The nineteenth century in the history of mankind is a century in which many sciences were reformed, including chemistry. It was at this time that Mendeleev's periodic system appeared, and with it the periodic law. It was he who became the basis of modern chemistry. The periodic system of D.I. Mendeleev is a systematization of elements that establishes the dependence of chemical and physical properties on the structure and charge of the atom of a substance.

Story

The beginning of the periodic period was laid by the book “The Correlation of Properties with the Atomic Weight of Elements,” written in the third quarter of the 17th century. It displayed the basic concepts of the known chemical elements (at that time there were only 63 of them). In addition, the atomic masses of many of them were determined incorrectly. This greatly interfered with the discovery of D.I. Mendeleev.

Dmitry Ivanovich began his work by comparing the properties of elements. First of all, he worked on chlorine and potassium, and only then moved on to working with alkali metals. Armed with special cards on which chemical elements were depicted, he repeatedly tried to assemble this “mosaic”: laying it out on his table in search of the necessary combinations and matches.

After much effort, Dmitry Ivanovich finally found the pattern he was looking for and arranged the elements in periodic rows. Having received as a result empty cells between the elements, the scientist realized that not all chemical elements were known to Russian researchers, and that it was he who must give this world the knowledge in the field of chemistry that had not yet been given by his predecessors.

Everyone knows the myth that the periodic table appeared to Mendeleev in a dream, and he collected the elements into a single system from memory. This is, roughly speaking, a lie. The fact is that Dmitry Ivanovich worked quite long and concentrated on his work, and it exhausted him greatly. While working on the system of elements, Mendeleev once fell asleep. When he woke up, he realized that he had not finished the table and rather continued filling in the empty cells. His acquaintance, a certain Inostrantsev, a university teacher, decided that the periodic table had been dreamed of by Mendeleev and spread this rumor among his students. This is how this hypothesis emerged.

Fame

Mendeleev's chemical elements are a reflection of the periodic law created by Dmitry Ivanovich back in the third quarter of the 19th century (1869). It was in 1869 that Mendeleev’s notification about the creation of a certain structure was read out at a meeting of the Russian chemical community. And in the same year, the book “Fundamentals of Chemistry” was published, in which Mendeleev’s periodic system of chemical elements was published for the first time. And in the book “The Natural System of Elements and Its Use to Indicate the Qualities of Undiscovered Elements,” D. I. Mendeleev first mentioned the concept of “periodic law.”

Structure and rules for placing elements

The first steps in creating the periodic law were taken by Dmitry Ivanovich back in 1869-1871, at that time he worked hard to establish the dependence of the properties of these elements on the mass of their atom. The modern version consists of elements summarized in a two-dimensional table.

The position of an element in the table carries a certain chemical and physical meaning. By the location of an element in the table, you can find out what its valence is and determine other chemical characteristics. Dmitry Ivanovich tried to establish a connection between elements, both similar in properties and differing.

He based the classification of chemical elements known at that time on valence and atomic mass. By comparing the relative properties of elements, Mendeleev tried to find a pattern that would unite all known chemical elements into one system. By arranging them based on increasing atomic masses, he still achieved periodicity in each of the rows.

Further development of the system

The periodic table, which appeared in 1969, has been refined more than once. With the advent of noble gases in the 1930s, it was possible to reveal a new dependence of elements - not on mass, but on atomic number. Later, it was possible to establish the number of protons in atomic nuclei, and it turned out that it coincides with the atomic number of the element. Scientists of the 20th century studied electronic energy. It turned out that it also affects periodicity. This greatly changed ideas about the properties of elements. This point was reflected in later editions of Mendeleev’s periodic table. Each new discovery of the properties and characteristics of elements fit organically into the table.

