Properties of not yet discovered elements of the periodic system. Great scientists

Plan:

Introduction

• 1 Prefixes
• 2 Initial Predictions, 1870
  • 2.1 Ekabor and scandium
  • 2.2 Ekaaluminum and gallium
  • 2.3 Ecamarganese and technetium
  • 2.4 Exasilicon and germanium
• 3 1871 predictions
• 4 Later predictions
Notes

• 6 For additional reading

Introduction

In 1869, Dmitri Ivanovich Mendeleev published the Periodic Table of the Elements, in which the chemical elements were arranged in accordance with the presence of similar properties, in order of increasing atomic mass. At the same time, Mendeleev left empty cells in the table for elements not yet discovered and predicted their properties.

1. Attachments

To give the predicted elements "temporary" names, Mendeleev used the prefixes "eka", "dvi" and "three", depending on how many positions down from the already discovered element with similar properties was the predicted element. So, germanium before its discovery in 1886 was called "ecasilicon", and rhenium, discovered in 1926, was called "dwimarganese".

Prefixes for designating undiscovered elements Mendeleev formed from the Sanskrit words "one", "two" and "three". There is an opinion that the choice of Sanskrit words by Mendeleev was influenced by the similarity of the Periodic system and the Sanskrit abugida, which is usually recorded in the form of a table.

Nowadays, the prefix "eka" (less often "dwi") is used to describe transuranium or not yet discovered elements: ekaslead (ununquadium), ekaradon (ununoctium), ekaactinium or dvilantan (untriennium). The official IUPAC practice is to give undiscovered or newly discovered elements a provisional systematic name based on their charge number rather than their position in the Periodic Table.

2. Initial Predictions, 1870

Four lighter than rare earth elements - ekabor ( Eb), ekaaluminum ( Ea), ecamarganese ( Em) and ekasilicon ( Es) - coincided quite well in properties with the elements discovered later: scandium, gallium, technetium and germanium, respectively.

In the original version of the Periodic Table, the rare earths were arranged differently than they are now, and this explains why Mendeleev's predictions for heavier elements did not come true as accurately as for light ones, and why these predictions are not as widely known.

2.1. Ekabor and scandium

Scandium oxide was isolated in late 1879 by the Swedish chemist Lars Frederik Nilson. Later, Per Theodor Cleve proved the coincidence of the properties of the predicted ekabor and the newly discovered scandium and informed Mendeleev about this. Mendeleev predicted an atomic mass of 44 for ekabor, and the atomic mass of scandium was 44.955910.

2.2. Ekaaluminum and gallium

In 1871, Mendeleev predicted the existence of an as yet undiscovered element, which he named ekaaluminum. The table below compares the properties predicted by Mendeleev with the actual properties of gallium, discovered in 1875.

2.3. Ecamarganese and technetium

Technetium was isolated by Carlo Perrier and Emilio Gino Segre in 1937, after the death of Mendeleev, from molybdenum samples bombarded with deuterium nuclei in the cyclotron by Ernest Lawrence. Mendeleev predicted an atomic mass of about 100 for ecamarganese, and 98 Tc is the most stable isotope of technetium.

2.4. Exasilicon and germanium

Germanium was first isolated in 1886. His discovery turned out to be the best confirmation of Mendeleev's theory at that time, since germanium in its properties differs much more sharply from neighboring elements than the two previously predicted elements.

3. Predictions of 1871

In 1871, Mendeleev predicted the existence of an element located between thorium and uranium. Thirty years later, in 1900, William Crookes isolated protactinium as an unknown radioactive impurity in a sample of uranium. Various isotopes of protactinium were then isolated in Germany in 1913 and 1918, but modern name element received only in 1948.

The 1869 version of the Periodic Table predicted the existence of a heavier analogue of titanium and zirconium, but in 1871 Mendeleev placed lanthanum in its place. The discovery of hafnium in 1923 confirmed Mendeleev's initial assumption.

