The structure of the atom is one of the basic topics of the chemistry course, which is based on the ability to use the table “Periodic Table of Chemical Elements by D. I. Mendeleev”. This is not only chemical elements systematized and located according to certain laws, but also a storehouse of information, including the structure of the atom. Knowing the peculiarities of reading this unique reference material, one can give a complete qualitative and quantitative description of an atom.

You will need

Table D.I. Mendeleev

P&G placement sponsor Related articles "How to determine the charge of an atomic nucleus" How to read the periodic table How to find the charge of a nucleus Why metal properties change

Instruction manual

In the table of D.I. Mendeleev, as in a multi-storey apartment building, chemical elements "live", each of which occupies its own apartment. Thus, each of the elements has a specific serial number indicated in the table. The numbering of chemical elements begins from left to right, and from above.

In the table, horizontal rows are called periods, and vertical columns are called groups. This is important, because by the number of the group or period, you can also characterize some parameters of the atom.

An atom is a chemically indivisible particle, but at the same time consisting of smaller components, which include protons (positively charged particles), electrons (negatively charged) and neutrons (neutral particles). The bulk of the atom is concentrated in the nucleus (due to protons and neutrons) around which electrons revolve. In general, an atom is electrically neutral, that is, in it the number of positive charges coincides with the number of negative ones, therefore, the number of protons and electrons is the same. The positive charge of the atomic nucleus takes place precisely at the expense of protons.

It must be remembered that the serial number of a chemical element quantitatively coincides with the charge of the atomic nucleus. Therefore, in order to determine the charge of the atomic nucleus, it is necessary to look at what number the given chemical element is.

Example No. 1. Determine the charge of the nucleus of a carbon atom (C). We begin to analyze the chemical element carbon, focusing on the table of D.I. Mendeleev. Carbon is located in “apartment” No. 6. Therefore, it has a +6 nucleus charge due to 6 protons (positively charged particles) that are located in the nucleus. Given that the atom is electrically neutral, it means that there will also be 6 electrons.

Example No. 2. Determine the charge of the nucleus of an aluminum atom (Al). Aluminum has a serial number - No. 13. Therefore, the charge of the nucleus of an aluminum atom is +13 (due to 13 protons). There will also be 13 electrons.

Example No. 3. Determine the charge of the nucleus of a silver atom (Ag). Silver has a serial number - No. 47. Therefore, the charge of the nucleus of a silver atom is + 47 (due to 47 protons). There are also 47 electrons.

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An atom of any chemical element consists of an atomic nucleus and electrons circulating around it. And what does an atomic nucleus consist of? In 1932, it was found that the atomic nucleus consists of protons and neutrons. You will need - a periodic table of chemical elements Mendeleev.

To find the number of protons in an atom, determine its place in the periodic table. Find its serial number in the periodic table. It will be equal to the number of protons in the atomic nucleus. If an isotope is being investigated, look at a couple of numbers describing its properties; the lower number will be equal to

To determine the number of protons in an atom, find the element of the periodic table that displays the properties of this atom. Its serial number in the table will display the number of protons in the nucleus of an atom. The number of protons can be found, knowing the charge of the nucleus of an atom, as well as the number of electrons in it. You

The charge of an atom, along with its quantum numbers, is one of the most important numerical characteristics of an atom. Knowledge of the atomic charge is necessary for solving various problems of electrostatics, electrodynamics, atomic and nuclear physics. You will need Knowledge of the structure of the atom, atomic number Placement sponsor P&G

For certain reasons, atoms and molecules can either acquire or lose their electrons. In this case, an ion is formed. Thus, an ion is a monatomic or polyatomic charged particle. Obviously, the most important characteristic of an ion will be its charge. You will need a chemical table

An atom of a chemical element consists of a nucleus and an electron shell. The nucleus is the central part of the atom, in which almost all of its mass is concentrated. Unlike the electron shell, the nucleus has a positive charge. You will need the Atomic Number of the chemical element, Mosley Law Placement Sponsor

Atom is the smallest particle of each element that carries it chemical properties. Both existence and the structure of the atom have been the subject of reasoning and study since ancient times. It was found that the structure of atoms is akin to the structure of the solar system: in the center of the nucleus, which takes up very little space,

Physical properties of atomic nuclei. Core charge. Kernel size. Moments of the nuclei. Spin the nucleus. Magnetic and electrical moments of the core. The mass of the nucleus and the mass of the atom. Mass defect. Communication energy. The main features of binding energy. The basic rule. Nuclear forces: basic characteristics, Coulomb and nuclear potentials of a nucleus. The exchange nature of nuclear forces.

