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Predicted by Mendeleev. The structure of the atom and the periodic law of D.I. Mendeleev

Plan:

1 Attachments
2 Initial predictions, 1870
- 2.1 Ekabor and scandium
- 2.2 Ekaaluminium and gallium
- 2.3 Ekamarganese and technetium
- 2.4 Ecasilicon and germanium
3 1871 predictions
4 Later predictions

6 For additional reading

Introduction

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

1. Attachments

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

Mendeleev formed the prefixes for undiscovered elements from the Sanskrit words "one", "two" and "three". It is believed that Mendeleev's choice of Sanskrit words was influenced by the similarity between the Periodic Table and the Sanskrit Abugida, which is usually written in the form of a table.

Nowadays, the prefix "eka" (less often "dwi") is used to describe transuranic or not yet discovered elements: ekaslead (ununcvadium), ekaradon (ununoctium), ekaactinium or dilanthan (untriennium). The official IUPAC practice is to give as yet undiscovered or newly discovered elements a tentative 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), ekamarganese ( Em) and ekasilicon ( Es) - quite well coincided in properties with the elements discovered later: scandium, gallium, technetium and germanium, respectively.

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

2.1. Ekabor and scandium

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

2.2. Ekaaluminium and gallium

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

2.3. Ekamarganese and technetium

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

2.4. Ecasilicon 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 contaminant in a uranium sample. Various isotopes of protactinium were then isolated in Germany in 1913 and 1918, but the element received its modern name only in 1948.

A version of the Periodic Table published in 1869 predicted the existence of a heavier analogue of titanium and zirconium, but in 1871 Mendeleev placed lanthanum in this place. The discovery in 1923 of hafnium confirmed Mendeleev's original 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 consider hydrogen to be the lightest of the elements and believed that a hypothetical, even lighter member of the chemically inert group zero could go unnoticed. By the existence of this element, Mendeleev tried to explain radioactivity.

The heavier of the two pre-Helium elements was identified by Mendeleev with coronium, which was named after its association with the unexplained spectral line of the solar corona. An incorrect calibration 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 group zero gases, the first in the Periodic Table, was assigned a theoretical atomic mass of between 5.3 · 10 −11 and 9.6 · 10 −7. Particles of this gas Mendeleev attributed a kinetic velocity of the order of 2.5 · 10 6 m / s. Almost weightless, the particles of both of these gases, according to Mendeleev, should easily pass through the thickness of matter, practically without entering into chemical reactions. The high mobility and very low atomic mass of trans-hydrogen gases would lead to the fact that they could be very rarefied, while remaining dense in appearance. Mendeleev was so sure of the existence of trans-hydrogen elements that he included them in later editions of the Periodic Table. [ a source?]

Later, Mendeleev published a theoretical development about the ether, which solved [ a source?] many of the contradictions of physics then existed. A book called "The Chemical Concept of Ether" was published in 1904, and it again contained a mention of two gases lighter than hydrogen. By "ethereal gas" Mendeleev understood the interstellar atmosphere, consisting of two trans-hydrogen gases with admixtures of other elements and formed as a result of internal processes going on in the stars.

Notes

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.
Mass number 98 differs from atomic mass in that it takes into account nucleons in the nucleus of one isotope and is not the mass of an average sample (containing a natural set of isotopes) in relation to 12 C. The atomic mass of the 98 Tc isotope is 97.907214. For elements that are too unstable to be in the earth's crust ever since the Earth was born, the atomic mass of the most common set of isotopes in nature is replaced by the atomic mass of the most stable isotope. - chemlab.pc.maricopa.edu/PERIODIC/Tc.html
Emsley john Nature's Building Blocks - (Hardcover, First Edition) - Oxford University Press, 2001. - P. 347. - ISBN 0198503407
Mendeleev D. Fundamentals of Chemistry. - 7th edition.
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
Mendeleev D. An attempt at a chemical understanding of the ether. - St. Petersburg, 1903.
English translation:
Mendeléeff 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, élément chimique: un essai malheureux de Mendéleev 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 BD Stepin, written by him in 1998 for the volume "Chemistry" of the Great Children's Encyclopedia

So 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 periodically dependent on the charge of the nuclei of their atoms.