4. Later Predictions

In 1902, after the discovery of helium and argon, Mendeleev placed them in the zero group of the table. Doubting the correctness of the atomic theory explaining the law of constancy of composition, he could not a priori considered hydrogen to be the lightest of the elements and believed that a hypothetical, even lighter member of the chemically inert zero group could go unnoticed. The existence of this element Mendeleev tried to explain radioactivity.

Mendeleev identified the heavier of the two pre-helium elements with coronium, which was named in association with the unexplained spectral line of the solar corona. A miscalibration of the instrument gave a wavelength of 531.68 nm, which was later corrected to 530.3 nm. This wavelength was correlated by Grotrian and Edlen in 1939 with the iron line.

The lightest of the zero group gases, the first in the Periodic Table, was assigned a theoretical atomic mass between 5.3·10 −11 and 9.6·10 −7 . Mendeleev attributed to the particles of this gas a kinetic velocity of the order of 2.5·10 6 m/s. Almost weightless, the particles of both these gases, according to Mendeleev, should have easily passed through the thickness of matter, practically without entering into chemical reactions. The high mobility and very low atomic mass of transhydrogen gases would lead to the fact that they could be very rarefied, while remaining dense in appearance. Mendeleev was so confident in the existence of transhydrogen elements that he included them in later editions of the Periodic Table. [ a source?]

Later, Mendeleev published a theoretical development on the ether, which solved [ a source?] many of the contradictions of the then existing physics. A book called The Chemical Conception of the Aether came out in 1904 and again contained a mention of two gases lighter than hydrogen. Under the "ethereal gas" Mendeleev understood the interstellar atmosphere, consisting of two transhydrogen gases with impurities of other elements and formed as a result of internal processes occurring on stars.

Notes

1. Kaji, Masanori (2002). "D.I. Mendeleev" s concept of chemical elements and The Principles of Chemistry- www.scs.uiuc.edu/~mainzv/HIST/awards/OPA Papers/2005-Kaji.pdf. Bulletin for the History of Chemistry 27 (1): 4–16.
2. The mass number 98 differs from the atomic mass in that it takes into account the nucleons in the nucleus of one isotope and is not the mass of an average sample (containing a natural set of isotopes) with respect to 12 C. The atomic mass of the 98 Tc isotope is 97.907214. For elements that are too unstable to be in earth's crust Since the very beginning of the Earth, the atomic mass of the most common set of isotopes in nature has been replaced by the atomic mass of the most stable isotope. - chemlab.pc.maricopa.edu/PERIODIC/Tc.html
3. Emsley John Nature's Building Blocks. - (Hardcover, First Edition). - Oxford University Press, 2001. - P. 347. - ISBN 0198503407
4. Mendeleev D. Fundamentals of chemistry. - 7th edition.
5. Swings, P. (July 1943). "Edlén" s Identification of the Coronal Lines with Forbidden Lines of Fe X, XI, XIII, XIV, XV; Ni XII, XIII, XV, XVI; Ca XII, XIII, XV; a X, XIV - adsabs.harvard.edu /cgi-bin/nph-bib_query?1943ApJ....98..116S". Astrophysical Journal 98 (119): 116–124. DOI:10.1086/144550 - dx.doi.org/10.1086/144550. and - laserstars.org/spectra/Coronium.html
6. Mendeleev D. An attempt at a chemical understanding of the world ether. - St. Petersburg, 1903.
   English translation:
   Mendeleeff D. An Attempt Towards A Chemical Conception Of The Ether / G. Kamensky (translator). - Longmans, Green & Co., 1904.
   see also
   Bensaude-Vincent, Bernadette (1982). "L'éther, element chimique: un essai malheureux de Mendeleev en 1904". British Journal for the History of Science 15 : 183–188. DOI:10.1086/144550 - dx.doi.org/10.1086/144550.

