Discovery of D.I. Mendeleev's periodic law is of great importance for the development of chemistry. The law was the scientific basis of chemistry. The author managed to systematize the richest, but disparate material accumulated by generations of chemists on the properties of elements and their compounds, to clarify many concepts, for example, the concepts of "chemical element" and "simple substance". In addition, D.I. Mendeleev predicted the existence and with amazing accuracy described the properties of many elements unknown at that time, for example, scandium (ekabor), gallium (ekaaluminum), germanium (ekasilicon). In a number of cases, based on the periodic law, the scientist changed the atomic masses of elements accepted at that time ( Zn, La, I, Er, Ce, Th,U), which were previously determined on the basis of erroneous ideas about the valence of elements and the composition of their compounds. In some cases, Mendeleev arranged the elements in accordance with the regular change in properties, assuming the possible inaccuracy of the values of their atomic masses ( Os, Ir, Pt, Au, Te, I, Ni, co) and for some of them, as a result of subsequent refinement, the atomic masses were corrected.
The periodic law and the periodic system of elements serve as the scientific basis for prediction in chemistry. Since the publication of the periodic system, more than 40 new elements have appeared in it. Based on the periodic law, transuranium elements were obtained artificially, including No. 101, called mendelevium.
The periodic law played a decisive role in elucidating the complex structure of the atom. We must not forget that the law was formulated by the author in 1869, i.e. almost 60 years before the modern theory of the structure of the atom finally took shape. And all the discoveries of scientists that followed the publication of the law and the periodic table of elements (we talked about them at the beginning of the presentation of the material) served as confirmation of the brilliant discovery of the great Russian chemist, his extraordinary erudition and intuition.
LITERATURE
1. Glinka N. A. General chemistry / N. A. Glinka. L.: Chemistry, 1984. 702 p.
2. Course of General Chemistry / ed. N. V. Korovina. M.: Higher school, 1990. 446 p.
3. Akhmetov N.S. general and inorganic chemistry / N.S. Akhmetov. M.: Higher school, 1988. 639 p.
4. Pavlov N.N. Inorganic chemistry / N.N. Pavlov. M.: Higher school, 1986. 336 p.
5. Ramsden E.N. Beginnings of modern chemistry / E.N. Ramsden. L.: Chemistry, 1989. 784 p.
The structure of the atom
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Periodic law and periodic system of chemical elements of D. I. Mendeleev on the basis of ideas about the structure of atoms. The value of the periodic law for the development of science.
In 1869, D. I. Mendeleev, based on an analysis of the properties of simple substances and compounds, formulated the Periodic Law:
The properties of simple bodies ... and compounds of elements are in a periodic dependence on the magnitude of the atomic masses of the elements.
On the basis of the periodic law, the periodic system of elements was compiled. In it, elements with similar properties were combined into vertical columns - groups. In some cases, when placing elements in the Periodic system, it was necessary to break the sequence of increasing atomic masses in order to observe the periodicity of the repetition of properties. For example, tellurium and iodine, as well as argon and potassium, had to be "swapped".
The reason is that Mendeleev proposed the periodic law at a time when nothing was known about the structure of the atom.
After the planetary model of the atom was proposed in the 20th century, the periodic law is formulated as follows:
The properties of chemical elements and compounds are in a periodic dependence on the charges of atomic nuclei.
The charge of the nucleus is equal to the number of the element in the periodic system and the number of electrons in the electron shell of the atom.
This formulation explained the "violations" of the Periodic Law.
In the Periodic system, the period number is equal to the number of electronic levels in the atom, the group number for elements of the main subgroups is equal to the number of electrons in the outer level.
The reason for the periodic change in the properties of chemical elements is the periodic filling of electron shells. After filling the next shell, a new period begins. The periodic change of elements is clearly seen in the change in the composition and properties and properties of oxides.