Mendeleev was then only 35 years old.

Mendeleev sent the printed leaflets with the table of elements to many domestic and foreign chemists, and only after that he left Petersburg to inspect the cheese dairy.

Before leaving, he still managed to hand over to NA Menshutkin, an organic chemist and future historian of chemistry, the manuscript of the article "Correlation 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 short report on the Periodic Law on behalf of Mendeleev. At first, the report did not attract much attention from 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, a lot of excellent convergence, even fun to read, God bless you in the 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 ordinal number of an element changes. Z and the appearance of a number of properties of maxima and minima, 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 at 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 of the same type: for chlorides MCl, for carbonates - M 2 CO 3, for acetates - CH 3 COOM, and so on (here the letter M denotes an alkaline element).

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

Not all elements were arranged by Mendeleev in the order of increasing atomic masses; in some cases he was more guided by the similarity of chemical properties. So, at cobalt Co atomic mass is greater than that of nickel Ni, y tellurium Te it is also larger than that of 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 selena Se. ||

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 Dmitry 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 the lectures, collecting material for his textbook "Fundamentals of Chemistry", DI Mendeleev pondered how to systematize the material in such a way that information about the chemical properties of elements does not look like a set of disparate facts.

D.I.Mendeleev was guided in this work by atomic masses (atomic weights) of elements. After the World Congress of Chemists in 1860, in which DI Mendeleev also participated, the problem of correct determination of atomic weights was constantly in the focus of attention of many leading chemists of the world, including DI 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 the elements change periodically in accordance with 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 composed of protons and neutrons. With an increase in the number of protons that determine the nuclear charge, so does the number of neutrons in the nuclei, and hence the mass of the atoms of the elements.

Before Mendeleev, several attempts were made to systematize the elements according to different criteria. Mainly united similar by their chemical properties elements. 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 in 1829, but it included only a small part of the elements known by that time.

In 1864, the Englishman J. Newlands noticed that if you arrange the elements in ascending order of their atomic weight, then approximately every eighth element is a kind of repetition of the first - just like the note "C" (like any other note) is repeated in musical octaves every 7 notes (law of octaves). Below is a version of the Newlands table dating back to 1865. Elements with the same atomic weight (according to the data of that time) were placed under the same number. You can see what difficulties Newlands faced - the outlined 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's paper, The Law of Octaves and the Causes of Chemical Relations among Atomic Weights, was discussed at a meeting of the London Chemical Society on March 1, 1866, and a summary of it was published in the Chemical News. Newlands was close to discovering the Periodic Law, but the very idea of \u200b\u200bsequential numbering of only the 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 not yet discovered 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 that were INSIDERABLE in their properties. This connection consists in the fact that the properties of elements change smoothly and approximately equally with an increase in their atomic weight, and then these changes REPEAT PERIODICALLY.

2. In those cases when the impression was created that some link was missing in the sequence of changes in the properties of elements, the SPACES were provided in the Periodic Table, which had to be filled in with not yet opened 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 for a modern reader (Fig. 4-5). Until atomic numbers are given, future groups of elements are located 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 were discovered at that time! He left 4 cells of his table free for still unknown elements and was even able to correctly estimate their atomic weight. The atomic mass units (amu) had not yet been accepted, and the atomic weights of the elements were measured in "shares" close in value to the mass of a hydrogen atom.

Figure: 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 finished a picture in which there was no place for elements not yet open. On the contrary, DI Mendeleev considered the most important part of his Periodic Table those cells that remained empty so far (question marks in Fig. 4-5). This made it possible predictthe existence of as yet unknown elements.

