The charge of the nucleus of an atom is determined by the quantity. Atomic nucleus: nuclear charge

Kernel charge() locates chemical element in the table D.I. Mendeleev. The Z number is the number of protons in the nucleus. Cl is the charge of the proton, which is equal in magnitude to the charge of the electron.

We emphasize once again that the nuclear charge determines the number of positive elementary charges carried by protons. And since the atom is generally a neutral system, the charge of the nucleus also determines the number of electrons in the atom. And we remember that the electron has a negative elementary charge. Electrons in an atom are distributed over energy shells and subshells depending on their number, therefore, the charge of the nucleus has a significant effect on the distribution of electrons over their states. The number of electrons at the last energy level depends on Chemical properties atom. It turns out that the charge of the nucleus determines the chemical properties of the substance.

It is now customary to denote various chemical elements as follows: , where X is the symbol of a chemical element in the periodic table, which corresponds to the charge.

Elements that have the same Z but different atomic masses (A) (this means that in the nucleus the same number protons but different numbers of neutrons) are called isotopes. So, hydrogen has two isotopes: 1 1 H-hydrogen; 2 1 H-deuterium; 3 1 H-tritium

There are stable and unstable isotopes.

Nuclei with the same masses but different charges are called isobars. Isobars are mainly found among heavy nuclei, and in pairs or triads. For example, and .

The first indirect measurement of the nuclear charge was made by Moseley in 1913. He established a relationship between the frequency of the characteristic x-ray radiation() and nuclear charge (Z):

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

The charge of the nucleus was directly determined by Chadwick in 1920 while studying the scattering of nuclei of the helium atom on metal films.

Core Composition

The nucleus of a hydrogen atom is called a proton. The mass of a proton is:

The nucleus is made up of protons and neutrons (collectively called nucleons). The neutron was discovered in 1932. The mass of the neutron is very close to the mass of the proton. Neutron electric charge does not have.

The sum of the number of protons (Z) and the number of neutrons (N) in the nucleus is called the mass number A:

Since the masses of the neutron and proton are very close, each of them is equal to almost an atomic mass unit. The mass of electrons in an atom is much less than the mass of the nucleus, so it is believed that mass number nucleus is approximately equal to the element's relative atomic mass when rounded to the nearest integer.

Examples of problem solving

EXAMPLE 1

Exercise

Nuclei are very stable systems, therefore, protons and neutrons must be kept inside the nucleus by some kind of force. What can you say about these forces?

Decision

It can be immediately noted that the forces that bind nucleons do not belong to gravitational ones, which are too weak. The stability of the nucleus cannot be explained by the presence of electromagnetic forces, since between protons, as particles carrying charges of the same sign, there can only be electrical repulsion. Neutrons are electrically neutral particles. Between nucleons act special kind forces that are called nuclear forces. These forces are almost 100 times stronger than electrical forces. Nuclear forces are the most powerful of all known forces in nature. The interaction of particles in the nucleus is called strong. The next feature of nuclear forces is that they are short-range. Nuclear forces become noticeable only at a distance of the order of cm, that is, at a distance of the size of the nucleus.

EXAMPLE 2

Exercise

What minimum distance can the nucleus of a helium atom, having a kinetic energy equal to that of a head-on collision, approach the motionless nucleus of a lead atom?

Decision

Let's make a drawing. Consider the motion of the nucleus of a helium atom ( - particles) in an electrostatic field, which creates a motionless nucleus of a lead atom. - the particle moves towards the nucleus of the lead atom with a speed decreasing to zero, since repulsive forces act between like-charged particles. The kinetic energy that the particle possessed will turn into the potential energy of interaction - particles and fields (), which creates the nucleus of the lead atom: We express the potential energy of a particle in an electrostatic field as: where is the charge of the nucleus of a helium atom; - tension electrostatic field, which creates the nucleus of the lead atom. From (2.1) - (2.3) we get:

Instruction

In the table of D.I. Mendeleev, as in a multi-storey apartment building"" chemical elements, each of which occupies its own own apartment. Thus, each of the elements has a certain serial number indicated in the table. The numbering of chemical elements starts from left to right, and from the top. In a table, the horizontal rows are called periods, and the vertical columns are called groups. This is important, because by the number of the group or period, you can also characterize some parameters. atom.