Mosley's Law.The electric charge of the nucleus is formed by the protons that make up its composition. Number of protons Z  call it a charge, bearing in mind that the absolute value of the nuclear charge is Ze.The core charge coincides with the serial number Z  element in the periodic system of periodic elements. For the first time, the charges of atomic nuclei were determined by the English physicist Mosley in 1913. Using a crystal to measure the wavelength λ   characteristic x-rays for atoms of certain elements, Mosley discovered a regular change in wavelength λ   for elements following each other in the periodic system (Fig. 2.1). Mosley interpreted this observation as an addiction. λ   from some atomic constant Z, changing by one from element to element and equal to unity for hydrogen:

where and are constants. From experiments on the scattering of X-ray quanta by atomic electrons and α -particles by atomic nuclei, it was already known that the charge of the nucleus is approximately equal to half the atomic mass and, therefore, is close to the ordinal number of the element. Since the emission of characteristic x-ray radiation is a consequence of electrical processes in the atom, Moseley concluded that the atom constant found in his experiments, which determines the wavelength of characteristic x-ray radiation and coincides with the serial number of the element, can only be the charge of the atomic nucleus (Mosley law).

Fig. 2.1. X-ray spectra of atoms of neighboring elements obtained by Moseley

The measurement of the wavelengths of x-rays is carried out with great accuracy, so that on the basis of Mosley's law, the atom’s belonging to a chemical element is absolutely reliable. However, the fact that the constant Z  in the last equation is the charge of the nucleus, although justified by indirect experiments, ultimately rests on the postulate - the law of Mosley. Therefore, after the discovery of Mosley, the charges of nuclei were repeatedly measured in experiments on scattering α -particles based on Coulomb's law. In 1920, Chadwig improved the method for measuring the proportion of scattered α -particles and received nuclear charges of atoms of copper, silver and platinum (see table 2.1). Chadwig's data leaves no doubt about the validity of Mosley's law. In addition to these elements, the charges of the nuclei of magnesium, aluminum, argon and gold were also determined in experiments.

Table 2.1. Chadwick Test Results

Definitions.  After the discovery of Moseley, it became clear that the main characteristic of an atom is the charge of the nucleus, and not its atomic mass, as the chemists of the 19th century assumed, because the charge of the nucleus determines the number of atomic electrons, and hence the chemical properties of atoms. The reason for the difference in the atoms of chemical elements is precisely because their nuclei have a different number of protons in their composition. On the contrary, a different number of neutrons in the nuclei of atoms with the same number of protons does not change the chemical properties of atoms. Atoms that differ only in the number of neutrons in the nuclei are called isotopes  chemical element.

An atom with a certain number of protons and neutrons in the composition of the nucleus is called nuclide.  The composition of the kernel is given by numbers Z  and A. They speak of an isotope only in view of their belonging to a chemical element, for example, 235 U is an isotope of uranium, but 235 U is a fissile nuclide, and not a fissile isotope.

Atoms whose nuclei contain the same number of neutrons but different numbers of protons are called isotones.  Atoms with the same mass numbers but different proton-neutron composition of nuclei are called isobars.

Atoms of any substance are electrically neutral particles. An atom consists of a nucleus and a collection of electrons. The nucleus carries a positive charge, the total charge of which is equal to the sum of the charges of all the electrons of the atom.

General information about the charge of the atomic nucleus

The charge of the nucleus of an atom determines the location of an element in the periodic system Mendeleev and, accordingly, the chemical properties of the substance consisting of these atoms and compounds of these substances. The magnitude of the nuclear charge is equal to:

where Z is the number of the element in the periodic table, e is the electron charge or.

Elements with the same Z numbers but different atomic masses are called isotopes. If the elements have the same Z, then their nucleus has an equal number of protons, and if the atomic masses are different, then the number of neutrons in the nuclei of these atoms is different. So, hydrogen has two isotopes: deuterium and tritium.

The nuclei of atoms have a positive charge, as they consist of protons and neutrons. A proton is a stable particle belonging to the hadron class, which is the nucleus of a hydrogen atom. A proton is a positively charged particle. Its charge is equal in absolute value to the elementary charge, that is, the magnitude of the electron charge. The proton charge is often denoted as, then we can write that:

The proton rest mass () is approximately equal to:

You can learn more about the proton by reading the section “Proton Charge”.

Nuclear Charge Measurement Experiments

The first nuclear charges were measured by Mosley in 1913. The measurements were indirect. The scientist has determined the relationship between the x-ray frequency () and the nuclear charge Z.

where C and B are constants independent of the element for the considered series of radiation.

