Number 8 on the periodic table. History of creation and development

Even at school, sitting in chemistry lessons, we all remember the table on the wall of the classroom or chemical laboratory. This table contained a classification of all chemical elements known to mankind, those fundamental components that make up the Earth and the entire Universe. Then we could not even think that Mendeleev table is undoubtedly one of the greatest scientific discoveries, which is the foundation of our modern knowledge of chemistry.

Periodic table of chemical elements by D. I. Mendeleev

At first glance, her idea looks deceptively simple: organize chemical elements in order of increasing weight of their atoms. Moreover, in most cases it turns out that the chemical and physical properties of each element are similar to the element preceding it in the table. This pattern appears for all elements except the very first few, simply because they do not have in front of them elements similar to them in atomic weight. It is thanks to the discovery of this property that we can place a linear sequence of elements in a table much like a wall calendar, and thus combine a huge number of types of chemical elements in a clear and coherent form. Of course, today we use the concept of atomic number (the number of protons) in order to order the system of elements. This helped solve the so-called technical problem of a “pair of permutations”, but did not lead to a fundamental change in the appearance of the periodic table.

IN periodic table all elements are ordered based on their atomic number, electronic configuration, and repeating chemical properties. The rows in the table are called periods, and the columns are called groups. The first table, dating back to 1869, contained only 60 elements, but now the table had to be enlarged to accommodate the 118 elements we know today.

Mendeleev's periodic table systematizes not only the elements, but also their most diverse properties. It is often enough for a chemist to have the Periodic Table in front of his eyes in order to correctly answer many questions (not only exam questions, but also scientific ones).

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Periodic law

There are two formulations periodic law chemical elements: classical and modern.

Classical, as presented by its discoverer D.I. Mendeleev: the properties of simple bodies, as well as the forms and properties of compounds of elements, are periodically dependent on the values ​​of the atomic weights of the elements.

Modern: the properties of simple substances, as well as the properties and forms of compounds of elements, are periodically dependent on the charge of the nucleus of the atoms of the elements (ordinal number).

A graphic representation of the periodic law is the periodic system of elements, which is a natural classification of chemical elements based on regular changes in the properties of elements depending on the charges of their atoms. The most common images of the periodic table of elements are D.I. Mendeleev's forms are short and long.

Groups and periods of the Periodic Table

In groups are called vertical rows in the periodic table. In groups, elements are combined based on the highest oxidation state in their oxides. Each group consists of a main and secondary subgroup. The main subgroups include elements of small periods and elements of large periods with the same properties. Side subgroups consist only of elements of large periods. The chemical properties of the elements of the main and secondary subgroups differ significantly.

Period called a horizontal row of elements arranged in order of increasing atomic numbers. There are seven periods in the periodic system: the first, second and third periods are called small, they contain 2, 8 and 8 elements, respectively; the remaining periods are called large: in the fourth and fifth periods there are 18 elements, in the sixth - 32, and in the seventh (not yet completed) - 31 elements. Each period, except the first, begins with an alkali metal and ends with a noble gas.

Physical meaning of the serial number chemical element: the number of protons in the atomic nucleus and the number of electrons rotating around the atomic nucleus are equal to the atomic number of the element.

Properties of the periodic table

Let us remind you that groups are called vertical rows in the periodic table and the chemical properties of the elements of the main and secondary subgroups differ significantly.

The properties of elements in subgroups naturally change from top to bottom:

• metallic properties increase and non-metallic properties weaken;
• the atomic radius increases;
• the strength of bases and oxygen-free acids formed by the element increases;
• electronegativity decreases.

All elements except helium, neon and argon form oxygen compounds; there are only eight forms of oxygen compounds. In the periodic table, they are often depicted by general formulas, located under each group in increasing order of the oxidation state of the elements: R 2 O, RO, R 2 O 3, RO 2, R 2 O 5, RO 3, R 2 O 7, RO 4, where the symbol R denotes an element of this group. The formulas of higher oxides apply to all elements of the group, except in exceptional cases when the elements do not exhibit an oxidation state equal to the group number (for example, fluorine).

