Periodic system of Mendeleev. Chemical elements of the periodic system. Periodic system of D. I. Mendeleev

D. I. Mendeleev came to the conclusion that their properties must be due to some fundamental general characteristics. He chose the atomic mass of the element as such a fundamental characteristic for a chemical element and briefly formulated the periodic law (1869):

The properties of the elements, as well as the properties of the simple and complex bodies formed by them, are in a periodic dependence on the values ​​of the atomic weights of the elements.

The merit of Mendeleev lies in the fact that he understood the manifested dependence as an objective law of nature, which his predecessors could not do. D. I. Mendeleev believed that the composition of compounds, their chemical properties, boiling and melting points, the structure of crystals, and the like are in a periodic dependence on the atomic mass. A deep understanding of the essence of periodic dependence gave Mendeleev the opportunity to draw several important conclusions and assumptions.

Modern periodic table

First, of the 63 elements known at that time, Mendeleev changed atomic masses almost 20 elements (Be, In, La, Y, Ce, Th, U). Secondly, he predicted the existence of about 20 new elements and left a place for them in the periodic table. Three of them, namely ecabor, ecaaluminum and ecasilicium, have been described in sufficient detail and with surprising accuracy. This was triumphantly confirmed over the next fifteen years, when the elements Gallium (ecaaluminum), scandium (ecabor) and germanium (ecasilicium) were discovered.

The periodic law is one of the fundamental laws of nature. Its impact on the development of the scientific worldview can only be compared with the law of conservation of mass and energy or quantum theory. Back in the days of D. I. Mendeleev, the periodic law became the basis of chemistry. Further discoveries of the structure and the phenomenon of isotopy showed that the main quantitative characteristic element is not the atomic mass, but the charge of the nucleus (Z). In 1913, Moseley and Rutherford introduced the concept of "atomic number of an element", numbered all the symbols in the periodic system and showed that the basis for the classification of elements is the ordinal number of an element, equal to the charge of the nuclei of their atoms.

This statement is now known as Moseley's Law.

That's why modern definition The periodic law is formulated as follows:

The properties of simple substances, as well as the forms and properties of compounds of elements, are periodically dependent on the value of the charge of their atomic nuclei (or on the ordinal number of the element in the periodic system).

The electronic structures of the atoms of elements clearly show that with an increase in the charge of the nucleus, a regular periodic repetition of electronic structures occurs, and hence the repetition of the properties of the elements. This is reflected in the periodic table of elements, for which several hundred variants have been proposed. Most often, two forms of tables are used - abbreviated and expanded - containing all known elements and having vacancies for not yet open.

Each element occupies a certain cell in the periodic table, which indicates the symbol and name of the element, its serial number, relative atomic mass, and for radioactive elements in square brackets the mass number of the most stable or available isotope is given. In modern tables, some other background information: density, boiling and melting points of simple substances, etc.

Periods

The main structural units of the periodic system are periods and groups - natural aggregates into which chemical elements are divided according to electronic structures.

A period is a horizontal successive row of elements in whose atoms electrons fill the same number of energy levels.

The period number coincides with the number of the outer quantum level. For example, the element calcium (4s 2) is in the fourth period, that is, its atom has four energy levels, and the valence electrons are in the outer, fourth level. The difference in the sequence of filling both the outer and closer to the nucleus electron layers explains the reason for the different lengths of the periods.

In the atoms of s- and p-elements, the external level is being built up, in the d-elements, the second energy level is outside, and in the f-elements, the third energy level is outside.

Therefore, the difference in properties is most clearly manifested in neighboring s- or p-elements. In d- and especially f-elements of the same period, the difference in properties is less significant.

As already mentioned, on the basis of the number of the energy sublevel built up by electrons, the elements are combined into electronic families. For example, in periods IV-VI there are families that contain ten d-elements each: 3d-family (Sc-Zn), 4d-family (Y-Cd), 5d-family (La, Hf-Hg). In the sixth and seventh periods, fourteen elements each make up the f-families: the 4f-family (Ce-Lu), which is called the lanthanide, and the 5f-family (Th-Lr) - the actinide. These families are placed under the periodic table.

The first three periods are called small or typical periods, since the properties of the elements of these periods are the basis for the distribution of all other elements into eight groups. All other periods, including the seventh, incomplete, are called large periods.

