Chemistry - Simply"

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Chemistry - Simply"
Chemistry - Simply"

We present another book from the popular science series "Gutenberg Library", which was jointly launched by the educational project "Gutenberg Smoking Room" and the publishing house AST. Alexander Ivanov, author of the book "Chemistry is simple", invites readers to get acquainted with the history of the development of human civilization, presented from the point of view of chemistry. N + 1 publishes a chapter from Ivanov's book dedicated to the discoveries of the great Russian chemist Dmitry Ivanovich Mendeleev.


Mendeleev. Our table

By the middle of the 19th century, scientists finally realized that they could not artificially transform some elements into others. But they constantly discovered more and more new chemical elements that had to be somehow systematized. For this, scientists came up with different theories about protohydrogen, about pra-matter, etc., but all of them were unsuccessful and had no success in scientific circles.

By the time you remember, the atomic weights of the elements had already been calculated. Therefore, before we move on, I advise you to pick up the periodic table. For a more visual, so to speak, idea of the topic of conversation.

So, in 1817, a German chemist Johann Döbereiner discovered that similar elements can be grouped into so-called triads - groups consisting of three elements. The atomic weight of the middle member of this triad was equal to the arithmetic mean weight of the two extreme elements. For example, in the triad potassium (39, 1), rubidium (85, 4) and cesium (132, 9), the average value between potassium and cesium is 86, which is approximately equal to the weight of rubidium.

Since then, the idea of a natural relationship between the chemical and physical properties of elements and their atomic weights has taken root in the minds of scientists. Many of them strove to discover the "general" law of atomic weights, but only in the 70s of the XIX century the chemists D. Newlands and L. Meyer managed to do this.

In 1864 Newlands set forth the idea of the periodicity of atomic weights in the Royal Society of London. He said: "If we arrange all the elements in rows, eight in each, according to their atomic weights, then we will make sure that every eight elements are followed by similar elements." Newlands called this rule "the law of octaves."

Alas, the idea of the dependence of atomic weights on other properties of elements seemed then so implausible that the chairman of the Society turned to the author with an ironic question: "Did the referent try to place the elements in alphabetical order?"

Another German chemist L. Meyer had already been using the system of elements based on the periodicity of their atomic weights in his lectures for several years, but he did not dare to publish it in scientific journals.

Only a Russian scientist-encyclopedist distinguished himself with unprecedented courage in this matter Dmitri Ivanovich Mendeleev (1834-1907). He brought his periodic table almost to perfection and, more interestingly, predicted a number of facts that were destined to come true pretty soon. Of course, at first there were some flaws in the table, but Mendeleev called them a consequence of the incompleteness of knowledge at that time.

Dmitry Mendeleev was born in Tobolsk, in a large family (he was the sixteenth child in a row). His father was the director of the Tobolsk gymnasium, and this circumstance partly helped Mendeleev, who had a persistent aversion to Latin, to graduate from this educational institution. According to the biographer Mendeleev, Dmitry's sister married a Latin teacher from the same gymnasium, and it was rumored that thanks to this circumstance, the future scientist safely bypassed all the obstacles associated with the study of Latin.

However, Mendeleev soon encountered more serious obstacles on the way to further education. His father went blind, a paltry pension was not enough even for the most essential food. Dmitry and his mother moved to her brother in Moscow. There he was supposed to enter the governor's office and become an ordinary official, but despite the lack of funds, he began to think about entering the St. Petersburg Pedagogical Institute. Thanks to the recommendation received at the school, without which there was nothing to go to St. Petersburg at that time, Dmitry entered the institute. The director of the institute, a former friend of Mendeleev's father, even gave him a place in the hostel.

After graduating from the institute, Mendeleev received the position of a teacher at the Simferopol gymnasium. From there he moved to Odessa, but in 1856 he returned to St. Petersburg, where he became a privat-docent of the university. Dmitry devoted three years to the development of several monographs, the publication and defense of his master's work "On specific volumes".

Soon he was sent abroad. For two years he worked in Heidelberg under the guidance of the scientists Bunsen, Kirchhoff and Kopp, which had a noticeable influence on the nature of his further work. A particularly significant role in the life of Mendeleev was played by the congress of German natural scientists held in Karlsruhe in 1860. It was at this congress that molecular theory first received universal recognition and was officially recognized as scientific.