The scientific significance of the periodic law. The periodic law made it possible to systematize the properties of chemical elements and their compounds. When compiling the periodic system, Mendeleev predicted the existence of many yet undiscovered elements, leaving free cells for them, and predicted many properties of undiscovered elements, which facilitated their discovery.
Periodic law of D. I. Mendeleev The properties of simple bodies, as well as the forms and properties of compounds of elements, are in a periodic dependence on. atomic weights of elements
Periodic system of elements. Series of elements within which properties change sequentially, such as a series of eight elements from lithium to neon or from sodium to argon, Mendeleev called periods. If we write these two periods one below the other so that sodium is under lithium, and argon is under neon, we get the following arrangement of elements:
With this arrangement, elements that are similar in their properties and have the same valency, for example, lithium and sodium, beryllium and magnesium, etc., fall into the vertical columns.
Dividing all the elements into periods and arranging one period under another so that elements similar in properties and type of compounds formed fall under each other, Mendeleev compiled a table, which he called the periodic system of elements by groups and series.
The value of the periodic system. The Periodic Table of the Elements had a great influence on the subsequent development of chemistry. It was not only the first natural classification of the chemical elements, which showed that they form a coherent system and are in close connection with each other, but was also a powerful tool for further research.
The dependence of atomic radii on the charge of the atomic nucleus Z has a periodic character. Within one period, with an increase in Z, there is a tendency for the size of the atom to decrease, which is especially clearly observed in short periods.
With the beginning of the construction of a new electron layer, more distant from the nucleus, i.e., during the transition to the next period, the atomic radii increase (compare, for example, the radii of fluorine and sodium atoms). As a result, within the subgroup, as the charge of the nucleus increases, the sizes of atoms increase.
The loss of electron atoms leads to a decrease in its effective dimensions, and the addition of excess electrons leads to an increase. Therefore, the radius of a positively charged ion (cation) is always less, and the radius of a negatively charged non (anion) is always greater than the radius of the corresponding electrically neutral atom.
Within one subgroup, the radii of ions of the same charge increase with increasing nuclear charge. This pattern is explained by an increase in the number of electron layers and a growing distance of outer electrons from the nucleus.
The most characteristic chemical property of metals is the ability of their atoms to easily give up external electrons and turn into positively charged ions, while non-metals, on the contrary, are characterized by the ability to attach electrons to form negative ions. To detach an electron from an atom with the transformation of the latter into a positive ion, you need to expend some energy, called the ionization energy.
The ionization energy can be determined by bombarding atoms with electrons accelerated in an electric field. The lowest field voltage at which the electron velocity becomes sufficient for the ionization of atoms is called the ionization potential of atoms of a given element and is expressed in volts.
With the expenditure of sufficient energy, two, three or more electrons can be torn off from an atom. Therefore, they speak of the first ionization potential (the energy of detachment from the atom of the first electron), the second ionization potential (the energy of detachment of the second electron)
As noted above, atoms can not only donate, but also add electrons. The energy released when an electron is attached to a free atom is called the affinity of the atom for the electron. Electron affinity, like ionization energy, is usually expressed in electronvolts. So, the electron affinity of a hydrogen atom is 0.75 eV, oxygen - 1.47 eV, fluorine - 3.52 eV.
The electron affinity of metal atoms is usually close to zero or negative; from this it follows that for the atoms of most metals, the addition of electrons is energetically unfavorable. The electron affinity of non-metal atoms is always positive and the greater, the closer the non-metal is to the noble gas in the periodic system; this indicates an increase in non-metallic properties as the end of the period is approached.
(?)nine. Chemical bond. Basic types and characteristics of chemical bonds. Conditions and mechanism of its formation. The method of valence bonds. Valency. The concept of the molecular orbital method
When atoms interact, a chemical bond can occur between them, leading to the formation of a stable polyatomic system - a molecule, a molecular non, a crystal. the condition for the formation of a chemical bond is a decrease in the potential energy of a system of interacting atoms.
