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The value of the periodic law of the Mendeleev system. The value of the periodic system and the periodic law D

In 1869, D. I. Mendeleev, based on an analysis of the properties of simple substances and compounds, formulated the Periodic Law: "The properties of simple bodies and compounds of elements are in a periodic dependence on the magnitude of the atomic masses of the elements." On the basis of the periodic law, the periodic system of elements was compiled. In it, elements with similar properties were combined into vertical columns of the group. In some cases, when placing elements in the Periodic system, it was necessary to violate the sequence of increasing atomic masses in order to observe the periodicity of the repetition of properties. For example, tellurium and iodine, as well as argon and potassium, had to be "swapped". The reason is that Mendeleev proposed the periodic law at a time when nothing was known about the structure of the atom. After the planetary model of the atom was proposed in the 20th century, the periodic law is formulated as follows:

"The properties of chemical elements and compounds are in a periodic dependence on the charges of atomic nuclei."

The charge of the nucleus is equal to the number of the element in the periodic system and the number of electrons in the electron shell of the atom. This formulation explained the "violations" of the Periodic Law. In the Periodic system, the period number is equal to the number of electronic levels in the atom, the group number for elements of the main subgroups is equal to the number of electrons in the outer level.

Scientific significance of the periodic law. The periodic law made it possible to systematize the properties of chemical elements and their compounds. When compiling the periodic system, Mendeleev predicted the existence of many yet undiscovered elements, leaving free cells for them, and predicted many properties of undiscovered elements, which facilitated their discovery. The first of these followed four years later.

But not only in the discovery of a new great merit of Mendeleev.

Mendeleev discovered a new law of nature. Instead of disparate, unrelated substances, a single harmonious system arose before science, uniting all the elements of the Universe into a single whole, atoms began to be considered as:

1. organically interconnected by a common pattern,

2. detecting the transition of quantitative changes in atomic weight to qualitative changes in their chemical. personalities,

3. indicating that the opposite of metallic. and non-metallic properties of atoms is not absolute, as previously thought, but only relative.

24. The emergence of structural theories in the development of organic chemistry. Atomic-molecular theory as a theoretical basis for structural theories.

Organic chemistry. Throughout the 18th century in the question of the chemical relationships between organisms and substances, scientists were guided by the doctrine of vitalism - a doctrine that considered life as a special phenomenon, subject not to the laws of the universe, but to the influence of special vital forces. This view was inherited by many scientists of the 19th century, although its foundations were shaken as early as 1777, when Lavoisier suggested that respiration is a process analogous to combustion.

In 1828, the German chemist Friedrich Wöhler (1800–1882), heating ammonium cyanate (this compound was unconditionally considered an inorganic substance), obtained urea, a waste product of humans and animals. In 1845, Adolf Kolbe, a student of Wöhler, synthesized acetic acid from the starting elements carbon, hydrogen, and oxygen. In the 1850s, the French chemist Pierre Berthelot began systematic work on the synthesis of organic compounds and obtained methyl and ethyl alcohols, methane, benzene, and acetylene. A systematic study of natural organic compounds has shown that they all contain one or more carbon atoms and very many contain hydrogen atoms. Type theory. The discovery and isolation of a huge number of complex carbon-containing compounds sharply raised the question of the composition of their molecules and led to the need to revise the existing classification system. By the 1840s, chemists realized that Berzelius' dualistic ideas only applied to inorganic salts. In 1853 an attempt was made to classify all organic compounds by type. A generalized "theory of types" was proposed by the French chemist Charles Frederic Gerard, who believed that the association of various groups of atoms is determined not by the electric charge of these groups, but by their specific chemical properties.

Structural chemistry. In 1857, Kekule, proceeding from the theory of valency (by valency was understood as the number of hydrogen atoms that combine with one atom of a given element), suggested that carbon is tetravalent and therefore can combine with four other atoms, forming long chains - straight or branched. Therefore, organic molecules began to be depicted not as combinations of radicals, but as structural formulas - atoms and bonds between them.

In 1874 a Danish chemist Jacob van't Hoff and the French chemist Joseph Achille Le Bel (1847–1930) extended this idea to the arrangement of atoms in space. They believed that molecules are not flat, but three-dimensional structures. This concept made it possible to explain many well-known phenomena, such as spatial isomerism, the existence of molecules of the same composition but with different properties. The data fit very well. Louis Pasteur about the isomers of tartaric acid.

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The first version of the Periodic Table of the Elements was published by Dmitri Ivanovich Mendeleev in 1869 - long before the structure of the atom was studied. The reference point in this work for D. I. Mendeleev was the atomic masses (atomic weights) of the elements. Arranging the elements in ascending order of their atomic weights, D. I. Mendeleev discovered a fundamental law of nature, which is now known as the Periodic Law: The properties of elements change periodically in accordance with their atomic weight.

The fundamental novelty of the Periodic Law, discovered and formulated by D. I. Mendeleev, was as follows:

1. A connection was established between elements NOT SIMILAR in their properties. This relationship lies in the fact that the properties of the elements change smoothly and approximately equally with an increase in their atomic weight, and then these changes are PERIODICALLY REPEATED.

2. In those cases where it seemed that some link was missing in the sequence of changes in the properties of elements, the Periodic Table provided for GAPS that had to be filled with yet undiscovered elements. Moreover, the Periodic Law made it possible to PREDICT the properties of these elements.

In all previous attempts to determine the relationship between elements, other researchers sought to create a complete picture in which there was no place for elements not yet discovered.

