In the winter of 1867-68, Mendeleev began to write the textbook "Fundamentals of Chemistry" and immediately encountered difficulties in systematizing the factual material. By mid-February 1869, while pondering the structure of the textbook, he gradually came to the conclusion that the properties of simple substances (and this is the form of the existence of chemical elements in a free state) and the atomic masses of elements are connected by a certain pattern.
Mendeleev did not know much about the attempts of his predecessors to arrange the chemical elements in order of increasing atomic masses and about the incidents that arose in this case. For example, he had almost no information about the work of Chancourtois, Newlands, and Meyer.
The decisive stage of his thoughts came on March 1, 1869 (February 14, old style). A day earlier, Mendeleev wrote a request for a ten-day vacation to inspect artel cheese factories in the Tver province: he received a letter with recommendations on studying cheese production from A. I. Khodnev, one of the leaders of the Free Economic Society.
Petersburg that day was cloudy and frosty. The trees creaked in the wind in the university garden, where the windows of Mendeleev's apartment looked out. While still in bed, Dmitry Ivanovich drank a mug of warm milk, then got up, washed himself and went to breakfast. His mood was wonderful.
At breakfast, Mendeleev had an unexpected idea: to compare close atomic masses of various chemical elements and their chemical properties.
Without thinking twice, on the reverse side of Khodnev's letter, he wrote down the symbols for chlorine Cl and potassium K with fairly similar atomic masses, equal to 35.5 and 39, respectively (the difference is only 3.5 units). On the same letter, Mendeleev sketched symbols of other elements, looking for similar "paradoxical" pairs among them: fluorine F and sodium Na, bromine Br and rubidium Rb, iodine I and cesium Cs, for which the mass difference increases from 4.0 to 5.0 and then to 6.0. At that time Mendeleev could not have known that the "indefinite zone" between explicit non-metals and metals contained elements - noble gases, the discovery of which would later significantly modify the Periodic Table.
After breakfast, Mendeleev closed himself in his office. He took out a pack of business cards from the desk and began to write the symbols of the elements and their main chemical properties on their reverse side.
After a while, the household heard how it began to be heard from the office: "Uuu! Horned one. Wow, what a horned one! I will overcome them. I will kill them!" These exclamations meant that Dmitry Ivanovich had a creative inspiration.
Mendeleev shifted the cards from one horizontal row to another, guided by the values of the atomic mass and the properties of simple substances formed by atoms of the same element. Once again, a thorough knowledge of inorganic chemistry came to his aid. Gradually, the appearance of the future Periodic Table of chemical elements began to take shape.
So, at first he put a card with the element beryllium Be (atomic mass 14) next to the card of the aluminum element Al (atomic mass 27.4), according to the then tradition, taking beryllium for an analog of aluminum. However, then, comparing the chemical properties, he placed beryllium over magnesium Mg. Having doubted the then generally accepted value of the atomic mass of beryllium, he changed it to 9.4, and changed the formula of beryllium oxide from Be2O3 to BeO (like magnesium oxide MgO). By the way, the "corrected" value of the atomic mass of beryllium was confirmed only ten years later. He acted just as boldly on other occasions.
Gradually, Dmitry Ivanovich came to the final conclusion that the elements, arranged in ascending order of their atomic masses, show a clear periodicity in physical and chemical properties.
Throughout the day, Mendeleev worked on the system of elements, taking short breaks to play with his daughter Olga, have lunch and dinner.
On the evening of March 1, 1869, he whitewashed the table he had compiled and, under the title "Experiment of a system of elements based on their atomic weight and chemical similarity," sent it to the printer, making notes for typesetters and putting the date "February 17, 1869" (according to the old style ).
Thus, 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.
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. So, cobalt Co has an atomic mass greater than nickel Ni, tellurium Te also has a greater atomic mass than iodine I, but Mendeleev placed them in the order Co - Ni, Te - I, and not vice versa. Otherwise, tellurium would fall into the group of halogens, and iodine would become a relative of selenium Se.
The most important thing in the discovery of the Periodic Law is the prediction of the existence of yet undiscovered chemical elements. Under aluminum Al, Mendeleev left a place for its analogue "ekaaluminum", under boron B - for "ekabor", and under silicon Si - for "ekasilicon". This is how Mendeleev called chemical elements that had not yet been discovered. He even gave them the symbols El, Eb and Es.