Characteristics of Mendeleev's periodic system

The periodic table is divided into periods (7 rows arranged horizontally), which, in turn, are divided into large and small. The period begins with an alkali metal and ends with an element with non-metallic properties.
Dmitry Ivanovich's table is vertically divided into groups (8 columns). Each of them in the periodic table consists of two subgroups, namely the main and secondary ones. After much debate, at the suggestion of D.I. Mendeleev and his colleague U. Ramsay, it was decided to introduce the so-called zero group. It includes inert gases (neon, helium, argon, radon, xenon, krypton). In 1911, scientists F. Soddy were asked to place indistinguishable elements, the so-called isotopes, in the periodic table - separate cells were allocated for them.

Despite the correctness and accuracy of the periodic system, the scientific community did not want to recognize this discovery for a long time. Many great scientists ridiculed the work of D.I. Mendeleev and believed that it was impossible to predict the properties of an element that had not yet been discovered. But after the supposed chemical elements were discovered (and these were, for example, scandium, gallium and germanium), the Mendeleev system and his periodic law became the science of chemistry.

Table in modern times

Mendeleev's periodic table of elements is the basis of most chemical and physical discoveries related to atomic-molecular science. The modern concept of an element was formed precisely thanks to the great scientist. The advent of Mendeleev's periodic system introduced fundamental changes in the understanding of various compounds and simple substances. The creation of the periodic table by scientists had a huge impact on the development of chemistry and all sciences related to it.

Periodic law D.I. Mendeleev and the periodic table of chemical elements is of great importance in the development of chemistry. Let's plunge back to 1871, when chemistry professor D.I. Mendeleev, through numerous trials and errors, came to the conclusion that “... the properties of the elements, and therefore the properties of the simple and complex bodies they form, are periodically dependent on their atomic weight.” The periodicity of changes in the properties of elements arises due to the periodic repetition of the electronic configuration of the outer electron layer with an increase in the charge of the nucleus.

Modern formulation of the periodic law is this:

“the properties of chemical elements (i.e., the properties and form of the compounds they form) are periodically dependent on the charge of the nucleus of the atoms of the chemical elements.”

While teaching chemistry, Mendeleev understood that remembering the individual properties of each element caused difficulties for students. He began to look for ways to create a systematic method to make it easier to remember the properties of elements. The result was natural table, later it became known as periodic.

Our modern table is very similar to the periodic table. Let's take a closer look at it.

Mendeleev table

Mendeleev's periodic table consists of 8 groups and 7 periods.

The vertical columns of a table are called groups . The elements within each group have similar chemical and physical properties. This is explained by the fact that elements of the same group have similar electronic configurations of the outer layer, the number of electrons on which is equal to the group number. In this case, the group is divided into main and secondary subgroups.

IN Main subgroups includes elements whose valence electrons are located on the outer ns- and np-sublevels. IN Side subgroups includes elements whose valence electrons are located on the outer ns-sublevel and the inner (n - 1) d-sublevel (or (n - 2) f-sublevel).

All elements in periodic table , depending on which sublevel (s-, p-, d- or f-) valence electrons are classified into: s-elements (elements of the main subgroups of groups I and II), p-elements (elements of the main subgroups III - VII groups), d-elements (elements of side subgroups), f-elements (lanthanides, actinides).

The highest valency of an element (with the exception of O, F, elements of the copper subgroup and group eight) is equal to the number of the group in which it is found.

For elements of the main and secondary subgroups, the formulas of higher oxides (and their hydrates) are the same. In the main subgroups, the composition of hydrogen compounds is the same for the elements in this group. Solid hydrides form elements of the main subgroups of groups I - III, and groups IV - VII form gaseous hydrogen compounds. Hydrogen compounds of type EN 4 are more neutral compounds, EN 3 are bases, H 2 E and NE are acids.

The horizontal rows of a table are called periods. The elements in the periods differ from each other, but what they have in common is that the last electrons are at the same energy level ( principal quantum numbern- the same ).

The first period differs from the others in that there are only 2 elements: hydrogen H and helium He.

In the second period there are 8 elements (Li - Ne). Lithium Li, an alkali metal, begins the period, and the noble gas neon Ne closes it.

In the third period, just like in the second, there are 8 elements (Na - Ar). The period begins with the alkali metal sodium Na, and the noble gas argon Ar closes it.

