2 Mendeleev's law is called. Periodic law and periodic system of D.I. Mendeleev (lecture). Manifestations of the periodic law of electronegativity
2.3. DI Mendeleev's periodic law.
The law was discovered and formulated by DI Mendeleev: "The properties of simple bodies, as well as the forms and properties of compounds of elements are periodically dependent on the atomic weights of the elements." The law was created on the basis of a deep analysis of the properties of elements and their compounds. Outstanding achievements in physics, mainly the development of the theory of the structure of the atom, made it possible to reveal the physical essence of the periodic law: the periodicity in the change in the properties of chemical elements is due to a periodic change in the nature of the filling of the outer electron layer with electrons as the number of electrons increases, determined by the charge of the nucleus. The charge is equal to the ordinal number of the element in the periodic system. The modern formulation of the periodic law: "The properties of elements and the simple and complex substances formed by them are periodically dependent on the charge of the atomic nucleus." Created by D.I. Mendeleev in 1869-1871. the periodic system is a natural classification of elements, a mathematical reflection of the periodic law.
Mendeleev was not only the first to accurately formulate this law and present its content in the form of a table, which became classical, but also comprehensively substantiated it, showed its enormous scientific significance, as a guiding classification principle and as a powerful instrument for scientific research.
The physical meaning of the periodic law. It was discovered only after it was found out that the charge of the atomic nucleus increases during the transition from one chemical element to the neighboring one (in the periodic system) per unit of elementary charge. Numerically, the charge of the nucleus is equal to the ordinal number (atomic number Z) of the corresponding element in the periodic system, that is, the number of protons in the nucleus, in turn equal to the number of electrons of the corresponding neutral atom. The chemical properties of atoms are determined by the structure of their outer electron shells, which periodically changes with an increase in the nuclear charge, and, therefore, the basis of the periodic law is the idea of a change in the charge of the nucleus of atoms, and not the atomic mass of elements. A clear illustration of the periodic law is the curves of periodic changes in some physical quantities (ionization potentials, atomic radii, atomic volumes) depending on Z. There is no general mathematical expression for the periodic law. The periodic law is of great natural scientific and philosophical significance. It made it possible to consider all the elements in their interconnection and predict the properties of unknown elements. Thanks to the periodic law, many scientific searches (for example, in the study of the structure of matter - in chemistry, physics, geochemistry, cosmochemistry, astrophysics) have become purposeful. The periodic law is a vivid manifestation of the operation of the general laws of dialectics, in particular the law of the transition from quantity to quality.
The physical stage of development of the periodic law can, in turn, be divided into several stages:
1. Establishment of the divisibility of the atom on the basis of the discovery of the electron and radioactivity (1896-1897);
2. Development of models of the structure of the atom (1911-1913);
3. Discovery and development of the isotope system (1913);
4. Discovery of Moseley's law (1913), which makes it possible to experimentally determine the nuclear charge and the number of an element in the periodic table;
5. Development of the theory of the periodic system based on the concepts of the structure of the electron shells of atoms (1921-1925);
6. Creation of the quantum theory of the periodic table (1926-1932).
2.4. Predicting the existence of unknown elements.
The most important thing in the discovery of the Periodic Law is the prediction of the existence of not yet discovered chemical elements. Under aluminum Al Mendeleev left a place for its analogue "ekaaluminium", under boron B - for "ekabor", and under silicon Si - for "ekasilicon". So named Mendeleev not yet discovered chemical elements. He even gave them the symbols El, Eb and Es.
Regarding the element "ekasilitsiya" 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 analogs, namely, the III row. This will be the metal immediately following silicon, and therefore we will call it ecasilicon. " 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.
Then he predicted the existence of eight more elements, including "dvitellura" - polonium (discovered in 1898), "ekaiod" - astatine (discovered in 1942-1943), "dvimarganese" - technetium (discovered in 1937) , "ecatsia" - France (opened in 1939)
In 1875, the French chemist Paul-Emile Lecoque de Boisbaudran discovered in the mineral wurtzite - zinc sulfide ZnS - predicted by Mendeleev "ekaaluminium" and named it in honor of his homeland gallium Ga (the Latin name for France is "Gaul").