Theory of chemical structure. The basis of the theory developed by A. M. Butlerov is the following provisions:
Atoms in molecules are connected to each other in a certain sequence. Changing this sequence leads to the formation of a new substance with new properties.
The connection of atoms occurs in accordance with their valency.
The properties of substances depend not only on their composition, but also on their "chemical structure", that is, on the order in which atoms are combined in molecules and the nature of their mutual influence. Atoms that are directly bonded to each other have the strongest influence on each other.
The ideas about the mechanism of formation of a chemical bond, developed by Heitler and London on the example of a hydrogen molecule, were also extended to more complex molecules. The theory of chemical bond developed on this basis was called the method of valence bonds (the VS method). The VS method gave a theoretical explanation of the most important properties of the covalent bond and made it possible to understand the structure of a large number of molecules. Although, as we will see below, this method did not turn out to be universal and in some cases is not able to correctly describe the structure and properties of molecules, nevertheless it played an important role in the development of the quantum mechanical theory of chemical bonding and has not lost its significance to this day. Valency is a complex concept. Therefore, there are several definitions of valence, expressing various aspects of this concept. The following definition can be considered the most general: the valency of an element is the ability of its atoms to combine with other atoms in certain ratios.
Initially, the valency of the hydrogen atom was taken as the unit of valence. The valence of another element can be expressed in this case by the number of hydrogen atoms that attaches to itself or replaces one atom of this other element.
We already know that the state of electrodes in an atom is described by quantum mechanics as a set of atomic electron orbitals (atomic electron clouds); each such orbital is characterized by a certain set of atomic quantum numbers. The MO method proceeds from the assumption that the state of electrons in a molecule can also be described as a set of molecular electron orbitals (molecular electron clouds), with each molecular orbital (MO) corresponding to a certain set of molecular quantum numbers. As in any other many-electron system, the Pauli principle remains valid in a molecule (see § 32), so that each MO can contain no more than two electrons, which must have oppositely directed spins.
On the basis of the Periodic Law, Mendeleev compiled a classification of chemical elements - the periodic system. It consists of 7 periods and 8 groups.
The periodic law marked the beginning of the modern stage in the development of chemistry. With its discovery, it became possible to predict new elements and describe their properties.
With the help of the Periodic Law, atomic masses were corrected and the valences of some elements were refined; the law reflects the interconnection of elements and the interdependence of their properties. The periodic law confirmed the most general laws of the development of nature, opened the way to knowledge of the structure of the atom.
The Periodic Table of the Elements had a great influence on the subsequent development of chemistry. It was not only the first natural classification of the chemical elements, which showed that they form a coherent system and are in close connection with each other, but was also a powerful tool for further research.
At the time when Mendeleev compiled his table on the basis of the periodic law he had discovered, many elements were still unknown. So, for example, the element located in the fourth row was unknown. In terms of atomic weight, it followed calcium, but it could not be placed immediately after calcium, since it would fall into the third group, while tetravalent forms the highest oxide TiO 2, and for all other properties it should be assigned to the fourth group. Therefore, Mendeleev skipped one cell, i.e., left a free space between calcium and titanium. On the same basis, two free cells were left in the fifth row between zinc and arsenic, now occupied by the elements thallium and germanium. There were also empty seats in other rows. Mendeleev was not only convinced that there must be still unknown elements that would fill these places, but also in advancepredicted the properties of such elements based on their position among other elements in the periodic table.
One of them, which in the future was to take a place between calcium and titanium, he gave the name eka-boron (since its properties were supposed to resemble boron); the other two, for which there were empty places in the table in the fifth row between zinc and arsenic, were called eka-aluminum and eka-silicon.
Predicting the properties of these unknown elements, Mendeleev wrote: “I decide to do this so that, although in time, when one of these predicted bodies is discovered, I will be able to finally convince myself and > assure other chemists of the validity of those assumptions that underlie the proposed system by me."