The fourth period contains 18 elements (K - Kr) - Mendeleev designated it as the first large period. It also begins with the alkali metal Potassium and ends with the inert gas krypton Kr. The composition of large periods includes transition elements (Sc - Zn) - d- elements.

In the fifth period, similar to the fourth, there are 18 elements (Rb - Xe) and its structure is similar to the fourth. It also begins with the alkali metal rubidium Rb, and ends with the inert gas xenon Xe. The composition of large periods includes transition elements (Y - Cd) - d- elements.

The sixth period consists of 32 elements (Cs - Rn). Except 10 d-elements (La, Hf - Hg) it contains a row of 14 f-elements (lanthanides) - Ce - Lu

The seventh period is not over. It begins with Franc Fr, it can be assumed that it will contain, like the sixth period, 32 elements that have already been found (up to the element with Z = 118).

Interactive periodic table

If you look at periodic table and draw an imaginary line starting at boron and ending between polonium and astatine, then all metals will be to the left of the line, and non-metals to the right. Elements immediately adjacent to this line will have the properties of both metals and non-metals. They are called metalloids or semimetals. These are boron, silicon, germanium, arsenic, antimony, tellurium and polonium.

Periodic law

Mendeleev gave the following formulation of the Periodic Law: “the properties of simple bodies, as well as the forms and properties of compounds of elements, and therefore the properties of the simple and complex bodies they form, are periodically dependent on their atomic weight.”
There are four main periodic patterns:

Octet rule states that all elements tend to gain or lose an electron in order to have the eight-electron configuration of the nearest noble gas. Because Since the outer s- and p-orbitals of noble gases are completely filled, they are the most stable elements.
Ionization energy is the amount of energy required to remove an electron from an atom. According to the octet rule, when moving across the periodic table from left to right, more energy is required to remove an electron. Therefore, elements on the left side of the table tend to lose an electron, and those on the right side tend to gain one. Inert gases have the highest ionization energy. The ionization energy decreases as you move down the group, because electrons at low energy levels have the ability to repel electrons at higher energy levels. This phenomenon is called shielding effect. Due to this effect, the outer electrons are less tightly bound to the nucleus. Moving along the period, the ionization energy smoothly increases from left to right.

Electron affinity– the change in energy when an atom of a substance in a gaseous state acquires an additional electron. As one moves down the group, the electron affinity becomes less negative due to the screening effect.

Electronegativity- a measure of how strongly it tends to attract electrons from another atom associated with it. Electronegativity increases when moving in periodic table from left to right and from bottom to top. It must be remembered that noble gases do not have electronegativity. Thus, the most electronegative element is fluorine.

Based on these concepts, let us consider how the properties of atoms and their compounds change in periodic table.

So, in a periodic dependence there are such properties of an atom that are associated with its electronic configuration: atomic radius, ionization energy, electronegativity.

Let us consider the change in the properties of atoms and their compounds depending on their position in periodic table of chemical elements.

The non-metallicity of the atom increases when moving in the periodic table left to right and bottom to top. Due to this the basic properties of the oxides decrease, and acidic properties increase in the same order - when moving from left to right and from bottom to top. Moreover, the acidic properties of oxides are stronger, the higher the oxidation state of the element that forms it.

By period from left to right basic properties hydroxides weaken; in the main subgroups, from top to bottom, the strength of the foundations increases. Moreover, if a metal can form several hydroxides, then with an increase in the oxidation state of the metal, basic properties hydroxides weaken.

By period from left to right the strength of oxygen-containing acids increases. When moving from top to bottom within one group, the strength of oxygen-containing acids decreases. In this case, the strength of the acid increases with increasing oxidation state of the acid-forming element.

By period from left to right the strength of oxygen-free acids increases. When moving from top to bottom within one group, the strength of oxygen-free acids increases.