In 1861, upon his return from a trip abroad, Mendeleev returned to the duties of a privat-docent of the university, but already in 1863 he became a professor at the Institute of Technology. By the same time, the release of his extensive doctoral work on the compounds of alcohol with water and the first edition of the well-known Fundamentals of Chemistry dates back to the same period. You can find out about what this work was and what experiments were carried out for it on the YouTube channel "Chemistry is simple" by watching the video "How Mendeleev did not invent vodka". By the way, it is possible that during the development of this particular work, he discovered his periodic law.

In the course of numerous experiments, Mendeleev came to the conviction that atomic weight is an essential basis for the classification of elements. Only 64 elements were known at the time. (Now, let me remind you, their number has reached 118.) His compilation of the periodic table can be compared to the assembly of a complex puzzle, which partially lacked parts.

Take a look at the periodic table. He placed all known elements in horizontal rows (lines) according to their atomic masses. In each row, the chemical and physical properties (melting points, atomic volumes) of the elements gradually change. In vertical rows (columns) there are similar, kind of related elements. So, in the first column there are alkali metals that react in the same way with water (reactions are accompanied by an explosion).


Periodic table of Mendeleev 1871

Of course, we could now consider many analogies in the periodic table, but this will require a deeper understanding of the chemical foundations. We are interested in what influence the periodic table had on the further fate of chemistry.

Mendeleev considered the periodic system to be a law of nature. And since the laws of nature do not allow any deviations, he attributed any exceptions to this system to the imperfection of human knowledge: errors in determining atomic masses and ignorance of some elements. And these conclusions were later confirmed by reality.

Mendeleev corrected the atomic weights of some elements, but one exception remained. Contrary to the periodic table, the atomic weight of tellurium is greater than that of iodine. Cobalt is also heavier than nickel. Although all the elements in the table were in ascending order of atomic masses, these elements were knocked out of the pattern and were in the opposite order.

It is also worth noting that in the table of that time, the first column contained inert gases, which are currently located in the very last column. What is the reason for this? It's simple. As I said above, before the elements in the table stood in increasing mass. It was logical to assume that gases are lighter than other elements (that is why they are, in fact, gases). However, we will soon see that the theory of the structure of the atom will expand, and the principle of arrangement will change slightly. And, nevertheless, it still coincides with the logic embedded in the periodic table.

Currently, the elements are arranged in an order that corresponds to the number of protons in the nucleus of each particular element. For example, there is one proton in the hydrogen nucleus, so it comes first. There are two protons in the nucleus of a helium atom, so it is in second place. In the nucleus, for example, of uranium there are 92 protons, therefore its serial number in the table is 92nd. It would be logical to assume that with an increase in the number of protons in the nucleus, the mass of each next element also increases. However, then Mendeleev did not yet have an idea of the structure of the atom, did not know that the atom has a nucleus consisting of protons and neutrons, and around "revolve" electrons.

But then, at the time of Mendeleev, the strongest impression on scientists was made by his come true prediction of new elements. Wherever there were spaces in the table, Mendeleev put question marks. In his opinion, all these empty cells corresponded to new, not yet discovered chemical elements. By the way, when I was in school, I also asked myself the question: how did Mendeleev manage to predict the properties of new, not yet discovered elements? Now I understand that everything is quite simple: he calculated the atomic weights of the unknown elements using … interpolation. Remember, just above we talked about triads, where the atomic mass of the middle element is equal to the average value of the extreme elements? So, this is how Mendeleev calculated the atomic masses of unknown elements. Simply put, he predicted their physical and chemical properties by analogy with other, neighboring, already known elements of the same group (elements of the same column).

Scientists, who soon discovered a number of new elements, thereby confirmed Mendeleev's brilliant predictions. By the way, many new elements were discovered by them thanks to the invention spectroscope - a device that allows you to detect a new element even when it is contained in an extremely small amount in any compound. The authors (inventors) of the spectroscope were a German physicist G. Kirchhoff and a german chemist R. Bunsen.