Mendeleev accurately predicted the properties of eka-aluminum: its atomic mass, metal density, the formula of the oxide El 2 O 3, chloride ElCl 3, sulfate El 2 (SO 4) 3. After the discovery of gallium, these formulas began to be written as Ga 2 O 3, GaCl 3 and Ga 2 (SO 4) 3. Mendeleev predicted that it would be a very low-melting metal, and indeed, the melting point of gallium turned out to be equal to 29.8 o C. In terms of low melting point, gallium is second only to mercury Hg and cesium Cs.
The average gallium content in the earth's crust is relatively high, 1.5-10-30% by weight, which is equal to the content of lead and molybdenum. Gallium is a typical trace element. The only gallium mineral, galdite CuGaS2, is very rare. Gallium is stable in air at ordinary temperatures. Above 260 ° C in dry oxygen, slow oxidation is observed (the oxide film protects the metal). Gallium dissolves slowly in sulfuric and hydrochloric acids, rapidly in hydrofluoric acids, and gallium is stable in nitric acid in the cold. Gallium slowly dissolves in hot alkali solutions. Chlorine and bromine react with gallium in the cold, iodine when heated. Molten Gallium at temperatures above 300 ° C interacts with all structural metals and alloys A distinctive feature of Gallium is a large interval of liquid state (2200 ° C) and low vapor pressure at temperatures up to 1100-1200 ° C. Geochemistry of Gallium is closely related to the geochemistry of aluminum, which is due to the similarity of their physicochemical properties. The bulk of gallium in the lithosphere is contained in aluminum minerals. The gallium content in bauxite and nepheline ranges from 0.002 to 0.01%. Increased concentrations of gallium are also observed in sphalerites (0.01-0.02%), in coal (together with germanium), and also in some iron ores. Gallium does not yet have wide industrial application. The potentially possible scale of the associated production of gallium in the production of aluminum still significantly exceeds the demand for the metal.
The most promising application of Gallium is in the form of chemical compounds such as GaAs, GaP, GaSb with semiconducting properties. They can be used in high-temperature rectifiers and transistors, solar batteries and other devices, where the photoelectric effect can be used in the blocking layer, as well as in infrared receivers. Gallium can be used to make highly reflective optical mirrors. An alloy of aluminum with Gallium has been proposed instead of mercury as the cathode of ultraviolet radiation lamps used in medicine. Liquid gallium and its alloys have been proposed to be used for the manufacture of high-temperature thermometers (600-1300 ° C) and manometers. Of interest is the use of Gallium and its alloys as a liquid coolant in nuclear power reactors (this is hindered by the active interaction of Gallium at operating temperatures with structural materials; the Ga-Zn-Sn eutectic alloy has a lower corrosive effect than pure Gallium).