It is admirable that DI Mendeleev made his discovery at a time when the atomic weights of many elements were determined very approximately, and only 63 of the elements themselves were known - that is, slightly 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 out elements that had not yet been discovered, but also predict their properties! Look at how accurately DI Mendeleev predicted the properties of the element, which he called "eka-silicium" (in Fig. 4-5 this is the element germanium). 16 years later, DI Mendeleev's prediction was brilliantly confirmed.

Table 4-5. Comparison of the properties predicted by DI Mendeleev for the not yet discovered element "ecasilicon" with the properties of the element germanium (Ge). In the modern Periodic Table germanium takes the place of "eka-silicium".

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

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

This law has predictive power. It made it possible to conduct a targeted search for new, not yet discovered elements. The atomic weights of many elements, which were previously determined insufficiently accurately, were subjected to verification and refinement precisely because their erroneous values \u200b\u200bconflicted with the Periodic Law.

** However, even after the tremendous and careful work of chemists to correct the atomic weights, in four places of the Periodic Table the elements "violate" the strict order of arrangement in ascending 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 DI Mendeleev, such deviations were considered the disadvantages of the Periodic Table. The theory of the structure of the atom has put everything in its place: the elements are located completely correctly - in accordance with the charges of their nuclei. How, then, can one 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 of its isotopes taking into account their prevalence in nature (remember paragraph 2.3 of Chapter 2). By chance, the atomic weight of argon is determined by the most "heavy" isotope (it is found in nature in large 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 gave preference to chemical properties, rather than atomic weights of elements when determining their final place in the Periodic Table.

Since the appearance of the Periodic Law, chemistry has ceased to be a descriptive science. As the famous Russian chemist ND 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 have repeatedly confirmed the fundamental meaning of the Periodic Law. Inert gases were discovered, which perfectly fit into the Periodic Table - this is especially clearly shown by the long form of the table. The ordinal number of the element turned out to be equal to the nuclear charge of the atom of this element. Many previously unknown elements were discovered thanks to a targeted search for exactly those properties that were predicted from the Periodic Table.

Discovery of the Periodic Law[edit | edit source]

Portrait of D. I. Mendeleev (1861)

Periodic table of D. I. Mendeleev 1871

Version of the periodic system of Mendeleev in 1891. There are no noble gases in it.

In March 1869, at a meeting of the Russian Chemical Society, a report was read by the Russian chemist Dmitry 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, which included his periodic table... In November 1870, he reported to the RFO the article "The natural system of elements and its application to indicating the properties of undiscovered elements", in which Mendeleev first used the term "Periodic law" and pointed out the existence of several elements not yet discovered.

In 1871, in the final article "Periodic legality of chemical elements" Mendeleev gave the following formulation of the Periodic Law: " the properties of simple bodies, as well as the shapes and properties of compounds of elements, and therefore the properties of the simple and complex bodies formed by them, are periodically dependent on their atomic weight". At the same time, Mendeleev gave his periodic table a form that became classic (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 \u200b\u200bof atomic masses, but also decided to call these patterns general law of nature... Based on the assumption that the atomic mass predeterminesproperties of an 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").

DI Mendeleev for many years fought for the recognition of the Periodic Law; his ideas received 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 ekaaluminium, ekabor and ecasilicium. From the mid-1880s, the Periodic Law was 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: history of discovery, interesting facts and tales