It is admirable that D. I. Mendeleev made his discovery at a time when the atomic weights of many elements were determined very approximately, and only 63 elements were known - that is, a little more than half of those known to us today.

The periodic law according to Mendeleev: "The properties of simple bodies ... and compounds of elements are in a periodic dependence on the magnitude of the atomic masses of the elements."

On the basis of the periodic law, the periodic system of elements was compiled. In it, elements with similar properties were combined into vertical columns of the group. In some cases, when placing elements in the Periodic system, it was necessary to violate the sequence of increasing atomic masses in order to observe the periodicity of the repetition of properties. For example, tellurium and iodine, as well as argon and potassium, had to be "swapped".

However, even after the huge and careful work of chemists to correct atomic weights, in four places of the Periodic Table the elements "violate" the strict order of arrangement in increasing atomic mass.

At the time of D. I. Mendeleev, such deviations were considered shortcomings of the Periodic system. The theory of the structure of the atom put everything in its place: the elements are arranged quite correctly - in accordance with the charges of their nuclei. How, then, to explain that the atomic weight of argon is greater than the atomic weight of potassium?

The atomic weight of any element is equal to the average atomic weight of all its isotopes, taking into account their abundance in nature. By chance, the atomic weight of argon is determined by the most "heavy" isotope (it occurs in nature in greater quantities). Potassium, on the contrary, is dominated by its "lighter" isotope (that is, an isotope with a lower mass number).

The reason is that Mendeleev proposed the periodic law at a time when nothing was known about the structure of the atom. After the planetary model of the atom was proposed in the 20th century, the periodic law is formulated as follows:

"The properties of chemical elements and compounds are in a periodic dependence on the charges of atomic nuclei."

The reason for the periodic change in the properties of chemical elements is the periodic filling of electron shells. After filling the next shell, a new period begins. The periodic change of elements is clearly seen in the change in the composition and properties of oxides.

The scientific significance of the periodic law.

The periodic law made it possible to systematize the properties of chemical elements and their compounds. When compiling the periodic system, Mendeleev predicted the existence of many yet undiscovered elements, leaving free cells for them, and predicted many properties of undiscovered elements, which facilitated their discovery. The first of these followed four years later. The element for which Mendeleev left a place and properties, the atomic weight of which he predicted, suddenly appeared! The young French chemist Lecoq de Boisbaudran sent a letter to the Paris Academy of Sciences. It said:<Позавчера, 27 августа 1875 года, между двумя и четырьмя часами ночи я обнаружил новый элемент в минерале цинковая обманка из рудника Пьерфитт в Пиренеях>. But the most amazing thing was yet to come. Mendeleev predicted, while still leaving room for this element, that its density should be 5.9. And Boisbaudran claimed: the element he discovered has a density of 4.7. Mendeleev, who did not see the new element in his eyes - that's all the more surprising - said that the French chemist made a mistake in the calculations. But Boisbaudran also turned out to be stubborn: he assured that he was accurate. A little later, after additional measurements, it turned out that Mendeleev was unconditionally right. The first element that filled the empty space in the table, Boisbaudran named gallium in honor of his homeland of France. And then it never occurred to anyone to give him the name of the person who predicted the existence of this element, the person who once and for all predetermined the path of development of chemistry. This was done by the scientists of the twentieth century. The name of Mendeleev is an element discovered by Soviet physicists.

But not only in the discovery of a new great merit of Mendeleev.

1. organically interconnected by a common pattern,

2. detecting the transition of quantitative changes in atomic weight to qualitative changes in their chemical. personalities,

3. indicating that the opposition between metallic and non-metallic properties of atoms is not absolute, as previously thought, but only relative.

The discovery of the mutual connection between all the elements, between their physical and chemical properties, posed a scientific and philosophical problem of great importance: this mutual connection, this unity must be explained.

Mendeleev's research gave a solid and reliable foundation to attempts to explain the structure of the atom: after the discovery of the periodic law, it became clear that the atoms of all elements must be built “according to a single plan”, that their structure must reflect the periodicity of the properties of the elements.

Only that model of the atom could have the right to recognition and development, which would bring science closer to understanding the riddle of the position of the element in the periodic table. The greatest scientists of our century, solving this big problem, revealed the structure of the atom - so Mendeleev's law had a huge impact on the development of all modern knowledge about the nature of matter.

All the successes of modern chemistry, the successes of atomic and nuclear physics, including atomic energy and the synthesis of artificial elements, have become possible only thanks to the periodic law. In turn, the successes of atomic physics, the emergence of new research methods, and the development of quantum mechanics have expanded and deepened the essence of the periodic law.

Over the past century, Mendeleev's law - the true law of nature - not only has not become outdated and has not lost its significance. On the contrary, the development of science has shown that its meaning is not yet fully known and not completed, that it is much wider than its creator could have imagined, than scientists thought until recently. It has recently been established that not only the structure of the outer electron shells of an atom, but also the fine structure of atomic nuclei obeys the law of periodicity. Apparently, the regularities that govern the complex and in many respects not understood world of elementary particles also have a periodic nature in their basis.

Further discoveries in chemistry and physics repeatedly confirmed the fundamental meaning of the Periodic Law. Inert gases were discovered that fit perfectly into the Periodic Table - this is especially clearly shown by the long form of the table. The serial number of the element turned out to be equal to the charge of the nucleus of the atom of this element. Many previously unknown elements were discovered thanks to a targeted search for precisely those properties that were predicted by the Periodic Table.