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

Example No. 1. Determine the charge nuclei atom carbon (C). We begin to analyze the chemical element carbon, focusing on the table of D.I. Mendeleev. Carbon is in “apartment” No. 6. Therefore, it nuclei+6 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 nuclei atom aluminum (Al). Aluminum has a serial number - No. 13. Therefore, the charge nuclei atom aluminum +13 (due to 13 protons). There will also be 13 electrons.

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

note

In the table of D.I. Mendeleev, two numerical values ​​are indicated in one cell for each chemical element. Do not confuse the atomic number and relative atomic mass of an element

An atom of a chemical element is made up of nuclei and 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

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

Instruction

Thus, charge nuclei equal to the number of protons. In turn, the number of protons in the nucleus is equal to the atomic number. For example, the atomic number of hydrogen is 1, that is, the nucleus of hydrogen consists of one proton has charge+1. The atomic number of sodium is 11, charge his nuclei equals +11.

In alpha decay nuclei its its atomic number is reduced by two by the emission of an alpha particle ( nuclei atom). Thus, the number of protons in a nucleus that has undergone alpha decay is also reduced by two.
Beta decay can occur in three different ways. In the case of "beta-minus" decay, the neutron turns into an antineutrino when emitted. Then charge nuclei per unit.
In the case of beta-plus decay, the proton turns into a neutron, a positron and a neutrino, charge nuclei decreases by one.
In case of electronic capture charge nuclei also decreases by one.

Charge nuclei can also be determined from the frequency of spectral lines characteristic radiation atom. According to Moseley's law: sqrt(v/R) = (Z-S)/n, where v is the spectral characteristic radiation, R is the Rydberg constant, S is the screening constant, n is the principal quantum number.
Thus Z = n*sqrt(v/r)+s.

Related videos

Sources:

• How does the nuclear charge change?

An atom is the smallest particle of each element that carries its chemical properties. Both the existence and the structure of the atom have been the subject of discussion and study since ancient times. It was found that the structure of atoms is similar to the structure solar system: in the center is the nucleus, which occupies very little space, but has concentrated in itself almost the entire mass; "planets" revolve around it - electrons carrying negative charges. How can you find charge? nuclei atom?

Instruction

Any atom is electrically neutral. But since they carry negative charges, they must be balanced by opposite charges. And there is. Positive charges carry particles called protons located in the nucleus of an atom. The proton is much more massive than the electron: it weighs as much as 1836 electrons!

The simplest case is the hydrogen atom of the first element in the Periodic Table. Looking at the table, you will see that it is at the first number, and its nucleus consists of a single proton, around which the only one revolves. It follows that nuclei hydrogen atom is +1.

The nuclei of other elements no longer consist only of protons, but also of the so-called "neutrons". As you can easily tell from the name itself, they carry no charge at all, neither negative nor positive. Therefore, remember: no matter how many neutrons are included in the atomic nuclei, they only affect its mass, but not its charge.

Therefore, the magnitude of the positive charge nuclei an atom depends only on how many protons it contains. But since, as already indicated, the atom is electrically neutral, its nucleus must contain the same number of protons, revolves around nuclei. The number of protons is determined by the serial number of the element in the periodic table.

Consider several elements. For example, famous and vital required oxygen is located in the "cell" at number 8. Therefore, its nucleus contains 8 protons, and the charge nuclei will be +8. Iron occupies a “cell” with number 26, and, accordingly, has a charge nuclei+26. And the metal - with serial number 79 - will have exactly the same charge nuclei(79), with + sign. Accordingly, an oxygen atom contains 8 electrons, an atom - 26, and a gold atom - 79.

Related videos

Under normal conditions, an atom is electrically neutral. In this case, the nucleus of an atom, consisting of protons and neutrons, is positive, and electrons carry a negative charge. With an excess or lack of electrons, an atom turns into an ion.

