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The history of the creation of the periodic table. Abstract: “Periodic table of elements D

Essay

“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. Opened by D.I. Mendeleev in February 1869. When comparing the properties of all elements known at that time and the values of their atomic masses (weights). Mendeleev first used the term “periodic law” 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 periodically dependent 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 elements was of great importance for the development of inorganic chemistry in the second half of the 19th century. This significance is currently colossal, because the system itself, as a result of studying the problems of the structure of matter, gradually acquired a 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 for 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 classify 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 with similar properties can be combined in groups of three, which he called triads: Li–Na–K; Ca–Sr–Ba; S–Se–Te; P–As–Sb; Cl–Br–I.

Essence of the proposed 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, did not succeed in breaking 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 complex than triads. In 1843, Gmelin published a table in which chemically similar elements were arranged into groups in order of increasing connecting (equivalent) weights. The elements were composed of 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 changes in the atomic weight of elements, which were developed in detail by the German chemists A. Strecker and G. Chermak.

In the early 60s of the XIX century. several works appeared that immediately preceded the Periodic Law.

Spiral de Chancourtois

A. de Chancourtois arranged all the chemical elements known at that time in a single sequence of increasing 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 unfolding the surface of the cylinder, it turned out that on vertical lines parallel to the cylinder axis, 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 were 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 in common 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 his proposed law of octaves. Newlands showed that in a series of elements arranged in order of increasing atomic weights, the properties of the eighth element are similar to the properties of the first. Newlands tried to give this dependence, which actually occurs for light elements, a universal character. In his table, similar elements were located in horizontal rows, but in the same row there were often elements completely different in properties. In addition, Newlands was forced to place two elements in some cells; finally, the table did not contain any empty seats; As a result, the law of octaves was accepted with extreme skepticism.

Odling and Meyer tables

In the same 1864, the first table of the German chemist L. Meyer appeared; it included 28 elements, arranged 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 work containing a new table entitled “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 the periodic law was discovered (February 17, 1869), he had probably already outlined the question of the relationship between 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 on the relationship between the alkali metals themselves in terms of their atomic weights. He also came close to the question of bringing together and comparing two groups of polar-opposite elements according to the atomic weights of their members, which in fact already meant abandoning the principle of distributing elements according to their atomicity and moving to the principle of their distribution according to atomic weights. This transition was not a preparation for the discovery of the periodic law, but the beginning of the discovery itself

By the beginning of 1869, a significant part of the elements was combined into separate natural groups and families based on common chemical properties; Along with this, another part of them were scattered, isolated 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 analogues of silicon and tin;

– a group of halogens (halogens) – fluorine, chlorine, bromine and iodine;

– copper group – copper and silver;

– zinc group – zinc and cadmium

– iron family – iron, cobalt, nickel, manganese and chromium;

– the family of platinum metals – platinum, osmium, iridium, palladium, ruthenium and rhodium.

The situation was more complicated with elements that could be classified into 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:

– family of rare earth elements – yttrium, erbium, cerium, lanthanum and didymium;

– niobium and tantalum;

– beryllium;

3. Day of the great discovery

DI. was a very versatile scientist. He had long been very interested in agricultural issues. He took a close 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 the 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 artel cheese dairies on the spot. Consent to this kind of trip was expressed by D.I. In December 1868, he examined a number of artel cheese dairies in the Tver province. An additional business trip was needed to complete the examination. The departure was precisely scheduled for February 17, 1869.

2.2. History of the creation of the Periodic Table.

In the winter of 1867-68, Mendeleev began writing the textbook “Fundamentals of Chemistry” and immediately encountered difficulties in systematizing the factual material. By mid-February 1869, pondering the structure of the textbook, he gradually came to the conclusion that the properties of simple substances (and this is the form of 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 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 leave for ten days to examine artel cheese dairies in the Tver province: he received a letter with recommendations for studying cheese production from A. I. Khodnev, one of the leaders of the Free Economic Society.

In St. Petersburg that day it was cloudy and frosty. The trees in the university garden, where the windows of Mendeleev’s apartment overlooked, creaked in the wind. While still in bed, Dmitry Ivanovich drank a mug of warm milk, then got up, washed his face and went to breakfast. He was in a wonderful mood.

At breakfast, Mendeleev had an unexpected idea: to compare the similar atomic masses of various chemical elements and their chemical properties. Without thinking twice, on the back of Khodnev’s letter he wrote down the symbols for chlorine Cl and potassium K with fairly close 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 up to 6.0. Mendeleev could not have known then that the “indefinite zone” between obvious non-metals and metals contained elements - noble gases, the discovery of which would subsequently significantly modify the Periodic Table.