Oxides of the composition R 2 O exhibit strong basic properties, and their basicity increases with increasing atomic number; oxides of the composition RO (with the exception of BeO) exhibit basic properties. Oxides of the composition RO 2, R 2 O 5, RO 3, R 2 O 7 exhibit acidic properties, and their acidity increases with increasing atomic number.

The elements of the main subgroups, starting from group IV, form gaseous hydrogen compounds. There are four forms of such compounds. They are located under the elements of the main subgroups and are represented by general formulas in the sequence RH 4, RH 3, RH 2, RH.

RH 4 compounds are neutral in nature; RH 3 - weakly basic; RH 2 - slightly acidic; RH - strongly acidic character.

Let us remind you that period called a horizontal row of elements arranged in order of increasing atomic numbers.

Within a period with increasing element serial number:

• electronegativity increases;
• metallic properties decrease, non-metallic properties increase;
• the atomic radius decreases.

Elements of the periodic table

Alkali and alkaline earth elements

These include elements from the first and second groups of the periodic table. Alkali metals from the first group - soft metals, silver in color, easy to cut with a knife. They all have a single electron in their outer shell and react perfectly. Alkaline earth metals from the second group also have a silvery tint. Two electrons are placed at the outer level, and, accordingly, these metals interact less readily with other elements. Compared to alkali metals, alkaline earth metals melt and boil at higher temperatures.

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Lanthanides (rare earth elements) and actinides

Lanthanides- a group of elements originally found in rare minerals; hence their name "rare earth" elements. Subsequently, it turned out that these elements are not as rare as initially thought, and therefore the name lanthanides was given to rare earth elements. Lanthanides and actinides occupy two blocks, which are located under the main table of elements. Both groups include metals; all lanthanides (except promethium) are non-radioactive; actinides, on the contrary, are radioactive.

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Halogens and noble gases

The halogens and noble gases are grouped into groups 17 and 18 of the periodic table. Halogens are non-metallic elements, they all have seven electrons in their outer shell. IN noble gases All the electrons are in the outer shell, so they hardly participate in the formation of compounds. These gases are called “noble” gases because they rarely react with other elements; that is, they refer to members of the noble caste who have traditionally shunned other people in society.

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Transition metals

Transition metals occupy groups 3-12 in the periodic table. Most of them are dense, hard, with good electrical and thermal conductivity. Their valence electrons (with the help of which they are connected to other elements) are located in several electron shells.

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Metalloids

Metalloids occupy groups 13-16 of the periodic table. Metalloids such as boron, germanium and silicon are semiconductors and are used to make computer chips and circuit boards.

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Post-transition metals

Elements called post-transition metals, belong to groups 13-15 of the periodic table. Unlike metals, they do not have shine, but have a matte color. Compared to transition metals, post-transition metals are softer, have lower melting and boiling points, and higher electronegativity. Their valence electrons, with which they attach other elements, are located only on the outer electron shell. Post-transition metal group elements have much higher boiling points than metalloids.

Now consolidate your knowledge by watching a video about the periodic table and more.

Great, the first step on the path to knowledge has been taken. Now you are more or less oriented in the periodic table and this will be very useful to you, because the Periodic System of Mendeleev is the foundation on which this amazing science stands.

The periodic table is one of the greatest discoveries of mankind, which made it possible to organize knowledge about the world around us and discover new chemical elements. It is necessary for schoolchildren, as well as for anyone interested in chemistry. In addition, this scheme is indispensable in other areas of science.

This scheme contains all the elements known to man, and they are grouped depending on atomic mass and atomic number. These characteristics affect the properties of the elements. In total, there are 8 groups in the short version of the table; the elements included in one group have very similar properties. The first group contains hydrogen, lithium, potassium, copper, whose Latin pronunciation in Russian is cuprum. And also argentum - silver, cesium, gold - aurum and francium. The second group contains beryllium, magnesium, calcium, zinc, followed by strontium, cadmium, barium, and the group ends with mercury and radium.

The third group includes boron, aluminum, scandium, gallium, followed by yttrium, indium, lanthanum, and the group ends with thallium and actinium. The fourth group begins with carbon, silicon, titanium, continues with germanium, zirconium, tin and ends with hafnium, lead and rutherfordium. The fifth group contains elements such as nitrogen, phosphorus, vanadium, below are arsenic, niobium, antimony, then comes tantalum, bismuth and completes the group with dubnium. The sixth begins with oxygen, followed by sulfur, chromium, selenium, then molybdenum, tellurium, then tungsten, polonium and seaborgium.

