Mendeleev's periodic law, the essence and history of the discovery. Great encyclopedia of oil and gas

The periodic law of chemical elements is a fundamental law of nature that establishes the periodicity of changes in the properties of chemical elements as the charges of the nuclei of their atoms increase. The date of discovery of the law is considered to be March 1 (February 17, old style) 1869, when D. I. Mendeleev completed the development of the “Experience of a system of elements based on their atomic weight and chemical similarity.” The scientist first used the term “periodic law” (“law of periodicity”) at the end of 1870. According to Mendeleev, “three types of data” contributed to the discovery of the periodic law. Firstly, the presence of a sufficiently large number of known elements (63); secondly, satisfactory knowledge of the properties of most of them; thirdly, the fact that the atomic weights of many elements were determined with good accuracy, thanks to which chemical elements could be arranged in a natural series in accordance with the increase in their atomic weights. Mendeleev considered the decisive condition for the discovery of the law to be the comparison of all elements according to their atomic weights (previously only chemically similar elements were compared).

The classic formulation of the periodic law, given by Mendeleev in July 1871, stated: “The properties of the elements, and therefore the properties of the simple and complex bodies they form, are periodically dependent on their atomic weight.” This formulation remained in force for more than 40 years, but the periodic law remained only a statement of facts and had no physical basis. It became possible only in the mid-1910s, when the nuclear planetary model of the atom was developed (see Atom) and it was established that the serial number of an element in the periodic table is numerically equal to the charge of the nucleus of its atom. As a result, the physical formulation of the periodic law became possible: “The properties of elements and the simple and complex substances they form are periodically dependent on the magnitude of the charges of the nuclei (Z) of their atoms.” It is still widely used today. The essence of the periodic law can be expressed in other words: “The configurations of the outer electron shells of atoms are periodically repeated as Z increases”; This is a kind of “electronic” formulation of the law.

An essential feature of the periodic law is that, unlike some other fundamental laws of nature (for example, the law of universal gravitation or the law of equivalence of mass and energy), it does not have a quantitative expression, that is, it cannot be written in the form of any or a mathematical formula or equation. Meanwhile, Mendeleev himself and other scientists tried to look for a mathematical expression of the law. In the form of formulas and equations, various patterns of constructing electronic configurations of atoms can be quantitatively expressed depending on the values ​​of the principal and orbital quantum numbers. As for the periodic law, it has a clear graphical reflection in the form of a periodic system of chemical elements, represented mainly by various types of tables.

The periodic law is a universal law for the entire Universe, manifesting itself wherever material structures of the atomic type exist. However, it is not only the configurations of atoms that periodically change as Z increases. It turned out that the structure and properties of atomic nuclei also change periodically, although the very nature of the periodic change here is much more complicated than in the case of atoms: a regular formation of proton and neutron shells occurs in the nuclei. Nuclei in which these shells are filled (they contain 2, 8, 20, 50, 82, 126 protons or neutrons) are called “magic” and are considered as a kind of boundaries of the periods of the periodic system of atomic nuclei.

Here the reader will find information about one of the most important laws ever discovered by man in the scientific field - the periodic law of Dmitry Ivanovich Mendeleev. You will become familiar with its significance and influence on chemistry; the general provisions, characteristics and details of the periodic law, the history of the discovery and the main provisions will be considered.

What is periodic law

The periodic law is a natural law of a fundamental nature, which was first discovered by D.I. Mendeleev back in 1869, and the discovery itself occurred through a comparison of the properties of some chemical elements and the atomic mass values ​​known at that time.

Mendeleev argued that, according to his law, simple and complex bodies and various compounds of elements depend on their periodic type dependence and on the weight of their atom.

The periodic law is unique in its kind and this is due to the fact that it is not expressed by mathematical equations, unlike other fundamental laws of nature and the universe. Graphically, it finds its expression in the periodic table of chemical elements.

History of discovery

The discovery of the periodic law occurred in 1869, but attempts to systematize all known x-th elements began long before that.

The first attempt to create such a system was made by I. V. Debereiner in 1829. He classified all the chemical elements known to him into triads, related to each other by the proximity of half the sum of the atomic masses included in this group of three components. Following Debereiner, an attempt was made to create a unique table of classification of elements by A. de Chancourtois, he called his system the “earthly spiral”, and after him the Newlands octave was compiled by John Newlands. In 1864, almost simultaneously, William Olding and Lothar Meyer published tables created independently of each other.