In 1879, Swedish chemist Lars Nilsson discovered scandium, predicted by Mendeleev as ekabor Eb. Nilsson wrote: "There is no doubt that an ekabor was discovered in scandium ... This is how the considerations of the Russian chemist are clearly confirmed, which not only made it possible to predict the existence of scandium and gallium, but also to foresee their most important properties in advance." Scandium was named after Nielson's homeland of Scandinavia, and he discovered it in the complex mineral gadolinite, which has the composition Be 2 (Y, Sc) 2 FeO 2 (SiO 4) 2. The average content of Scandium in the earth's crust (clarke) is 2.2-10-3% by weight. In rocks, the content of Scandium is different: in the ultrabasic 5-10-4, in the basic 2.4-10-3, in the middle 2.5-10-4, in granites and syenites 3.10-4; in sedimentary rocks (1-1.3) .10-4. Scandium is concentrated in the earth's crust as a result of magmatic, hydrothermal and hypergene (surface) processes. There are two known Scandium minerals of their own - tortveitite and sterrettite; they are extremely rare. Scandium is a soft metal; in its pure state it can be easily processed - forging, rolling, stamping. The scope of Scandium application is very limited. Scandium oxide is used to make ferrites for memory elements in high-speed computers. The radioactive 46Sc is used in neutron activation analysis and in medicine. Scandium alloys with a low density and high melting point are promising as structural materials in rocket and aircraft construction, and a number of Scandium compounds can be used in the manufacture of phosphors, oxide cathodes, in glass and ceramic industries, in the chemical industry (as catalysts) and others. areas. In 1886, a professor at the Mining Academy in Freiburg, German chemist Clemens Winkler, while analyzing a rare mineral argyrodite of the composition Ag 8 GeS 6, discovered another element predicted by Mendeleev. Winkler named the element Ge, which he discovered, after his homeland, but for some reason this provoked strong objections from some chemists. They began to accuse Winkler of nationalism, of appropriating the discovery made by Mendeleev, who had already given the element the name "ekasilicium" and the symbol Es. Discouraged, Winkler turned to Dmitry Ivanovich himself for advice. He explained that it was the discoverer of the new element that should give it a name. The total content of Germanium in the earth's crust is 7.10-4% by weight, that is, more than, for example, antimony, silver, bismuth. However, the native minerals Germanium are extremely rare. Almost all of them are sulfosalts: germanite Cu2 (Cu, Fe, Ge, Zn) 2 (S, As) 4, argyrodite Ag8GeS6, confildite Ag8 (Sn, Ce) S6, etc. The bulk of Germanium is scattered in the earth's crust in large numbers rocks and minerals: in sulfide ores of non-ferrous metals, in iron ores, in some oxide minerals (chromite, magnetite, rutile, etc.), in granites, diabases and basalts. In addition, Germanium is present in almost all silicates, in some deposits of coal and oil. Germanium is one of the most valuable materials in modern semiconductor technology. It is used to make diodes, triodes, crystal detectors, and power rectifiers. Monocrystalline Germanium is also used in dosimetric instruments and instruments that measure the strength of constant and alternating magnetic fields. An important field of application of germanium is infrared technology, in particular the production of infrared detectors operating in the 8-14 micron range. Many alloys, which include Germanium, GeO2-based glasses, and other Germanium compounds, are promising for practical use.
Mendeleev could not predict the existence of a group of noble gases, and at first there was no place for them in the Periodic Table.
The discovery of argon Ar by the English scientists W. Ramsay and J. Rayleigh in 1894 immediately caused heated discussions and doubts about the Periodic Law and the Periodic Table of Elements. Mendeleev initially considered argon to be an allotropic modification of nitrogen, and only in 1900, under the pressure of immutable facts, agreed with the presence in the Periodic Table of the "zero" group of chemical elements, which was occupied by other noble gases that were discovered after argon. This group is now known under the number VIIIA.
In 1905, Mendeleev wrote: "Apparently, the future does not threaten the periodic law, but only superstructures and development promises, although they wanted to wipe me out as a Russian, especially the Germans."
The discovery of the Periodic Law hastened the development of chemistry and the discovery of new chemical elements.
Lyceum exam, at which old man Derzhavin blessed young Pushkin. Academician Yu.F. Fritzsche, a well-known specialist in organic chemistry, had a chance to play the role of meter. D. I. Mendeleev graduated from the Main Pedagogical Institute in 1855. The candidate thesis "Isomorphism in connection with other relations of the crystalline form to the 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. Botkin, I.M. Sechenov, I.A. Vyshnegradskiy, 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 ...
Periodic Mendeleev's Law... Discovered by DI Mendeleev while working on the textbook "Fundamentals of Chemistry" (1868-1871). Initially, the table "Experience of a system of elements based on their atomic weight and chemical similarity" was developed (March 1, 1869) (see. Periodic Table of Chemical Elements). Classic Mendeleev's formulation periodic. of the law read: "The properties of elements, and therefore the properties of the simple and complex bodies formed by them, are periodically dependent on their atomic weight." Phys. the periodic law was substantiated thanks to the development of the nuclear model of the atom (see. Atom) and experiment. proof of numbers. equality of the ordinal number of the element in the periodic. the system of the nuclear charge (Z) of its atom (1913). As a result, there was a modern. the formulation of the periodic law: the properties of the elements, as well as the simple and complex substances formed by them, are in the periodic. dependence on the nuclear charge Z. Within the framework of the quantum theory of the atom, it was shown that as Z increases, the structure of the external is periodically repeated. electronic shells of atoms, which directly determines the specificity of the chemical. properties of elements.