After breakfast, Mendeleev locked himself in his office. He took out a stack of business cards from the desk and began writing on the back of them the symbols of the elements and their main chemical properties. After some time, the household heard the sound coming from the office: “Oooh! Horned one. Wow, what a horned one! I’ll defeat them. I’ll kill them!” These exclamations meant that Dmitry Ivanovich had creative inspiration. Mendeleev moved cards from one horizontal row to another, guided by the values of 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 shape of the future Periodic Table of Chemical Elements began to emerge. So, at first he put a card with the element beryllium Be (atomic mass 14) next to a card with the element aluminum Al (atomic mass 27.4), according to the then tradition, mistaking beryllium for an analogue of aluminum. However, then, after comparing the chemical properties, he placed beryllium over magnesium Mg. Doubting 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 Be 2 O 3 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 elements arranged in increasing order of their atomic masses exhibit a clear periodicity of physical and chemical properties. Throughout the day, Mendeleev worked on the system of elements, breaking off briefly to play with his daughter Olga and have lunch and dinner.

On the evening of March 1, 1869, he completely rewrote the table he had compiled and, under the title “Experience of a system of elements based on their atomic weight and chemical similarity,” sent it to the printing house, making notes for typesetters and putting the date “February 17, 1869” (this is the old style).

This is how the Periodic Law was discovered, the modern formulation of which is as follows: The properties of simple substances, as well as the forms and properties of compounds of elements, are periodically dependent on the charge of the nuclei of their atoms.

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

Before leaving, 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 was the company's clerk at that time, made a short report on the Periodic Law on behalf of Mendeleev. The report at first 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 Some Elements,” Zinin changed his mind and wrote to Mendeleev: “Very, very good, very excellent connections, even fun to read, God grant you good luck in experimental confirmation of your conclusions. Your sincerely devoted and deeply respectful N. Zinin.” Mendeleev did not place all elements in order of increasing atomic masses; in some cases he was more guided by the similarity of chemical properties. Thus, the atomic mass of cobalt Co is greater than that of nickel Ni, and tellurium Te is also greater 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 halogen group, and iodine would become a relative of selenium Se.

To my wife and children. Or maybe he knew that he was dying, but did not want to disturb and worry the family in advance, whom he loved warmly and tenderly.” At 5:20 a.m. On January 20, 1907, Dmitry Ivanovich Mendeleev died. He was buried at the Volkovskoye cemetery in St. Petersburg, not far from the graves of his mother and son Vladimir. In 1911, on the initiative of advanced Russian scientists, the D.I. Museum was organized. Mendeleev, where...

Moscow metro station, research vessel for oceanographic research, 101st chemical element and mineral - mendeleevite. Russian-speaking scientists and jokers sometimes ask: “Isn’t Dmitry Ivanovich Mendeleev a Jew, that’s a very strange surname, didn’t it come from the surname “Mendel”?” The answer to this question is extremely simple: “All four sons of Pavel Maksimovich Sokolov, ...

The lyceum exam, at which old Derzhavin blessed young Pushkin. The role of the meter happened to be played by Academician Yu.F. Fritzsche, a famous specialist in organic chemistry. Candidate's thesis D.I. Mendeleev graduated from the Main Pedagogical Institute in 1855. His thesis "Isomorphism in connection with other relationships of crystalline form to composition" became his first major scientific...

Mainly on the issue of capillarity and surface tension of liquids, and spent his leisure hours in the circle of young Russian scientists: S.P. Botkina, I.M. Sechenova, I.A. Vyshnegradsky, A.P. Borodin and others. In 1861, Mendeleev returned to St. Petersburg, where he resumed lecturing on organic chemistry at the university and published a textbook, remarkable for that time: "Organic Chemistry", in...

At the gymnasium, D.I. Mendeleev studied mediocrely at first. In the quarterly reports preserved in his archive there are many satisfactory grades, and there are more of them in the lower and middle grades. In high school, D.I. Mendeleev became interested in physical and mathematical sciences, as well as history and geography, and he was also interested in the structure of the Universe. Gradually, the young school student’s successes grew in his graduation certificate, received on July 14, 1849. there were only two satisfactory grades: in the law of God (a subject that he did not like) and in Russian literature (there could not be a good grade in this subject, since Mendeleev did not know the Church Slavonic language well). The gymnasium left in the soul of D.I. Mendeleev many bright memories of teachers: about Pyotr Pavlovich Ershov - (author of the fairy tale “The Little Humpbacked Horse”), who was first a mentor, then the director of the Tobolsk gymnasium; about I.K. Rummel - (teacher of physics and mathematics), who revealed to him the ways of understanding nature. Summer 1850 passed in trouble. At first, D.I. Mendeleev submitted documents to the Medical-Surgical Academy, but he did not pass the first test - presence in the anatomical theater. My mother suggested another path - to become a teacher. But admission to the Main Pedagogical Institute took place a year later and precisely in 1850. there was no reception. Fortunately, the petition had an effect, He was enrolled in the institute on government support. Already in his second year, Dmitry Ivanovich became interested in laboratory classes and 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 appointing him as a senior teacher in Simferopol. Dmitry Ivanovich works a lot: he teaches mathematics, physics, biology, and physical geography. Over the course of two years, he published 70 articles in the Journal of the Ministry of Public Education.