Regarding the element "ecasilicon", 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 analogues, namely, to the III series. It will be a metal immediately following silicon, and therefore we will name his exacilitation." Indeed, this as yet undiscovered element should have 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 established ideas. 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". The German chemist Robert Bunsen, who discovered in 1861 two new alkaline elements, rubidium Rb and cesium Cs, wrote that Mendeleev was taking chemists "into a far-fetched world of pure abstractions."
Hermann Kolbe, a professor at the University of Leipzig, called Mendeleev's discovery "speculative" in 1870. Kolbe was distinguished by 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 sharply attacked Jacob van't Hoff's article "Chemistry in Space". Van't Hoff later became the first Nobel laureate for his research. But Kolbe suggested that 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 won more and more supporters, and its discoverer - more and more recognition. High-ranking visitors began to appear in Mendeleev's laboratory, including even Grand Duke Konstantin Nikolayevich, head of the naval department.
At the gymnasium, D. I. Mendeleev studied mediocre at first. There are many satisfactory grades in the quarterly statements preserved in his archive, and there are more of them in the lower and middle grades. In high school, D. I. Mendeleev became interested in the physical and mathematical sciences, as well as in history and geography, he was also interested in the structure of the universe. Gradually, the success of the young schoolboy grew in the graduation certificate received on July 14, 1849. there were only two satisfactory marks: according to the law of God (a subject that he did not like) and in Russian literature (a good mark on this subject could not be, since Mendeleev did not know Church Slavonic well). The gymnasium left in the soul of D. I. Mendeleev many bright memories of teachers: about Pyotr Pavlovich Ershov - (the author of the fairy tale "The Little Humpbacked Horse"), who was first a mentor, then director of the Tobolsk gymnasium; about I. K. Rummel - (teacher of physics and mathematics), who opened before him the ways of knowing nature. Summer 1850 went through trouble. First, D. I. Mendeleev submitted documents to the Medical and Surgical Academy, but he did not pass the first test - the presence in the anatomical theater. Mother suggested another way - to become a teacher. But in the Main Pedagogical Institute, recruitment was made a year later and just in 1850. there was no reception. Fortunately, the petition had an effect, He was enrolled in the institute on state support. Dmitry Ivanovich already in his second year was carried away by classes in laboratories, interesting lectures.
In 1855, D. I. Mendeleev brilliantly graduated from the institute with a gold medal. He was awarded the title of senior teacher. August 27, 1855 Mendeleev received documents on his appointment as a senior teacher in Simferopol. Dmitry Ivanovich works a lot: he teaches mathematics, physics, biology, physical geography. In two years, he published 70 articles in the Journal of the Ministry of National Education.
In April 1859, the young scientist Mendeleev was sent abroad "for improvement in the sciences." He meets with the Russian chemist N. N. Beketov, with the famous chemist M. Berthelot.
In 1860, D. I. Mendeleev participated in the first International Congress of Chemists in the German city of Karlsruhe.
In December 1861, Mendeleev became the rector of the university.
Mendeleev saw three circumstances that, in his opinion, contributed to the discovery of the periodic law:
First, the atomic weights of most of the known chemical elements have been more or less accurately determined;
Secondly, a clear concept appeared about groups of elements similar in chemical properties (natural groups);
Thirdly, by 1869. The chemistry of many rare elements was studied, without knowledge of which it would be difficult to come to any generalization.
Finally, the decisive step towards the discovery of the law was that Mendeleev compared all the elements with each other according to the magnitude of the atomic weights.
In September 1869 D. I. Mendeleev showed that the atomic volumes of simple substances are in a periodic dependence on atomic weights, and in October he discovered the valencies of elements in salt-forming oxides.
In the summer of 1870 Mendeleev considered it necessary to change the incorrectly determined atomic weights of indium, cerium, yttrium, thorium, and uranium, and in connection with this he changed the placement of these elements in the system. So, uranium turned out to be the last element in the natural series, the heaviest in terms of atomic weight.