Over the next 15 years, Mendeleev's predictions were brilliantly confirmed: all three expected elements were indeed discovered. First, the French chemist Lecoq de Boisbaudran discovered a new element that has all the properties of eca-aluminum; after that, Nilson discovered in Sweden, which had the properties of eka-boron, and, finally, a few more years later in Germany, Winkler discovered an element that he called germanium, which turned out to be identical with eka-silicium.
To judge the amazing accuracy of Mendeleev's predictions, let's compare the properties of eca-silicon predicted by him in 1871 with the properties of germanium discovered in 1886:
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eca-silicon properties Eka-silicon Es is a fusible metal capable of volatilizing in extreme heat The atomic weight of Es is close to 72 Specific gravity Es approx. 5.5 EsO 2 should be easy to recover The specific gravity of EsO 2 will be close to 4.7 EvCl 4 - a liquid boiling at about 90 °, its specific gravity is close to 1.9 |
germanium properties Atomic weight Ge 72.6 Specific gravity Ge 5.35 at 20° GeO 2 is easily reduced by coal or hydrogen to metal Specific gravity of GeO 2 4.703 at 18° GeCl 4 - liquid boiling at 83 °, its specific gravity is 1.88 at 18 ° |
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The discovery of gallium, scandium and germanium was the greatest triumph of the periodic law. The whole world started talking about the theoretical predictions of the Russian chemist that had come true and about his periodic law, which after that received universal recognition.
Mendeleev himself greeted these discoveries with deep satisfaction. “While writing in 1871 an article on the application of periodic law to determine the properties of elements not yet discovered, he said, I did not think that I would live to justify this consequence of the periodic law, but reality answered differently. Three elements were described by me: ecabor, ecaaluminum and ecasilicium, and in less than 20 years I had the greatest joy to see all three open ... ".
The periodic system was also of great importance in solving the problem of the valence and the values of the atomic weights of certain elements. So, for example, the element has long been considered an analogue of aluminum and its oxide was assigned the formula Be 2 O 3. By analysis, it was found that in beryllium oxide, 16 weight parts of oxygen account for 9 weight. including beryllium. But since the volatile compounds of beryllium were not known, it was not possible to accurately determine the atomic weight of this element. Based on the percentage composition and the proposed formula of beryllium oxide, its atomic weight was considered equal to 13.5. The periodic system showed that there is only one place for beryllium in the table, namely above magnesium, so that its oxide must have the formula BeO, whence the atomic weight of beryllium is nine. This conclusion was soon confirmed by determinations of the vapor density of beryllium chloride, which made it possible to calculate the atomic weight of beryllium.
Similarly, the periodic table gave impetus to the correction of the atomic weights of certain rare elements. For example, cesium was previously assigned an atomic weight of 123.4. Mendeleev, arranging the elements in a table, found that, according to its properties, cesium should be in the left column of the first group under rubidium and therefore will have an atomic weight of about 130. The latest definitions show that the atomic weight of cesium is 132.91.
Initially, he was met very coldly and incredulously. When Mendeleev, relying on his discovery, called into question a number of experimental data on atomic weights and decided to predict the existence and properties of elements not yet discovered, many chemists reacted to his bold statements with undisguised disdain. So, for example, L. Meyer wrote in 1870 about the periodic law: "It would be hasty to change the hitherto accepted atomic weights on such shaky grounds."
However, after Mendeleev's predictions were confirmed and received universal recognition, attempts were made in a number of countries to challenge Mendeleev's primacy and attribute the discovery of the periodic law to other scientists.
Protesting against such attempts, Mendeleev wrote: “The approval of a law is possible only with the help of deriving consequences from it, without which it is impossible and not expected, and justifying those consequences in experimental verification. That is why, having seen, I, for my part (1869-1871), deduced from it such logical consequences that could show whether it was true or not. Without such a method of testing, no law of nature can be established. Neither Chancourtois, to whom the French attribute the right to discover the periodic law, nor Newlands, whom the British put forward, nor L. Meyer, whom others have quoted as the founder of the periodic law, dared to predict properties of undiscovered elements, to change the "accepted weights of atoms" and in general to consider the periodic law as a new, strictly established law of nature, capable of covering hitherto ungeneralized facts, as I did from the very beginning (1869).