In April 1859, the young scientist Mendeleev was sent abroad “to improve his science.” 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 rector of the university.

Mendeleev saw three circumstances that, in his opinion, contributed to the discovery of the periodic law:

Firstly, the atomic weights of most known chemical elements were more or less accurately determined;

Secondly, a clear concept appeared about groups of elements with similar 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 according to their atomic weights.

In September 1869 D.I. Mendeleev showed that the atomic volumes of simple substances are periodically dependent on atomic weights, and in October he discovered the valences of elements in salt-forming oxides.

Summer 1870 Mendeleev found it necessary to change the incorrectly determined atomic weights of indium, cerium, yttrium, thorium and uranium and, in connection with this, changed the placement of these elements in the system. Thus, uranium turned out to be the last element in the natural series and the heaviest in terms of atomic weight.

As new chemical elements were discovered, the need for their systematization became increasingly felt. In 1869, D.I. Mendeleev created the periodic table of elements and discovered the law underlying it. This discovery was a theoretical synthesis of the entire previous development of the 10th century. : Mendeleev compared the physical and chemical properties of all 63 then known chemical elements with their atomic weights and discovered the relationship between the two most important quantitatively measured properties of atoms on which all chemistry was built - atomic weight and valency.

Many years later, Mendeleev described his system as follows: “This is the best summary of my views and considerations on the periodicity of elements.” Mendeleev first cited 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 periodically depending on their atomic weight."

Less than six years later, news spread throughout the world: in 1875. The young French spectroscopist P. Lecoq de Boisbaudran isolated a new element from a mineral mined in the Pyrenees mountains. Boisbaudran was led to the trail 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 to work harder to obtain it in quantities little more than the head of a pin. Imagine 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 density: gallium is heavier than water not 4.7 times, as Boisbaudran claimed, but 5. 9 times. Did someone else discover gallium first? Boisbaudran re-determined the density of gallium by subjecting the metal to more thorough purification. And it turned out that he was mistaken, and the author of the letter - it was, of course, Mendeleev, who had never seen gallium - was right: the relative density of gallium is 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 been predicted by him earlier. Winkler noted that germanium fully corresponds to Mendeleev’s eca-silicon. Winkler wrote in his work: “One can hardly find another more striking proof of the validity of the doctrine of periodicity than in the newly discovered element. This is not just confirmation of a bold theory, here we see an obvious expansion of chemical horizons, 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 came true brilliantly - three new elements were discovered: gallium, scandium, germanium. The beryllium mystery, which has long tormented scientists, has been resolved. Its atomic weight was finally accurately determined, and the element’s place next to lithium was confirmed once and for all. By the 90s of the 19th century. , according to Mendeleev, “periodic legality has become stronger.” Chemistry textbooks in different countries have undoubtedly begun to include the Mendeleev periodic system. The great discovery received universal recognition.

The fate of great discoveries is sometimes very difficult. On their way they encounter trials that sometimes even cast doubt on the truth of the discovery. This was the case 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 to 1868. and this event is associated with the French astronomer J. Jansen and the English astrophysicist N. Lockyer. Jansen was present at a total solar eclipse in India in August 1868. And his main merit is that he managed 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 the same 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 arrived at the addressee on October 26. Not about any new element supposedly present on the Sun. There was not a word in these letters.

Scientists began to study in detail the spectra of prominences. And soon reports appeared that they contained a line that could not belong to the spectrum of any of the elements existing on Earth. In January 1869 Italian astronomer A. Secchi designated it as. In this recording, it entered the history of science as a spectral “continent”. On August 3, 1871, physicist W. Thomson spoke publicly about the new solar cell at an 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 or what its properties are. Some scientists generally rejected the existence of helium on earth, since it could only exist in conditions of high temperatures. Helium was discovered on Earth only in 1895.

This is the nature of the origin of D.I. Mendeleev’s table.

At breakfast, Mendeleev had an unexpected idea: to compare the similar atomic masses of various chemical elements and their chemical properties.

Without thinking twice, on the back of Khodnev’s letter he wrote down the symbols for chlorine Cl and potassium K with fairly close 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 up to 6.0. Mendeleev could not have known then that the “indefinite zone” between obvious non-metals and metals contained elements - noble gases, the discovery of which would subsequently significantly modify the Periodic Table.