6. For additional reading

• Scerri Eric The Periodic Table: Its Story and Its Significance. - New York: Oxford University Press, 2007. - ISBN 0195305736

Mendeleev and the Periodic Law

Read the continuation of the article by B. D. Stepin, written by him in 1998 for the volume "Chemistry" of the Great Children's Encyclopedia

This is how the Periodic Law was discovered, the modern formulation of which is as follows:

The properties of simple substances, as well as the forms and properties of compounds of elements, are in a periodic dependence on the charge of the nuclei of their atoms.

Mendeleev was then only 35 years old.

Mendeleev sent printed sheets with a table of elements to many domestic and foreign chemists, and only after that he left St. Petersburg to inspect cheese factories.

Before his departure, he still managed to hand over to N. A. Menshutkin, an organic chemist and future historian of chemistry, the manuscript of the article "Relationship of properties with the atomic weight of elements" - for publication in the Journal of the Russian Chemical Society and for communication at the upcoming meeting of the society.

On March 18, 1869, Menshutkin, who at that time was the clerk of the society, made a small report on the Periodic Law on behalf of Mendeleev. The report at first did not attract much attention of chemists, and the President of the Russian Chemical Society, Academician Nikolai Zinin (1812-1880) stated that Mendeleev was not doing what a real researcher should do. True, two years later, after reading Dmitry Ivanovich's article "The natural system of elements and its application to indicating the properties of certain elements," Zinin changed his mind and wrote to Mendeleev: "Very, very good, very excellent approximations, even fun to read, God bless you good luck in experimental confirmation of your conclusions. Sincerely devoted to you and deeply respecting you N. Zinin.

So what is periodicity?

This is the repeatability of the chemical properties of simple substances and their compounds when the element's serial number changes. Z and the appearance of maxima and minima in a number of properties, depending on the value of the ordinal (atomic) number of the element.

For example, what makes it possible to combine all alkaline elements into one group?

First of all, repeatability through some intervals of values Z electronic configuration. The atoms of all alkaline elements have only one electron in the outer atomic orbital, and therefore, in their compounds, they exhibit the same oxidation state, equal to + I. The formulas of their compounds are the same: for MCl chlorides, for carbonates - M 2 CO 3, for acetates - CH 3 COOM and so on (here the letter M denotes an alkaline element).

Mendeleev still had a lot to do after the discovery of the Periodic Law. The reason for the periodic change in the properties of the elements remained unknown, and the very structure of the Periodic Table, where the properties were repeated through seven elements in the eighth, did not find an explanation. However, the first veil of mystery was removed from these numbers: in the second and third periods of the system, there were then just seven elements each.

Mendeleev did not place all the elements in ascending order of atomic masses; in some cases he was more guided by the similarity of chemical properties. Yes, at cobalt Co atomic mass is greater than that of nickel Ni, y tellurium Te she is also bigger than that iodine I, but Mendeleev placed them in the order Co - Ni, Te - I, and not vice versa. Otherwise, tellurium would fall into the group halogens, and iodine became a relative Selene Se. ||

They were arranged according to the presence of similar properties in order of increasing atomic weight.

Unlike the works of his predecessors, Mendeleev proceeded from the assumption of the existence of yet undiscovered elements on the basis of periodic changes in the physical and chemical properties of known elements. They left empty cells in the table for elements not yet discovered and predicted their properties. To give the predicted elements "temporary" names, Mendeleev used the prefixes "eka", "dvi" and "three" (from the Sanskrit words "one", "two" and "three"), depending on how many positions down from already discovered element with similar properties was the predicted element. So, germanium before its discovery in 1886 was called "ecasilicon", and rhenium, discovered in 1926, was called "dwimarganese".

Already in the first version of the Periodic Table, published by D. I. Mendeleev in 1869, more elements were included than were discovered at that time. Four free cells are left in it for still unknown elements and their atomic weights are indicated (in "shares" close in value to the mass of a hydrogen atom).