As new chemical elements were discovered, the need for their systematization was felt more and more acutely. In 1869, D. I. Mendeleev created the periodic system of elements and discovered the law underlying it. This discovery was a theoretical synthesis of all previous developments of the 10th century. : Mendeleev compared the physical and chemical properties of all the then known 63 chemical elements with their atomic weights and revealed the relationship between the two most important quantitatively measured properties of atoms, on which all chemistry was built - atomic weight and valence.
Many years later, Mendeleev described his system as follows: “This is the best set of my views and considerations on the periodicity of the elements.” Mendeleev for the first time gave the canonical formulation of the periodic law, which existed before its physical justification: “The properties of the elements, and therefore the properties of the simple and complex bodies formed by them, stand in a periodic relationship with their atomic weight.
In less than six years, the news spread around the world: in 1875. The young French spectroscopist P. Lecoq de Boisbaudran isolated a new element from a mineral mined in the Pyrenees. Boisbaudran was traced by a faint violet line in the spectrum of the mineral, which could not be attributed to any of the known chemical elements. In honor of his homeland, which in ancient times was called Gaul, Boisbaudran named the new element gallium. Gallium is a very rare metal, and Boisbaudran had more difficulty in extracting it in quantities little more than a pinhead. What was Boisbaudran's surprise when, through the Paris Academy of Sciences, he received a letter with a Russian stamp, which stated: in the description of the properties of gallium, everything is correct, except for the density: gallium is heavier than water not 4.7 times, as Boisbaudran claimed, but 5, 9 times. Has anyone else discovered gallium before? Boisbaudran re-determined the density of gallium by subjecting the metal to a more thorough purification. And it turned out that he was mistaken, and the author of the letter - it was, of course, Mendeleev, who did not see gallium - was right: the relative density of gallium was not 4.7, but 5.9.
And 16 years after Mendeleev's prediction, the German chemist K. Winkler discovered a new element (1886) and named it germanium. This time, Mendeleev himself did not have to point out that this newly discovered element had also been predicted by him earlier. Winkler noted that germanium fully corresponds to Mendeleev's ekasilition. Winkler wrote in his work: “It is hardly possible to find another more striking proof of the validity of the doctrine of periodicity, as in a newly discovered element. This is not just confirmation of a bold theory, here we see an obvious expansion of the chemical outlook, a powerful step in the field of knowledge.
The existence in nature of more than ten new elements unknown to anyone was predicted by Mendeleev himself. For a dozen elements, he predicted
correct atomic weight. All subsequent searches for new elements in nature were carried out by researchers using the periodic law and the periodic system. They not only helped scientists in their search for truth, but also contributed to the correction of errors and misconceptions in science.
Mendeleev's predictions were brilliantly justified - three new elements were discovered: gallium, scandium, germanium. The riddle of beryllium, which has long tormented scientists, has been resolved. Its atomic weight was finally precisely determined, and the place of the element next to lithium was confirmed once and for all. By the 90s of the 19th century. , according to Mendeleev, "periodic legality has been strengthened." In textbooks on chemistry in different countries, no doubt, Mendeleev's periodic system began to be included. The great discovery received universal recognition.
The fate of great discoveries is sometimes very difficult. On their way there are tests that sometimes even cast doubt on the truth of the discovery. So it was with the periodic table of elements.
It was associated with the unexpected discovery of a set of gaseous chemical elements, called inert or noble gases. The first of these is helium. Almost all reference books and encyclopedias date the discovery of helium in 1868. and associate this event with the French astronomer J. Jansen and the English astrophysicist N. Lockyer. Jansen was present at the total solar eclipse in India in August 1868. And his main merit is that he was able to observe solar prominences after the eclipse ended. They were observed only during an eclipse. Lockyer also observed prominences. Without leaving the British Isles, in mid-October of that year. Both scientists sent descriptions of their observations to the Paris Academy of Sciences. But since London is much closer to Paris than Calcutta, the letters almost simultaneously reached the addressee on October 26th. Not about any new element allegedly present on the Sun. There was not a word in these letters.
Scientists began to study in detail the spectra of prominences. And soon there were reports that they contain a line that cannot belong to the spectrum of any of the elements existing on Earth. In January 1869 the Italian astronomer A. Secchi designated it as. In such a record, it entered the history of science as a spectral "continent". On August 3, 1871, the physicist V. Thomson spoke publicly about the new solar element at the annual meeting of British scientists.