All periods, except for the first, begin with alkaline (Li, Na, K, Rb, Cs, Fr) and end, with the exception of the seventh, incomplete, inert elements (He, Ne, Ar, Kr, Xe, Rn). Alkali metals have the same external electronic configuration n s 1 , where n- period number. Inert elements, except for helium (1s 2), have the same structure of the outer electronic layer: n s2 n p 6 , that is, electronic counterparts.

The considered regularity makes it possible to come to the conclusion:

Periodic repetition of the same electronic configurations The outer electron layer is the reason for the similarity of the physical and chemical properties of analogous elements, since it is the outer electrons of atoms that mainly determine their properties.

In small typical periods, with an increase in the serial number, a gradual decrease in metallic and an increase in non-metallic properties is observed, since the number of valence electrons at the external energy level increases. For example, the atoms of all elements of the third period have three electron layers. The structure of the two inner layers is the same for all elements of the third period (1s 2 2s 2 2p 6), while the structure of the outer, third, layer is different. In the transition from each previous element to each subsequent element, the charge of the atomic nucleus increases by one and, accordingly, the number of external electrons increases. As a result, their attraction to the nucleus increases, and the radius of the atom decreases. This leads to a weakening of the metallic properties and the growth of non-metallic ones.

The third period begins with a very active sodium metal (11 Na - 3s 1), followed by a slightly less active magnesium (12 Mg - 3s 2). Both of these metals belong to the 3s family. The first p-element of the third period, aluminum (13 Al - 3s 2 3p 1), whose metallic activity is less than that of magnesium, has amphoteric properties, that is, it can also behave like a non-metal in chemical reactions. This is followed by non-metals silicon (14 Si - 3s 2 3p 2), phosphorus (15 P - 3s 2 3p 3), sulfur (16 S - 3s 2 3p 4), chlorine (17 Cl - 3s 2 3p 5). They are not metallic properties intensify from Si to Cl, which is an active non-metal. The period ends with the inert element argon (18 Ar - 3s 2 3p 6).

Within one period, the properties of elements change gradually, and during the transition from the previous period to the next, abrupt change properties, as the construction of a new energy level begins.

The gradual change in properties is typical not only for simple substances, but also for complex compounds, as shown in Table 1.

Table 1 - Some properties of the elements of the third period and their compounds

In long periods, the metallic properties weaken more slowly. This is due to the fact that, starting from fourth period, ten transition d-elements appear, in which not the outer, but the second outside d-sublevel is built up, and on the outer layer of the d-elements there are one or two s-electrons, which determine to a certain extent the properties of these elements. Thus, for d-elements, the pattern becomes somewhat more complicated. For example, in the fifth period, the metallic properties gradually decrease from the alkaline Rb, reaching a minimum strength in the metals of the platinum family (Ru, Rh, Pd).

However, after inactive silver Ag, cadmium Cd is placed, in which an abrupt increase in metallic properties is observed. Further, with an increase in the ordinal number of the element, non-metallic properties appear and gradually increase up to the typical non-metal iodine. This period ends, like all previous ones, with an inert gas. The periodic change in the properties of elements within large periods makes it possible to divide them into two series, in which the second part of the period repeats the first.

Groups

Vertical columns of elements in the periodic table - groups consist of subgroups: main and secondary, they are sometimes denoted by the letters A and B, respectively.

The main subgroups include s- and p-elements, and the secondary subgroups include d- and f-elements of large periods.

The main subgroup is a collection of elements that is placed vertically in the periodic table and has the same configuration of the outer electron layer in atoms.

As follows from the above definition, the position of an element in the main subgroup is determined by total electrons (s- and p-) of the external energy level, equal to the group number. For example, sulfur (S - 3s 2 3p 4 ), whose atom contains six electrons at the outer level, belongs to the main subgroup of the sixth group, argon (Ar - 3s 2 3p 6 ) - to the main subgroup of the eighth group, and strontium (Sr - 5s 2 ) - to the IIA-subgroup.

Elements of one subgroup are characterized by similar chemical properties. As an example, consider the elements of ІА and VІІА subgroups (Table 2). With an increase in the charge of the nucleus, the number of electron layers and the radius of the atom increase, but the number of electrons at the external energy level remains constant: for alkali metals (subgroup IA) - one, and for halogens (subgroup VIIA) - seven. Since it is the outer electrons that most significantly affect the chemical properties, it is clear that each of the considered groups of analogue elements has similar properties.