The discovery of the periodic law and the creation of a system of chemical elements was of great importance not only for chemistry and other natural sciences, but also for philosophy, for our entire understanding of the world. Revealing the relationship between the properties of chemical elements and the quantity in their atoms, the periodic law was a brilliant confirmation of the universal law of the development of nature, the law of the transition of quantity into quality.
Before Mendeleev, chemists grouped elements according to their chemical similarity, seeking to bring together only similar elements. Mendeleev approached the consideration of elements in a completely different way. He embarked on the path of convergence of dissimilar elements, placing next to him chemically different elements that had close values of atomic weights. It was this comparison that made it possible to reveal a deep organic connection between all elements and led to the discovery of the periodic law.
periodic law of mendeleev atom
The periodic law made it possible to bring into the system and generalize a huge amount of scientific information in chemistry. This function of the law is called integrative. It manifests itself especially clearly in the structuring of the scientific and educational material of chemistry. Academician A.E. Fersman said that the system united all chemistry within the framework of a single spatial, chronological, genetic, energy connection.
The integrative role of the Periodic Law was also manifested in the fact that some data on the elements, allegedly falling out of the general patterns, were verified and refined both by the author himself and by his followers.
This happened with the characteristics of beryllium. Prior to Mendeleev's work, it was considered a trivalent analogue of aluminum due to their so-called diagonal similarity. Thus, in the second period there were two trivalent elements and not a single divalent element. It was at this stage, first at the level of mental model constructions, that Mendeleev suspected an error in the study of the properties of beryllium. Then he found the work of the Russian chemist Avdeev, who claimed that beryllium is divalent and has an atomic weight of 9. Avdeev's work remained unnoticed by the scientific world, the author died early, apparently having been poisoned by extremely poisonous beryllium compounds. The results of Avdeev's research were established in science thanks to the Periodic Law.
Such changes and refinements of the values of both atomic weights and valences were made by Mendeleev for nine more elements (In, V, Th, U, La, Ce and three other lanthanides). Ten more elements had only atomic weights corrected. And all these refinements were subsequently confirmed experimentally.
In the same way, the work of Karl Karlovich Klaus helped Mendeleev to form a kind of VIII group of elements, explaining the horizontal and vertical similarities in the triads of elements:
iron cobalt nickel
Ruthenium Rhodium Palladium
octium iridium platinum
The prognostic (predictive) function of the Periodic Law received the most striking confirmation in the discovery of unknown elements with serial numbers 21, 31 and 32. Their existence was first predicted on an intuitive level, but with the formation of the system, Mendeleev was able to calculate their properties with a high degree of accuracy. The well-known story of the discovery of scandium, gallium and germanium was the triumph of Mendeleev's discovery. F. Engels wrote: “By unconsciously applying the Hegelian law on the transition of quantity into quality, Mendeleev accomplished a scientific feat that can be safely put next to the discovery of Laverrier, who calculated the orbit of the unknown planet Neptune.” However, there is a desire to argue with the classic. First, all of Mendeleev's research, starting from his student years, quite consciously relied on the Hegelian law. Secondly, Laverrier calculated the orbit of Neptune according to the long-known and proven laws of Newton, and D. I. Mendeleev made all predictions on the basis of the universal law of nature discovered by him.
At the end of his life, Mendeleev noted with satisfaction: “While writing in 1871 an article on the application of the periodic law to the determination of the properties of elements not yet discovered, I did not think that I would live to justify this consequence of the periodic law, but reality answered differently. Three elements were described by me: ecabor, ecaaluminum and ecasilicium, and in less than 20 years I had the greatest joy to see all three discovered ... L. de Boisbaudran, Nilsson and Winkler, for my part, I consider true reinforcers of the periodic law. Without them, it would not have been recognized to the same extent as it is now.” In total, Mendeleev predicted twelve elements.