The periodic law of D. I. Mendeleev is of exceptionally great importance. He laid the foundation for modern chemistry, made it a single, holistic science. Elements began to be considered in interrelation, depending on what place they occupy in the periodic system. Chemistry has ceased to be a descriptive science. With the discovery of the periodic law, scientific foresight became possible in it. It became possible to predict and describe new elements and their compounds. A brilliant example of this is the prediction by D. I. Mendeleev of the existence of elements not yet discovered in his time, of which for three - Ga, Sc, Ge - he gave an accurate description of their properties.

Based on the law of D. I. Mendeleev, all empty cells of his system from Z=1 to Z=92 were filled, and transuranium elements were also discovered. And today this law serves as a guideline for the discovery or artificial creation of new chemical elements. So, guided by the periodic law, it can be argued that if the element Z=114 is synthesized, then it will be an analogue of lead (ekaslead), if the element Z=118 is synthesized, then it will be a noble gas (ekaradon).

Russian scientist N. A. Morozov in the 80s of the XIX century predicted the existence of noble gases, which were then discovered. In the periodic system, they complete the periods and constitute the main subgroup of group VII. “Before the periodic law,” D. I. Mendeleev wrote, “the elements represented only fragmentary random phenomena of nature; there was no reason to expect any new ones, and the newly found ones were a complete unexpected novelty. Periodic regularity was the first to make it possible to see still undiscovered elements in such a distance, to which sight, unarmed with this regularity, until then had not reached.

The periodic law served as the basis for correcting the atomic masses of the elements. For 20 elements, D. I. Mendeleev corrected the atomic masses, after which these elements took their places in the periodic system.

On the basis of the periodic law and the periodic system of D. I. Mendeleev, the theory of the structure of the atom rapidly developed. It revealed the physical meaning of the periodic law and explained the arrangement of elements in the periodic system. The correctness of the doctrine of the structure of the atom has always been tested by the periodic law. Here is another example. In 1921, N. Bohr showed that the element Z = 72, whose existence was predicted by D. I. Mendeleev in 1870 (ekabor), should have an atomic structure similar to that of zirconium (Zr - 2.8.18.10 . 2; a Hf - 2. 8. 18. 32. 10. 2), and therefore it should be sought among zirconium minerals. Following this advice, in 1922 the Hungarian chemist D. Hevesy and the Dutch scientist D. Koster discovered the element Z=72 in Norwegian zirconium ore, calling it hafnium (from the Latin name of Copenhagen, the place where the element was discovered). This was the greatest triumph of the theory of the structure of the atom: on the basis of the structure of the atom, the location of the element in nature was predicted.

The doctrine of the structure of atoms led to the discovery of atomic energy and its use for human needs. We can say that the periodic law is the primary source of all the discoveries of chemistry and physics of the XX century. He played an outstanding role in the development of other natural sciences related to chemistry.

The periodic law and the system underlie the solution of modern problems of chemical science and industry. Taking into account the periodic system of chemical elements of D. I. Mendeleev, work is underway to obtain new polymer and semiconductor materials, heat-resistant alloys, substances with desired properties, to use nuclear energy, the bowels of the Earth and the Universe are used.

The Periodic Table of the Elements had a great influence on the subsequent development of chemistry.

Dmitry Ivanovich Mendeleev (1834-1907)

Not only was it the first natural classification of the chemical elements, which showed that they form a coherent system and are in close connection with each other, but it was also a powerful tool for further research.

At the time when Mendeleev compiled his table on the basis of the periodic law he discovered, many elements were still unknown. So, the element of the fourth period, scandium, was unknown. In terms of atomic weight, titanium followed calcium, but titanium could not be placed immediately after calcium, since it would fall into the third group, while titanium forms the highest oxide, and, according to other properties, should be assigned to the fourth group. Therefore, Mendeleev skipped one cell, i.e., left a free space between calcium and titanium. On the same basis, in the fourth period, two free cells were left between zinc and arsenic, now occupied by the elements gallium and germanium. There were also empty seats in other rows. Mendeleev was not only convinced that there must be elements yet unknown to fill these places, but he also predicted the properties of such elements in advance, based on their position among other elements of the periodic system. One of them, which in the future was to take a place between calcium and titanium, he gave the name ekabor (since its properties were supposed to resemble boron); the other two, for which there were empty places in the table between zinc and arsenic, were called eka-aluminum and ekasilicium.

Over the next 15 years, Mendeleev's predictions were brilliantly confirmed: all three expected elements were discovered. First, the French chemist Lecoq de Boisbaudran discovered gallium, which has all the properties of ekaaluminum; after that, scandium, which had the properties of ecabor, was discovered in Sweden by L. F. Nilson, and, finally, a few more years later, in Germany, K. A. Winkler discovered an element that he called germanium, which turned out to be identical to ecasilium.

To judge the amazing accuracy of Mendeleev's prediction, let's compare the properties of ecasilicon predicted by him in 1871 with the properties of germanium discovered in 1886:

The discovery of gallium, scandium and germanium was the greatest triumph of the periodic law.

The periodic system was also of great importance in establishing the valency and atomic masses of certain elements. Thus, the element beryllium has long been considered an analogue of aluminum, and its oxide was assigned the formula . Based on the percentage composition and the proposed formula of beryllium oxide, its atomic mass was considered equal to 13.5. The periodic system showed that there is only one place for beryllium in the table, namely, above magnesium, so its oxide must have the formula , whence the atomic mass of beryllium is equal to ten. This conclusion was soon confirmed by the determination of the atomic mass of beryllium from the vapor density of its chloride.