But within the same subgroup, along with the similarity of properties, some change is observed. So, the elements of the subgroup ІА are all, except for H, active metals. But with an increase in the radius of the atom and the number of electron layers shielding the influence of the nucleus on valence electrons, the metallic properties increase. Therefore, Fr is a more active metal than Cs, and Cs is more active than R, etc. And in subgroup VIIA, for the same reason, the non-metallic properties of elements are weakened with an increase in the serial number. Therefore, F is a more active non-metal than Cl, and Cl is a more active non-metal than Br, and so on.

Table 2 - Some characteristics of the elements of ІА and VІІА-subgroups

A side subgroup is a collection of elements that are placed vertically in the periodic table and have the same number of valence electrons due to the building of the outer s- and the second outside d-energy sublevels.

All elements of secondary subgroups belong to the d-family. These elements are sometimes called transition metals. In side subgroups, the properties change more slowly, since in the atoms of d-elements, electrons build up the second energy level from the outside, and only one or two electrons are located at the external level.

The position of the first five d-elements (subgroups IIIB-VIIB) of each period can be determined using the sum of external s-electrons and d-electrons of the second outside level. For example, from electronic formula scandium (Sc - 4s 2 3d 1 ) it can be seen that it is located in a side subgroup (since it is a d-element) of the third group (since the sum of valence electrons is three), and manganese (Mn - 4s 2 3d 5 ) is placed in the secondary subgroup of the seventh group.

The position of the last two elements of each period (subgroups IB and IIB) can be determined by the number of electrons at the outer level, since in the atoms of these elements the previous level is completely completed. For example Ag(5s 1 5d 10) is placed in a secondary subgroup of the first group, Zn (4s 2 3d 10) - in the secondary subgroup of the second group.

The Fe-Co-Ni, Ru-Rh-Pd, and Os-Ir-Pt triads are located in the secondary subgroup of the eighth group. These triads form two families: iron and platinoids. In addition to these families, the lanthanide family (fourteen 4f elements) and the actinide family (fourteen 5f elements) are separately distinguished. These families belong to a secondary subgroup of the third group.

An increase in the metallic properties of elements in subgroups from top to bottom, as well as a decrease in these properties within one period from left to right, cause the appearance of a diagonal pattern in the periodic system. Thus, Be is very similar to Al, B is similar to Si, Ti is very similar to Nb. This is clearly manifested in the fact that in nature these elements form similar minerals. For example, in nature, Te always occurs with Nb, forming minerals - titanium oniobates.

If the periodic table seems difficult for you to understand, you are not alone! Although it can be difficult to understand its principles, learning to work with it will help in the study of natural sciences. To get started, study the structure of the table and what information can be learned from it about each chemical element. Then you can start exploring the properties of each element. And finally, using the periodic table, you can determine the number of neutrons in an atom of a particular chemical element.

Steps

Part 1

The periodic table, or periodic table of chemical elements, begins at the top left and ends at the end of the last line of the table (bottom right). The elements in the table are arranged from left to right in ascending order of their atomic number. The atomic number tells you how many protons are in one atom. In addition, as the atomic number increases, so does the atomic mass. Thus, by the location of an element in the periodic table, you can determine its atomic mass.

As you can see, each next element contains one more proton than the element that precedes it. This is obvious when you look at the atomic numbers. Atomic numbers increase by one as you move from left to right. Since the elements are arranged in groups, some table cells remain empty.

• For example, the first row of the table contains hydrogen, which has atomic number 1, and helium, which has atomic number 2. However, they are on opposite ends because they belong to different groups.

1. Learn about groups that include elements with similar physical and chemical properties. The elements of each group are located in the corresponding vertical column. As a rule, they are indicated by the same color, which helps to identify elements with similar physical and chemical properties and predict their behavior. All elements of a particular group have the same number of electrons in the outer shell.

   • Hydrogen can be attributed both to the group of alkali metals and to the group of halogens. In some tables it is indicated in both groups.
   • In most cases, the groups are numbered from 1 to 18, and the numbers are placed at the top or bottom of the table. Numbers can be given in Roman (eg IA) or Arabic (eg 1A or 1) numerals.
   • When moving along the column from top to bottom, they say that you are "browsing the group".