The periodic law was presented to the scientific community for review on March 8, 1869, and this happened during a meeting of the Russian Society. Dmitry Ivanovich Mendeleev announced his discovery in front of everyone, and in the same year Mendeleev’s textbook “Fundamentals of Chemistry” was published, where the periodic table created by him was shown for the first time. A year later, in 1870, he wrote an article and submitted it to the Russian Chemical Society, where the concept of the periodic law was first used. In 1871, Mendeleev gave a comprehensive description of his concept in his famous article on the periodic law of chemical elements.

Invaluable contribution to the development of chemistry

The importance of the periodic law is incredibly great for the scientific community around the world. This is due to the fact that its discovery gave a powerful impetus to the development of both chemistry and other natural sciences, for example, physics and biology. The relationship between elements and their qualitative chemical and physical characteristics was open; this also made it possible to understand the essence of the construction of all elements according to one principle and gave rise to the modern formulation of concepts about chemical elements, to concretize the knowledge of substances of complex and simple structure.

The use of the periodic law made it possible to solve the problem of chemical forecasting and determine the reason for the behavior of known chemical elements. Atomic physics, including nuclear energy, became possible as a result of the same law. In turn, these sciences made it possible to expand the horizons of the essence of this law and deepen its understanding.

Chemical properties of elements of the periodic table

In essence, chemical elements are interconnected by the characteristics inherent in them in the state of a free atom or ion, solvated or hydrated, in a simple substance and the form that their numerous compounds can form. However, these properties usually consist of two phenomena: properties characteristic of an atom in a free state and of a simple substance. There are many types of properties of this kind, but the most important are:

1. Atomic ionization and its energy, depending on the position of the element in the table, its ordinal number.
2. The energy affinity of an atom and an electron, which, like atomic ionization, depends on the location of the element in the periodic table.
3. Electronegativity of an atom, which does not have a constant value, but can change depending on various factors.
4. Radii of atoms and ions - here, as a rule, empirical data are used, which is associated with the wave nature of electrons in a state of motion.
5. Atomization of simple substances - a description of the reactivity capabilities of an element.
6. Oxidation states are a formal characteristic, but they appear as one of the most important characteristics of an element.
7. Oxidation potential for simple substances is a measurement and indication of the potential of a substance to act in aqueous solutions, as well as the level of manifestation of redox properties.

Periodicity of internal and secondary type elements

The periodic law gives an understanding of another important component of nature - internal and secondary periodicity. The above-mentioned areas of studying atomic properties are actually much more complex than one might think. This is due to the fact that the elements s, p, d of the table change their qualitative characteristics depending on their position in the period (internal periodicity) and group (secondary periodicity). For example, the internal process of transition of element s from the first group to the eighth to the p-element is accompanied by minimum and maximum points on the curve of the energy line of the ionized atom. This phenomenon shows the internal instability of the periodicity of changes in the properties of an atom according to its position in the period.

Results

Now the reader has a clear understanding and definition of what Mendeleev’s periodic law is, realizes its significance for man and the development of various sciences, and has an idea of ​​its modern provisions and the history of its discovery.

2.3. Periodic law of D.I.Mendeleev.

The law was discovered and formulated by D.I. 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 atomic structure, made it possible to reveal the physical essence of the periodic law: the periodicity in changes in the properties of chemical elements is due to a periodic change in the nature of filling 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 atomic number of the element in the periodic table. The modern formulation of the periodic law: “The properties of elements and the simple and complex substances they form are periodically dependent on the charge of the nuclei of atoms.” 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 precisely formulate this law and present its contents in the form of a table, which became classic, but also comprehensively substantiated it, showed its enormous scientific significance, as a guiding classification principle and as a powerful tool for scientific research.

Physical meaning of the periodic law. It was opened only after it was discovered that the charge of the nucleus of an atom increases when moving from one chemical element to a neighboring one (in the periodic table) by a unit of elementary charge. Numerically, the charge of the nucleus is equal to the atomic number (atomic number Z) of the corresponding element in the periodic table, 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 increasing nuclear charge, and, therefore, the periodic law is based on the idea of ​​​​a change in the charge of the nucleus of atoms, and not the atomic mass of the elements. A clear illustration of the periodic law is the curves of periodic changes in certain physical quantities (ionization potentials, atomic radii, atomic volumes) depending on Z. There is no general mathematical expression for the periodic law. The periodic law has enormous natural scientific and philosophical significance. It made it possible to consider all elements in their mutual connection and predict the properties of unknown elements. Thanks to the periodic law, many scientific searches (for example, in the field of studying the structure of matter - in chemistry, physics, geochemistry, cosmochemistry, astrophysics) have become purposeful. The periodic law is a clear manifestation of the general laws of dialectics, in particular the law of the transition of quantity into 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 based on the discovery of the electron and radioactivity (1896-1897);