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The discovery of the table of periodic chemical elements became one of the important milestones in the history of the development of chemistry as a science. The discoverer of the table was the Russian scientist Dmitry Mendeleev. An extraordinary scientist with the broadest scientific outlook managed to combine all ideas about the nature of chemical elements into a single harmonious concept. M24.RU will tell you about the history of the discovery of the table of periodic elements, interesting facts related to the discovery of new elements, and folk tales that surrounded Mendeleev and the table of chemical elements he created in this article. Table opening history By the middle of the 19th century, 63 chemical elements were discovered, and scientists around the world have repeatedly made attempts to combine all existing elements into a single concept. The elements were proposed to be placed in the order of increasing atomic mass and divided into groups according to the similarity of chemical properties. In 1863, chemist and musician John Alexander Newland proposed his theory, who proposed a scheme of arrangement of chemical elements similar to that discovered by Mendeleev, but the scientist's work was not taken seriously by the scientific community due to the fact that the author was carried away by the search for harmony and 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 world's leading scientists. In the future, the chemist refined and improved the scheme more than once until it acquired its usual form. The essence of Mendeleev's discovery is that with an increase in atomic mass, the chemical properties of elements change not monotonically, but periodically. After a certain number of elements with different properties, the properties begin to repeat. So, 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 a 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

An engraving depicting Mendeleev. Photo: ITAR-TASS

Many tales circulated about the famous scientist and his discoveries. People at that time had little idea of \u200b\u200bchemistry and believed that doing chemistry was something like eating baby soup and stealing on an industrial scale. Therefore, Mendeleev's activities quickly acquired a mass of rumors and legends. One of the legends says that Mendeleev opened the table of chemical elements in a dream. The case is not the only one; August Kekule, who dreamed of the formula of the benzene ring, also spoke about his discovery. However, Mendeleev only laughed at the critics. “I’ve been thinking about it for maybe twenty years, but you say: I sat and suddenly ... it’s ready!”, The scientist once said about his discovery. Another tale 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 chemist's contemporaries laughed, saying that the scientist "does a good job under the influence of alcohol combined with water," and the next generations already called Mendeleev the discoverer of vodka. They also laughed at the scientist's way of life, and especially at the fact that Mendeleev equipped his laboratory in the hollow of a huge oak tree. Also, contemporaries made fun of Mendeleev's passion for suitcases. The scientist, during his involuntary inactivity in Simferopol, had to while away the time weaving suitcases. Later, he independently made cardboard containers for the needs of the laboratory. Despite the clearly "amateur" nature of this hobby, Mendeleev was often called the "master of the suitcase". The 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. The new chemical element was discovered by the spouses Maria and Pierre Curie, who discovered that the waste left after the separation of uranium from uranium ore is more radioactive than pure uranium. Since then no one knew what radioactivity was, then rumor quickly attributed healing properties and the ability to cure almost all diseases known to science to the new element. Radium has been included in foods, toothpaste, and face creams. The wealthy wore watches, the dials of which 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 years - until the 30s of the twentieth century, when scientists discovered the true properties of radioactivity and found out how harmful the effect of radiation on the human body is. Marie Curie died in 1934 from radiation sickness caused by long-term exposure to radium. Nebulium and Coronium

The periodic table not only ordered chemical elements into a single harmonious system, but also made it possible to predict many discoveries of new elements. At the same time, some chemical "elements" were declared non-existent on the grounds that they did not fit into the concept of the periodic law. The most famous story is the "discovery" of new elements nebulium and corona. While studying the solar atmosphere, astronomers found 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 called coronium (because the lines were discovered while studying the Sun's "corona" - 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, since there was no room for elements with the properties of nebulium and coronium in the periodic table. After testing, it was found that nebulium is the usual terrestrial oxygen, and coronium is highly ionized iron. Note that today in the Moscow Central House of Scientists of the Russian Academy of Sciences will solemnly name two chemical elements discovered by scientists from Dubna near Moscow.

Mendeleev was then only 35 years old.

Mendeleev sent the printed leaflets with the table of elements to many domestic and foreign chemists, and only after that he left Petersburg to inspect the cheese dairy.
Before leaving, he still managed to hand over to NA Menshutkin, an organic chemist and future historian of chemistry, the manuscript of the article "Correlation 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 short report on the Periodic Law on behalf of Mendeleev. At first, the report did not attract much attention from chemists, and the President of the Russian Chemical Society, Academician Nikolai Nikolayevich 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, a lot of excellent convergence, even fun to read, God bless you in experimental confirmation of your conclusions. Sincerely devoted to you and deeply respecting you N. Zinin. "

So what is periodicity?