In the seventh group, the first element is fluorine, followed by chlorine, manganese, bromine, technetium, followed by iodine, then rhenium, astatine and bohrium. The last group is the most numerous. It includes gases such as helium, neon, argon, krypton, xenon and radon. This group also includes metals iron, cobalt, nickel, rhodium, palladium, ruthenium, osmium, iridium, and platinum. Next come hannium and meitnerium. The elements that form the actinide series and lanthanide series. They have similar properties to lanthanum and actinium.

This scheme includes all types of elements, which are divided into 2 large groups - metals and non-metals, having different properties. How to determine whether an element belongs to one group or another will be helped by a conventional line that must be drawn from boron to astatine. It should be remembered that such a line can only be drawn in the full version of the table. All elements that are above this line and are located in the main subgroups are considered non-metals. And those below, in the main subgroups, are metals. Metals are also substances found in side subgroups. There are special pictures and photos in which you can familiarize yourself in detail with the position of these elements. It is worth noting that those elements that are on this line exhibit the same properties of both metals and non-metals.

A separate list is made up of amphoteric elements, which have dual properties and can form 2 types of compounds as a result of reactions. At the same time, they manifest both basic and acid properties. The predominance of certain properties depends on the reaction conditions and substances with which the amphoteric element reacts.

It is worth noting that this scheme, in its traditional design of good quality, is colored. At the same time, for ease of orientation, they are indicated in different colors. main and secondary subgroups. Elements are also grouped depending on the similarity of their properties.
However, nowadays, along with the color scheme, the black and white periodic table of Mendeleev is very common. This type is used for black and white printing. Despite its apparent complexity, working with it is just as convenient if you take into account some of the nuances. So, in this case, you can distinguish the main subgroup from the secondary one by differences in shades that are clearly visible. In addition, in the color version, elements with the presence of electrons on different layers are indicated different colors.
It is worth noting that in a single-color design it is not very difficult to navigate the scheme. For this purpose, the information indicated in each individual cell of the element will be sufficient.

The Unified State Exam today is the main type of test at the end of school, which means that special attention must be paid to preparing for it. Therefore, when choosing final exam in chemistry, you need to pay attention to materials that can help you pass it. As a rule, schoolchildren are allowed to use some tables during the exam, in particular, the periodic table in good quality. Therefore, in order for it to bring only benefits during testing, attention should be paid in advance to its structure and the study of the properties of the elements, as well as their sequence. You also need to learn use the black and white version of the table so as not to encounter some difficulties in the exam.

In addition to the main table characterizing the properties of elements and their dependence on atomic mass, there are other diagrams that can help in the study of chemistry. For example, there are tables of solubility and electronegativity of substances. The first can be used to determine how soluble a particular compound is in water at normal temperature. In this case, anions are located horizontally - negatively charged ions, and cations - that is, positively charged ions - are located vertically. To find out degree of solubility of one or another compound, it is necessary to find its components using the table. And at the place of their intersection there will be the necessary designation.

If it is the letter “p”, then the substance is completely soluble in water under normal conditions. If the letter “m” is present, the substance is slightly soluble, and if the letter “n” is present, it is almost insoluble. If there is a “+” sign, the compound does not form a precipitate and reacts with the solvent without residue. If a "-" sign is present, it means that such a substance does not exist. Sometimes you can also see the “?” sign in the table, then this means that the degree of solubility of this compound is not known for certain. Electronegativity of elements can vary from 1 to 8; there is also a special table to determine this parameter.

Another useful table is the metal activity series. All metals are located in it according to increasing degrees of electrochemical potential. The series of metal voltages begins with lithium and ends with gold. It is believed that the further to the left a metal occupies a place in a given row, the more active it is in chemical reactions. Thus, the most active metal Lithium is considered an alkaline metal. The list of elements also contains hydrogen towards the end. It is believed that the metals located after it are practically inactive. These include elements such as copper, mercury, silver, platinum and gold.