Periodic table of chemical elements (periodic table)- classification of chemical elements, establishing the dependence of various properties of elements on the charge of the atomic nucleus. The system is a graphic expression of the periodic law established by the Russian chemist D. I. Mendeleev in 1869. Its original version was developed by D.I. Mendeleev in 1869-1871 and established the dependence of the properties of elements on their atomic weight (in modern terms, on atomic mass). In total, several hundred options for depicting the periodic system (analytical curves, tables, geometric figures, etc.) have been proposed. In the modern version of the system, it is assumed that the elements are summarized in a two-dimensional table, in which each column (group) defines the main physical and chemical properties, and the rows represent periods that are to a certain extent similar to each other.

Periodic table of chemical elements by D.I. Mendeleev

The discovery made by the Russian chemist Mendeleev played (by far) the most important role in the development of science, namely in the development of atomic-molecular science. This discovery made it possible to obtain the most understandable and easy-to-learn ideas about simple and complex chemical compounds. It is only thanks to the table that we have the concepts about the elements that we use in the modern world. In the twentieth century, the predictive role of the periodic system in assessing the chemical properties of transuranium elements, shown by the creator of the table, emerged.

Developed in the 19th century, Mendeleev's periodic table in the interests of the science of chemistry provided a ready-made systematization of the types of atoms for the development of PHYSICS in the 20th century (physics of the atom and the atomic nucleus). At the beginning of the twentieth century, physicists, through research, established that the atomic number (also known as atomic number) is also a measure of the electrical charge of the atomic nucleus of this element. And the number of the period (i.e., horizontal series) determines the number of electron shells of the atom. It also turned out that the number of the vertical row of the table determines the quantum structure of the outer shell of the element (thus, elements of the same row are obliged to have similar chemical properties).

The discovery of the Russian scientist marked a new era in the history of world science; this discovery not only made it possible to make a huge leap in chemistry, but was also invaluable for a number of other areas of science. The periodic table provided a coherent system of information about the elements, based on it, it became possible to draw scientific conclusions, and even anticipate some discoveries.

Periodic Table One of the features of the periodic table is that the group (column in the table) has more significant expressions of the periodic trend than for periods or blocks. Nowadays, the theory of quantum mechanics and atomic structure explains the group essence of elements by the fact that they have the same electronic configurations of valence shells, and as a result, elements that are located within the same column have very similar (identical) features of the electronic configuration, with similar chemical properties. There is also a clear tendency for a stable change in properties as the atomic mass increases. It should be noted that in some areas of the periodic table (for example, in blocks D and F), horizontal similarities are more noticeable than vertical ones.

The periodic table contains groups that are assigned serial numbers from 1 to 18 (from left to right), according to the international group naming system. In the past, Roman numerals were used to identify groups. In America, there was a practice of placing after the Roman numeral, the letter “A” when the group is located in blocks S and P, or the letter “B” for groups located in block D. The identifiers used at that time are the same as the latter the number of modern indexes in our time (for example, the name IVB corresponds to elements of group 4 in our time, and IVA is the 14th group of elements). In European countries of that time, a similar system was used, but here, the letter “A” referred to groups up to 10, and the letter “B” - after 10 inclusive. But groups 8,9,10 had ID VIII, as one triple group. These group names ceased to exist after the new IUPAC notation system, which is still used today, came into force in 1988.

Many groups received unsystematic names of a herbal nature (for example, “alkaline earth metals”, or “halogens”, and other similar names). Groups 3 to 14 did not receive such names, due to the fact that they are less similar to each other and have less compliance with vertical patterns; they are usually called either by number or by the name of the first element of the group (titanium, cobalt, etc.) .

Chemical elements belonging to the same group of the periodic table show certain trends in electronegativity, atomic radius and ionization energy. In one group, from top to bottom, the radius of the atom increases as the energy levels are filled, the valence electrons of the element move away from the nucleus, while the ionization energy decreases and the bonds in the atom weaken, which simplifies the removal of electrons. Electronegativity also decreases, this is a consequence of the fact that the distance between the nucleus and valence electrons increases. But there are also exceptions to these patterns, for example, electronegativity increases, instead of decreasing, in group 11, in the direction from top to bottom. There is a line in the periodic table called “Period”.