Chadwick measured the direct charge of the nucleus in 1920. He carried out the scattering of particles on metal films, essentially repeating Rutherford’s experiments that led Rutherford to build a nuclear model of the atom.

In these experiments, particles were passed through a thin metal foil. Rutherford found that in most cases the particles passed through the foil, deviating at small angles from the original direction of motion. This is because - particles are deflected under the influence of the electric forces of electrons, which have a significantly lower mass than - particles. Sometimes, quite rarely - particles deviated by angles in excess of 90 o. Rutherford explained this fact by the presence of a charge in the atom, which is localized in a small volume, and this charge is associated with a mass that is much larger than the y-particle.

For a mathematical description of the results of his experiments, Rutherford derived a formula that determines the angular distribution of particles after their scattering by atoms. In deriving this formula, the scientist used the Coulomb law for point charges, and at the same time believed that the mass of the nucleus of an atom is much larger than the mass of the particle. Rutherford's formula can be written as:

where n is the number of scattering nuclei per unit area of \u200b\u200bthe foil; N is the number of particles that pass in 1 second through a unit area, perpendicular to the direction of flow of particles; - the number of particles that are scattered inside the solid angle is the charge of the scattering center; - mass - particles; - the angle of deviation of the particles; v - velocity - particles.

Rutherford's formula (3) can be used to find the atomic nucleus charge (Z), if we compare the number of incident particles (N) with the number (dN) of particles scattered at an angle, then the function will depend only on the charge of the scattering nucleus. Carrying out experiments and applying the Rutherford formula, Chadwick found the charges of the nuclei of platinum, silver and copper.

Examples of solving problems

EXAMPLE 1

The task	A metal plate is irradiated with particles having a high speed. Some of these particles during elastic interaction with the nuclei of metal atoms change the direction of their movement in the opposite direction. What is the charge of the nucleus of metal atoms (q) if the minimum distance of approach of the particle and the nucleus is r. Mass - a particle is equal to its speed v. In solving the problem, relativistic effects can be neglected. Particles are considered point, the core is fixed and point.
Decision	Let's make a drawing. Moving in the direction of the atomic nucleus, the particle overcomes the Coulomb force, pushing it away from the nucleus, since the particle and nucleus have positive charges. Kinetic energy of a moving particle transforms into potential energy  interactions of the nucleus of a metal atom and - particles. The basis for solving the problem should be the law of conservation of energy .: The potential energy of point charged particles is found as: where the charge of the particles is equal to: since and of the particles is the nucleus of the helium atom, which consists of two protons and two neutrons, since we assume that the experiment is carried out in air. Kinetic energy - particles before collision with the nucleus of an atom is equal to: In accordance with (1.1), we equate the right-hand sides of expressions (1.2) and (1.3), we have: From the formula (1.4) we express the nuclear charge:
Answer

The atom of a chemical element consists of the cores

And an electronic shell. The nucleus is the central part of the atom, in which almost all of its mass is concentrated. Unlike the electron shell, the core has a positive charge.

You will need

• Atomic number of a chemical element, Mosley's law

Instruction manual

The nucleus of an atom consists of two types of particles - protons and neutrons. Neutrons are electrically neutral particles, i.e. their electric charge  equal to zero. Protons are positively charged particles and their electric charge equals +1.

In this way, charge the cores  equal to the number of protons. In turn, the number of protons in the nucleus is equal to the atomic number of the chemical element. For example, the atomic number of hydrogen is 1, that is, the hydrogen nucleus consists of one proton has charge  +1 The atomic number of sodium is 11, charge  him the cores  equal to +11.

With alpha decay the cores  its atomic number decreases by two due to the emission of an alpha particle ( the cores  helium atom). Thus, the number of protons in the nucleus that underwent alpha decay also decreases by two.
Beta decay can occur in three different forms. In the case of beta-minus decay, the neutron turns into a proton when an electron and antineutrino are emitted. Then charge the cores  increases by one.
In the case of beta-plus decay, the proton turns into a neutron, positron and neutrino, charge the cores  decreases by one.
In the case of electronic capture charge the cores  also decreases by one.

Charge the cores  can also be determined by the frequency of the spectral lines of the characteristic radiation of the atom. According to Mosley’s law: sqrt (v / R) \u003d (Z-S) / n, where v is the spectral frequency of the characteristic radiation, R is the Rydberg constant, S is the screening constant, n is the main quantum number.
So Z \u003d n * sqrt (v / r) + s.