The peculiarity of the periodic law is that it has no quantities. mat. expressions in the form of an equation. A clear reflection of the periodic law is periodic. chemical system elements. The frequency of changes in their properties is clearly illustrated by the curves of changes in some physical. quantities, for example, ionization potentials. atomic radii and volumes.
The periodic law is universal for the Universe, retaining its force wherever atomic structures of matter exist. However, its specific manifestations are determined by the conditions in which decomp. chemical properties elements. For example, on Earth, the specificity of these properties is due to the abundance of oxygen and its compounds, incl. oxides, which, in particular, largely contributed to the identification of the very property of periodicity.
The structure of the periodic system. The modern periodic system includes 109 chemical elements (there is information about the synthesis of an element with Z = 110 in 1988). Of these, in nature. objects found 89; all elements following U, or transuranic elements (Z = 93 109), as well as Tc (Z = 43), Pm (Z = 61) and At (Z = 85) were artificially synthesized using decomp. nuclear reactions. Elements with Z = 106 109 have not yet received names, therefore the corresponding symbols in the tables are absent; for the element with Z = 109, the mass numbers of Naib are still unknown. long-lived isotopes.
Over the entire history of the periodic system, more than 500 different versions of its image have been published. This was due to attempts to find a rational solution to certain controversial problems of the structure of the periodic system (placement of H, noble gases, lantanoids and transuranic elements, etc.). Naib. distribution got a trace. tabular forms of expression of the periodic system: 1) the short one was proposed by Mendeleev (in modern form it is placed at the beginning of the volume on a colored flyleaf); 2) long was developed by Mendeleev, improved in 1905 by A. Werner (Fig. 2); 3) the staircase was published in 1921 by H. Bohr (Fig. 3). In recent decades, the short and long forms have been especially widely used, as illustrative and practically convenient. All listed. forms have certain advantages and disadvantages. However, it is hardly possible to suggest K.-L. universal a version of the image of the periodic system, to-ry would adequately reflect all the variety of sv-in chem. elements and the specifics of changing their chemical. behavior as Z increases.
Fund. the principle of constructing the periodic system is to distinguish periods (horizontal rows) and groups (vertical columns) of elements in it. The modern periodic system consists of 7 periods (the seventh, not yet completed, should end with a hypothetical element with Z = 118) and 8 groups. a set of elements, beginning with an alkali metal (or hydrogen in the first period) and ending with a noble gas. The numbers of elements in periods regularly increase and, starting from the second, repeat in pairs: 8, 8, 18, 18, 32, 32, ... (a special case of the first period containing only two elements). The group of elements has no clear definition; formally, its number corresponds to max. the value of the oxidation state of its constituent elements, but this condition is not met in some cases. Each group is subdivided into main (a) and secondary (b) subgroups; each of them contains elements that are similar in chemistry. St. you, the atoms of which are characterized by the same structure externally. electronic shells. In most groups, elements of subgroups a and b show a certain chemical. similarity, preim. in higher oxidation states.
Group VIII occupies a special place in the structure of the periodic system. Throughout the duration. time, only the elements of the "triads" were attributed to it: Fe-Co-Ni and platinum metals (Ru Rh Pd and Os-Ir-Pt), and all noble gases were located on their own. zero group; therefore, the periodic table contained 9 groups. After in the 60s. were received conn. Xe, Kr and Rn, noble gases began to be placed in subgroup VIIIa, and the zero group was abolished. The elements of the triads constituted subgroup VIII6. This "structural design" of group VIII appears now in almost all published versions of the expression of the periodic system.