Instruction

Chemical compounds may be molecular or ionic in nature. Molecules are also electrically neutral, and ions carry some charge. So, the ammonia molecule NH3 is neutral, but the ammonium ion NH4+ is positively charged. Bonds in the ammonia molecule, formed by the exchange type. The fourth hydrogen atom is added according to the donor-acceptor mechanism, this is also covalent bond. Ammonium is formed when ammonia reacts with acid solutions.

It is important to understand that the charge of the nucleus of an element does not depend on chemical transformations. No matter how many electrons you add or take away, the charge of the nucleus remains the same. For example, an O atom, an O- anion, and an O+ cation are characterized by the same nuclear charge +8. In this case, the atom has 8 electrons, the anion 9, the cation - 7. The nucleus itself can be changed only through nuclear transformations.

The most common type nuclear reactions- radioactive decay that can take place in natural environment. The atomic mass of the elements undergoing such decay is enclosed in square brackets. This means that the mass number is not constant, changing over time.

In the periodic table of elements D.I. Mendeleev silver has serial number 47 and the designation "Ag" (argentum). The name of this metal probably comes from the Latin "argos", which means "white", "shiny".

Instruction

Silver was known to mankind as early as the 4th millennium BC. AT Ancient Egypt it was even called "white gold". This metal is found in nature both in native form and in the form of compounds, for example, sulfides. Silver nuggets are heavy and often contain impurities of gold, mercury, copper, platinum, antimony and bismuth.

Chemical properties of silver.

Silver belongs to the group of transition metals and has all the properties of metals. However, the activity of silver is low - in the electrochemical series of voltages of metals, it is located to the right of hydrogen, almost at the very end. In compounds, silver most often exhibits an oxidation state of +1.

Under normal conditions, silver does not react with oxygen, hydrogen, nitrogen, carbon, silicon, but interacts with sulfur, forming silver sulfide: 2Ag+S=Ag2S. When heated, silver interacts with halogens: 2Ag+Cl2=2AgCl↓.

Soluble silver nitrate AgNO3 is used for qualitative determination of halide ions in solution – (Cl-), (Br-), (I-): (Ag+)+(Hal-)=AgHal↓. For example, when interacting with chlorine anions, silver gives an insoluble white precipitate AgCl↓.

Why does silverware darken when exposed to air?

The reason for the gradual production of silver products is because silver reacts with hydrogen sulfide contained in the air. As a result, an Ag2S film is formed on the metal surface: 4Ag+2H2S+O2=2Ag2S+2H2O.

From planetary model structure of atoms, we know that an atom is a nucleus, and a cloud of electrons revolving around it. Moreover, the distance between the electrons and the nucleus is tens and hundreds of thousands of times greater than the size of the nucleus itself.

What is the core itself? Is it a small hard indivisible ball or is it made up of smaller particles? Not a single microscope that exists in the world is able to clearly show us what is happening at this level. Everything is too small. Then how to be? Is it even possible to study the physics of the atomic nucleus? How to find out the composition and characteristics of the atomic nucleus, if it is not possible to study it?

The charge of the nucleus of an atom

With a wide variety of indirect experiments, expressing hypotheses and testing them in practice, through trial and error, scientists managed to investigate the structure of the atomic nucleus. It turned out that the nucleus consists of even smaller particles. The size of the nucleus, its charge and the chemical properties of the substance depend on the number of these particles. Moreover, these particles have a positive charge, which compensates for the negative charge of the electrons of the atom. These particles are called protons. Their number in the normal state is always equal to the number of electrons. The question of how to determine the charge of the nucleus no longer stood. The charge of the nucleus of an atom in a neutral state is always equal to the number of electrons revolving around it and is opposite in sign to the charge of the electrons. And physicists have already learned how to determine the number and charge of electrons.

The structure of the atomic nucleus: protons and neutrons

However, in the process of further research, a new problem arose. It turned out that protons, having the same charge, in some cases differ twice in mass. This caused a lot of questions and inconsistencies. In the end, it was possible to establish that the composition of the atomic nucleus, in addition to protons, also includes some particles that are almost equal in mass to protons, but do not have any charge. These particles are called neutrons. The detection of neutrons resolved all inconsistencies in the calculations. As a result, protons and neutrons, as the constituent elements of the nucleus, were called nucleons. The calculation of any values ​​relating to the characteristics of the core has become much easier to understand. Neutrons do not take part in the formation of the nuclear charge, therefore, their influence on the chemical properties of matter is practically not manifested, however, neutrons participate in the formation of the mass of nuclei, respectively, affect the gravitational properties of the atomic nucleus. Thus, there is some indirect influence of neutrons on the properties of matter, but it is extremely insignificant.