Exactly And today the periodic law remains the guiding thread and the guiding principle of chemistry. It is on its basis that transuranium elements have been artificially created in recent decades, located in the periodic system after uranium. One of them - element No. 101, first obtained in 1955 - was named mendelevium in honor of the great Russian scientist.

The discovery of the periodic law and the creation of a system of chemical elements was of great importance not only for chemistry, but also for philosophy, for our entire understanding of the world. Mendeleev showed that the chemical elements constitute a coherent system, which is based on the fundamental law of nature. This is the expression of the position of materialist dialectics on the interconnection and interdependence of natural phenomena. Revealing the relationship between the properties of chemical elements and the mass of their atoms, the periodic law was a brilliant confirmation of one of the universal laws of the development of nature - the law of the transition of quantity into quality.

The subsequent development of science made it possible, relying on the periodic law, to know the structure of matter much more deeply than was possible during the life of Mendeleev.

The theory of the structure of the atom developed in the 20th century, in turn, gave the periodic law and the periodic system of elements a new, deeper illumination. Brilliant confirmation was found by Mendeleev's prophetic words: "The periodic law is not threatened with destruction, but only a superstructure and development are promised."

Introduction

Chemistry has ceased to be a descriptive science. With the discovery of the periodic law, scientific foresight became possible in it. It became possible to predict and describe new elements and their compounds ... A brilliant example of this is the prediction by D. I. Mendeleev of the existence of elements not yet discovered in his time, of which for three - Ga, Sc and Ge - he gave an accurate description of their properties.

The periodic system and its significance for understanding the scientific picture of the world

The periodic system of elements of D. I. Mendeleev, the natural classification of chemical elements, which is a tabular (or other graphical) expression periodic law of Mendeleev. P. s. e. developed by D.I. Mendeleev in 1869-1871.

P.'s history with. e. Attempts to systematize the chemical elements have been made by various scientists in Germany, France, England, and the USA since the 1930s. Mendeleev's predecessors - I. Döbereiner, AND. Dumas, French chemist A. Shancourtua, eng. chemists W. Odling, J. Newlands, and others established the existence of groups of elements that are similar in chemical properties, the so-called "natural groups" (for example, Döbereiner's "triad"). However, these scientists did not go further than establishing particular patterns within groups. In 1864 L. Meyer based on data on atomic weights, he proposed a table showing the ratio of atomic weights for several characteristic groups of elements. Meyer did not make theoretical reports from his table.

The prototype of scientific P. s. e. the table “Experience of a system of elements based on their atomic weight and chemical similarity” appeared, compiled by Mendeleev on March 1, 1869. Over the next two years, the author improved this table, introduced ideas about groups, series and periods of elements; made an attempt to estimate the capacity of small and large periods, containing, in his opinion, 7 and 17 elements, respectively. In 1870 he called his system natural, and in 1871 - periodic. Even then P.'s structure with. e. took on a more modern shape.

Extremely important for P.'s evolution of page. e. the idea introduced by Mendeleev about the place of an element in the system turned out to be; the position of the element is determined by the period and group numbers. Based on this idea, Mendeleev came to the conclusion that it was necessary to change the then accepted atomic weights of certain elements (U, In, Ce, and its analogues), which was the first practical application of P. s. e., and also for the first time predicted the existence and basic properties of several unknown elements, which corresponded to the empty cells of P. s. e. A classic example is the prediction of "ekaaluminum" (the future Ga, discovered by P. Lecoq de Boisbaudran in 1875), "ekabora" (Sc, discovered by the Swedish scientist L. Nilson in 1879) and “ecasilience” (Ge, discovered by the German scientist K. Winkler in 1886). In addition, Mendeleev predicted the existence of analogues of manganese (future Tc and Re), tellurium (Po), iodine (At), cesium (Fr), barium (Ra), tantalum (Pa).

P. s. e. did not immediately win recognition as a fundamental scientific generalization; the situation changed significantly only after the discovery of Ga, Sc, Ge and the establishment of the divalence of Be (it was considered trivalent for a long time). Nevertheless P. with. e. in many respects represented an empirical generalization of facts, since the physical meaning of the periodic law was unclear and there was no explanation of the reasons for the periodic change in the properties of elements depending on the increase in atomic weights. Therefore, up to the physical substantiation of the periodic law and the development of the theory of P. s. e. many facts could not be explained. So, unexpected was the discovery at the end of the 19th century. inert gases, which seemed to find no place in P. s. e.; this difficulty was eliminated thanks to inclusion in P. of page. e. independent zero group (later VIII a-subgroups). The discovery of many "radio elements" at the beginning of the 20th century. led to the contradiction between necessity of their placement in P. of page. e. and its structure (for more than 30 such elements, there were 7 "vacant" places in the sixth and seventh periods). This contradiction was overcome by the discovery isotopes. Finally, the value of the atomic weight (atomic mass) as a parameter that determines the properties of elements gradually lost its significance.