Developing the ideas of periodicity in 1869-1871, D. I. Mendeleev introduced the concept of the place of an element in the periodic system as a set of its properties in comparison with the properties of other elements. To predict the properties of simple substances and compounds, he proceeded from the fact that the properties of each element are intermediate between the corresponding properties of two neighboring elements in the group periodic table, two neighboring elements in the period and elements along the diagonal - the so-called "star rule". On this basis, in particular, based on the results of studying the sequence of changes in glass-forming oxides, I corrected the values ​​of the atomic masses of 9 elements. In 1870, he predicted the existence, calculated atomic masses and described the properties of three elements not yet discovered at that time - "ekaaluminum", "ecabor" and "ecasilicon". Then he predicted the existence of eight more elements, including "ditellurium" - polonium, "ekaioda" - astatine, "ecamarganese" - technetium, "ecacesia" - francium.

Mendeleev's predictions called in scientific world skepticism and sharp criticism. Thus, the German physical chemist Wilhelm Ostwald, the future Nobel Prize winner, argued that it was not the law that was discovered, but the principle of classifying "something indefinite." Robert Bunsen, discoverer of rubidium and cesium, wrote that Mendeleev enthralls chemists " into a far-fetched world of pure abstractions”, and Hermann Kolbe in 1870 called the work of Mendeleev speculative. The correctness of Mendeleev was convincingly proven when the elements predicted by him were discovered: gallium (Paul Lecoq de Boisbaudran, 1875), scandium (Lars Nilsson, 1879) and germanium (Clemens Winkler, 1886) - respectively ekaaluminum, ecabor and ekasilicium.

The lightest of the zero group gases, the first in the Periodic Table, was assigned a theoretical atomic mass between 5.3·10 −11 and 9.6·10 −7 . Particles of this gas, which he called newtonium, Mendeleev attributed a kinetic velocity of the order of 2.5 10 6 m/s. Almost weightless, the particles of both these gases, according to Mendeleev, should have easily passed through the thickness of matter, practically without entering into chemical reactions. The high mobility and very low atomic mass of transhydrogen gases would lead to the fact that they could be very rarefied, while remaining dense in appearance.

Later, Mendeleev published a theoretical development on the ether. A book called The Chemical Conception of the Aether came out in 1904 and again contained a mention of two hypothetical inert gases lighter than hydrogen, coronium and newtonium. Under the "ethereal gas" Mendeleev understood the interstellar atmosphere, consisting of two transhydrogen gases with impurities of other elements and formed as a result of internal processes occurring on stars.

4.5 Discovery of the Periodic Law by D. I. Mendeleev. Significance of the Periodic Law for Chemistry and Natural Science.

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. At this time, Mendeleev taught chemistry at St. Petersburg University. Preparing for lectures, collecting material for his textbook "Fundamentals of Chemistry", D. I. Mendeleev thought about how to systematize the material in such a way that information about the chemical properties of elements did not look like a set of disparate facts.

In this work, D. I. Mendeleev was guided by atomic masses(atomic weights) of the elements. After the World Congress of Chemists in 1860, in which D. I. Mendeleev also participated, the problem of the correct determination of atomic weights was constantly at the center of attention of many leading chemists of the world, including D. I. Mendeleev.

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 according to their atomic weight.

The above formulation does not in the least contradict the modern one, in which the concept of "atomic weight" is replaced by the concept of "nuclear charge". Today we know that atomic mass is concentrated mainly in the nucleus of an atom. The nucleus is made up of protons and neutrons. With an increase in the number of protons that determine the charge of the nucleus, the number of neutrons in the nuclei also increases, and hence the mass of the atoms of the elements.

Before Mendeleev, several attempts were made to systematize the elements according to various criteria. Basically united similar elements according to their chemical properties. For example: Li, Na, K. Or: Cl, Br, I. These and some other elements were combined into the so-called "triads". A table of five such "triads" was published by Dobereiner as early as 1829, but it included only a small part of the elements known at that time.

In 1864, the Englishman J. Newlands noticed that if the elements are arranged in ascending order of their atomic weight, then approximately every eighth element is a kind of repetition of the first - just as the note "do" (like any other note) is repeated in musical octaves every 7 notes (the law of octaves). Below is a version of the Newlands table from 1865. Elements having the same atomic weight (according to the data of that time) were placed under the same number. One can see what difficulties Newlands faced - the emerging patterns quickly collapsed, since his system did not take into account the possibility of the existence of elements that had not yet been discovered.