Will distinguish. the feature of the first period is that it contains only 2 elements: H and He. Hydrogen due to the specificity of sv-in - unity. an element that does not have a clearly defined place in the periodic system. The symbol H is placed either in subgroup Ia, or in subgroup VIIa, or both at the same time, enclosing the symbol in brackets in one of the subgroups, or, finally, depicting it as dec. fonts. These methods of arrangement of H are based on the fact that it has certain formal features of similarity with both alkali metals and halogens.
Rice. 2. Long form periodic. chemical systems elements (modern version). Rice. 3. Ladder form periodic. chemical systems elements (H. Bohr, 1921).
The second period (Li-Ne), containing 8 elements, begins with the alkali metal Li (unity, oxidation state + 1); it is followed by the metal Be (oxidation state + 2). Metallich. the character B (oxidation state +3) is weakly expressed, and the following C is a typical non-metal (oxidation state +4). Subsequent N, O, F and Ne are non-metals, and only N has the highest oxidation state + 5 corresponds to the group number; O and F are among the most reactive non-metals.
The third period (Na-Ar) also includes 8 elements, the nature of the chemical change. sv-in to-ryh is in many respects similar to that observed in the second period. However, Mg and Al are more "metallic" than respectively. Be and B. The remaining elements - Si, P, S, Cl and Ar - are non-metals; they all exhibit oxidation states equal to the group number, except for Ar. T. arr., In the second and third periods, as Z increases, there is a weakening of metallic and strengthening of non-metallic. the nature of the elements.
All elements of the first three periods belong to subgroups a. According to modern terminology, elements belonging to subgroups Ia and IIa are called. I-elements (in the color table, their symbols are given in red), to subgroups IIIa-VIIIa-p-elements (orange symbols).
The fourth period (K-Kr) contains 18 elements. After alkali metal K and alkali-earth. Ca (s-elements) follows a series of 10 so-called. transitional (Sc-Zn), or d-elements (blue symbols), which are included in subgroups b. Most of the transition elements (all of them are metals) exhibit the highest oxidation states equal to the group number, excluding the Fe-Co-Ni triad, where Fe, under certain conditions, has an oxidation state of +6, and Co and Ni are maximally trivalent. Elements from Ga to Kr belong to subgroups a (p-elements), and the nature of the change in their sv-in is in many ways similar to the change in sv-in elements of the second and third periods in the corresponding intervals of values of Z. For Kr, several. relatively stable connections., in the main. with F.
The fifth period (Rb-Xe) is built similarly to the fourth; it also has an insert of 10 transition, or d-elements (Y-Cd). Peculiarities of changes in sv-in elements in the period: 1) in the triad Ru-Rh-Pd ruthenium exhibits max, oxidation state 4-8; 2) all elements of subgroups a, including Xe, exhibit the highest oxidation states equal to the group number; 3) weak metallicity is noted in I. Holy Island. T. arr., St. Islands of the elements of the fourth and fifth periods, as Z increases, change more difficult than St. Islands of the elements in the second and third periods, which is primarily due to the presence of transition d-elements.
The sixth period (Cs-Rn) contains 32 elements. In addition to ten d-elements (La, Hf-Hg), it includes a family of 14 f-elements (black symbols, from Ce to Lu) -lanthanoids. They are very similar in chemistry. sv-you (predominantly in the oxidation state +3) and therefore not m. b. posted on decomp. groups of the system. In the short form of the periodic table, all lantanoids are included in subgroup IIIa (cell La), and their totality is deciphered under the table. This technique is not without its drawbacks, since 14 elements seem to be outside the system. In the long and ladder forms of the periodic table, the specificity of lanthanides is reflected in the general background of its structure. Dr. features of period elements: 1) in the triad Os Ir Pt, only Os exhibits max. oxidation state +8; 2) At has a more pronounced metallicity in comparison with I. character; 3) Rn naib. reactive from noble gases, but strong radioactivity makes it difficult to study its chemical. St.