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

The most important thing in the discovery of the Periodic Law is prediction existence of not yet discovered chemical elements. Under aluminum Al Mendeleev left room for his analogue " ekaaluminium", under boron B - for " ekabora"and under silicon Si - for " ekasilicon"That is how Mendeleev called the not yet discovered chemical elements. He even gave them the symbols El, Eb and Es.

Regarding the element "ekasilitsiya" Mendeleev wrote: "It seems to me that the most interesting of the undoubtedly missing metals will be the one that belongs to the IV group of carbon analogs, namely, the III row. This will be the metal immediately following silicon, and therefore we will call its ekasilicon ". Indeed, this not yet open element was supposed to become a kind of "lock" connecting two typical non-metals - carbon C and silicon Si - with two typical metals - tin Sn and lead Pb.

Not all foreign chemists immediately appreciated the significance of Mendeleev's discovery. It changed a lot in the world of the prevailing ideas. Thus, the German physicochemist Wilhelm Ostwald, the future Nobel laureate, argued that it was not the law that was discovered, but the principle of classifying "something indefinite." German chemist Robert Bunsen, who discovered two new alkaline elements in 1861, rubidium Rb and cesium Cs, wrote that Mendeleev carried chemists "into the contrived world of pure abstractions."

Professor of Leipzig University Hermann Kolbe in 1870 called Mendeleev's discovery "speculative". Kolbe was distinguished by his rudeness and rejection of new theoretical views in chemistry. In particular, he was an opponent of the theory of the structure of organic compounds and at one time attacked the article by Jacob van't Hoff "Chemistry in Space". Later, Van't Hoff became the first Nobel laureate for his research. But Kolbe suggested such researchers as Van't Hoff "exclude from the ranks of real scientists and enroll them in the camp of spiritualists"!

Every year the Periodic Law has won an increasing number of supporters, and its discoverer - more and more recognition. High-ranking visitors began to appear in Mendeleev's laboratory, including even the Grand Duke Konstantin Nikolaevich, the head of the naval department.

Triumph

Finally, it was time for triumph. In 1875, the French chemist Paul-Émile Lecoq de Boisbaudran discovered in the mineral wurtzite - zinc sulfide ZnS - predicted by Mendeleev " ekaaluminum"and named him after his homeland gallium Ga (the Latin name for France is "Gaul"). He wrote: "I think there is no need to insist on the great importance of confirming the theoretical conclusions of Mr. Mendeleev."

Note that in the name of the element there is a hint of the name of Boisbaudran himself. The Latin word "gallus" means rooster, and in French the rooster means "le coke". This word is also in the name of the discoverer. What Lecoq de Boisbaudran had in mind when he gave the name to the element - himself or his country - this, apparently, will never be clear.

Mendeleev accurately predicted the properties of eka-aluminum: its atomic mass, metal density, the formula of the oxide El 2 O 3, chloride ElCl 3, sulfate El 2 (SO 4) 3. After the discovery of gallium, these formulas began to be written as Ga 2 O 3, GaCl 3 and Ga 2 (SO 4) 3. Mendeleev predicted that it would be a very low-melting metal, and indeed, the melting point of gallium turned out to be equal to 29.8 ° C. In terms of low melting point, gallium is second only to mercury Hg and cesium Cs.

In 1879, the Swedish chemist Lars Nilsson discovered scandium, which Mendeleev predicted as ekabor Eb. Nilsson wrote: "There is no doubt that in scandia open ekabor... This is how the considerations of the Russian chemist are vividly confirmed, which not only made it possible to predict the existence of scandium and gallium, but also to foresee their most important properties in advance. " composition Be 2 (Y, Sc) 2 FeO 2 (SiO 4) 2.