Newlands' report "The Law of Octaves and the Causes of Chemical Ratios Among Atomic Weights" was discussed at the meeting of the London Chemical Society on March 1, 1866, and a brief account of it was published in the journal "Chemical News". Newlands was close to the discovery of the Periodic Law, but the very idea of ​​sequential numbering of only elements known by that time did not just "break" the smooth change in their chemical properties - this idea excluded the possibility of the existence of yet undiscovered elements for which there was simply no place in the Newlands system. The fundamental novelty of the Periodic Law, discovered and formulated by D. I. Mendeleev exactly three years later, 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.

The first version of the Periodic Table, published by Mendeleev in 1869, looks unusual to the modern reader (Fig. 4-5). Until atomic numbers are affixed, future groups of elements are arranged horizontally (and future periods - vertically), inert gases have not yet been discovered, unfamiliar symbols of elements are encountered, many atomic masses differ markedly from modern ones. However, it is important for us to see that already in the first version of the Periodic Table, D. I. Mendeleev included more elements than they were discovered at that time! He left 4 cells of his table free for the still unknown elements and was even able to correctly estimate their atomic weight. Atomic units of mass (a.m.u.) had not yet been accepted and the atomic weights of elements were measured in "shares" close in value to the mass of a hydrogen atom.

Rice. 4-5. The first version of the Periodic Table, published in 1869 year. Elements predicted by D. I. Mendeleev and subsequently discovered.

In all previous attempts to determine the relationship between elements, other researchers have sought to create completed a picture in which there was no place for yet undiscovered elements. On the contrary, D. I. Mendeleev considered the most important part of his Periodic Table to be those of its cells that were still empty (question marks in Fig. 4-5). This made it possible predict existence of as yet unknown elements.

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.

A deep knowledge of the chemical properties of various elements allowed Mendeleev not only to point to yet undiscovered elements, but also predict their properties! See how accurately D. I. Mendeleev predicted the properties of the element he called "eka-silicium" (in Fig. 4-5 this is the element germanium). After 16 years, the prediction of D. I. Mendeleev was brilliantly confirmed.

Table 4-5. Comparison of the properties predicted by D. I. Mendeleev for the yet undiscovered element "eka-silicon" with the properties of the element germanium (Ge). In the modern Periodic Table, germanium occupies the place of "eka-silicon".

In the same way, during the lifetime of D. I. Mendeleev, the properties of "eka-aluminum" (the element gallium Ga) and "eka-boron" (the element scandium Sc) were brilliantly confirmed.

After that, it became clear to scientists around the world that the Periodic Table of D. I. Mendeleev not only systematizes the elements, but is a graphic expression of the fundamental law of nature - the Periodic Law.

This law has predictive power. He allowed to conduct a targeted search for new, not yet discovered elements. The atomic weights of many elements, previously determined insufficiently accurately, were subjected to verification and refinement precisely because their erroneous values ​​conflicted with the Periodic Law.

** 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. These are pairs of elements:

18 Ar (39.948) – 19 K (39.098);

27 Co(58.933) – 28 Ni (58.69);

52 Te (127.60) – 53 I (126.904);

90 Th (232.038) – 91 Pa (231.0359).

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 given their prevalence in nature (remember paragraph 2.3 from Chapter 2). 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 experimental determination of the charges of the nuclei of elements, carried out by G. Moseley in 1914, confirmed the correctness of D. I. Mendeleev, who preferred the chemical properties, rather than the atomic weights of the elements, when determining their final place in the Periodic Table.

Since the advent of the Periodic Law, chemistry has ceased to be a descriptive science. As the famous Russian chemist N. D. Zelinsky figuratively noted, the Periodic Law was "the discovery of the mutual connection of all atoms in the universe."