The seventh period, like the sixth, should contain 32 elements, but is not yet complete. Fr and Ra elements acc. subgroups Ia and IIa, Ac analogue of elements of subgroup III6. According to the actinide concept of G. Seaborg (1944), after Ac follows a family of 14 f-elements of actinides (Z = 90 103). In the short form of the periodic table, the latter are included in the Ac cell and, like the lanthanides, are written separately. line below the table. This technique assumed the presence of a certain chemical. similarities between elements of two f-families. However, a detailed study of the chemistry of actinides showed that they exhibit a much wider range of oxidation states, including such as +7 (Np, Pu, Am). In addition, the stabilization of lower oxidation states (+ 2 or even +1 for Md) is characteristic of heavy actinides.
Assessment of chem. nature Ku (Z = 104) and Ns (Z = 105), synthesized in the number of single very short-lived atoms, made it possible to conclude that these elements are analogs, respectively. Hf and Ta, i.e. d-elements, and should be located in subgroups IV6 and V6. Chem. the identification of elements with Z = 106 109 was not carried out, but it can be assumed that they belong to the transitional elements of the seventh period. Computer calculations indicate that elements with Z = 113,118 belong to p-elements (subgroups IIIa VIIIa).
In 1871 Mendeleev's periodic law was formulated. By this time, 63 elements were known to science, and Dmitry Ivanovich Mendeleev ordered them on the basis of relative atomic mass. The modern periodic table has expanded significantly.
Story
In 1869, while working on a chemistry textbook, Dmitry Mendeleev faced the problem of systematizing the material accumulated over many years by various scientists - his predecessors and contemporaries. Even before Mendeleev's work, attempts were made to systematize the elements, which served as prerequisites for the development of the periodic system.
Rice. 1. Mendeleev D.I ..
Element classification searches are summarized in the table.
Mendeleev ordered the elements according to their relative atomic mass, arranging them in ascending order. There are nineteen horizontal and six vertical rows in total. This was the first edition of the periodic table of the elements. This is where the history of the discovery of the periodic law begins.
It took the scientist almost three years to create a new, more perfect table. Six columns of elements turned into horizontal periods, each of which began with an alkali metal and ended with a non-metal (inert gases were not yet known). The horizontal rows formed eight vertical groups.
Unlike his colleagues, Mendeleev used two criteria for the distribution of elements:
- atomic mass;
- Chemical properties.
It turned out that there is a pattern between these two criteria. After a certain number of elements with increasing atomic mass, the properties begin to repeat themselves.
Rice. 2. The table compiled by Mendeleev.
Initially, the theory was not expressed mathematically and could not be fully confirmed experimentally. The physical meaning of the law became clear only after the creation of the atomic model. The idea is to repeat the structure of the electron shells with a sequential increase in the charges of the nuclei, which is reflected in the chemical and physical properties of the elements.
Law
Having established the periodicity of changes in properties with an increase in atomic mass, Mendeleev in 1871 formulated the periodic law, which became fundamental in chemical science.
Dmitry Ivanovich determined that the properties of simple substances are periodically dependent on the relative atomic masses.
The science of the 19th century did not have modern knowledge about the elements, therefore the modern formulation of the law is somewhat different from Mendeleev's. However, the essence remains the same.
With the further development of science, the structure of the atom was studied, which influenced the formulation of the periodic law. According to the modern periodic law, the properties of chemical elements depend on the charges of atomic nuclei.
table
Since the time of Mendeleev, the table he created has significantly changed and began to reflect almost all the functions and characteristics of the elements. The ability to use the table is essential for further study of chemistry. The modern table is presented in three forms:
- short - periods occupy two lines, and hydrogen is often referred to as group 7;
- long - isotopes and radioactive elements are taken out of the table;
- extra long - each period occupies a separate line.
Rice. 3. Long modern table.
The short table is the most obsolete version that was canceled in 1989, but is still used in many textbooks. The long and extra long shapes are internationally recognized and used all over the world. Despite the established forms, scientists continue to improve the periodic system, offering the latest options.
What have we learned?
Mendeleev's periodic law and periodic system were formulated in 1871. Mendeleev identified the regularities of the properties of elements and ordered them on the basis of the relative atomic mass. As the mass increased, the properties of the elements changed and then repeated. Subsequently, the table was supplemented, and the law was adjusted in accordance with modern knowledge.
