For a long time many properties of matter remained a secret for researchers. Why do some substances conduct electricity well, while others do not? Why does iron gradually break down under the influence of the atmosphere, while noble metals are perfectly preserved for thousands of years? Many of these questions were answered after a person became aware of the structure of the atom: its structure, the number of electrons in each electron layer. Moreover, mastering even the very basics of the structure of atomic nuclei opened up a new era for the world.
From what elements is the elementary brick of matter built, how do they interact with each other, what can we learn from this?
The structure of the atom in the view of modern science
Currently, most scientists tend to adhere to the planetary model of the structure of matter. According to this model, at the center of each atom there is a nucleus, tiny even in comparison with the atom (it is tens of thousands of times smaller than the wholeatom). But the same cannot be said about the mass of the nucleus. Almost all the mass of an atom is concentrated in the nucleus. The nucleus is positively charged.
Electrons revolve around the nucleus in different orbits, not circular, as is the case with the planets of the solar system, but three-dimensional (spheres and volume eights). The number of electrons in an atom is numerically equal to the charge of the nucleus. But it is very difficult to consider an electron as a particle that moves along some kind of trajectory.
Its orbit is tiny, and the speed is almost like that of a light beam, so it is more correct to consider the electron together with its orbit as a kind of negatively charged sphere.
Members of the nuclear family
All atoms are made up of 3 constituent elements: protons, electrons and neutrons.
Proton is the main building material of the nucleus. Its weight is equal to an atomic unit (the mass of a hydrogen atom) or 1.67 ∙ 10-27 kg in the SI system. The particle is positively charged, and its charge is taken as a unit in the system of elementary electric charges.
The neutron is the mass twin of the proton, but is not charged in any way.
The above two particles are called nuclides.
An electron is the opposite of a proton in charge (the elementary charge is −1). But the electron let us down in weight, its mass is only 9, 12 ∙ 10-31 kg, which is almost 2 thousand times lighter than a proton or neutron.
How it was "seen"
How could you see the structure of the atom, if even the most modern technical means do not allowand in the short term will not allow to obtain images of its constituent particles. How did scientists know the number of protons, neutrons and electrons in the nucleus and their location?
The assumption about the planetary structure of atoms was made on the basis of the results of the bombardment of a thin metal foil with various particles. The figure clearly shows how various elementary particles interact with matter.
The number of electrons that passed through the metal in the experiments was equal to zero. This is explained simply: negatively charged electrons are repelled from the electron shells of the metal, which also have a negative charge.
The beam of protons (charge +) passed through the foil, but with "losses". Some were repelled by the nuclei that got in the way (the probability of such hits is very small), some deviated from the original trajectory, flying too close to one of the nuclei.
Neutrons became the most "effective" in terms of overcoming metal. A neutrally charged particle was lost only in the case of a direct collision with the core of the substance, while 99.99% of the neutrons successfully passed through the thickness of the metal. By the way, it was possible to calculate the size of the nuclei of certain chemical elements based on the number of neutrons at the input and output.
Based on the data obtained, the currently dominant theory of the structure of matter was built, which successfully explains most of the issues.
What and how much
The number of electrons in an atom depends on the atomic number. For example, an ordinary hydrogen atom hasjust one proton. A single electron is circling around in an orbit. The next element of the periodic table, helium, is a little more complicated. Its nucleus consists of two protons and two neutrons and thus has an atomic mass of 4.
With the growth of the serial number, the size and mass of the atom grow. The serial number of a chemical element in the periodic table corresponds to the charge of the nucleus (the number of protons in it). The number of electrons in an atom is equal to the number of protons. For example, a lead atom (atomic number 82) has 82 protons in its nucleus. There are 82 electrons in orbit around the nucleus. To calculate the number of neutrons in a nucleus, it is enough to subtract the number of protons from the atomic mass:
207 – 82=125.
Why are there always equal numbers
Every system in our universe strives for stability. As applied to the atom, this is expressed in its neutrality. If for a second we imagine that all atoms without exception in the Universe have one or another charge of different magnitudes with different signs, one can imagine what kind of chaos would come in the world.
But since the number of protons and electrons in an atom is equal, the total charge of each "brick" is zero.
The number of neutrons in an atom is an independent value. Moreover, atoms of the same chemical element can have a different number of these particles with zero charge. Example:
- 1 proton + 1 electron + 0 neutrons=hydrogen (atomic mass 1);
- 1 proton + 1 electron + 1 neutron=deuterium (atomic mass 2);
- 1 proton + 1 electron + 2neutron=tritium (atomic mass 3).
In this case, the number of electrons in the atom does not change, the atom remains neutral, its mass changes. Such variations of chemical elements are called isotopes.
Is an atom always neutral
No, the number of electrons in an atom is not always equal to the number of protons. If an electron or two could not be “taken away” from an atom for a while, there would be no such thing as galvanization. An atom, like any matter, can be influenced.
Under the influence of a sufficiently strong electric field from the outer layer of the atom, one or more electrons can "fly away". In this case, the particle of the substance ceases to be neutral and is called an ion. It can move in a gas or liquid medium, transferring an electric charge from one electrode to another. In this way, an electric charge is stored in batteries, and the thinnest films of some metals are applied to the surfaces of others (gold plating, silver plating, chromium plating, nickel plating, etc.).
The number of electrons is also unstable in metals - conductors of electric current. The electrons of the outer layers, as it were, walk from atom to atom, transferring electrical energy through the conductor.