2. Find out why there are empty cells in the table. Elements are ordered not only according to their atomic number, but also according to groups (elements of the same group have similar physical and chemical properties). This makes it easier to understand how an element behaves. However, as the atomic number increases, elements that fall into the corresponding group are not always found, so there are empty cells in the table.

   • For example, the first 3 rows have empty cells, since transition metals are found only from atomic number 21.
   • Elements with atomic numbers from 57 to 102 belong to the rare earth elements, and they are usually placed in a separate subgroup in the lower right corner of the table.

3. Each row of the table represents a period. All elements of the same period have the same number of atomic orbitals in which electrons are located in atoms. The number of orbitals corresponds to the period number. The table contains 7 rows, that is, 7 periods.

   • For example, the atoms of the elements of the first period have one orbital, and the atoms of the elements of the seventh period have 7 orbitals.
   • As a rule, periods are indicated by numbers from 1 to 7 on the left of the table.
   • As you move along a line from left to right, you are said to be "scanning through a period".

4. Learn to distinguish between metals, metalloids and non-metals. You will better understand the properties of an element if you can determine what type it belongs to. For convenience, in most tables, metals, metalloids and non-metals are designated different colors. Metals are on the left, and non-metals are on the right side of the table. Metalloids are located between them.

   Part 2

   Element designations

   1. Each element is designated by one or two Latin letters. As a rule, the element symbol is shown in large letters in the center of the corresponding cell. A symbol is an abbreviated name for an element that is the same in most languages. When doing experiments and working with chemical equations, the symbols of the elements are commonly used, so it is useful to remember them.

      • Typically, element symbols are shorthand for them. Latin name, although for some, especially recently discovered elements, they are derived from the common name. For example, helium is denoted by the symbol He, which is close to the common name in most languages. At the same time, iron is designated as Fe, which is an abbreviation of its Latin name.

   2. Pay attention to the full name of the element, if it is given in the table. This "name" of the element is used in normal texts. For example, "helium" and "carbon" are the names of the elements. Usually, although not always, full names elements are listed below their chemical symbol.

      • Sometimes the names of the elements are not indicated in the table and only their chemical symbols are given.

   3. Find the atomic number. Usually the atomic number of an element is located at the top of the corresponding cell, in the middle or in the corner. It can also appear below the symbol or element name. Elements have atomic numbers from 1 to 118.

      • The atomic number is always an integer.

   4. Remember that the atomic number corresponds to the number of protons in an atom. All atoms of an element contain the same number of protons. Unlike electrons, the number of protons in the atoms of an element remains constant. Otherwise, another chemical element would have turned out!

Attempts to systematize the chemical elements were made by many scientists. But only in 1869, D. I. Mendeleev managed to create a classification of elements that established a connection and dependence chemical substances and the charge of the atomic nucleus.

Story

The modern formulation of the periodic law is as follows: the properties of chemical elements, as well as the forms and properties of compounds of elements, are in a periodic dependence on the charge of the nucleus of the element's atoms.

By the time the law was discovered, 63 chemical elements were known. However, the atomic masses of many of these elements have been erroneously determined.

D. And Mendeleev himself in 1869 formulated his law as a periodic dependence on the magnitude of the atomic weights of elements, since in the 19th century science did not yet have information about the structure of the atom. However, the ingenious foresight of the scientist allowed him to understand more deeply than all his contemporaries the patterns that determine the periodicity of the properties of elements and substances. He took into account not only the increase in the atomic mass, but also the already known properties of substances and elements, and, taking the idea of ​​periodicity as a basis, he was able to accurately predict the existence and properties of elements and substances unknown at that time to science, correct the atomic masses of a number of elements, correctly arrange the elements in system, leaving empty spaces and making permutations.

Rice. 1. D. I. Mendeleev.

There is a myth that Mendeleev dreamed of the periodic system. However, this is only beautiful story which is not a proven fact.

Structure of the periodic system

Periodic system chemical elements of D. I. Mendeleev is a graphic reflection of his own law. Elements are arranged in a table according to a certain chemical and physical meaning. By the location of the element, you can determine its valence, the number of electrons, and many other features. The table is divided horizontally into large and small periods, and vertically into groups.

Rice. 2. Periodic table.

There are 7 periods that start with alkali metal, and end with substances having non-metallic properties. Groups, in turn, consisting of 8 columns, are divided into main and secondary subgroups.