From the very beginning, Mendeleev pointed out that the law describes the properties not only of the chemical elements themselves, but also of many of their compounds, including hitherto unknown ones. It suffices to give an example to confirm this. Since 1929, when Academician P. L. Kapitsa first discovered the non-metallic conductivity of germanium, the development of the theory of semiconductors began in all countries of the world. It immediately became clear that elements with such properties occupy the main subgroup of group IV. Over time, the understanding came that compounds of elements located in periods equidistant from this group (for example, with a general formula like AzB;) should have semiconductor properties to a greater or lesser extent. This immediately made the search for new practically important semiconductors purposeful and predictable. Almost all modern electronics is based on such connections.
It is important to note that predictions within the framework of the Periodic System were made even after its universal recognition. In 1913 Mose-lee discovered that the wavelength of X-rays, which are obtained from anticathodes made from different elements, changes regularly depending on the serial number conventionally assigned to the elements in the Periodic system. The experiment confirmed that the atomic number of an element has a direct physical meaning. Only later were serial numbers associated with the value of the positive charge of the nucleus. On the other hand, Moseley's law made it possible to immediately experimentally confirm the number of elements in periods and, at the same time, to predict the places of hafnium (No. 72) and rhenium (No. 75) that had not yet been discovered by that time.
The same studies by Moseley made it possible to remove the serious "headache" that Mendeleev was given by certain deviations from the correct series of elements increasing in the table of atomic masses. Mendeleev made them under the pressure of chemical analogies, partly at the expert level, and partly at the intuitive level. For example, cobalt was ahead of nickel in the table, and iodine with a lower atomic weight followed heavier tellurium. It has long been known in the natural sciences that one "ugly" fact, which does not fit into the framework of the most beautiful theory, can ruin it. Similarly, unexplained deviations threatened the Periodic Law. But Moseley experimentally proved that the serial numbers of cobalt (No. 27) and nickel (No. 28) correspond exactly to their position in the system. It turned out that these exceptions only confirm the general rule.
An important prediction was made in 1883 by Nikolai Alexandrovich Morozov. For participation in the Narodnaya Volya movement, chemistry student Morozov was sentenced to death, later commuted to life imprisonment in solitary confinement. He spent about thirty years in royal prisons. A prisoner of the Shlisselburg fortress had the opportunity to receive some scientific literature on chemistry. Based on the analysis of the intervals of atomic weights between neighboring groups of elements in the periodic table, Morozov came to an intuitive conclusion about the possibility of the existence of another group of unknown elements with "zero properties" between the groups of halogens and alkali metals. He suggested looking for them in the composition of the air. Moreover, he put forward a hypothesis about the structure of atoms and, on its basis, tried to reveal the causes of periodicity in the properties of elements.
However, Morozov's hypotheses became available for discussion much later, when he was released after the events of 1905. But by that time, inert gases had already been discovered and studied.
For a long time, the fact of the existence of inert gases and their position in the periodic table caused serious controversy in the chemical world. Mendeleev himself for some time believed that an unknown simple substance of the type Nj could be hidden under the name of the discovered argon. The first rational assumption about the place of inert gases was made by the author of their discovery, William Ramsay. And in 1906, Mendeleev wrote: “When the Periodic Table (18b9) was established, not only was argon not known, but there was no reason to suspect the possibility of the existence of such elements. Today ... these elements, in terms of their atomic weights, have taken the exact place between the halogens and the alkali metals.
For a long time there was a dispute: to separate inert gases into an independent zero group of elements or to consider them the main subgroup of group VIII. Each point of view has its pros and cons.
Based on the position of the elements in the Periodic Table, theoretical chemists led by Linus Pauling have long doubted the complete chemical passivity of inert gases, directly pointing to the possible stability of their fluorides and oxides. But only in 1962, the American chemist Neil Bartlett for the first time carried out the reaction of platinum hexafluoride with oxygen under the most ordinary conditions, obtaining xenon hexafluoroplatinate XePtF ^, and after it other gas compounds, which are now more correctly called noble rather than inert.
