was not correct and it was necessary to create new models.
The next model is Ernest Rutherford's 1908-1910 model, which irradiated metal plates of thin gold foil with radioactive radiation, or more precisely with special alpha particles. At the same time, if you remove the plate on a circular screen (a phosphor that glowed), a point appeared, and when the plate was placed, this point scattered to form a spot, but in addition, some of these rays were reflected more than 90 degrees (right angle). And if we assume that the atom consists as the Thompsons were supposed to, then because of such a simply huge "smeared" positive charge on the size of the atom, the deviation should not have exceeded hundredths of a degree, and here there was a deviation of almost 180 degrees.
Then Rutherford suggested that in order to satisfy the results of the experiment, it should be assumed that the positive charge is strongly concentrated in a small area, and all the remaining space is practically empty, so the particles were only slightly scattered under the influence of an electric field or bumped into electrons that simply revolved around the atomic nucleus. This is how Rutherford first created a planetary model of an atom, according to which there is a single nucleus inside, and electrons already rotate around it in their orbits. However, there was still a lot to prove, for example, why did the electrons not fall to the atom, spending their energy on rotation, radiating energy at the same time?
But there was an answer to this question, thanks to Rutherfords colleague Niels Bohr, who created the model of the hydrogen atom of Bohr, some postulates were accepted according to his model. Namely, the statements that an electron does not emit energy while in stationary orbits and can emit energy in the form of electromagnetic radiation (photons or light particles) only when moving from one orbit to another, and strictly with the energy equal to the energy difference in these two orbits. This has already led to the statement about the quantization of energy, that is, about operating with energy, particles, and their other parameters only in the form of portions. That is, there can be no smooth transition, either the electron is here, or it is not here, or it has released a certain amount of energy, or it has not. This idea was also supported by Max Planck when studying a «completely black body», a topic that would explain the glow when objects are heated.
Figure 2.4. Ernest Rutherford
Figure 2.5. Niels Bohr
Thus, when objects are heated, part of the energy from the collision of atoms flows to the nucleus, and after transferring it to an electron and its transition to another energy level, and then back, there is the release of a photon with a certain wavelength, so when bodies are heated, they emit light. And already when an external photon hits an atom, there is also an exit through the electron transition, but with a longer wavelength and, accordingly, a lower frequency, due to which such a phenomenon as absorption and reflection of light is observed. As for the passage of alpha particles during Rutherford's bombardment of gold foil, it was the nucleus with a high potential that caused such results, as well as the fact that almost 99.9% of the atom is empty and the same 99.9% of the atom's mass is concentrated in its nucleus. Thus, the Rutherford model was able to explain not only the results of the Rutherford experiment itself, but also many other phenomena, which confirms the validity of this model.