In 1821, the German optical physicist Josef Fraunhofer studied the solar spectrum by omitting sunlight through a prism … Visually, the observation looked like a rainbow, and suddenly Fraunhofer discovered that there were black lines in his "rainbow". The physical significance of these lines remained unknown for a long 35 years, until G. Kirchhoff deduced a general theory of the phenomena of light absorption, thereby laying the foundation for spectral analysis.

Based energy conservation law Kirchhoff came to the discovery of an important general law that sounds like this.

Any body in a red-hot state emits certain rays, namely those that it is capable of absorbing at this temperature.

Thus, the Fraunhofer lines are explained by the presence in the atmosphere of the sun of certain elements that absorb rays of a certain wavelength. For example, hydrogen has an absorption spectrum that lacks red at a wavelength of 656 nanometers.

When Bunsen and Kirchhoff determined the spectra of other known elements and compounds, it became possible to determine the chemical composition of substances without carrying out chemical reactions, that is, by determining only the spectrum of a particular substance (this method was called spectral analysis). Figuratively speaking, the spectrum is a kind of fingerprint for every substance.

On September 20, 1875, the French research chemist Lecoq de Boisbaudran discovered a new chemical element - gallium. The one that melts in the hands. The properties of this element completely coincided with Mendeleev's predictions regarding "ekabor" (as gallium was called before its discovery).

And so it began. In 1879 a Swedish chemist L. Nilsson discovered scandium, and a German chemist K. Winkler discovered germanium in 1886. And both of these elements also perfectly fit into the periodic system of D. I. Mendeleev, and their properties completely coincided with his predictions.

The fulfilled prophecy caused a real sensation in the scientific world! The periodic system began to be reprinted and used in all countries, the name of Mendeleev gained worldwide fame.

It seemed that his periodic system had finally established the boundaries of the search for the remaining new elements, which were supposed to fill in the empty gaps in it. But reality threw scientists an interesting surprise: new elements were discovered where they were not expected at all.

So, it was believed that the air has long been thoroughly studied. Ever since the times of K. Scheele and A. Lavoisier, it was known that "clean" air consists of only two gases - nitrogen and oxygen, with 21 parts of oxygen accounting for 79 parts of nitrogen.

However, in 1892, the British physicist Lord Rayleigh, while determining the density of atmospheric nitrogen, made an unexpected discovery. He carried out all physicochemical measurements in his laboratory with extreme accuracy, and then one day, comparing the density of nitrogen, which is part of ordinary air, with the density of nitrogen obtained artificially, he found that the density of atmospheric nitrogen is 2.31, and the density of artificial nitrogen is 2, 30. The difference seems to be small, but it was enough to induce Rayleigh to further research.

And these studies, which he conducted together with the Scottish chemist W. Ramsay, led to the discovery of a new gas. This gas turned out to be chemically less active than nitrogen, moreover, it did not enter into compounds with any other elements, therefore it was called "argon" ("inactive"). The argon content in the air is less than 1%.

Rayleigh and Ramsay carefully purified argon and studied its density, spectrum and other physical properties in the gaseous state. Almost simultaneously with this, Professor K. Olszewski from Krakow managed to liquefy argon and determine its physical properties in the liquefied state. (If you, my dear reader, want to see with your own eyes what liquid and even solid argon looks like, then you just need to go to the "Chemistry - Simple" YouTube channel and find a video called "Argon".) But since it was already opened a new chemical element argon, which means that it was necessary to find a place for it in the periodic table of elements. The atomic weight of argon is 39.9, and therefore it would be logical to place it between potassium and calcium. It didn't work out! There was no room for him! Of course, a natural question immediately arose: what to do with argon if it does not fit into the periodic table ?!

D. Mendeleev himself stated that it is necessary to deprive argon of the right to be considered an element, and proposed to recognize it as a modified nitrogen. However, the ingenious solution in this matter belonged to W. Ramsay.

The impossibility of placing a new element in the generally accepted periodic system led Ramsay to the idea that, in addition to argon, other unknown gases with similar properties must exist in nature. While looking for compounds of argon with other elements, Ramsay began to study the gas contained in the mineral kleveite. Initially, the gas was analyzed by another scientist - Gillebrandt, who considered it to be nitrogen. Ramsay repeated the study and found a similarity in the spectrum of the gas from the mineral to the solar spectrum. The density of this gas was only twice that of hydrogen. Ramsay realized that he was dealing with a new gas. And since this gas was present in the solar spectrum, he named it "Helium" (from the Greek "helios" - the sun).