The periodic law retains its predictive function to this day.
It should be noted that the predictions of the unknown members of any set can be of two types. If the properties of an element that is inside a known series of similar ones are predicted, then such a prediction is called interpolation. It is natural to assume that these properties will be subject to the same laws as the properties of neighboring elements. This is how the properties of the missing elements within the periodic table were predicted. It is much more difficult to foresee the characteristics of new set members if they are outside the described part. Extrapolation - the prediction of function values that are outside a set of known patterns - is always less certain.
It was this problem that confronted scientists when the search for elements beyond the known boundaries of the system began. At the beginning of the XX century. the periodic table ended with uranium (No. 92). The first attempts to obtain transuranium elements were made in 1934, when Enrico Fermi and Emilio Segre bombarded uranium with neutrons. Thus began the road to actinoids and transactinoids.
Nuclear reactions are also used to synthesize other previously unknown elements.
Element No. 101, artificially synthesized by Yeyenne Theodor Seaborg and his collaborators, was named Mendelevium. Seaborg himself said this about it: “It is especially significant to note that element 101 is named after the great Russian chemist D. I. Mendeleev by American scientists, who have always considered him a pioneer in chemistry.”
The number of newly discovered, or rather, artificially created elements is constantly growing. The synthesis of the heaviest nuclei of elements with atomic numbers 113 and 115 was carried out at the Russian Joint Institute for Nuclear Research in Dubna by bombarding the nuclei of artificially obtained americium with nuclei of the heavy calcium-48 isotope. In this case, the core of element No. 115 arises, which immediately decays with the formation of the nucleus of element No. 113. Such superheavy elements do not exist in nature, but they arise during supernova explosions, and could also exist during the Big Bang. Their study helps to understand how our universe came into being.
In total, 39 naturally occurring radioactive isotopes are found in nature. Different isotopes decay at different rates, which is characterized by the half-life. The half-life of uranium-238 is 4.5 billion years, and for some other elements it can be equal to millionths of a second.
Radioactive elements, sequentially decaying, turning into each other, make up whole rows. Three such series are known: according to the initial element, all members of the series are combined into families of uranium, actinouranium and thorium. Another family is made up of artificially obtained radioactive isotopes. In all families, transformations culminate in the formation of non-radioactive lead atoms.
Since only isotopes can be found in the earth's crust, the half-life of which is commensurate with the age of the Earth, it can be assumed that over the course of billions of years of its history there were also such short-lived isotopes that have now died out in the literal sense of the word. These probably included the heavy isotope of potassium-40. As a result of its complete decay, the table value of the atomic mass of potassium today is 39.102, so it is inferior in mass to element No. 18 argon (39.948). This explains the exceptions in the successive increase in the atomic masses of the elements in the periodic table.
Academician V. I. Gol'danskii in a speech dedicated to the memory of Mendeleev noted "the fundamental role that Mendeleev's works play even in completely new areas of chemistry that emerged decades after the death of the brilliant creator of the Periodic System."
Science is the history and repository of the wisdom and experience of the ages, their rational contemplation and tried judgment.
D. I. Mendeleev
It rarely happens that a scientific discovery turns out to be something completely unexpected, almost always it is anticipated:
however, it is often difficult for later generations, who use tried and tested answers to all questions, to appreciate how hard it was for their predecessors.
C. Darwin
Each of the sciences about the world around us has the subject of study of specific forms of motion of matter. The prevailing ideas consider these forms of movement in order of increasing their complexity:
mechanical - physical - chemical - biological - social. Each of the subsequent forms does not reject the previous ones, but includes them.