2. Development of models of atomic structure (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 element number in the periodic table;

5. Development of the theory of the periodic system based on ideas about the structure of the electronic shells of atoms (1921-1925);

6. Creation of the quantum theory of the periodic system (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 chemical elements that have not yet been discovered. Under aluminum Al, Mendeleev left a place for its analogue “eka-aluminium”, under boron B - for “eca-boron”, and under silicon Si - for “eca-silicon”. This is what Mendeleev called the yet undiscovered chemical elements. He even gave them the symbols El, Eb and Es.

Regarding the element “exasilicon,” Mendeleev wrote: “It seems to me that the most interesting of the undoubtedly missing metals will be the one that belongs to the IV group of carbon analogues, namely, to the III row. This will be the metal immediately following silicon, and therefore let us call it ekasilicium." Indeed, this not yet discovered element was supposed to become a kind of “lock” connecting two typical non-metals - carbon C and silicon Si - with two typical metals - tin Sn and lead Pb.

Then he predicted the existence of eight more elements, including “dwitellurium” - polonium (discovered in 1898), “ecaiod” - astatine (discovered in 1942-1943), “dimanganese” - technetium (discovered in 1937) , "ecacesia" - France (opened in 1939)

In 1875, the French chemist Paul-Emile Lecoq de Boisbaudran discovered the “eka-aluminum” predicted by Mendeleev in the mineral wurtzite - zinc sulfide ZnS - and named it gallium Ga (the Latin name for France is “Gallia”) in honor of his homeland.

Mendeleev accurately predicted the properties of eka-aluminum: its atomic mass, the density of the metal, the formula of El 2 O 3 oxide, ElCl 3 chloride, El 2 (SO 4) 3 sulfate. 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 fusible metal, and indeed, the melting point of gallium turned out to be equal to 29.8 o C. In terms of fusibility, gallium is second only to mercury Hg and cesium Cs.

The average content of gallium in the earth's crust is relatively high, 1.5-10-30% by mass, which is equal to the content of lead and molybdenum. Gallium is a typical trace element. The only Gallium mineral is galdite CuGaS2, which is very rare. Gallium is stable in air at ordinary temperatures. Above 260°C, slow oxidation is observed in dry oxygen (the oxide film protects the metal). Gallium dissolves slowly in sulfuric and hydrochloric acids, quickly in hydrofluoric acid, and is stable in the cold in nitric acid. Gallium dissolves slowly 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 the large range of the liquid state (2200° C) and low vapor pressure at temperatures up to 1100-1200° C. Geochemistry Gallium is closely related to the geochemistry of aluminum, which is due to the similarity of their physicochemical properties. The main part 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 hard coals (together with germanium), and also in some iron ores. Gallium does not yet have widespread industrial use. The potential scale of by-product production of gallium in aluminum production 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, which have semiconductor properties. They can be used in high-temperature rectifiers and transistors, solar batteries and other devices where the photoelectric effect in the blocking layer can be used, as well as in infrared radiation receivers. Gallium can be used to make optical mirrors that are highly reflective. An alloy of aluminum with gallium has been proposed instead of mercury as the cathode of ultraviolet radiation lamps used in medicine. It is proposed to use liquid gallium and its alloys for the manufacture of high-temperature thermometers (600-1300 ° C) and pressure gauges. Of interest is the use of Gallium and its alloys as a liquid coolant in power nuclear reactors (this is hampered by the active interaction of Gallium at operating temperatures with structural materials; the eutectic Ga-Zn-Sn alloy has a less corrosive effect than pure Gallium).