The further development of science showed that the periodic repetition of the properties of elements at certain intervals, especially clearly manifested in 2 and 3 small periods, is explained by the repetition of the electronic structure of the external energy levels, where valence electrons are located, due to which chemical bonds and new substances are formed in reactions. Therefore, in each vertical column-group there are elements with repeating characteristic features. This is clearly manifested in groups where there are families of very active alkali metals (group I, main subgroup) and non-halogen metals (group VII, main subgroup). From left to right along the period, the number of electrons increases from 1 to 8, while there is a decrease in the metallic properties of the elements. Thus, the metallic properties manifest themselves the stronger, the fewer electrons there are in the outer level.

Rice. 3. Small and big periods in the periodic table.

Such properties of atoms as ionization energy, electron affinity energy and electronegativity are also periodically repeated. These quantities are related to the ability of an atom to donate an electron from an external level (ionization) or to keep an alien electron at its external level (electron affinity). Total ratings received: 117.

The nineteenth century in the history of mankind is a century in which many sciences were reformed, including chemistry. It was at this time that Mendeleev's periodic system appeared, and with it the periodic law. It was he who became the basis of modern chemistry. The periodic system of D. I. Mendeleev is a systematization of elements that establishes the dependence of chemical and physical properties on the structure and charge of the atom of matter.

Story

The beginning of the periodical was laid by the book "The Correlation of Properties with the Atomic Weight of Elements", written in the third quarter of the 17th century. It displayed the basic concepts of relatively known chemical elements (at that time there were only 63 of them). In addition, for many of them, the atomic masses were determined incorrectly. This greatly interfered with the discovery of D. I. Mendeleev.

Dmitry Ivanovich began his work by comparing the properties of elements. First of all, he took up chlorine and potassium, and only then moved on to work with alkali metals. Armed with special cards depicting chemical elements, he repeatedly tried to assemble this “mosaic”: he laid it out on his desk in search of the necessary combinations and matches.

After much effort, Dmitry Ivanovich nevertheless found the pattern he was looking for, and built the elements into periodic series. Having received empty cells between the elements as a result, the scientist realized that not all chemical elements were known to Russian researchers, and that it was he who should give this world the knowledge in the field of chemistry that had not yet been given by his predecessors.

Everyone knows the myth that the periodic table appeared to Mendeleev in a dream, and he collected the elements from memory in single system. This is, roughly speaking, a lie. The fact is that Dmitry Ivanovich worked on his work for quite a long time and with concentration, and it exhausted him greatly. While working on the system of elements, Mendeleev once fell asleep. When he woke up, he realized that he had not finished the table, and rather continued filling in the empty cells. An acquaintance of his, a certain Inostrantsev, a university teacher, decided that Mendeleev's table was a dream and spread this rumor among his students. Thus, this hypothesis was born.

Fame

The chemical elements of Mendeleev is a reflection of what Dmitry Ivanovich created in the third quarter XIX century (1869) of the periodic law. It was in 1869 at a meeting of the Russian chemical community that Mendeleev's notification about the creation of a certain structure was read out. And in the same year, the book "Fundamentals of Chemistry" was published, in which Mendeleev's periodic system of chemical elements was first published. And in the book natural system elements and its use to indicate the qualities of undiscovered elements "D. I. Mendeleev first mentioned the concept of" periodic law ".

Structure and placement rules

The first steps in creating the periodic law were made by Dmitry Ivanovich back in 1869-1871, at that time he worked hard to establish the dependence of the properties of these elements on the mass of their atom. The modern version is a two-dimensional table of elements.

The position of an element in the table has a certain chemical and physical meaning. By the location of the element in the table, you can find out what its valency is, and determine other chemical features. Dmitry Ivanovich tried to establish a connection between elements, both similar in properties and different.

He put valency and atomic mass as the basis for the classification of chemical elements known at that time. Comparing the relative properties of elements, Mendeleev tried to find a pattern that would unite all known chemical elements into one system. Having arranged them, based on the increase in atomic masses, he nevertheless achieved periodicity in each of the rows.