In 1886, a professor at the Mining Academy in Freiburg, German chemist Clemens Winkler, while analyzing a rare mineral argyrodite of the composition Ag 8 GeS 6, discovered another element predicted by Mendeleev. Winkler named the element he discovered germany Ge in honor of his homeland, but for some reason this caused strong objections from some chemists. They began to accuse Winkler of nationalism, of appropriating the discovery made by Mendeleev, who had already given the name to the element " ekasilicon"and the symbol E. The discouraged Winkler turned to Dmitry Ivanovich himself for advice. He explained that it was the discoverer of the new element who should give it a name.

Mendeleev could not predict the existence of a group of noble gases, and at first there was no place for them in the Periodic Table.
Opening argon English scientists W. Ramsay and J. Rayleigh in 1894 immediately caused heated discussions and doubts about the Periodic Law and the Periodic Table of Elements. Mendeleev at first considered argon to be an allotropic modification of nitrogen and only in 1900, under the pressure of immutable facts, agreed with the presence in the Periodic Table of the "zero" group of chemical elements, which was occupied by other noble gases, which were discovered after argon. This group is now known under the number VIIIA.

In 1905, Mendeleev wrote: "Apparently, the future does not threaten the periodic law with destruction, but only promises superstructures and development, although they wanted to wipe me out as a Russian, especially the Germans."

The discovery of the Periodic Law hastened the development of chemistry and the discovery of new chemical elements.

DI Mendeleev accurately predicted the properties of those not yet discovered elements that follow boron, aluminum and silicon in the groups of the periodic table and which the Russian scientist designated as ekabor, ekaaluminium and ekasilicon. The great search for the predicted elements could begin.

When 5 years later, in August 1875, the French scientist P.E. Lecoq de Boisabaudran announced his discovery of a new element - gallium, which he discovered spectrally in zinc blende, Mendeleev immediately expressed the opinion that this might be ekaaluminium ... For the new element, Mendeleev predicted an atomic mass of 68 and a density of 5.9 to 6.0 g / cm. The French scientist first found the density to be 4.7 g / cm. Only later, after Mendeleev's persistent instructions, when large quantities of pure gallium were at his disposal, Boisbaudran was able to give more accurate information: the density is 5.96 g / cm; atomic mass 69.9.

Chemist K. Winkler describes the situation at that time in the following way: "To assess the voltage with which everyone expected when the properties of gallium were established, it is necessary to imagine that until that time there was not a single proof of the validity and importance of the conclusions drawn from the law of periodicity."

In March 1879, Nilsson, a professor of chemistry at the Swedish University of Uppsala, discovered another unknown element, which he christened scandium.

Nilsson worked with scandium compounds. Metallic Sc \u200b\u200bwas first obtained and investigated in 1937.

When it became known that the physicochemical properties of scandium are close to the predicted properties of ekabor, Mendeleev joyfully exclaimed: "I never expected that during my lifetime I would wait for such a brilliant confirmation of the periodic law!"

DI Mendeleev predicted the properties of ecasilicon in the most detailed way.

Mendeleev not only predicted the properties of ekasilicon and its compounds, but also tried to experimentally discover this element in titanium and niobium ores. However, his attempts were unsuccessful.

Therefore, the scientific world with special interest awaited the discovery of this element.

In September 1885, miners stumbled upon an unusual silver ore at the Freiberg Himmelsfürst mine. The hitherto unknown mineral was named argyrodite. Clemens Winkler, professor of inorganic chemistry at the Freiberg Mining Academy, analyzed this mysterious ore.