This is the true story of the discovery of helium in the Sun. For a long time, no one could say what this element is, what properties it has. Some scientists generally rejected the existence of helium on earth, since it could only exist at high temperatures. Helium was found on Earth only in 1895.
Such is the nature of the origin of the table of D. I. Mendeleev.
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 related to 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 around the world have 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 an increase in the atomic mass, the chemical properties of elements do not change 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
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 soup from babies 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, who dreamed of the formula of the benzene ring, spoke in the same way about his discovery. However, Mendeleev only laughed at the critics. “I’ve been thinking about it for maybe twenty years, and you say: I was sitting in suddenly ... 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 inaction 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 declared 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, since 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.
The material was created on the basis of information from open sources. Prepared by Vasily Makagonov @vmakagonov
abstract
“The history of the discovery and confirmation of the periodic law by D.I. Mendeleev"
St. Petersburg 2007
Introduction
Periodic law D.I. Mendeleev is a fundamental law that establishes a periodic change in the properties of chemical elements depending on the increase in the charges of the nuclei of their atoms. Discovered by D.I. Mendeleev in February 1869. When comparing the properties of all the elements known at that time and the values of their atomic masses (weights). The term "periodic law" was first used by Mendeleev in November 1870, and in October 1871 he gave the final formulation of the Periodic Law: "... the properties of the elements, and therefore the properties of the simple and complex bodies they form, are in periodic dependence on their atomic weight." The graphical (tabular) expression of the periodic law is the periodic system of elements developed by Mendeleev.
1. Attempts by other scientists to derive the periodic law
The periodic system, or periodic classification, of the elements was of great importance for the development of inorganic chemistry in the second half of the 19th century. This value is currently colossal, because the system itself, as a result of studying the problems of the structure of matter, gradually acquired that degree of rationality that could not be achieved by knowing only atomic weights. The transition from empirical regularity to law is the ultimate goal of any scientific theory.
The search for the basis of the natural classification of chemical elements and their systematization began long before the discovery of the Periodic Law. The difficulties faced by the natural scientists who were the first to work in this area were caused by the lack of experimental data: at the beginning of the 19th century. the number of known chemical elements was still too small, and the accepted values of the atomic masses of many elements were inaccurate.
Apart from the attempts of Lavoisier and his school to give a classification of elements based on the criterion of analogy in chemical behavior, the first attempt at a periodic classification of elements belongs to Döbereiner.
Döbereiner triads and the first systems of elements
In 1829, the German chemist I. Döbereiner attempted to systematize the elements. He noticed that some elements similar in their properties can be combined into groups of three, which he called triads: Li–Na–K; Ca-Sr-Ba; S-Se-Te; P–As–Sb; Cl–Br–I.
The essence of the proposed the law of triads Döbereiner was that the atomic mass of the middle element of the triad was close to half the sum (arithmetic mean) of the atomic masses of the two extreme elements of the triad. Although Döbereiner naturally failed to break all known elements into triads, the law of triads clearly indicated the existence of a relationship between atomic mass and the properties of elements and their compounds. All further attempts at systematization were based on the placement of elements in accordance with their atomic masses.
Döbereiner's ideas were developed by L. Gmelin, who showed that the relationship between the properties of elements and their atomic masses is much more complicated than triads. In 1843, Gmelin published a table in which chemically similar elements were arranged into groups in ascending order of their connecting (equivalent) weights. The elements formed triads, as well as tetrads and pentads (groups of four and five elements), and the electronegativity of the elements in the table changed smoothly from top to bottom.
In the 1850s M. von Pettenkofer and J. Dumas proposed the so-called. differential systems aimed at identifying general patterns in the change in the atomic weight of elements, which were developed in detail by German chemists A. Strekker and G. Chermak.
In the early 60s of the XIX century. several works appeared at once that immediately preceded the Periodic Law.