One of the main reasons for the impossibility of explaining the physical meaning of the periodic law and P. s. e. consisted in the absence of a theory of the structure of the atom. Therefore, the most important milestone on the path of P.'s development with. e. was the planetary model of the atom, proposed by E. Rutherford(1911). On its basis, the Dutch scientist A. van den Broek suggested (1913) that the ordinal number of an element in P. s. e. (atomic number Z) is numerically equal to the charge of the atomic nucleus (in units of elementary charge). This was experimentally confirmed by G. Moseley(1913-14, see mosley law). So it was possible to establish that the periodicity of changes in the properties of elements depends on the atomic number, and not on the atomic weight. As a result, on a scientific basis, the lower limit of P. s was determined. e. (hydrogen as element with minimum Z = 1); the number of elements between hydrogen and uranium has been accurately estimated; it is established that "gaps" in P. of page. e. correspond to unknown elements with Z = 43, 61, 72, 75, 85, 87.

However, the question of the exact number of rare-earth elements remained unclear, and (which is especially important) the reasons for the periodic change in the properties of elements depending on Z were not revealed. These reasons were found in the course of further development of the theory of P. s. e. based on quantum ideas about the structure of the atom (see below). The physical substantiation of the periodic law and the discovery of the phenomenon of isotonia made it possible to scientifically define the concept of "atomic mass" ("atomic weight"). The attached periodic table contains the modern values of the atomic masses of the elements on the carbon scale in accordance with the International Table of 1973. The mass numbers of the longest-lived isotopes of radioactive elements are given in square brackets. Instead of the mass numbers of the most stable isotopes 99 Tc, 226 Ra, 231 Pa, and 237 Np, the atomic masses of these isotopes adopted (1969) by the International Commission on Atomic Weights are given.

P.'s structure with. e. Modern (1975) P. s. e. covers 106 chemical elements; of these, all transuranium (Z = 93-106), as well as elements with Z = 43 (Tc), 61 (Pm), 85 (At) and 87 (Fr) were obtained artificially. For the entire history of P. s. e. a large number (several hundreds) of variants of its graphic representation were proposed, mainly in the form of tables; images are also known in the form of various geometric figures (spatial and planar), analytical curves (for example, spirals), etc. The most widespread are three forms of P. s. e .: short, proposed by Mendeleev and received universal recognition; long staircase. The long form was also developed by Mendeleev, and in an improved form it was proposed in 1905 by A. Werner. The ladder form was proposed by the English scientist T. Bailey (1882), the Danish scientist J. Thomsen (1895) and improved by N. Borom(1921). Each of the three forms has advantages and disadvantages. The fundamental principle of constructing P. s. e. is the division of all chemical elements into groups and periods. Each group, in turn, is divided into the main (a) and secondary (b) subgroups. Each subgroup contains elements that have similar chemical properties. Elements A- And b- subgroups in each group, as a rule, show a certain chemical similarity among themselves, mainly in higher oxidation states, which, as a rule, correspond to the group number. A period is a set of elements starting with an alkali metal and ending with an inert gas (a special case is the first period); Each period contains a strictly defined number of elements. P. s. e. consists of 8 groups and 7 periods (the seventh has not yet been completed).

The specificity of the first period is that it contains only 2 elements: H and He. The place of H in the system is ambiguous: since it exhibits properties common with alkali metals and halogens, it is placed either in I a-, or (preferably) in VII a-subgroup. Helium - the first representative of VII a- subgroups (however, for a long time, He and all inert gases were combined into an independent zero group).

The second period (Li - Ne) contains 8 elements. It begins with the alkali metal Li, whose only oxidation state is I. Then comes Be, a metal, oxidation state II. The metallic nature of the next element B is weakly expressed (oxidation state III). The C following it is a typical non-metal, it can be both positively and negatively tetravalent. The subsequent N, O, F and Ne are non-metals, and only N has the highest oxidation state V corresponding to the group number; oxygen only in rare cases exhibits a positive valency, and for F, the oxidation state VI is known. The period is completed by the inert gas Ne.

The third period (Na - Ar) also contains 8 elements, the nature of the change in the properties of which is largely similar to that observed in the second period. However, Mg, unlike Be, is more metallic, as is Al compared to B, although Al is inherently amphoteric. Si, P, S, Cl, Ar are typical non-metals, but all of them (except Ar) exhibit higher oxidation states equal to the group number. Thus, in both periods, as Z increases, a weakening of the metallic and strengthening of the non-metallic nature of the elements is observed. Mendeleev called the elements of the second and third periods (small, in his terminology) typical. It is significant that they are among the most common in nature, and C, N and O, along with H, are the main elements of organic matter (organogens). All elements of the first three periods are included in subgroups A .

According to modern terminology (see below), the elements of these periods refer to s-elements (alkali and alkaline earth metals), constituting I a- and II a subgroups (highlighted in red in the color table), and R-elements (B - Ne, At - Ar) included in III a- VIII a-subgroups (their symbols are highlighted in orange). For elements of small periods, with increasing serial numbers, a decrease is first observed atomic radii, and then, when the number of electrons in the outer shell of the atom already increases significantly, their mutual repulsion leads to an increase in atomic radii. The next maximum is reached at the beginning of the next period on an alkaline element. Approximately the same regularity is typical for ionic radii.

The fourth period (K - Kr) contains 18 elements (the first large period, according to Mendeleev). The alkali metal K and the alkaline earth Ca (s-elements) are followed by a series of ten so-called transition elements(Sc - Zn), or d- elements (symbols are given in blue) that are included in subgroups b the corresponding groups of P. of page. e. Most transition elements (all of them metals) exhibit higher oxidation states equal to the group number. The exception is the triad Fe - Co - Ni, where the last two elements are maximally positively trivalent, and iron under certain conditions is known in the oxidation state VI. Elements from Ga to Kr ( R-elements), belong to subgroups A, and the nature of the change in their properties is the same as in the corresponding intervals Z for elements of the second and third periods. It has been established that Kr is able to form chemical compounds (mainly with F), but the oxidation state VIII is unknown for it.