Periodic table pictures in good quality

This scheme is one of the largest achievements in the field of chemistry. Wherein there are many types of this table– short version, long, as well as extra-long. The most common is the short table, but the long version of the diagram is also common. It is worth noting that the short version of the circuit is not currently recommended for use by IUPAC.
In total there were More than a hundred types of tables have been developed, differing in presentation, form and graphical representation. They are used in different fields of science, or are not used at all. Currently, new circuit configurations continue to be developed by researchers. The main option is either a short or long circuit in excellent quality.

Instructions

The periodic system is a multi-story “house” containing a large number of apartments. Each “tenant” or in his own apartment under a certain number, which is permanent. In addition, the element has a “surname” or name, such as oxygen, boron or nitrogen. In addition to this data, each “apartment” contains information such as relative atomic mass, which may have exact or rounded values.

As in any house, there are “entrances”, namely groups. Moreover, in groups the elements are located on the left and right, forming. Depending on which side there are more of them, that side is called the main one. The other subgroup, accordingly, will be secondary. The table also has “floors” or periods. Moreover, periods can be both large (consist of two rows) and small (have only one row).

The table shows the structure of an atom of an element, each of which has a positively charged nucleus consisting of protons and neutrons, as well as negatively charged electrons rotating around it. The number of protons and electrons is numerically the same and is determined in the table by the serial number of the element. For example, the chemical element sulfur is #16, therefore it will have 16 protons and 16 electrons.

To determine the number of neutrons (neutral particles also located in the nucleus), subtract its atomic number from the relative atomic mass of the element. For example, iron has a relative atomic mass of 56 and an atomic number of 26. Therefore, 56 – 26 = 30 protons for iron.

Electrons are located at different distances from the nucleus, forming electron levels. To determine the number of electronic (or energy) levels, you need to look at the number of the period in which the element is located. For example, it is in the 3rd period, therefore it will have 3 levels.

By the group number (but only for the main subgroup) you can determine the highest valency. For example, elements of the first group of the main subgroup (lithium, sodium, potassium, etc.) have a valency of 1. Accordingly, elements of the second group (beryllium, calcium, etc.) will have a valence of 2.

You can also use the table to analyze the properties of elements. From left to right, metallic, and non-metallic are amplified. This is clearly seen in the example of period 2: it begins with an alkali metal, then the alkaline earth metal magnesium, after it the element aluminum, then non-metals silicon, phosphorus, sulfur and the period ends with gaseous substances - chlorine and argon. In the next period, a similar dependence is observed.

From top to bottom, a pattern is also observed - metallic properties increase, and non-metallic properties weaken. That is, for example, cesium is much more active compared to sodium.

Helpful advice

For convenience, it is better to use the color version of the table.

Discovery of the periodic law and creation of an ordered system of chemical elements D.I. Mendeleev became the apogee of the development of chemistry in the 19th century. The scientist summarized and systematized extensive knowledge about the properties of elements.

Instructions

In the 19th century there was no idea about the structure of the atom. Discovery by D.I. Mendeleev was only a generalization of experimental facts, but their physical meaning remained unclear for a long time. When the first data appeared on the structure of the nucleus and the distribution of electrons in atoms, it was possible to look at the law and system of elements in a new way. Table D.I. Mendeleev makes it possible to visually trace the properties of the elements found in.

Each element in the table is assigned a specific serial number (H - 1, Li - 2, Be - 3, etc.). This number corresponds to the nucleus (the number of protons in the nucleus) and the number of electrons orbiting the nucleus. The number of protons is thus equal to the number of electrons, which means that under normal conditions the atom is electrically .

The division into seven periods occurs according to the number of energy levels of the atom. Atoms of the first period have a single-level electron shell, the second - a two-level, the third - a three-level, etc. When a new energy level is filled, a new period begins.

The first elements of any period are characterized by atoms that have one electron at the outer level - these are alkali metal atoms. The periods end with atoms of noble gases, which have an external energy level completely filled with electrons: in the first period, noble gases have 2 electrons, in subsequent periods - 8. It is precisely because of the similar structure of the electron shells that groups of elements have similar physics.

In the table D.I. Mendeleev has 8 main subgroups. This number is determined by the maximum possible number of electrons at the energy level.