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Alchemists also tried to find a law of nature on the basis of which chemical elements could be systematized. But they lacked reliable and detailed information about the elements. By the middle of the XIX century. knowledge about chemical elements has become enough, and the number of elements has increased so much that in science a natural need arose for their classification. The first attempts to classify elements into metals and non-metals were untenable. D. I. Mendeleev's predecessors (I. V. Debereiner, J. A. Newlands, L. Yu. Meyer) did a lot to prepare the discovery of the periodic law, but could not comprehend the truth. Dmitry Ivanovich established a connection between the mass of elements and their properties.
Dmitry Ivanovich was born in Tobolsk. He was the seventeenth child in the family. After graduating from high school in his hometown, Dmitry Ivanovich entered the Main Pedagogical Institute in St. Petersburg, after which he left with a gold medal for two years on a scientific trip abroad. After his return, he was invited to the St. Petersburg University. Starting to lecture in chemistry, Mendeleev did not find anything that could be recommended to students as a textbook. And he decided to write a new book - "Fundamentals of Chemistry".
The discovery of the periodic law was preceded by 15 years of hard work. On March 1, 1869, Dmitry Ivanovich intended to leave Petersburg for the province on business.
The periodic law was discovered based on the characteristics of the atom - the relative atomic mass .
Mendeleev arranged the chemical elements in the order of increasing their atomic masses and noticed that the properties of the elements are repeated after a certain interval - a period, Dmitry Ivanovich arranged the periods one below the other, so that similar elements are located one below the other - on the same vertical, this is how the periodic system was built elements.
March 1, 1869 The wording of the periodic law of D.I. Mendeleev.
The properties of simple substances, as well as the forms and properties of compounds of elements, are periodically dependent on the value of the atomic weights of the elements.
Unfortunately, at first there were very few supporters of the periodic law, even among Russian scientists. There are many opponents, especially in Germany and England.
The discovery of the periodic law is a brilliant example of scientific foresight: in 1870, Dmitry Ivanovich predicted the existence of three then still unknown elements, which he called ekasilicium, ekaaluminium and ekabor. He was able to correctly predict the most important properties of the new elements. And now, 5 years later, in 1875, the French scientist P.E. Lecoq de Boisbaudran, who knew nothing about the works of Dmitry Ivanovich, discovered a new metal, calling it gallium. In a number of properties and method of discovery, gallium coincided with the eka-aluminum predicted by Mendeleev. But its weight turned out to be less than predicted. Despite this, Dmitry Ivanovich sent a letter to France, insisting on his prediction.
The scientific world was stunned that Mendeleev's prediction of properties ekaaluminium
turned out to be so accurate. From this moment on, the periodic law begins to establish itself in chemistry.
In 1879, L. Nilsson in Sweden discovered scandium, which embodied the predicted by Dmitry Ivanovich ekabor
.
In 1886 K. Winkler discovered germanium in Germany, which turned out to be ecasilicon
.
But the genius of Dmitry Ivanovich Mendeleev and his discoveries are not only these predictions!
In four places of the periodic table D.I.Mendeleev arranged the elements not in the order of increasing atomic masses:
Back at the end of the 19th century, D.I. Mendeleev wrote that, apparently, the atom consists of other smaller particles. After his death in 1907, it was proved that the atom consists of elementary particles. The theory of the structure of the atom confirmed Mendeleev's correctness, the rearrangement of these elements not in accordance with the increase in atomic masses is fully justified.
The modern formulation of the periodic law.
The properties of chemical elements and their compounds are periodically dependent on the value of the charge of the nuclei of their atoms, which is expressed in the periodic recurrence of the structure of the outer valence electron shell.
And now, more than 130 years after the discovery of the periodic law, we can return to the words of Dmitry Ivanovich, taken as the motto of our lesson: "The future does not threaten the periodic law with destruction, but only the superstructure and development are promised." How many chemical elements have been discovered at the moment? And this is far from the limit.
The graphical representation of the periodic law is the periodic table of chemical elements. This is a short synopsis of the entire chemistry of the elements and their compounds.