Further development of the system

The periodic table, which appeared in 1969, has been refined more than once. With the advent of noble gases in the 1930s, it was possible to reveal the newest dependence of elements - not on mass, but on serial number. Later, it was possible to establish the number of protons in atomic nuclei, and it turned out that it coincides with the serial number of the element. Scientists of the 20th century studied the electron. It turned out that it also affects the periodicity. This greatly changed the idea of ​​the properties of elements. This point was reflected in later editions of Mendeleev's periodic system. Each new discovery of the properties and features of the elements organically fit into the table.

Characteristics of the periodic system of Mendeleev

The periodic table is divided into periods (7 lines arranged horizontally), which, in turn, are divided into large and small. The period begins with an alkali metal, and ends with an element with non-metallic properties.
Vertically, Dmitry Ivanovich's table is divided into groups (8 columns). Each of them in the periodic system consists of two subgroups, namely, the main and secondary. After long disputes, at the suggestion of D. I. Mendeleev and his colleague W. Ramsay, it was decided to introduce the so-called zero group. It includes inert gases (neon, helium, argon, radon, xenon, krypton). In 1911, scientists F. Soddy proposed to place indistinguishable elements, the so-called isotopes, in the periodic system - separate cells were allocated for them.

Despite the fidelity and accuracy of the periodic system, the scientific community did not want to recognize this discovery for a long time. Many great scientists ridiculed the activities of D. I. Mendeleev and believed that it was impossible to predict the properties of an element that had not yet been discovered. But after the alleged chemical elements were discovered (and these were, for example, scandium, gallium and germanium), Mendeleev's system and his periodic law became the science of chemistry.

Table in modern times

Mendeleev's periodic system of elements is the basis of most chemical and physical discoveries related to atomic and molecular science. Modern concept element was formed just thanks to the great scientist. The advent of Mendeleev's periodic system has made fundamental changes in the ideas about various compounds and simple substances. The creation of a periodic system by a scientist had a huge impact on the development of chemistry and all sciences related to it.

Anyone who went to school remembers that one of the required subjects to study was chemistry. She could like it, or she could not like it - it does not matter. And it is likely that much knowledge in this discipline has already been forgotten and is not applied in life. However, everyone probably remembers the table of chemical elements of D. I. Mendeleev. For many, it has remained a multi-colored table, where certain letters are inscribed in each square, denoting the names of chemical elements. But here we will not talk about chemistry as such, and describe hundreds of chemical reactions and processes, but we will talk about how the periodic table appeared in general - this story will be of interest to any person, and indeed to all those who are hungry for interesting and useful information.

A little background

Back in 1668, the outstanding Irish chemist, physicist and theologian Robert Boyle published a book in which many myths about alchemy were debunked, and in which he talked about the need to search for indecomposable chemical elements. The scientist also gave a list of them, consisting of only 15 elements, but allowed the idea that there may be more elements. This became the starting point not only in the search for new elements, but also in their systematization.

A hundred years later, the French chemist Antoine Lavoisier compiled a new list, which already included 35 elements. 23 of them were later found to be indecomposable. But the search for new elements continued by scientists around the world. And leading role the famous Russian chemist Dmitry Ivanovich Mendeleev played in this process - he was the first to put forward the hypothesis that there could be a relationship between the atomic mass of elements and their location in the system.

Thanks to painstaking work and comparison of chemical elements, Mendeleev was able to discover a relationship between elements in which they can be one, and their properties are not something taken for granted, but are a periodically repeating phenomenon. As a result, in February 1869, Mendeleev formulated the first periodic law, and already in March, his report “The relationship of properties with the atomic weight of elements” was submitted to the Russian Chemical Society by the historian of chemistry N. A. Menshutkin. Then in the same year, Mendeleev's publication was published in the journal Zeitschrift fur Chemie in Germany, and in 1871 a new extensive publication of the scientist dedicated to his discovery was published by another German journal Annalen der Chemie.

Creating a Periodic Table

The main idea by 1869 had already been formed by Mendeleev, and for quite a short time, but for a long time he could not arrange it into some sort of ordered system that clearly displays what's what. In one of the conversations with his colleague A. A. Inostrantsev, he even said that everything had already worked out in his head, but he could not bring everything to the table. After that, according to Mendeleev's biographers, he began painstaking work on his table, which lasted three days without a break for sleep. All sorts of ways to organize the elements in a table were sorted out, and the work was complicated by the fact that at that time science did not yet know about all the chemical elements. But, despite this, the table was still created, and the elements were systematized.