At the bottom of the periodic table, lanthanides and actinides are distinguished as independent series.

Using the table D.I. Mendeleev, one can observe the periodicity of the following properties of elements: atomic radius, atomic volume; ionization potential; electron affinity forces; electronegativity of the atom; ; physical properties of potential compounds.

Clearly traceable periodicity of the arrangement of elements in the table D.I. Mendeleev is rationally explained by the sequential nature of filling energy levels with electrons.

Sources:

• Mendeleev table

The periodic law, which is the basis of modern chemistry and explains the patterns of changes in the properties of chemical elements, was discovered by D.I. Mendeleev in 1869. The physical meaning of this law is revealed by studying the complex structure of the atom.

In the 19th century, it was believed that atomic mass was the main characteristic of an element, so it was used to classify substances. Nowadays, atoms are defined and identified by the amount of charge on their nucleus (the number and atomic number on the periodic table). However, the atomic mass of elements, with some exceptions (for example, the atomic mass is less than the atomic mass of argon), increases in proportion to their nuclear charge.

With an increase in atomic mass, a periodic change in the properties of elements and their compounds is observed. These are the metallicity and non-metallicity of atoms, atomic radius, ionization potential, electron affinity, electronegativity, oxidation states, compounds (boiling points, melting points, density), their basicity, amphotericity or acidity.

How many elements are in the modern periodic table

The periodic table graphically expresses the law he discovered. The modern periodic table contains 112 chemical elements (the last ones are Meitnerium, Darmstadtium, Roentgenium and Copernicium). According to the latest data, the following 8 elements have also been discovered (up to 120 inclusive), but not all of them have received their names, and these elements are still few in any printed publications.

Each element occupies a specific cell in the periodic table and has its own serial number, corresponding to the charge of the nucleus of its atom.

How is the periodic table constructed?

The structure of the periodic table is represented by seven periods, ten rows and eight groups. Each period begins with an alkali metal and ends with a noble gas. The exceptions are the first period, which begins with hydrogen, and the seventh incomplete period.

Periods are divided into small and large. Small periods (first, second, third) consist of one horizontal row, large periods (fourth, fifth, sixth) - of two horizontal rows. The upper rows in large periods are called even, the lower rows are called odd.

In the sixth period of the table after (serial number 57) there are 14 elements similar in properties to lanthanum - lanthanides. They are listed at the bottom of the table as a separate line. The same applies to actinides located after actinium (with number 89) and largely repeating its properties.

The even rows of large periods (4, 6, 8, 10) are filled only with metals.

Elements in groups exhibit the same valency in oxides and other compounds, and this valency corresponds to the group number. The main ones contain elements of small and large periods, only large ones. From top to bottom they strengthen, non-metallic ones weaken. All atoms of side subgroups are metals.

Tip 4: Selenium as a chemical element on the periodic table

The chemical element selenium belongs to group VI of the periodic table of Mendeleev, it is a chalcogen. Natural selenium consists of six stable isotopes. There are also 16 radioactive isotopes of selenium known.

Instructions

Selenium is considered a very rare and trace element; it migrates vigorously in the biosphere, forming more than 50 minerals. The most famous of them are: berzelianite, naumannite, native selenium and chalcomenite.

Selenium is found in volcanic sulfur, galena, pyrite, bismuthin and other sulfides. It is mined from lead, copper, nickel and other ores, in which it is found in a dispersed state.

The tissues of most living beings contain from 0.001 to 1 mg/kg; some plants, marine organisms and fungi concentrate it. For a number of plants, selenium is an essential element. The need for humans and animals is 50-100 mcg/kg of food; this element has antioxidant properties, affects many enzymatic reactions and increases the sensitivity of the retina to light.

Selenium can exist in various allotropic modifications: amorphous (vitreous, powdery and colloidal selenium), as well as crystalline. By reducing selenium from a solution of selenous acid or by rapidly cooling its vapor, red powdered and colloidal selenium is obtained.

When any modification of this chemical element is heated above 220°C and subsequently cooled, glassy selenium is formed; it is fragile and has a glassy luster.

