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MOST IMPORTANT SCIENTIFIC DISCOVERIES
Periodic law. History and essence of scientific discovery
Directory / The most important scientific discoveries In the history of the development of science, many major discoveries are known. But few of them can be compared with what Mendeleev, the world's greatest chemist, did. Although many years have passed since the discovery of his law, no one can say when the entire content of the famous "Mendeleev's table" will be fully understood. In the words of Dmitri Ivanovich Mendeleev, the discovery of the periodic law was facilitated by the accumulation "by the end of the 60s of such new information about rare elements that opened their many-sided relationships between themselves and other elements." One can list a number of other data that supplemented the idea of the similarity of elements and their properties: the study of isomorphism, the introduction of the concept of valence, the development of new methods for determining atomic masses, the discussion of the Prout hypothesis, etc. Indeed, already in the fifties and sixties, more than a dozen noteworthy attempts to find a system of elements. Increasingly, in some works, thoughts about the need to classify chemical elements appear. So, in the work of A. Berenfeld it is indicated that the study of rare elements is of great importance: "... they more and more fill in the gaps between the known ... bodies of nature and help to make a continuous series of these bodies in which any element would have its specific place." Particularly interesting in this regard is the dissertation of N. Alyshevsky (1865), who wrote: “Recently, with an enormous abundance of materials in chemistry, the desire to systematize and group the facts worked out more and more breaks through. Modern chemists have come to the conclusion that many chemical elements are very different in their external physical properties, in their chemical functions they are very similar, even identical with each other. And again: "If ... natural groups are established in inorganic chemistry for all, as yet isolated, chemically indivisible bodies, then the study of these reactions will be facilitated to the highest degree, and at the same time it will be possible to draw those conclusions, establish such laws that before have hitherto been the domain of organic chemistry alone. N. Alyshevsky himself compared some properties based on the position of elements in their natural groups. But if the level of knowledge of the era objectively determined the possibility of a scientific solution to the problem, then it depended on the level of knowledge of the scientist and his worldview to turn this possibility into reality. It is no coincidence that Mendeleev succeeded in doing this. Dmitry Mendeleev (1834-1907) was born in Tobolsk in the family of the director of the gymnasium and the trustee of public schools in the Tobolsk province, Ivan Pavlovich Mendeleev, and Maria Dmitrievna Mendeleeva, nee Kornilieva. He was raised by his mother, since the father of the future chemist went blind shortly after the birth of his son. In the autumn of 1841, Mitya entered the Tobolsk gymnasium. He was admitted to the first class on the condition that he stay there for two years until he was eight years old. Misfortune haunted the Mendeleev family. In the autumn of 1847, his father died, and three months later, his sister Apollinaria. In the spring of 1849, Mitya graduated from high school, and Marya Dmitrievna, having sold her property, went first to Moscow with her children, and then to St. Petersburg. She wanted her youngest son to go to university. Only at the request of his mother, on August 9, 1850, Dmitry was enrolled as a student at the Main Pedagogical Institute in St. Petersburg in the Faculty of Physics and Mathematics. The first scientific work of Mendeleev "Chemical analysis of orthite from Finland" was published in 1854, the next year he graduated from the institute. In May 1855, the Academic Council awarded Mendeleev the title of "Senior Teacher" and awarded him a gold medal. Doctors recommended that he change the unhealthy Petersburg climate and move south. In Odessa, Mendeleev was appointed teacher of mathematics, physics and natural sciences at the gymnasium at the Richelieu Lyceum. He devoted a lot of time to work on his master's thesis, in which he considered the problem of "specific volumes" from the point of view of Gerard's unitary theory, completely rejecting the dualistic theory of Berzelius. This work showed Mendeleev's amazing ability to generalize and his wide knowledge of chemistry. In the fall, Mendeleev brilliantly defended his thesis, successfully read the introductory lecture "The Structure of Silicate Compounds," and at the beginning of 1857 he became assistant professor at St. Petersburg University. In 1859 he was sent abroad. Mendeleev spent two years in Germany, where he organized his own laboratory. At the end of February 1861, Mendeleev arrived in St. Petersburg. Finding a teaching job in the middle of the school year was impossible. And he decides to write a textbook of organic chemistry. The textbook, which was published soon, as well as the translation of Wagner's "Chemical Technology", brought Mendeleev great fame. On January 1, 1864, Mendeleev was appointed to the post of staff assistant professor of organic chemistry at St. Petersburg University. Simultaneously with this position, Mendeleev received a professorship at the St. Petersburg Institute of Technology. Now there were fewer worries about the material support of the family, and Mendeleev began work on his doctoral dissertation. Thesis defense took place on January 31, 1865. Two months later, Mendeleev was appointed extraordinary professor in the Department of Technical Chemistry at St. Petersburg University, and in December, an ordinary professor. At that time, there was an urgent need to create a new textbook on inorganic chemistry, which would reflect the current level of development of chemical science. This idea captured Mendeleev. At the same time, he began to collect material for the second edition of the textbook, which was to include a description of the chemical elements. Mendeleev carefully studied the description of the properties of elements and their compounds. But in what order should they be carried out? There was no