Belkin I.K. The charge of the atomic nucleus and Mendeleev's periodic system of elements // Kvant. - 1984. - No. 3. - S. 31-32.

By special agreement with the editorial board and the editors of the journal "Kvant"

Modern ideas about the structure of the atom arose in 1911-1913, after the famous experiments of Rutherford on the scattering of alpha particles. In these experiments, it was shown that α -particles (their charge is positive), falling on a thin metal foil, are sometimes deflected at large angles and even thrown back. This could only be explained by the fact that the positive charge in the atom is concentrated in a negligible volume. If we imagine it in the form of a ball, then, as Rutherford established, the radius of this ball should be approximately 10 -14 -10 -15 m, which is tens and hundreds of thousands of times smaller sizes atom as a whole (~10 -10 m). Only near such a small positive charge can there be electric field capable of discarding α - a particle moving at a speed of about 20,000 km/s. Rutherford called this part of the atom the nucleus.

This is how the idea arose that an atom of any substance consists of a positively charged nucleus and negatively charged electrons, the existence of which in atoms was established earlier. Obviously, since the atom as a whole is electrically neutral, the charge of the nucleus must be numerically equal to the charge of all the electrons present in the atom. If we denote the electron charge modulus by the letter e(elementary charge), then the charge q i cores should be equal q i = Ze, where Z is an integer equal to the number of electrons in the atom. But what is the number Z? What is the charge q i core?

From the experiments of Rutherford, which made it possible to determine the size of the nucleus, in principle, it is possible to determine the value of the charge of the nucleus. After all, the electric field that rejects α -particle, depends not only on the size, but also on the charge of the nucleus. And Rutherford really estimated the charge of the nucleus. According to Rutherford, the nuclear charge of an atom of a chemical element is approximately equal to half of its relative atomic mass BUT, multiplied by the elementary charge e, i.e

\(~Z = \frac(1)(2)A\).

But, oddly enough, the true charge of the nucleus was established not by Rutherford, but by one of the readers of his articles and reports, the Dutch scientist Van den Broek (1870-1926). It is strange because Van den Broek was not a physicist by education and profession, but a lawyer.

Why did Rutherford, when evaluating the charges of atomic nuclei, correlate them with atomic masses? The fact is that when in 1869 D. I. Mendeleev created periodic system chemical elements, he arranged the elements in ascending order of their relative atomic masses. And over the past forty years, everyone has become accustomed to the fact that the most important characteristic of a chemical element is its relative atomic mass that it is what distinguishes one element from another.

Meanwhile, it was at this time, at the beginning of the 20th century, that difficulties arose with the system of elements. In the study of the phenomenon of radioactivity, a number of new radioactive elements were discovered. And there seemed to be no place for them in Mendeleev's system. It seemed that Mendeleev's system needed to be changed. This was what Van den Broek was especially concerned about. Over the course of several years, he proposed several options for an expanded system of elements, in which there would be enough space not only for the still undiscovered stable elements (D. I. Mendeleev himself “took care” of the places for them), but also for radioactive elements too. Van den Broek's last version was published in early 1913, it had 120 places, and uranium occupied cell number 118.

In the same year, 1913, the results of the latest research on scattering were published. α -particles at large angles, carried out by Rutherford's collaborators Geiger and Marsden. Analyzing these results, Van den Broek made major discovery. He found that the number Z in formula q i = Ze is not equal to half the relative mass of an atom of a chemical element, but to its serial number. And, moreover, the ordinal number of the element in the Mendeleev system, and not in his, Van den Broek, 120-local system. Mendeleev's system, it turns out, did not need to be changed!