The most thermally stable is hexagonal gray selenium, the lattice of which is built from spiral chains of atoms located parallel to each other. It is produced by heating other forms of selenium until melting and slowly cooling to 180-210°C. Within hexagonal selenium chains, the atoms are bonded covalently.

Selenium is stable in air, it is not affected by oxygen, water, dilute sulfuric and hydrochloric acids, but it dissolves well in nitric acid. Interacting with metals, selenium forms selenides. There are many known complex compounds of selenium, all of them are poisonous.

Selenium is obtained from paper or production waste by electrolytic refining of copper. This element is present in sludge along with heavy metals, sulfur and tellurium. To extract it, the sludge is filtered, then heated with concentrated sulfuric acid or subjected to oxidative roasting at a temperature of 700°C.

Selenium is used in the production of rectifying semiconductor diodes and other converter equipment. In metallurgy, it is used to give steel a fine-grained structure and also improve its mechanical properties. In the chemical industry, selenium is used as a catalyst.

Sources:

• KhiMiK.ru, Selen

Calcium is a chemical element belonging to the second subgroup of the periodic table with the symbol Ca and an atomic mass of 40.078 g/mol. It is a fairly soft and reactive alkaline earth metal with a silvery color.

Instructions

From Latin, “” is translated as “lime” or “soft stone”, and it owes its discovery to the Englishman Humphry Davy, who in 1808 was able to isolate calcium using the electrolytic method. The scientist then took a mixture of wet slaked lime, “flavored” with mercuric oxide, and subjected it to the process of electrolysis on a platinum plate, which appeared in the experiment as an anode. The cathode was a wire that the chemist immersed in liquid mercury. It is also interesting that calcium compounds such as limestone, marble and gypsum, as well as lime, were known to mankind many centuries before Davy’s experiment, during which scientists believed some of them to be simple and independent bodies. It was not until 1789 that the Frenchman Lavoisier published a work in which he suggested that lime, silica, barite and alumina were complex substances.

Calcium has a high degree of chemical activity, which is why it is practically never found in nature in its pure form. But scientists estimate that this element accounts for about 3.38% of the total mass of the entire earth's crust, making calcium fifth most abundant after oxygen, silicon, aluminum and iron. This element is found in sea water - about 400 mg per liter. Calcium is also included in the composition of silicates of various rocks (for example, granite and gneisses). There is a lot of it in feldspar, chalk and limestones, consisting of the mineral calcite with the formula CaCO3. The crystalline form of calcium is marble. In total, through the migration of this element in the earth's crust, it forms 385 minerals.

The physical properties of calcium include its ability to exhibit valuable semiconducting abilities, although it does not become a semiconductor and a metal in the traditional sense of the word. This situation changes with a gradual increase in pressure, when calcium is given a metallic state and the ability to exhibit superconducting properties. Calcium easily interacts with oxygen, air moisture and carbon dioxide, which is why in laboratories this chemical element is kept tightly closed for work and chemist John Alexander Newland - however, the scientific community ignored his achievement. Newland's proposal was not taken seriously because of his search for harmony and the connection between music and chemistry.

Dmitri Mendeleev first published his periodic table in 1869 in the pages of the Journal of the Russian Chemical Society. The scientist also sent notices of his discovery to all the world's leading chemists, after which he repeatedly improved and finalized the table until it became what it is known today. The essence of Dmitry Mendeleev's discovery was a periodic, rather than monotonous change in the chemical properties of elements with increasing atomic mass. The final unification of the theory into the periodic law occurred in 1871.

Legends about Mendeleev

The most common legend is the discovery of the periodic table in a dream. The scientist himself has repeatedly ridiculed this myth, claiming that he had been coming up with the table for many years. According to another legend, Dmitry Mendeleev vodka - it appeared after the scientist defended his dissertation “Discourse on the combination of alcohol with water.”

Mendeleev is still considered by many to be the discoverer, who himself loved to create under an aqueous-alcohol solution. The scientist’s contemporaries often laughed at Mendeleev’s laboratory, which he set up in the hollow of a giant oak tree.

A separate reason for jokes, according to rumors, was Dmitry Mendeleev’s passion for weaving suitcases, which the scientist was engaged in while living in Simferopol. Later, he made crafts from cardboard for the needs of his laboratory, for which he was sarcastically called a master of suitcase making.