Further discoveries in chemistry and physics repeatedly confirmed the fundamental meaning of the Periodic Law. Inert gases were discovered, which 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.

Discovery of the Periodic Law[edit | edit source]

Portrait of D. I. Mendeleev (1861)

Periodic system of D. I. Mendeleev 1871

Version periodic system Mendeleev in 1891. It contains no noble gases.

In March 1869, at a meeting of the Russian Chemical Society, a message was read by the Russian chemist Dmitri Ivanovich Mendeleev about his discovery of the Periodic Law of Chemical Elements. In the same year, the first edition of Mendeleev's textbook "Fundamentals of Chemistry" was published, in which his periodic table. In November 1870, he reported to the RCS the article "The natural system of elements and its application to indicate the properties of undiscovered elements", in which Mendeleev first used the term "Periodic Law" and pointed out the existence of several undiscovered elements.

In 1871, in the final article "Periodic Law of Chemical Elements", Mendeleev gave the following formulation of the Periodic Law: " the properties of simple bodies, as well as the forms and properties of the compounds of elements, and therefore the properties of the simple and complex bodies formed by them, stand in a periodic dependence on their atomic weight» . At the same time, Mendeleev gave his periodic table a form that became classical (the so-called short-period version).

Unlike his predecessors, Mendeleev not only compiled a table and pointed out the presence of undoubted patterns in the numerical values ​​of atomic masses, but also decided to name these patterns general law of nature. Based on the assumption that the atomic mass determines properties of the element, he took the liberty of changing the accepted atomic weights of some elements and describing in detail the properties of elements not yet discovered. To predict the properties of simple substances and compounds, Mendeleev proceeded from the fact that the properties of each element are intermediate between the corresponding properties of two neighboring elements in the group of the periodic table (that is, above and below) and simultaneously two neighboring elements in the period (left and right) (i.e., n "rule of the star").

D. I. Mendeleev for many years fought for the recognition of the Periodic Law; his ideas gained recognition only after the elements predicted by Mendeleev were discovered: gallium (Paul Lecoq de Boisbaudran, 1875), scandium (Lars Nilsson, 1879) and germanium (Clemens Winkler, 1886) - respectively ekaaluminum, ecabor and ekasilicon. Since the mid-1880s, the Periodic Law has been finally recognized as one of the theoretical foundations of chemistry.

English: Monument to the periodic table, in front of the Faculty of Chemical and Food Technology of the Slovak University of Technology in Bratislava, Slovakia. The monument honors Dmitri Mendeleev.

Periodic table: discovery history, interesting facts and stories

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The discovery of the table of periodic chemical elements was one of the important milestones in the history of the development of chemistry as a science. The pioneer of the table was the Russian scientist Dmitry Mendeleev. An extraordinary scientist with the broadest scientific horizons managed to combine all ideas about the nature of chemical elements into a single coherent concept. About the history of the discovery of the table of periodic elements, interesting facts associated with the discovery of new elements, and folk tales that surrounded Mendeleev and the table of chemical elements he created, M24.RU will tell in this article. Table opening history By the middle of the 19th century, 63 chemical elements had been discovered, and scientists all over the world repeatedly attempted to combine all the existing elements into a single concept. The elements were proposed to be placed in ascending order of atomic mass and divided into groups according to the similarity of chemical properties. In 1863, the chemist and musician John Alexander Newland proposed his theory, who proposed a layout of chemical elements similar to that discovered by Mendeleev, but the work of the scientist was not taken seriously by the scientific community due to the fact that the author was carried away by the search for harmony and the connection of music with chemistry. In 1869, Mendeleev published his scheme of the periodic table in the journal of the Russian Chemical Society and sent out a notice of the discovery to the leading scientists of the world. In the future, the chemist repeatedly refined and improved the scheme until it acquired its familiar form. The essence of Mendeleev's discovery is that with the growth of the atomic mass Chemical properties elements change not monotonously, but periodically. After a certain number of elements with different properties, the properties begin to repeat. Thus, potassium is similar to sodium, fluorine is similar to chlorine, and gold is similar to silver and copper. In 1871, Mendeleev finally united the ideas into the Periodic Law. Scientists predicted the discovery of several new chemical elements and described their chemical properties. Subsequently, the chemist's calculations were fully confirmed - gallium, scandium and germanium fully corresponded to the properties that Mendeleev attributed to them. Tales about Mendeleev