Legend of Mendeleev's dream

Many have heard the story that D. I. Mendeleev dreamed of his table. This version was actively distributed by the aforementioned colleague of Mendeleev A. A. Inostrantsev as funny story with which he entertained his students. He said that Dmitry Ivanovich went to bed and in a dream he clearly saw his table, in which all the chemical elements were arranged in right order. After that, the students even joked that 40° vodka was discovered in the same way. But real prerequisites for the story with sleep, there were still: as already mentioned, Mendeleev worked on the table without sleep and rest, and Inostrantsev once found him tired and exhausted. In the afternoon, Mendeleev decided to take a break, and some time later, he woke up abruptly, immediately took a piece of paper and depicted a ready-made table on it. But the scientist himself refuted this whole story with a dream, saying: “I’ve been thinking about it for maybe twenty years, and you think: I was sitting and suddenly ... it’s ready.” So the legend of the dream may be very attractive, but the creation of the table was only possible through hard work.

Further work

In the period from 1869 to 1871, Mendeleev developed the ideas of periodicity, to which the scientific community was inclined. And one of the important stages of this process was the understanding that any element in the system should be located based on the totality of its properties in comparison with the properties of other elements. Based on this, and also based on the results of research in the change of glass-forming oxides, the chemist managed to amend the values ​​of the atomic masses of some elements, among which were uranium, indium, beryllium and others.

Of course, Mendeleev wanted to fill the empty cells that remained in the table as soon as possible, and in 1870 he predicted that chemical elements unknown to science would soon be discovered, the atomic masses and properties of which he was able to calculate. The first of these were gallium (discovered in 1875), scandium (discovered in 1879) and germanium (discovered in 1885). Then the forecasts continued to be realized, and eight more new elements were discovered, including: polonium (1898), rhenium (1925), technetium (1937), francium (1939) and astatine (1942-1943). By the way, in 1900, D. I. Mendeleev and the Scottish chemist William Ramsay came to the conclusion that the elements of the zero group should also be included in the table - until 1962 they were called inert, and after - noble gases.

Organization of the periodic system

Chemical elements in the table of D. I. Mendeleev they are arranged in rows, in accordance with the increase in their mass, and the length of the rows is chosen so that the elements in them have similar properties. For example, noble gases such as radon, xenon, krypton, argon, neon, and helium do not easily react with other elements, and also have low chemical activity, which is why they are located in the far right column. And the elements of the left column (potassium, sodium, lithium, etc.) react perfectly with other elements, and the reactions themselves are explosive. To put it simply, within each column, the elements have similar properties, varying from one column to the next. All elements up to No. 92 are found in nature, and with No. 93 artificial elements begin, which can only be created in the laboratory.

In its original version, the periodic system was understood only as a reflection of the order existing in nature, and there were no explanations why everything should be that way. And only when it appeared quantum mechanics, true meaning the order of the elements in the table became clear.

Creative Process Lessons

Speaking about what lessons of the creative process can be drawn from the entire history of the creation of the periodic table of D. I. Mendeleev, one can cite as an example the ideas of the English researcher in the field of creative thinking Graham Wallace and the French scientist Henri Poincaré. Let's take them briefly.

According to Poincaré (1908) and Graham Wallace (1926), there are four main stages in creative thinking:

• Training- the stage of formulating the main task and the first attempts to solve it;
• Incubation- the stage during which there is a temporary distraction from the process, but work on finding a solution to the problem is carried out at a subconscious level;
• insight- stage at which intuitive solution. Moreover, this solution can be found in a situation that is absolutely not relevant to the task;
• Examination- the stage of testing and implementation of the solution, at which the verification of this solution and its possible further development takes place.

As we can see, in the process of creating his table, Mendeleev intuitively followed these four stages. How effective this is can be judged by the results, i.e. because the table was created. And given that its creation was a huge step forward not only for chemical science, but for the whole of humanity, the above four stages can be applied both to the implementation of small projects and to the implementation of global plans. The main thing to remember is that not a single discovery, not a single solution to a problem can be found on its own, no matter how much we want to see them in a dream and no matter how much we sleep. In order to succeed, whether it is the creation of a table of chemical elements or the development of a new marketing plan, you need to have certain knowledge and skills, as well as skillfully use your potential and work hard.

We wish you success in your endeavors and successful implementation conceived!