After some time, the household heard the sound coming from the office: “Uh-oh! Horned. Wow, what a horned one! I’ll defeat them. I’ll kill them!” These exclamations meant that Dmitry Ivanovich had creative inspiration.

Mendeleev moved cards from one horizontal row to another, guided by the values of 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 shape of the future Periodic Table of Chemical Elements began to emerge.

So, at first he put a card with the element beryllium Be (atomic mass 14) next to a card with the element aluminum Al (atomic mass 27.4), according to the then tradition, mistaking beryllium for an analogue of aluminum. However, then, after comparing the chemical properties, he placed beryllium over magnesium Mg. Doubting 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 elements arranged in increasing order of their atomic masses exhibit a clear periodicity of physical and chemical properties.

Throughout the day, Mendeleev worked on the system of elements, breaking off briefly to play with his daughter Olga and have lunch and dinner.

This is how the Periodic Law was discovered, the modern formulation of which is as follows: “The properties of simple substances, as well as the forms and properties of compounds of elements, are periodically dependent on the charge of the nuclei of their atoms.”

Mendeleev was only 35 years old at that time.

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

After the discovery of the Periodic Law, Mendeleev had much more to do. The reason for the periodic change in the properties of the elements remained unknown, and the structure of the Periodic System itself, where the properties were repeated through seven elements at 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 then just seven elements.

Mendeleev did not place all elements in order of increasing atomic masses; in some cases he was more guided by the similarity of chemical properties. Thus, the atomic mass of cobalt Co is greater than that of nickel Ni, and tellurium Te is also greater 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 halogen group, 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 chemical elements that have not yet been discovered. Under aluminum Al, Mendeleev left a place for its analogue “eka-aluminium”, under boron B - for “eca-boron”, and under silicon Si - for “eca-silicon”. This is what Mendeleev called the yet undiscovered chemical elements. He even gave them the symbols El, Eb and Es.

Regarding the element “exasilicon,” 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 row. This will be the metal immediately following silicon, and therefore we will call his ekasilicium." Indeed, this not yet discovered 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 established ideas. Thus, the German physical chemist Wilhelm Ostwald, a future Nobel Prize laureate, argued that it was not a law that had been discovered, but a principle of classification of “something uncertain.” The German chemist Robert Bunsen, who discovered two new alkali elements, rubidium Rb and cesium Cs, in 1861, wrote that Mendeleev carried chemists “into the far-fetched world of pure abstractions.”

Leipzig University professor Hermann Kolbe called Mendeleev's discovery "speculative" in 1870. 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 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 proposed that researchers such 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 gained more and more recognition. High-ranking visitors began to appear in Mendeleev's laboratory, including even Grand Duke Konstantin Nikolaevich, manager of the naval department.

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. Currently, the law has been refined, and the dependence of the properties is explained by the charge of the atomic nucleus.

The law was discovered by a Russian scientist 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 provide a logical systematization of chemical elements. It also presented for the first time a table with periodically arranged elements, as a graphic 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 three new elements were discovered (gallium in 1875, scandium in 1879 and germanium in 1886), predicted and described by Mendeleev in his famous report, the periodic law was recognized.

Is a universal law of nature.
The table, which 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 being improved and changed, but its essence has remained unchanged.
Made it possible to clarify the atomic weights and other characteristics of some elements and to predict the existence of new elements.
Chemists received a reliable hint 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.
Played a huge role in the development of inorganic chemistry in the 19th century.

History of discovery

There is a beautiful legend that Mendeleev saw his table in a dream, and woke up in the morning and wrote it down. In fact, this is 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 planned to systematize all the knowledge known at that moment. And naturally, he relied on the achievements and discoveries of his predecessors. For the first time, attention to the relationship between atomic weights and the properties of elements was drawn by the German chemist Döbereiner, who tried to divide 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 outer elements. The scientist was thus able to form five groups, for example, Li–Na–K; Cl–Br–I. But these were not all known elements. In addition, the three elements clearly did not exhaust the list of elements with similar properties. Attempts to find a general pattern were later made by the Germans Gmelin and von Pettenkofer, the French J. Dumas and de Chancourtois, and the English 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 draw up a table that includes all known elements arranged according to a certain system. At the same time, he left some cells blank, approximately 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 “periodic law.” Having said “ah,” he went ahead and corrected the atomic weights of the elements that did not fit into the table. Upon closer inspection, it turned out that his corrections were correct, and the discovery of the hypothetical elements he described became the final confirmation of the truth of the new law: practice proved the validity of the theory.

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The history of the creation of the periodic table. Abstract: “Periodic table of elements D

Spiral de Chancourtois

Newlands table

Odling and Meyer tables

History of discovery

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