Engraving depicting Mendeleev. Photo: ITAR-TASS

There were many tales about the famous scientist and his discoveries. People at that time had little idea of ​​chemistry and believed that doing chemistry was something like eating baby soup and stealing on an industrial scale. Therefore, the activities of Mendeleev quickly acquired a mass of rumors and legends. One of the legends says that Mendeleev discovered the table of chemical elements in his sleep. The case is not the only one, August Kekule spoke about his discovery in the same way, who dreamed of the formula of the benzene ring. However, Mendeleev only laughed at the critics. “I’ve been thinking about it for maybe twenty years, and you say: I sat and suddenly ... it’s ready!”, the scientist once said about his discovery. Another story credits Mendeleev with the discovery of vodka. In 1865, the great scientist defended his dissertation on the topic "Discourse on the combination of alcohol with water", and this immediately gave rise to a new legend. The contemporaries of the chemist laughed, saying that the scientist “does well under the influence of alcohol combined with water,” and the next generations already called Mendeleev the discoverer of vodka. They also laughed at the way of life of the scientist, and especially at the fact that Mendeleev equipped his laboratory in the hollow of a huge oak. Also, contemporaries teased Mendeleev's passion for suitcases. The scientist at the time of his involuntary inactivity in Simferopol was forced to pass the time weaving suitcases. In the future, he independently made cardboard containers for the needs of the laboratory. Despite the clearly "amateur" nature of this hobby, Mendeleev was often called a "suitcase master." Discovery of radium One of the most tragic and at the same time famous pages in the history of chemistry and the appearance of new elements in the periodic table is associated with the discovery of radium. A new chemical element was discovered by the spouses Marie and Pierre Curie, who discovered that the waste remaining after the separation of uranium from uranium ore is more radioactive than pure uranium. Since no one knew what radioactivity was then, the rumor quickly attributed healing properties and the ability to cure almost all diseases known to science to the new element. Radium was included in food products, toothpaste, face creams. The rich wore watches whose dials were painted with paint containing radium. The radioactive element was recommended as a means to improve potency and relieve stress. Such "production" lasted for twenty whole years - until the 30s of the twentieth century, when scientists discovered the true properties of radioactivity and found out how detrimental the effect of radiation on the human body. Marie Curie died in 1934 from radiation sickness caused by long-term exposure to radium. Nebulium and Coronium

The periodic table not only ordered the chemical elements into a single coherent system, but also made it possible to predict many discoveries of new elements. At the same time, some chemical "elements" were recognized as non-existent on the basis that they did not fit into the concept of the periodic law. The most famous story is the "discovery" of new elements of nebulium and coronium. When studying the solar atmosphere, astronomers discovered spectral lines that they could not identify with any of the chemical elements known on earth. Scientists have suggested that these lines belong to a new element, which was called coronium (because the lines were discovered during the study of the "crown" of the Sun - the outer layer of the star's atmosphere). A few years later, astronomers made another discovery by studying the spectra of gaseous nebulae. The discovered lines, which again could not be identified with anything terrestrial, were attributed to another chemical element - nebulium. The discoveries were criticized because Mendeleev's periodic table no longer had room for elements with the properties of nebulium and coronium. After checking, it was found that nebulium is ordinary terrestrial oxygen, and coronium is highly ionized iron. It should be noted that today in the Moscow Central House of Scientists of the Russian Academy of Sciences, names will be solemnly assigned to two chemical elements discovered by scientists from Dubna near Moscow.