Spiral de Chancourtois
A. de Chancourtua arranged all the chemical elements known at that time in a single sequence of increasing their atomic masses and applied the resulting series to the surface of the cylinder along a line emanating from its base at an angle of 45 ° to the plane of the base (the so-called. earth spiral). When the surface of the cylinder was unfolded, it turned out that on vertical lines parallel to the axis of the cylinder, there were chemical elements with similar properties. So, lithium, sodium, potassium fell on one vertical; beryllium, magnesium, calcium; oxygen, sulfur, selenium, tellurium, etc. The disadvantage of the de Chancourtois spiral was the fact that elements of a completely different chemical behavior appeared on the same line with elements that were similar in their chemical nature. Manganese fell into the group of alkali metals, and titanium, which had nothing to do with them, fell into the group of oxygen and sulfur.
Newlands table
The English scientist J. Newlands in 1864 published a table of elements reflecting the proposed by him law of octaves. Newlands showed that in a series of elements arranged in ascending order of atomic weights, the properties of the eighth element are similar to those of the first. Newlands tried to give this dependence, which actually takes place for light elements, a universal character. In his table, similar elements were arranged in horizontal rows, but elements of completely different properties often turned out to be in the same row. In addition, Newlands was forced to place two elements in some cells; finally, the table did not contain empty seats; as a result, the law of octaves was accepted extremely skeptically.
Odling and Meyer tables
In the same 1864, the first table of the German chemist L. Meyer appeared; 28 elements were included in it, placed in six columns according to their valencies. Meyer deliberately limited the number of elements in the table in order to emphasize the regular (similar to Döbereiner's triads) change in atomic mass in series of similar elements.
In 1870, Meyer published a new table called "The Nature of the Elements as a Function of Their Atomic Weight", consisting of nine vertical columns. Similar elements were located in the horizontal rows of the table; Meyer left some cells blank. The table was accompanied by a graph of the dependence of the atomic volume of an element on the atomic weight, which has a characteristic sawtooth shape, perfectly illustrating the term "periodicity", already proposed by that time by Mendeleev.
2. What was done before the day of the great discovery
The prerequisites for the discovery of the periodic law should be sought in the book of D.I. Mendeleev (hereinafter D.I.) "Fundamentals of Chemistry". The first chapters of the 2nd part of this book by D.I. wrote at the beginning of 1869. The 1st chapter was devoted to sodium, the 2nd - to its analogues, the 3rd - to heat capacity, the 4th - to alkaline earth metals. By the day of the discovery of the periodic law (February 17, 1869), he probably already managed to set out the question of the ratio of such polar-opposite elements as alkali metals and halides, which were close to each other in terms of their atomicity (valency), as well as the question about the ratio of the alkali metals themselves in terms of their atomic weights. He came close to the issue of bringing together and comparing two groups of polar opposite elements in terms of the atomic weights of their members, which in fact already meant the rejection of the principle of distributing elements according to their atomicity and the transition to the principle of their distribution according to atomic weights. This transition was not a preparation for the discovery of the periodic law, but already the beginning of the discovery itself.
By the beginning of 1869, a significant part of the elements were combined into separate natural groups and families on the basis of common chemical properties; along with this, the other part of them was scattered, separate individual elements that were not united into special groups. The following were considered firmly established:
- a group of alkali metals - lithium, sodium, potassium, rubidium and cesium;
- a group of alkaline earth metals - calcium, strontium and barium;
– oxygen group – oxygen, sulfur, selenium and tellurium;
- nitrogen group - nitrogen, phosphorus, arsenic and antimony. In addition, bismuth was often added here, and vanadium was considered as an incomplete analogue of nitrogen and arsenic;
- carbon group - carbon, silicon and tin, and titanium and zirconium were considered as incomplete analogs of silicon and tin;
- a group of halogens (halides) - fluorine, chlorine, bromine and iodine;
– copper group – copper and silver;
– zinc group – zinc and cadmium
– iron family – iron, cobalt, nickel, manganese and chromium;
- family of platinum metals - platinum, osmium, iridium, palladium, ruthenium and rhodium.
The situation was more complicated with such elements that could be assigned to different groups or families:
- lead, mercury, magnesium, gold, boron, hydrogen, aluminum, thallium, molybdenum, tungsten.