Changes in properties in the periodic table with an increase in the value of atomic weights in the period (from left to right):
1. Metallic properties decrease
2. Non-metallic properties increase
3. The properties of higher oxides and hydroxides vary from basic through amphoteric to acidic.
4. The valence of elements in the formulas of higher oxides increases from IbeforeVii, and in the formulas of volatile hydrogen compounds decreases from IV beforeI.
Basic principles of constructing the periodic system.|
Comparison attribute |
D.I. Mendeleev |
|
1. How is the sequence of elements by numbers established? (What is the basis of the ps?) |
The elements are arranged in order of increasing relative atomic masses. However, there are exceptions. Ar - K, Co - Ni, Te - I, Th - Pa |
|
2. The principle of combining elements into groups. |
Qualitative trait. The similarity of the properties of simple substances and complex ones of the same type. |
|
3. The principle of combining elements into periods. |
The famous Russian scientist Dmitry Ivanovich Mendeleev formulated the periodic law back in the 19th century, which had an exceptionally great influence on the development of physics, chemistry and science in general. But since then, the corresponding concept has undergone a number of changes. What are they?
Periodic Mendeleev's Law: Initial Formulation
In 1871 D.I.Mendeleev proposed to the scientific community a fundamental formulation, according to which the properties of simple bodies, compounds of elements (as well as their forms), as a result, and the properties of bodies formed by them (simple and complex), should be considered as being in periodic dependence on the indicators of their atomic weight.
This formulation was published in the author's article by DI Mendeleev "The periodic legality of chemical elements." The corresponding publication was preceded by a great work of the scientist in the field of research of physical and chemical processes. In 1869, news appeared in the Russian scientific community about the discovery by D. I. Mendeleev of the Periodic Law of Chemical Elements. Soon a textbook was published, in which one of the first versions of the famous Periodic Table was published.
DI Mendeleev was the first to introduce the term "periodic law" to the general public in 1870, in one of his scientific articles. In this material, the scientist pointed out the fact that there are not yet discovered chemical elements. Mendeleev justified this by the fact that the properties of each individual chemical element are intermediate between the characteristics of those that are adjacent to it on the periodic table. Moreover, both in the group and in the period. That is, the properties of an element are intermediate between the characteristics of elements located above and below the table relative to it, as well as those located to the right and left.
The periodic table has become a unique result of scientific works. In addition, the fundamental novelty of Mendeleev's concept was that, firstly, he explained the regularities in the ratios of the atomic masses of chemical elements, and secondly, he invited the research community to consider these regularities as a law of nature.
Within several years after the publication of Mendeleev's periodic law, chemical elements that were not known at the time of publication of the corresponding concept, but predicted by scientists, were discovered. Gallium was discovered in 1875. In 1879 - scandium, in 1886 - germanium. Mendeleev's periodic law has become the undeniable theoretical basis of chemistry.
Modern formulation of the periodic law
With the development of chemistry and physics, DI Mendeleev's concept developed. So, in the late 19th - early 20th centuries, scientists were able to explain the physical meaning of a particular atomic number of a chemical element. Later, the researchers developed a model of changes in the electronic structure of atoms in correlation with the growth of charges of the nuclei of the corresponding atoms.
Now the formulation of the periodic law - taking into account the above and other discoveries of scientists - is somewhat different from the one proposed by D.I.Mendeleev. In accordance with it, the properties of the elements, as well as the substances formed by them (as well as their forms) are characterized by a periodic dependence on the charges of the nuclei of the atoms of the corresponding elements.
Comparison
The main difference between the classical formulation of Mendeleev's periodic law and the modern one is that the initial interpretation of the corresponding scientific law presupposes the dependence of the properties of elements and the compounds formed by them on the indicators of their atomic weight. The modern interpretation also assumes the presence of a similar dependence - but predetermined by the charge of the nuclei of atoms of chemical elements. One way or another, scientists came to the second formulation, over time developing the first through painstaking work.
Having determined what is the difference between the classical and modern formulations of the periodic law of Mendeleev, we will reflect the conclusions in the table.