It was to be expected that other gases similar to helium and argon would soon be discovered. However, Ramsay's search for new gases in minerals, meteorites and mineral waters was unsuccessful. Fortunately, around the same time, a new machine for liquefying air was invented by the English engineer Gampson. It was this machine that helped to discover new elements of the argon group.

Ramsay described his next discovery as follows: “Wanting to learn the art of working with this extraordinary material, I asked Dr. Gampson for one liter of liquid air. Dr. Travers and I played with it, doing various small experiments to prepare for the big experiment, that is, liquefying argon. However, I was sorry to vaporize the entire supply of liquid air without examining the rest. For, although this sought gas, probably, could not be contained in it, it did not seem impossible that argon was accompanied by a heavier gas. This assumption was confirmed."

So, in that very small part of the air, two new gases were discovered: krypton and xenon. From the most volatile part of the air, another gas was released, lighter than argon - neon. Thus, the question of the ratio of argon and other inert gases (helium, krypton, xenon and neon) to the periodic table was resolved. Since all these elements do not combine with other elements, they were assigned a valency equal to zero, and placed them in the zero group - before the alkali metals. (In the modern table, the zero group is absent: inert gases are located in the rightmost column in the last group in accordance with their electronic configuration.)

As a result, these discoveries not only did not undermine the authority of the periodic table of Mendeleev, but also supplemented it, even if in a completely unpredictable way.

However, back to Dmitry Ivanovich. His scientific activity at St. Petersburg University was interrupted unexpectedly even for himself.

In 1890, riots broke out in the higher educational institutions of Russia. Student unrest manifested itself especially strongly at St. Petersburg University. During one of their "gatherings" the students turned to Professor Mendeleev, who was present at it, with a request to convey to the Minister of Education their petition with all sorts of demands. Mendeleev agreed. However, as expected, the minister did not accept him and, in addition, made a stern remark, reprimanding him for interfering in other matters. Because of the conflict that arose, Mendeleev immediately resigned.

Leaving the university at the age of 56, Mendeleev did not stay idle: on the recommendation of the Minister of Finance S. Yu. Witte, he became a member of the Council of Trade and Industry.

The last years of his life Dmitry Ivanovich worked in the Chamber of Weights and Measures founded on his initiative. In addition to carrying out basic scientific measurements, the tasks of this Chamber included the observation of measures and weights, as well as the gradual introduction of the metric system into practical life.


Dmitri Ivanovich Mendeleev

Unfortunately, most of our contemporaries know Mendeleev only for his periodic law. But he conducted research in many fields of activity! So, Mendeleev is the author of fundamental research in physics, metrology, meteorology, economics, works on aeronautics, chemical technology, agriculture, public education and many other works closely related to the needs of the development of production in Russia.

In the process of studying gases, Mendeleev derived the general equation of state for an ideal gas, which included - as a special case - the dependence of the state of the gas on temperature, revealed in 1834 by the French physicist B. P. E. Clapeyron. So, by the way, the Mendeleev-Clapeyron equation, known to all of us from school, appeared.

In addition, it was Mendeleev who proposed the method of fractional distillation of oil with its subsequent separation into components. He was even a member of the commission for the consideration of spiritualistic phenomena and superstitions, which were widespread in society in the mid-19th century. Mendeleev's work on environmental resistance and aeronautics was continued in works devoted to shipbuilding and the development of Arctic navigation. In 1894, at the request of Mendeleev, a pool was built for testing sea vessels in order to create a large Arctic icebreaker.

DI Mendeleev managed to work on improving the quality of the gunpowder used in those years. At the same time, he was an outstanding economist who was able to competently substantiate the main directions of economic development in tsarist Russia.

Summing up, I want to quote a proverb: "A talented person is talented in everything." I am sure that these words characterize Dmitri Ivanovich Mendeleev in the best possible way.

Read in full:

Ivanov, Alexander. Chemistry is simple. History of one science. - M.: Publishing house AST, 2018. - 256 p., [1] p.: ill. - (Gutenberg Library).

You can order this book here.

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