Among the groups, there are those in which horizontal directions are more significant (unlike others in which vertical directions are more important), such groups include block F, in which lanthanides and actinides form two important horizontal sequences.

Elements show certain patterns in atomic radius, electronegativity, ionization energy, and electron affinity energy. Due to the fact that for each subsequent element the number of charged particles increases, and electrons are attracted to the nucleus, the atomic radius decreases from left to right, along with this the ionization energy increases, and as the bond in the atom increases, the difficulty of removing an electron increases. Metals located on the left side of the table are characterized by a lower electron affinity energy indicator, and accordingly, on the right side the electron affinity energy indicator is higher for non-metals (not counting the noble gases).

Different regions of the periodic table, depending on which shell of the atom the last electron is located on, and in view of the importance of the electron shell, are usually described as blocks.

The S-block includes the first two groups of elements (alkali and alkaline earth metals, hydrogen and helium).
The P-block includes the last six groups, from 13 to 18 (according to IUPAC, or according to the system adopted in America - from IIIA to VIIIA), this block also includes all metalloids.

Block - D, groups 3 to 12 (IUPAC, or IIIB to IIB in American), this block includes all transition metals.
Block - F, is usually placed outside the periodic table, and includes lanthanides and actinides.

Periodic table of chemical elements. Periodic table of chemistry. el tov PERIODIC SYSTEM OF CHEMICAL ELEMENTS, a natural classification of chemical elements, which is a tabular expression of the periodic law. Modern... ... Illustrated Encyclopedic Dictionary

PERIODIC SYSTEM OF CHEMICAL ELEMENTS- created by D.I. Mendeleev and consists in the location of x. e. in a strictly defined order according to their atomic weight; properties x. e. are in close connection with their location in p.s., and the correct location is in the last x. e. made it possible... Dictionary of foreign words of the Russian language

periodic table of chemical elements- a natural system of chemical elements developed by D.I. Mendeleev on the basis of the periodic law discovered by him (1869). The modern formulation of this law is as follows: the properties of elements are periodically dependent on the charge... ... encyclopedic Dictionary

PERIODIC SYSTEM OF CHEMICAL ELEMENTS- natural chemical system elements, developed by D.I. Mendeleev on the basis of the periodicity discovered by him (1869). law. Modern The formulation of this law is as follows: the properties of elements are periodic. depending on the charge of their atomic nuclei. Charge... ...

PERIODIC SYSTEM OF CHEMICAL ELEMENTS- an ordered set of chemicals. elements, their natures. classification, which is a tabular expression of Mendeleev's periodic law. The prototype of the periodic chemical systems elements (P.s.) served as the table Experience of a system of elements based on their... ... Chemical encyclopedia

PERIODIC SYSTEM OF CHEMICAL ELEMENTS- Relative masses are given according to the 1995 International Table (accuracy given to the last significant digit). For elements that do not have stable nuclides (with the exception of Th, Pa and U, common in the earth’s crust), in square brackets ... ... Natural science. encyclopedic Dictionary

Periodic validity of chemical elements

Periodic Table of Chemical Elements- The periodic system of chemical elements (Mendeleev’s table) is a classification of chemical elements that establishes the dependence of various properties of elements on the charge of the atomic nucleus. The system is a graphic expression of the periodic law, ... ... Wikipedia

Periodic system of chemical elements- a system of chemical elements developed by the Russian scientist D.I. Mendeleev (1834-1907) based on the periodic law discovered by him (1869). The modern formulation of this law is as follows: the properties of elements are in a periodic... ... Concepts of modern natural science. Glossary of basic terms

PERIODIC SYSTEM OF ELEMENTS- PERIODIC SYSTEM OF ELEMENTS, periodic law. For a long time, attempts have been made to establish the dependence of the properties of elements on their atomic weight: Dobereiner (1817) pointed out triads of similar elements, between atomic weights to ... ... Great Medical Encyclopedia