The fifth period (Rb - Xe) is constructed similarly to the fourth; it also has an insert of 10 transition elements (Y - Cd), d-elements. Specific features of the period: 1) in the triad Ru - Rh - Pd, only ruthenium exhibits oxidation state VIII; 2) all elements of subgroups a show the highest oxidation states equal to the group number, including Xe; 3) I has weak metallic properties. Thus, the nature of the change in properties as Z increases for the elements of the fourth and fifth periods is more complicated, since the metallic properties are preserved in a large range of serial numbers.

The sixth period (Cs - Rn) includes 32 elements. In addition to 10 d-elements (La, Hf - Hg) contains a set of 14 f-elements, lanthanides, from Ce to Lu (characters in black). The elements La to Lu are chemically very similar. In short form P. s. e. the lanthanides are included in the box La (because their predominant oxidation state is III) and are listed on a separate line at the bottom of the table. This technique is somewhat inconvenient, since 14 elements are, as it were, outside the table. The long and ladder forms P. of page are deprived of a similar lack. e., well reflecting the specifics of lanthanides against the background of the integral structure of P. s. e. Features of the period: 1) in the triad Os - Ir - Pt, only osmium exhibits oxidation state VIII; 2) At has a more pronounced (compared to 1) metallic character; 3) Rn, apparently (its chemistry is little studied), should be the most reactive of the inert gases.

The seventh period, starting from Fr (Z = 87), should also contain 32 elements, of which 20 are known so far (before the element with Z = 106). Fr and Ra - elements respectively I a- and II a-subgroups (s-elements), Ac - analogue of elements III b-subgroups ( d-element). The next 14 elements, f-elements (with Z from 90 to 103), make up the family actinides. In short form P. s. e. they occupy the Ac cell and are written in a separate line at the bottom of the table, like the lanthanides, in contrast to which they are characterized by a significant variety of oxidation states. In connection with this, the series of lanthanides and actinides show noticeable differences in chemical terms. The study of the chemical nature of elements with Z = 104 and Z = 105 showed that these elements are analogues of hafnium and tantalum, respectively, that is d-elements, and should be placed in IV b- and V b-subgroups. Members b-subgroups there should be subsequent elements up to Z = 112, and then (Z = 113-118) will appear R-elements (III a- VIll a-subgroups).

P.'s theory with. e. At the heart of P.'s theory of page. e. lies the idea of the specific regularities in the construction of electron shells (layers, levels) and subshells (shells, sublevels) in atoms as Z increases. e. and the results of studying their atomic spectra. Bohr revealed three essential features of the formation of electronic configurations of atoms: 1) the filling of electron shells (except for shells corresponding to the values of the main quantum number n= 1 and 2) does not occur monotonically until their full capacity, but is interrupted by the appearance of sets of electrons belonging to shells with large values n; 2) similar types of electronic configurations of atoms are periodically repeated; 3) the boundaries of the periods of P. s. e. (with the exception of the first and second) do not coincide with the boundaries of successive electron shells.

P.'s value with. e. P. s. e. played and continues to play a huge role in the development of natural sciences. It was the most important achievement of atomic and molecular science, made it possible to give a modern definition of the concept of "chemical element" and clarify the concepts of simple substances and compounds. Patterns revealed by P. s. e., had a significant impact on the development of the theory of the structure of atoms, contributed to the explanation of the phenomenon of isotony. THX. e. A strictly scientific formulation of the problem of forecasting in chemistry is connected, which manifested itself both in the prediction of the existence of unknown elements and their properties, and in the prediction of new features of the chemical behavior of already discovered elements. P. s. e. - the foundation of chemistry, primarily inorganic; it significantly helps in solving problems of synthesizing substances with predetermined properties, developing new materials, in particular semiconductor materials, selecting specific catalysts for various chemical processes, and so on. P. s. e. is also the scientific basis for teaching chemistry.

Conclusion

The periodic system of D. I. Mendeleev has become an important milestone in the development of atomic and molecular science. Thanks to her, a modern concept of a chemical element was formed, ideas about simple substances and compounds were clarified.

The predictive role of the periodic system, shown by Mendeleev himself, in the 20th century manifested itself in the assessment of the chemical properties of transuranium elements.

The appearance of the periodic system opened a new, truly scientific era in the history of chemistry and a number of related sciences - instead of scattered information about elements and compounds, a harmonious system appeared, on the basis of which it became possible to generalize, draw conclusions, and foresee.

periodic law of mendeleev atom

The periodic law made it possible to bring into the system and generalize a huge amount of scientific information in chemistry. This function of the law is called integrative. It manifests itself especially clearly in the structuring of the scientific and educational material of chemistry. Academician A.E. Fersman said that the system united all chemistry within the framework of a single spatial, chronological, genetic, energy connection.

The integrative role of the Periodic Law was also manifested in the fact that some data on the elements, allegedly falling out of general patterns, were verified and refined both by the author himself and by his followers.