In 1879, Swedish chemist Lars Nilsson discovered scandium, predicted by Mendeleev as ecaboron Eb. Nilsson wrote: “There remains no doubt that ecaboron was discovered in scandium... This clearly confirms the considerations of the Russian chemist, 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 in honor of Nilsson'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 mass. Scandium content in rocks varies: in ultrabasic rocks 5-10-4, in basic rocks 2.4-10-3, in intermediate rocks 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 supergene (surface) processes. Two of Scandium's own minerals are known - tortveitite and sterrettite; they are extremely rare. Scandium is a soft metal, in its pure state it can be easily processed - forged, rolled, stamped. The scope of use of scandium is very limited. Scandium oxide is used to make ferrites for memory elements of high-speed computers. Radioactive 46Sc is used in neutron activation analysis and in medicine. Scandium alloys, which have a low density and high melting point, are promising as structural materials in rocket and aircraft construction, and a number of scandium compounds can find application in the manufacture of phosphors, oxide cathodes, in glass and ceramic production, in the chemical industry (as catalysts) and in others areas. In 1886, a professor at the Mining Academy in Freiburg, the German chemist Clemens Winkler, while analyzing the rare mineral argyrodite with the composition Ag 8 GeS 6, discovered another element predicted by Mendeleev. Winkler named the element he discovered germanium Ge in honor of his homeland, but for some reason this caused sharp 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 who should give it a name. The total content of germanium in the earth's crust is 7.10-4% by mass, i.e. more than, for example, antimony, silver, bismuth. However, germanium's own minerals are extremely rare. Almost all of them are sulfosalts: germanite Cu2 (Cu, Fe, Ge, Zn)2 (S, As)4, argyrodite Ag8GeS6, confieldite Ag8(Sn, Ce) S6, etc. The bulk of germanium is scattered in large quantities in the earth’s crust 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 coal and oil deposits. 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 devices that measure the strength of constant and alternating magnetic fields. An important area of ​​application for germanium is infrared technology, in particular the production of infrared radiation detectors operating in the region of 8-14 microns. Many alloys containing 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 they did not find a place in the Periodic Table.

The discovery of argon Ar by 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 an allotropic modification of nitrogen and only in 1900, under the pressure of immutable facts, agreed with the presence of a “zero” group of chemical elements in the Periodic Table, which was occupied by other noble gases discovered after argon. Now this group is known as VIIIA.

In 1905, Mendeleev wrote: “Apparently, the future does not threaten the periodic law with destruction, but only promises superstructures and development, although as a Russian they wanted to erase me, especially the Germans.”

The discovery of the Periodic Law accelerated the development of chemistry and the discovery of new chemical elements.

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

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

Periodic law D.I. Mendeleev:Properties of simple bodies, as well as shapes and properties of compoundsdifferences of elements are periodically dependent onthe values ​​of the atomic weights of elements. (The properties of elements are periodically dependent on the charge of the atoms of their nuclei).

Periodic table of elements. Series of elements within which properties change sequentially, such as the 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.

Having divided all the elements into periods and placing one period under another so that elements similar in properties and type of compounds formed were located under each other, Mendeleev compiled a table that he called the periodic system of elements by groups and series.

The meaning of the periodic systemWe. The periodic table of elements had a great influence on the subsequent development of chemistry. Not only was it the first natural classification of chemical elements, showing that they form a harmonious system and are in close connection with each other, but it was also a powerful tool for further research.

7. Periodic changes in the properties of chemical elements. Atomic and ionic radii. Ionization energy. Electron affinity. Electronegativity.

The dependence of atomic radii on the charge of the nucleus of an atom Z is periodic. Within one period, as Z increases, 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 electronic layer, more distant from the nucleus, i.e., during the transition to the next period, atomic radii increase (compare, for example, the radii of fluorine and sodium atoms). As a result, within a subgroup, with increasing nuclear charge, the sizes of atoms increase.

The loss of electron atoms leads to a decrease in its effective size, and the addition of excess electrons leads to an increase. Therefore, the radius of a positively charged ion (cation) is always smaller, 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 electronic layers and the 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 transform into positively charged ions, while non-metals, on the contrary, are characterized by the ability to add electrons to form negative ions. To remove an electron from an atom and transform the latter into a positive ion, it is necessary to expend some energy, called ionization energy.

Ionization energy can be determined by bombarding atoms with electrons accelerated in an electric field. The lowest field voltage at which the electron speed becomes sufficient to ionize atoms is called the ionization potential of the atoms of a given element and is expressed in volts. With the expenditure of sufficient energy, two, three or more electrons can be removed from an atom. Therefore, they speak of the first ionization potential (the energy of the removal of the first electron from the atom) and the second ionization potential (the energy of the removal of the second electron)

As noted above, atoms can not only donate, but also gain electrons. The energy released when an electron attaches to a free atom is called the atom's electron affinity. Electron affinity, like ionization energy, is usually expressed in electron volts. Thus, the electron affinity of the hydrogen atom is 0.75 eV, oxygen - 1.47 eV, fluorine - 3.52 eV.

The electron affinities of metal atoms are typically close to zero or negative; It follows from this that for atoms of most metals the addition of electrons is energetically unfavorable. The electron affinity of nonmetal atoms is always positive and the greater, the closer the nonmetal is located to the noble gas in the periodic table; this indicates an increase in non-metallic properties as the end of the period approaches.