system for the arrangement of elements. Then the scientist made cardboard cards. On each card, he entered the name of the element, its atomic weight, formulas of compounds and basic properties. Gradually, the basket was filled with cards containing information about all the elements known by that time. And yet, for a long time, nothing happened. They say that the scientist saw the periodic table of elements in a dream, it only remained to write it down and substantiate it. But, of course, the discovery was made by him not by chance, since his activities organically combined theory and practice, knowledge of the physical side of the phenomenon, mathematical intuition and philosophical understanding. In addition, Mendeleev was able to critically treat the work of his predecessors and contemporaries. Without oversaturating himself with information, he, as it were, passed the data already received through the prism of a concept that had not yet been fully formed and, like a sculptor, cut off everything superfluous. Gradually, Mendeleev realized that with a change in atomic weight, the properties of the elements also change. February 1869 was drawing to a close. A few days later, the manuscript of the article containing the table of elements was completed and submitted for publication. March 1, 1869 D.I. Mendeleev sent a leaflet to the printing house, on which his "Experience of a system - elements based on their atomic weight and chemical similarity" was written. Two weeks later, he submitted to the Russian Chemical Society an article "Relationship of properties with the atomic weight of elements." The report on the discovery of Mendeleev was made by the editor of the Journal of the Russian Chemical Society, Professor N.A. Menshutkin at a meeting of the society on March 6, 1869. Mendeleev himself was not present at the meeting, since at that time, on the instructions of the Free Economic Society, he examined the cheese factories of the Tver and Novgorod provinces. Since the day when Mendeleev saw the manifestation of the law of nature behind the simple rows of symbols of chemical elements, other problems have faded into the background. He abandoned work on the textbook "Fundamentals of Chemistry", and did not engage in research. The distribution of elements in the table seemed imperfect to him. In his opinion, atomic weights in many cases were not determined accurately, and therefore some elements did not fall into places corresponding to their properties. Taking the periodic law as a basis, Mendeleev changed the atomic weights of these elements and put them on a par with elements similar in properties. In an article published in German in the "Annals" published by Liebig, Mendeleev gave a large place to the section "Application of the Periodic Law to determine the properties of elements not yet discovered." He predicted and described in detail the properties of three elements still unknown to science - eka-boron, eka-aluminum and eka-silicon. It seemed that for Mendeleev the question of the periodic law was settled. But one day in the autumn of 1875, when Mendeleev was looking through the reports of the Paris Academy of Sciences, his eyes fell on the message of Lecoq de Boisbaudran about the discovery of a new element, which he called gallium. However, the French researcher indicated the specific gravity of gallium - 4,7, and according to Mendeleev's calculations, eka-aluminum turned out to be 5,9. Mendeleev decided to write to the scientist, pointing out that, judging by the properties of gallium discovered by him, this is nothing more than eka-aluminum predicted in 1869. And, indeed, more accurate determinations of the specific gravity of gallium gave a value of 5,94. The discovery of gallium caused a real sensation among scientists. The names of Mendeleev and Lecoq de Boisbaudran immediately became known to the whole world. Encouraged by the first success, scientists began to look for other, not yet discovered elements that were predicted by Mendeleev. In dozens of laboratories in Europe, work began to boil, hundreds of scientists dreamed of extraordinary discoveries. And success was not long in coming. In 1879, Professor Lare Frederik Nilson, who worked at Uppsala University (Sweden), discovered a new element that fully corresponds to the eka-boron described by Mendeleev. He named it scandium. The repeated proof of Mendeleev's predictions caused a real triumph. Reports soon began to come in about the election of Mendeleev as an honorary member of various European universities and academies. An excellent confirmation of Mendeleev's law was the group of inert gases discovered by Ramsay, which made it possible to include in the system the "zero" group - the boundary between alkali metals and metalloids. Mendeleev himself wrote about the “strengtheners” of the law: “While writing in 1871 an article on the application of the periodic law to the determination of the properties of still undiscovered elements, I did not think that I would live to justify this consequence of the periodic law, but reality answered differently. I described three elements: eka-boron, eka-aluminum and eka-silicium, and less than 20 years have passed since I already had the greatest joy to see all three discovered and received their names from those three countries where rare minerals containing them were found and where their discovery was made : gallium, scandium and germanium L. de Boisbaudran, Nilsson and Winkler, who discovered them, I, for my part, consider the true strengtheners of the periodic law. Without them, it would not have been recognized to the same extent as it has now happened to the same extent I consider Ramsay the affirmer of the validity of the periodic law ... "Today it is clear that in Mendeleev's discovery three lines of development of chemistry merged together: the search for a systematics of various objects of chemistry (from atoms to crystals) in their relationship - the concept of "chemical element" united them; the study of the individuality of elements, especially rare elements that were then rarely used, which made it possible to reveal the concept of element-analogy; the study of the relationship of properties with the composition and structure of compounds, which led to the formation of a holistic doctrine of periodicity. Author: Samin D.K.
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