It is no coincidence that at the celebration of the centenary of the discovery of the Periodic Law, G. T. Seaborg devoted his report to the latest achievements in chemistry. In it, he praised the amazing merits of the Russian scientist: “When considering the evolution of the Periodic System since the time of Mendeleev, the most impressive impression is that he was able to create the Periodic System of the Elements, although Mendeleev did not know such now generally accepted concepts as nuclear structure and isotopes. , the relationship of serial numbers with valency, the electronic nature of atoms, the periodicity of chemical properties explained by electronic structure, and, finally, radioactivity.
We can cite the words of Academician A.E. Fersman, who paid attention to the future: “New theories, brilliant generalizations will appear and die. New ideas will replace our already outdated concepts of the atom and electron. The greatest discoveries and experiments will nullify the past and open horizons of incredible novelty and breadth for today - all this will come and go, but the Periodic Law of Mendeleev will always live and guide searches.
The Periodic Table of the Elements had a great influence on the subsequent development of chemistry. It was not only the first natural classification of the chemical elements, which showed that they form a coherent system and are in close connection with each other, but was also a powerful tool for further research.
At the time when Mendeleev compiled his table on the basis of the periodic law he had discovered, many elements were still unknown. So, element 4 of the scandium period was unknown. In terms of atomic mass, Ca was followed by Ti, but Ti could not be placed immediately after Ca, because it would fall into group 3, but according to the properties of Ti it should be assigned to group 4. Therefore, Mendeleev skipped one cell. On the same basis, two free cells were left between Zn and As in period 4. There were also empty seats in other rows. Mendeleev was not only convinced that there must be still unknown elements that fill these places, but also predicted in advance the properties of such elements, based on their position among other elements of the periodic system. These elements were given the names ekabor (since its properties were supposed to resemble boron), ekaaluminum, ekasilicium ..
The scientific significance of the periodic law. Life and work of D.I. Mendeleev
The discovery of the periodic law and the creation of the Periodic system of chemical elements is the greatest achievement of science in the 19th century. Experimental confirmation of the relative atomic masses changed by D. I. Mendeleev, the discovery of elements with their properties, the arrangement of discovered inert gases in the periodic system led to the universal recognition of the periodic law.
The discovery of the periodic law led to the further rapid development of chemistry: over the next thirty years, 20 new chemical elements were discovered. The periodic law contributed to the further development of work on the study of the structure of the atom, as a result of which the relationship between the structure of the atom and the periodic change in their properties was established. Based on the periodic law, scientists were able to extract substances with desired properties, to synthesize new chemical elements. The periodic law allowed scientists to build hypotheses about the evolution of chemical elements in the universe.
The periodic law of D. I. Mendeleev has general scientific significance and is a fundamental law of nature.
Dmitry Ivanovich Mendeleev was born in 1834 in the city of Tobolsk. After graduating from the Tobolsk gymnasium, he studied at the St. Petersburg Pedagogical Institute, which he graduated with a gold medal. As a student, D. I. Mendeleev began to engage in scientific research. After studying, he spent two years abroad in the laboratory of the famous chemist Robert Bunsen. In 1863 he was elected a professor first at the St. Petersburg Technological Institute, and later at St. Petersburg University.
Mendeleev conducted research in the field of the chemical nature of solutions, the state of gases, and the heat of combustion of fuel. He was interested in various problems of agriculture, mining, metallurgy, worked on the problem of underground fuel gasification, and studied oil business. The most significant result of his creative activity, which brought D. I. Mendeleev worldwide fame, was the discovery in 1869 of the Periodic Law and the Periodic Table of Chemical Elements. He wrote about 500 articles on chemistry, physics, technology, economics, geodesy. He organized and was the director of the first Russian chamber of measures and weights, concluded the beginning of modern metrology. Invented the general equation of state of an ideal gas, generalized the Clapeyron equation (Clapeyron-Mendeleev equation).
Mendeleev lived for 73 years. For his achievements he was elected a member of 90 foreign academies of sciences and an honorary doctorate of many universities. The 101st chemical element (Mendelevius) is named in his honor.