It follows from the idea of ​​Van den Broek that every atom consists of an atomic nucleus, the charge of which is equal to the serial number of the corresponding element in the Mendeleev system, multiplied by the elementary charge, and electrons, the number of which in the atom is also equal to the serial number of the element. (A copper atom, for example, consists of a nucleus with a charge of 29 e, and 29 electrons.) It became clear that D. I. Mendeleev intuitively arranged the chemical elements in ascending order not of the atomic mass of the element, but of the charge of its nucleus (although he did not know about this). Consequently, one chemical element differs from another not by its atomic mass, but by the charge of the atomic nucleus. The charge of the nucleus of an atom is main characteristic chemical element. There are atoms of completely different elements, but with the same atomic masses (they have a special name - isobars).

The fact that it is not atomic masses that determine the position of an element in the system can also be seen from the periodic table: in three places, the rule of increasing atomic mass is violated. So, the relative atomic mass of nickel (No. 28) is less than that of cobalt (No. 27), for potassium (No. 19) it is less than that of argon (No. 18), for iodine (No. 53) it is less than that of tellurium ( No. 52).

The assumption about the relationship between the charge of the atomic nucleus and the ordinal number of the element easily explained the displacement rules for radioactive transformations, discovered in the same 1913 (Physics 10, § 103). Indeed, when emitted by the nucleus α -particle, the charge of which is equal to two elementary charges, the charge of the nucleus, and hence its serial number (now they usually say - atomic number) should decrease by two units. When emitting β -particle, that is, a negatively charged electron, it must increase by one unit. This is what the displacement rules are about.

The idea of ​​Van den Broek very soon (literally in the same year) received the first, albeit indirect, experimental confirmation. Somewhat later, its correctness was proved by direct measurements of the charge of the nuclei of many elements. It is clear that she played an important role in further development physics of the atom and the atomic nucleus.

That all things are made up of elementary particles, scientists have assumed Ancient Greece. But in those days there was no way to prove this fact or disprove it. Yes, and the properties of atoms in antiquity could only guess, based on their own observations of various substances.

It was possible to prove that all substances consist of elementary particles only in the 19th century, and then indirectly. At the same time, physicists and chemists around the world tried to create a unified theory of elementary particles, describing their structure and explaining various properties, such as, for example, the charge of the nucleus.

The works of many scientists have been devoted to the study of molecules, atoms and their structure. Physics gradually moved into the study of the microworld - elementary particles, their interactions and properties. Scientists began to wonder what it consists of putting forward hypotheses and trying to prove them, at least indirectly.

As a result, the planetary theory proposed by Ernest Rutherford and Niels Bohr was adopted as the basic theory. According to this theory, the charge of the nucleus of any atom is positive, while negatively charged electrons rotate in its orbits, eventually making the atom electrically neutral. Over time, this theory has been repeatedly confirmed. different kind experiments, starting with the experiments of one of her co-authors.

Modern nuclear physics considers the Rutherford-Bohr theory fundamental, all studies of atoms and their elements are based on it. On the other hand, most of the hypotheses that have emerged over the past 150 years have not been practically confirmed. It turns out that most nuclear physics is theoretical due to the ultra-small sizes of the objects under study.

Of course, in modern world determining the charge of the nucleus of aluminum, for example (or any other element) is much easier than in the 19th century, and even more so in ancient Greece. But making new discoveries in this area, scientists sometimes come to surprising conclusions. Trying to find a solution to one problem, physics faces new problems and paradoxes.

Initially, Rutherford's theory says that the chemical properties of a substance depend on the charge of the nucleus of its atom and, as a result, on the number of electrons revolving in its orbits. Modern chemistry and physics fully confirm this version. Despite the fact that the study of the structure of molecules was initially repelled by the simplest model- a hydrogen atom, the nuclear charge of which is 1, the theory fully applies to all elements of the periodic table, including those obtained artificially at the end of the last millennium.

It is curious that long before Rutherford's research, an English chemist, a doctor by education, William Prout, noticed that specific gravity various substances is a multiple of this hydrogen index. He then suggested that all other elements simply consist of hydrogen at some simplest level. That, for example, a nitrogen particle is 14 such minimal particles, oxygen is 16, etc. If we consider this theory globally in a modern interpretation, then in general it is correct.