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PERIODIC SYSTEM, an ordered set of chemicals. elements, their natures. , which is a table expression. The prototype of the periodic chemical systems elements was based on the table “Experience of a system of elements based on their chemical similarity,” compiled by D. I. Mendeleev on March 1, 1869 (Fig. 1). Lastly Over the years, the scientist improved the table, developed ideas about periods and groups of elements and the place of an element in the system. In 1870, Mendeleev called the system natural, and in 1871 periodic. As a result, even then the periodic system in many respects acquired its modern form.

structural outlines. Based on it, Mendeleev predicted the existence of saints ca. 10 unknown elements; these predictions were subsequently confirmed.

Rice. 1 Table “Experience of a system of elements based on their chemical similarity” (D. I. Mendeleev. I myrtle 1869).

However, over the next more than 40 years, the periodic table means. degree was only empirical. generalization of facts, since there was no physical explanation of reasons periodic. changes in CB-B elements depending on their increase. Such an explanation was impossible without well-founded ideas about the structure (see). The modern periodic system includes 109 chemical elements (there is information about the synthesis in 1988 of an element with Z = 110). Of these in natural objects found 89; all elements following U, or (Z = 93 109), as well as Tc (Z = 43), Pm (Z = 61) and At (Z = 85) were artificially synthesized using decomp. .

Elements with Z = 106 109 have not yet received names, so there are no corresponding symbols in the tables; for an element with Z = 109 the maximum values ​​are still unknown. long-lived

Over the entire history of the periodic table, more than 500 different versions of its image have been published. This was due to attempts to find a rational solution to certain controversial problems of the structure of the periodic table (placement of H, lanthanides, etc.). Naib.

Group VIII occupies a special place in the structure of the periodic table. For a long time time, only elements of the “triads” were attributed to it: Fe-Co-Ni and (Ru Rh Pd and Os-Ir-Pt), and all were placed in independent positions. zero group; therefore, the periodic table contained 9 groups. After in the 60s. were received conn. Xe, Kr and Rn began to be placed in subgroup VIIIa, and the zero group was abolished.

The elements of the triads made up subgroup VIII6. This “structural design” of group VIII now appears in almost all published expressions of the periodic table.

Will distinguish. The feature of the first period is that it contains only 2 elements: H and He. due to the holy - unities. an element that does not have a clearly defined place in the periodic table. The symbol H is placed either in subgroup Ia, or in subgroup VIIa, or in both at the same time, enclosing the symbol in brackets in one of the subgroups, or, finally, depicting it as separated. fonts. These ways of arranging H are based on the fact that it has certain formal similarities with both .

Rice. 2. Long form periodic.

chemical systems elements (modern version). Rice. 3. Ladder form periodic. chemical systems elements (H., 1921).The second period (Li-Ne), containing 8 elements, begins with Li (unity, + 1); followed by Be(+2). Metallic character B (+3) is weakly expressed, and the next one, C, is typical (+4). The following are N, O, F and Ne-non-metals, with only N having the highest + 5 corresponding to the group number; O and F are among the most active.

The third period (Na-Ar) also includes 8 elements, the nature of the chemical change. St. in which is in many ways similar to that observed in the second period. However, Mg and Al are more “metallic” than the corresponding ones. Be and B. The remaining elements are Si, P, S, Cl and Ar non-metals; they all exhibit , equal to the group number, except Ar. T.

The fourth period (K-Kr) contains 18 elements. After K and alkaline-earth. Ca (s-elements) follows a series of 10 so-called. transition (Sc-Zn), or d-elements (blue symbols), which are included in subgroups b. The majority (all of them - ) exhibit higher , equal to the group number, excluding the Fe-Co-Ni triad, where Fe under certain conditions has +6, and Co and Ni are maximally trivalent. Elements from Ga to Kr belong to subgroups a (p-elements), and the nature of the change in their properties is in many ways similar to the change in the properties of elements of the second and third periods in the corresponding intervals of Z values. For Kr, several were obtained. relatively stable compounds, mainly with F.