However, having determined its chemical composition - 74.7% silver, 17.3% sulfur and over 1% impurities, he found that almost 7% was missing. In addition, from the calculated atomic ratio of silver: sulfur, equal to 1.3, it followed that this is by no means pure silver sulfide Ag2S. Winkler's calculations led to compounds: 2Ag2S * XS or 4Ag2S * YS2. In the first case, X is a bivalent element, such as lead, in the second case, Y is a tetravalent element, like tin .. However, Winkler, as an experienced analyst, immediately determined that argyrodite does not contain either these metals or others known by that time. The difference in analytical data could only mean one thing: there is an unknown element in this new silver ore!

Winkler honestly confessed that the thought of a new element in his hands caused him dizziness and nervous excitement. Without catching his breath, he worked day and night. All his thoughts and feelings were possessed by an unknown chemical element. His iron health was already threatening to shake when on February 6, 1886, Winkler unexpectedly isolated a sulfide of an unknown substance. The latter turned out to be soluble in water. That is why, during the usual washing of sulfide sediments, it so stubbornly escaped our hands.

A researcher is always seized with a feeling of amazing happiness when he follows the trail of a new elementary brick that makes up our planet. Having learned about Mendeleev's predictions, Winkler, like others, feverishly searched for missing elements to fill in the "holes" in the periodic table. He pinned great hopes on the analysis of minerals and ash thrown out from the depths of the earth during the powerful eruption of the Krakatoa volcano in August 1883. However, there was no luck. And now he found a new element in the Freiberg ore. This was the ekasilicon predicted by Mendeleev. When Winkler studied its properties, he was amazed, because with great accuracy the constants coincided with the values \u200b\u200bpredicted by D.I.Mendeleev.

For the atomic mass of ekasilicon, Mendeleev predicted the value 72, for the density - 5.5 g / cm. Winkler found 72.3 and 5.47. The German researcher was also able to confirm the valency equal to IV.

The density of germanium dioxide predicted by D.I.Mendeleev was 4.7 g / cm3. Experimentally, Winkler got 4.70. The density of tetrachloride predicted by Mendeleev is 1.9. In the experiment GeCl4 showed a density of 1.887.

This accuracy of coincidence with chemical predictions amazed Winkler: "You can hardly find a clearer proof of the correctness of the doctrine of the periodicity of the properties of elements, and this is truly not only a simple confirmation of a bold theory, but also means a significant expansion of the chemical horizons, a major step into the field of knowledge."

The joy of the discovery of the element made Winkler enthusiastically take up the pen. Already on February 26, 1886, he wrote to Mendeleev: "I hope that soon I will be able to inform you in more detail about this interesting substance. Today I limit myself to informing you about the triumph of your brilliant research and want to testify my deep reverence and respect."

"Since germanium, discovered by you, is the crown of the periodic system," DI Mendeleev modestly rejected the praise, "this crown belongs to you ... and I will be content with the role of a harbinger."

In reality, this story did not look as smooth as described by the author. After the discovery of germanium, Winkler suggested that the new element is an analogue of antimony and should take a place between antimony and bismuth in the periodic table. Mendeleev did not agree with this and expressed a different assumption: germanium is ecacadmium. For the first time, V. Yu. Richter identified germanium with ecasilicon, who convinced Mendeleev and Winkler of this.

The matter was initially complicated by the fact that Winkler did not indicate its atomic weight in the first reports on the discovery of germanium. In a letter to Mendeleev dated March 5 (New Style), 1886, he wrote: “Until now I have not yet managed to establish the atomic and specific gravity of the new substance, and therefore the question of what place it occupies in the periodic system should remain open ... ". Only by May 1886, Winkler isolated a sufficient amount of Ge and determined its atomic weight (72.75).

The discovery of a new element is like the discovery of the planet Neptune. Its existence was predicted by the French astronomer Le Verrier based on the anomalous orbits of its satellites. Shortly after this prediction, Neptune was discovered. However, since such a name had already been used for the erroneously discovered element, he called the element germanium. Now the composition of argyrodite was no longer a mystery - 4Ag2S * GeS2 - and it could be argued that scientifically grounded, purposeful predictions are possible not only in astronomy.