This happened with the characteristics of beryllium. Prior to Mendeleev's work, it was considered a trivalent analogue of aluminum due to their so-called diagonal similarity. Thus, in the second period there were two trivalent elements and not a single divalent element. It was at this stage, first at the level of mental model constructions, that Mendeleev suspected an error in the study of the properties of beryllium. Then he found the work of the Russian chemist Avdeev, who claimed that beryllium is divalent and has an atomic weight of 9. Avdeev's work remained unnoticed by the scientific world, the author died early, apparently having been poisoned by extremely poisonous beryllium compounds. The results of Avdeev's research were established in science thanks to the Periodic Law.

Such changes and refinements of the values of both atomic weights and valences were made by Mendeleev for nine more elements (In, V, Th, U, La, Ce and three other lanthanides). Ten more elements had only atomic weights corrected. And all these refinements were subsequently confirmed experimentally.

In the same way, the work of Karl Karlovich Klaus helped Mendeleev to form a kind of VIII group of elements, explaining the horizontal and vertical similarities in the triads of elements:

iron cobalt nickel

Ruthenium Rhodium Palladium

octium iridium platinum

The prognostic (predictive) function of the Periodic Law received the most striking confirmation in the discovery of unknown elements with serial numbers 21, 31 and 32. Their existence was first predicted on an intuitive level, but with the formation of the system, Mendeleev was able to calculate their properties with a high degree of accuracy. The well-known story of the discovery of scandium, gallium and germanium was the triumph of Mendeleev's discovery. F. Engels wrote: “By unconsciously applying the Hegelian law on the transition of quantity into quality, Mendeleev accomplished a scientific feat that can be safely put next to the discovery of Laverrier, who calculated the orbit of the unknown planet Neptune.” However, there is a desire to argue with the classic. First, all of Mendeleev's research, starting from his student years, quite consciously relied on the Hegelian law. Secondly, Laverrier calculated the orbit of Neptune according to the long-known and proven laws of Newton, and D. I. Mendeleev made all predictions on the basis of the universal law of nature discovered by him.

At the end of his life, Mendeleev noted with satisfaction: “While writing in 1871 an article on the application of the periodic law to the determination of the properties of elements not yet discovered, I did not think that I would live to justify this consequence of the periodic law, but reality answered differently. Three elements were described by me: ecabor, ecaaluminum and ecasilicium, and less than 20 years later I had the greatest joy to see all three discovered ... L. de Boisbaudran, Nilsson and Winkler, for my part, I consider true reinforcers of the periodic law. Without them, it would not have been recognized to the same extent as it is now.” In total, Mendeleev predicted twelve elements.

From the very beginning, Mendeleev pointed out that the law describes the properties not only of the chemical elements themselves, but also of many of their compounds, including hitherto unknown ones. It suffices to give an example to confirm this. Since 1929, when Academician P. L. Kapitsa first discovered the non-metallic conductivity of germanium, the development of the theory of semiconductors began in all countries of the world. It immediately became clear that elements with such properties occupy the main subgroup of group IV. Over time, the understanding came that compounds of elements located in periods equidistant from this group (for example, with a general formula like AzB;) should have semiconductor properties to a greater or lesser extent. This immediately made the search for new practically important semiconductors purposeful and predictable. Almost all modern electronics is based on such connections.

It is important to note that predictions within the framework of the Periodic System were made even after its universal recognition. In 1913 Mose-lee discovered that the wavelength of X-rays, which are obtained from anticathodes made from different elements, changes regularly depending on the serial number conventionally assigned to the elements in the Periodic system. The experiment confirmed that the atomic number of an element has a direct physical meaning. Only later were serial numbers associated with the value of the positive charge of the nucleus. On the other hand, Moseley's law made it possible to immediately experimentally confirm the number of elements in periods and, at the same time, to predict the places of hafnium (No. 72) and rhenium (No. 75) that had not yet been discovered by that time.

The same studies by Moseley made it possible to remove the serious "headache" that Mendeleev was given by certain deviations from the correct series of elements increasing in the table of atomic masses. Mendeleev made them under the pressure of chemical analogies, partly at the expert level, and partly at the intuitive level. For example, cobalt was ahead of nickel in the table, and iodine with a lower atomic weight followed heavier tellurium. It has long been known in the natural sciences that one "ugly" fact, which does not fit into the framework of the most beautiful theory, can ruin it. Similarly, unexplained deviations threatened the Periodic Law. But Moseley experimentally proved that the serial numbers of cobalt (No. 27) and nickel (No. 28) correspond exactly to their position in the system. It turned out that these exceptions only confirm the general rule.

An important prediction was made in 1883 by Nikolai Aleksandrovich Morozov. For participation in the Narodnaya Volya movement, chemistry student Morozov was sentenced to death, later commuted to life imprisonment in solitary confinement. He spent about thirty years in royal prisons. A prisoner of the Shlisselburg fortress had the opportunity to receive some scientific literature on chemistry. Based on the analysis of the intervals of atomic weights between neighboring groups of elements in the periodic table, Morozov came to an intuitive conclusion about the possibility of the existence of another group of unknown elements with "zero properties" between the groups of halogens and alkali metals. He suggested looking for them in the composition of the air. Moreover, he put forward a hypothesis about the structure of atoms and, on its basis, tried to reveal the causes of periodicity in the properties of elements.

However, Morozov's hypotheses became available for discussion much later, when he was released after the events of 1905. But by that time, inert gases had already been discovered and studied.

For a long time, the fact of the existence of inert gases and their position in the periodic table caused serious controversy in the chemical world. Mendeleev himself for some time believed that an unknown simple substance of the type Nj could be hidden under the name of the discovered argon. The first rational assumption about the place of inert gases was made by the author of their discovery, William Ramsay. And in 1906, Mendeleev wrote: “When the Periodic Table (18b9) was established, not only was argon not known, but there was no reason to suspect the possibility of the existence of such elements. Today ... these elements, in terms of their atomic weights, have taken the exact place between the halogens and the alkali metals.