The fifth period (Rb-Xe) is constructed similarly to the fourth; it also has an insert of 10 transition, or d-elements (Y-Cd). Peculiarities of changes in the strength of elements in the period: 1) in the triad Ru-Rh-Pd shows a maximum of 4-8; 2) all elements of subgroups a, including Xe, exhibit higher values ​​equal to the group number; 3) I has weak metallic properties. St. T. example, the properties of the elements of the fourth and fifth periods change more complexly as Z increases than the properties of the elements in the second and third periods, which is primarily due to the presence of transition d-elements.

The sixth period (Cs-Rn) contains 32 elements. In addition to ten d-elements (La, Hf-Hg), it includes a family of 14 f-elements (black symbols, from Ce to Lu)-lanthanides. They are very similar in chemistry. Holy to you (preferably at +3) and therefore cannot. placed according to different system groups. In the short form of the periodic table, all lanthanides are included in subgroup IIIa (La), and their totality is deciphered below the table. This technique is not without its drawbacks, since the 14 elements appear to be outside the system.

The seventh period, like the sixth, should contain 32 elements, but is not yet completed. Fr and Ra elements respectively.

subgroups Ia and IIa, Ac is an analogue of elements of subgroup III6. According to the actinide concept of G. Seaborg (1944), after Ac comes a family of 14 f elements (Z = 90 103). In the short form of the periodic table, the latter are included in Ac and are similarly written as dept. line below the table. This technique assumed the presence of a certain chemical. similarities between elements of two f-families.

However, a detailed study showed that they exhibit a much wider range, including such as +7 (Np, Pu, Am). In addition, heavy ones are characterized by stabilization of lower ones (+ 2 or even +1 for Md). Chemical assessment nature of Ku (Z = 104) and Ns (Z = 105), synthesized in a number of single, very short-lived ones, allowed us to conclude that these elements are analogues of respectively. Hf and Ta, i.e. d-elements, and should be located in subgroups IV6 and V6.

The scheme for the formation of electronic configurations, which underlies the theory of the periodic system, thus reflects a certain sequence of appearance as Z grows of aggregates (subshells), characterized by certain values ​​of the principal and orbital (l) quantum numbers. This scheme is generally written in the form of a table.

(see below).

Vertical lines separate the subshells, which are filled into the elements that make up the sequence.

n

l

Number of elements in period

Starting from the sixth period, the construction of electronic configurations actually becomes more complex, which is expressed in the violation of clear boundaries between successively filled subshells. For example, the 4f electron appears not in La with Z = 57, but in the next one Ce (Z = 58); sequential the construction of the 4f subshell is interrupted in Gd (Z = 64, presence of a 5d electron).

Such a “blurring of periodicity” clearly affects the seventh period for Z > 89, which is reflected in the properties of the elements.

The real scheme was not originally derived from the k.-l. rigorous theoretical representations. It was based on well-known chem. holy elements and information about their spectra. Valid physical the real scheme received its justification through the application of methods to the description of the structure. In quantum mech. interpretation of the theory of structure, the concept of electronic shells and subshells with a strict approach has lost its original meaning; the concept of atomic is now widely used.

Nevertheless, the developed principle of physical interpretation of the phenomenon of periodicity has not lost its significance and, to a first approximation, explains the theoretical theory quite comprehensively. basics of the periodic table. In any case, the published forms of the periodic table reflect the idea of ​​the nature of the distribution among shells and subshells.Structure and chemical properties of elements.

Meaning of the periodic table. This system has played and continues to play a huge role in the development of pluralism. natural science disciplines.She became an important link in the atomic pier. teachings, contributed to the formulation of modern. the concept of "chemical element" and the clarification of ideas about simple substances and compounds. influence on the development of the theory of structure and the emergence of the concept of isotopy. Strictly scientific is connected with the periodic system. formulation of the forecasting problem in that

manifested itself both in the prediction of the existence of unknown elements and their properties, as well as new chemical features. behavior of already opened elements. The periodic table is the most important basis of inorg.