In compiling the periodic system, D. I. Mendeleev had to overcome many difficulties associated with the fact that some elements had not yet been discovered at that time, the properties of others were little studied, and the atomic masses of the third were determined incorrectly. The scientist deeply believed in the correctness of the law he discovered, was firmly convinced that the periodic law reflects objective reality. On the basis of the periodic system, he corrected the atomic masses of a number of elements, predicted the existence in nature of several as yet undiscovered elements, and even described the properties of these elements and their compounds. These elements were discovered over the next fifteen years: in 1875 P. E. Lecoq de Boisbaudran discovered element number 31, calling it gallium; in 1879, L. F. Nilson discovered element number 21 and named it scandium; in 1886, K. A. Winkler discovered element 32, which was named germanium.

Mendeleev predicted the physical and chemical properties of these three elements based on the properties of the elements surrounding them in the table. For example, he calculated the atomic mass and density of element number 21 as the arithmetic mean of the atomic masses and densities of boron, yttrium, calcium, and titanium.

Below, as an example, are the properties of the element with the atomic number 32 - germanium, which were predicted by Mendeleev and subsequently experimentally confirmed by Winkler.

Element Properties No. 32, Germanium Properties, Established

predicted by Mendeleev in 1871: empirically in 1886:

atomic mass - 72; atomic mass - 72.6;

gray refractory metal; gray refractory metal;

density - 5.5 g/cm3; density - 5.35 g/cm3;

should be obtained by reduction is obtained by reduction of the oxide

hydrogen oxide; hydrogen;

oxide formula - EO2; oxide formula - GeO2;

oxide density - 4.7 g/cm3; oxide density - 4.7 g/cm3;

chloride ECl4 - liquid; chloride GeCl4 - liquid;

density ECl4 - 1.9 g/cm3; GeCl4 density - 1.887 g/cm3;

the boiling point of ECl4 is 90 °C. the boiling point of GeCl4 is 90 °C.

The discovery of the elements predicted by Mendeleev and the brilliant coincidence of the properties predicted by him with those established empirically led to the universal recognition of the periodic law.

It should be noted that Mendeleev doubted the possibility of a sharp transition from such active non-metals as halogens to alkali metals. He believed that this transition should be smoother. Soon this scientific prediction came true: inert gases were discovered. There were no free places in the periodic system for these elements, and they were allocated to an independent group. In order to emphasize the great chemical inertness of these elements, the group was called zero.

At present, many variants of the periodic system of elements are known, but the table proposed by D. I. Mendeleev remains the most convenient. Some additions were made to the original version of the table later. Some of them were made by the scientist himself.

To date, a number of compounds of heavy noble gases have been obtained, in which the oxidation state is +6 and +8 (XeF6, XeO3, XeO4, etc.). In this regard, inert gases are included in the eighth group of the periodic system, in which they form the main subgroup.

Periodic system of elements of D. I. Mendeleev.

The modern periodic system of elements has seven periods, of which I, II and III are called small periods, and IV, V, VI and VI are called large periods. I, II and III periods contain one row of elements, IV, V and VI - two rows each, VII period is unfinished. All periods, with the exception of I, which contains only two elements, begin with an alkali metal and end with a noble gas.

CHOREA (from the Greek. choreia - dance) (Witt's dance), fast involuntary uncoordinated movements, twitching of the limbs, etc .; type of hyperkinesis. A sign of organic brain damage in rheumatism (rheumatic, or small, chorea) or an independent hereditary disease.

DARRELL (Durrell) Gerald Malcolm (1925-1995), English zoologist and writer. Brother of L. J. Durrell. Organizer and participant of expeditions for collections of animals to Africa, South. America, Australia. Created a zoo on about. Jersey (1958) for endangered animals. Popular books: "The Land of Rustles" (1961), "The Zoo in My Luggage" (1960), "The Ark on the Island" (1976), etc.

Bulbenkova Olga Nikolaevna (1835-1918), creator of a fashion workshop in St. Petersburg in the middle. 19th century, which existed until 1917, known as "Ms. Olga". Court ceremonial dresses, the so-called "trains", made by this workshop, were especially popular. See also plume.