In addition, a number of elements were known, the properties of which were not yet sufficiently studied:
- a family of rare earth elements - yttrium, "erbium", cerium, lanthanum and "didim";
– niobium and tantalum;
– beryllium;
3. Grand opening day
DI. was a very versatile scientist. He had a long and very strong interest in agricultural issues. He took the closest part in the activities of the Free Economic Society in St. Petersburg (VEO), of which he was a member. VEO organized artel cheese-making in a number of northern provinces. One of the initiators of this initiative was N.V. Vereshchagin. At the end of 1868, i.e. while D.I. finished issue. 2 of his book, Vereshchagin turned to the VEO with a request to send one of the members of the Society in order to inspect the work of the artel cheese factories on the spot. Consent to this kind of trip was expressed by D.I. In December 1868, he examined a number of artel cheese factories in the Tver province. An additional business trip was needed to complete the survey. Just on February 17, 1869, the departure was scheduled.
The periodic law of Dmitry Ivanovich Mendeleev is one of the fundamental laws of nature, which links the dependence of the properties of chemical elements and simple substances with their atomic masses. At present, the law has been refined, and the dependence of properties is explained by the charge of the atomic nucleus.
The law was discovered by Russian scientists in 1869. Mendeleev presented it to the scientific community in a report to the congress of the Russian Chemical Society (the report was made by another scientist, since Mendeleev was forced to urgently leave on the instructions of the Free Economic Society of St. Petersburg). In the same year, the textbook "Fundamentals of Chemistry" was published, written by Dmitry Ivanovich for students. In it, the scientist described the properties of popular compounds, and also tried to give a logical systematization of chemical elements. It also presented for the first time a table with periodically arranged elements as a graphical interpretation of the periodic law. All subsequent years, Mendeleev improved his table, for example, he added a column of inert gases, which were discovered 25 years later.
The scientific community did not immediately accept the ideas of the great Russian chemist, even in Russia. But after the discovery of three new elements (gallium in 1875, scandium in 1879 and germanium in 1886), predicted and described by Mendeleev in his famous report, the periodic law was recognized.
- It is a universal law of nature.
- The table that graphically represents the law includes not only all known elements, but also those that are still being discovered.
- All new discoveries did not affect the relevance of the law and the table. The table is improved and changed, but its essence has remained unchanged.
- It made it possible to clarify the atomic weights and other characteristics of some elements, to predict the existence of new elements.
- Chemists have received reliable clues on how and where to look for new elements. In addition, the law allows, with a high degree of probability, to determine in advance the properties of yet undiscovered elements.
- He played a huge role in the development of inorganic chemistry in the 19th century.
Discovery history
There is a beautiful legend that Mendeleev saw his table in a dream, and woke up in the morning and wrote it down. Actually, it's just a myth. The scientist himself said many times that he devoted 20 years of his life to the creation and improvement of the periodic table of elements.
It all started with the fact that Dmitry Ivanovich decided to write a textbook on inorganic chemistry for students, in which he was going to systematize all the knowledge known at that time. And of course, he relied on the achievements and discoveries of his predecessors. For the first time, attention was paid to the relationship between atomic weights and the properties of elements by the German chemist Döbereiner, who tried to break the elements known to him into triads with similar properties and weights that obey a certain rule. In each triple, the middle element had a weight close to the arithmetic mean of the two extreme elements. The scientist was thus able to form five groups, for example, Li-Na-K; Cl–Br–I. But these were far from all known elements. In addition, the trio of elements obviously did not exhaust the list of elements with similar properties. Attempts to find a common pattern were later made by the Germans Gmelin and von Pettenkofer, the French J. Dumas and de Chancourtua, the British Newlands and Odling. The German scientist Meyer advanced the furthest, who in 1864 compiled a table very similar to the periodic table, but it contained only 28 elements, while 63 were already known.
Unlike his predecessors, Mendeleev succeeded in 
make a table that includes all known elements located in a certain system. At the same time, he left some cells blank, roughly calculating the atomic weights of some elements and describing their properties. In addition, the Russian scientist had the courage and foresight to declare that the law he discovered was a universal law of nature and called it a "periodic law." Saying "a", he went further and corrected the atomic weights of elements that did not fit into the table. Upon closer examination, it turned out that his corrections were correct, and the discovery of the hypothetical elements he described was the final confirmation of the truth of the new law: practice proved the validity of the theory.