For a long time there was a dispute: to separate inert gases into an independent zero group of elements or to consider them the main subgroup of group VIII. Each point of view has its pros and cons.

Based on the position of the elements in the Periodic Table, theoretical chemists led by Linus Pauling have long doubted the complete chemical passivity of inert gases, directly pointing to the possible stability of their fluorides and oxides. But only in 1962, the American chemist Neil Bartlett for the first time carried out the reaction of platinum hexafluoride with oxygen under the most ordinary conditions, obtaining xenon hexafluoroplatinate XePtF ^, and after it other gas compounds, which are now more correctly called noble rather than inert.

The periodic law retains its predictive function to this day.

It should be noted that the predictions of the unknown members of any set can be of two types. If the properties of an element that is inside a known series of similar ones are predicted, then such a prediction is called interpolation. It is natural to assume that these properties will be subject to the same laws as the properties of neighboring elements. This is how the properties of the missing elements within the periodic table were predicted. It is much more difficult to foresee the characteristics of new set members if they are outside the described part. Extrapolation - the prediction of function values that are outside a set of known patterns - is always less certain.

It was this problem that confronted scientists when the search for elements beyond the known boundaries of the system began. At the beginning of the XX century. the periodic table ended with uranium (No. 92). The first attempts to obtain transuranium elements were made in 1934, when Enrico Fermi and Emilio Segre bombarded uranium with neutrons. Thus began the road to actinoids and transactinoids.

Nuclear reactions are also used to synthesize other previously unknown elements.

Element No. 101, artificially synthesized by Yeyenne Theodor Seaborg and his collaborators, was named Mendelevium. Seaborg himself said this about it: “It is especially significant to note that element 101 is named after the great Russian chemist D. I. Mendeleev by American scientists, who have always considered him a pioneer in chemistry.”

The number of newly discovered, or rather, artificially created elements is constantly growing. The synthesis of the heaviest nuclei of elements with atomic numbers 113 and 115 was carried out at the Russian Joint Institute for Nuclear Research in Dubna by bombarding the nuclei of artificially obtained americium with nuclei of the heavy calcium-48 isotope. In this case, the core of element No. 115 arises, which immediately decays with the formation of the nucleus of element No. 113. Such superheavy elements do not exist in nature, but they arise during supernova explosions, and could also exist during the Big Bang. Their study helps to understand how our universe came into being.

In total, 39 naturally occurring radioactive isotopes are found in nature. Different isotopes decay at different rates, which is characterized by the half-life. The half-life of uranium-238 is 4.5 billion years, and for some other elements it can be equal to millionths of a second.

Radioactive elements, sequentially decaying, turning into each other, make up whole rows. Three such series are known: according to the initial element, all members of the series are combined into families of uranium, actinouranium and thorium. Another family is made up of artificially obtained radioactive isotopes. In all families, transformations culminate in the formation of non-radioactive lead atoms.

Since only isotopes can be found in the earth's crust, the half-life of which is commensurate with the age of the Earth, it can be assumed that over the course of billions of years of its history there were also such short-lived isotopes that have now died out in the literal sense of the word. These probably included the heavy isotope of potassium-40. As a result of its complete decay, the table value of the atomic mass of potassium today is 39.102, so it is inferior in mass to element No. 18 argon (39.948). This explains the exceptions in the successive increase in the atomic masses of the elements in the periodic table.

Academician V. I. Gol'danskii in a speech dedicated to the memory of Mendeleev noted "the fundamental role that Mendeleev's works play even in completely new areas of chemistry that emerged decades after the death of the brilliant creator of the Periodic System."

Science is the history and repository of the wisdom and experience of the ages, their rational contemplation and tried judgment.

D. I. Mendeleev

It rarely happens that a scientific discovery turns out to be something completely unexpected, almost always it is anticipated:

however, it is often difficult for later generations, who use tried and tested answers to all questions, to appreciate how hard it was for their predecessors.

C. Darwin

Each of the sciences about the world around us has the subject of study of specific forms of motion of matter. The prevailing ideas consider these forms of movement in order of increasing their complexity:

mechanical - physical - chemical - biological - social. Each of the subsequent forms does not reject the previous ones, but includes them.

It is no coincidence that at the celebration of the centenary of the discovery of the Periodic Law, G. T. Seaborg devoted his report to the latest achievements in chemistry. In it, he praised the amazing merits of the Russian scientist: “When considering the evolution of the Periodic System since the time of Mendeleev, the most impressive impression is that he was able to create the Periodic System of the Elements, although Mendeleev did not know such now generally accepted concepts as nuclear structure and isotopes. , the relationship of serial numbers with valency, the electronic nature of atoms, the periodicity of chemical properties explained by electronic structure, and, finally, radioactivity.

We can cite the words of Academician A.E. Fersman, who paid attention to the future: “New theories, brilliant generalizations will appear and die. New ideas will replace our already outdated concepts of the atom and electron. The greatest discoveries and experiments will nullify the past and open horizons of incredible novelty and breadth for today - all this will come and go, but the Periodic Law of Mendeleev will always live and guide searches.

24. The emergence of structural theories in the development of organic chemistry. Atomic-molecular theory as a theoretical basis for structural theories.

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