The periodic table, in addition to ordering chemical elements into a single system, made it possible to predict the discovery of many new elements. However, at the same time, scientists recognized some of them as non-existent, since they were incompatible with the concept. The most famous story at that time was the discovery of such new elements as coronium and nebulium.

The periodic system is an ordered set of chemical elements, their natural classification, which is a graphic (tabular) expression of the periodic law of chemical elements. Its structure, in many ways similar to the modern one, was developed by D. I. Mendeleev on the basis of the periodic law in 1869–1871.

The prototype of the periodic system was the “Experience of a system of elements based on their atomic weight and chemical similarity”, compiled by D. I. Mendeleev on March 1, 1869. Over the course of two and a half years, the scientist continuously improved the “Experience of a System”, introduced the idea of ​​groups, series and periods of elements. As a result, the structure of the periodic table acquired largely modern outlines.

The concept of the place of an element in the system, determined by the numbers of the group and period, became important for its evolution. Based on this concept, Mendeleev came to the conclusion that it was necessary to change the atomic masses of some elements: uranium, indium, cerium and its satellites. This was the first practical application of the periodic table. Mendeleev also predicted for the first time the existence and properties of several unknown elements. The scientist described in detail the most important properties of eka-aluminium (the future of gallium), eka-boron (scandium) and eka-silicon (germanium). In addition, he predicted the existence of analogues of manganese (future technetium and rhenium), tellurium (polonium), iodine (astatine), cesium (France), barium (radium), tantalum (protactinium). The scientist's predictions regarding these elements were of a general nature, since these elements were located in little-studied areas of the periodic table.

The first versions of the periodic system largely represented only an empirical generalization. After all, the physical meaning of the periodic law was unclear; there was no explanation for the reasons for the periodic change in the properties of elements depending on the increase in atomic masses. In this regard, many problems remained unresolved. Are there boundaries of the periodic table? Is it possible to determine the exact number of existing elements? The structure of the sixth period remained unclear - what was the exact amount of rare earth elements? It was unknown whether elements between hydrogen and lithium still existed, what the structure of the first period was. Therefore, right up to the physical substantiation of the periodic law and the development of the theory of the periodic system, serious difficulties arose more than once. The discovery in 1894–1898 was unexpected. five inert gases that seemed to have no place in the periodic table. This difficulty was eliminated thanks to the idea of ​​including an independent zero group in the structure of the periodic table. Mass discovery of radioelements at the turn of the 19th and 20th centuries. (by 1910 their number was about 40) led to a sharp contradiction between the need to place them in the periodic table and its existing structure. There were only 7 vacancies for them in the sixth and seventh periods. This problem was solved by the establishment of shift rules and the discovery of isotopes.

One of the main reasons for the impossibility of explaining the physical meaning of the periodic law and the structure of the periodic system was that it was unknown how the atom was structured (see Atom). The most important milestone in the development of the periodic table was the creation of the atomic model by E. Rutherford (1911). On its basis, the Dutch scientist A. Van den Broek (1913) suggested that the serial number of an element in the periodic table is numerically equal to the charge of the nucleus of its atom (Z). This was experimentally confirmed by the English scientist G. Moseley (1913). The periodic law received a physical justification: the periodicity of changes in the properties of elements began to be considered depending on the Z - charge of the nucleus of the element's atom, and not on the atomic mass (see Periodic law of chemical elements).

As a result, the structure of the periodic table was significantly strengthened. The lower limit of the system has been determined. This is hydrogen - the element with a minimum Z = 1. It has become possible to accurately estimate the number of elements between hydrogen and uranium. “Gaps” in the periodic table were identified, corresponding to unknown elements with Z = 43, 61, 72, 75, 85, 87. However, questions about the exact number of rare earth elements remained unclear and, most importantly, the reasons for the periodicity of changes in the properties of elements were not revealed depending on Z.

Based on the established structure of the periodic system and the results of studying atomic spectra, the Danish scientist N. Bohr in 1918–1921. developed ideas about the sequence of construction of electronic shells and subshells in atoms. The scientist came to the conclusion that similar types of electronic configurations of the outer shells of atoms are periodically repeated. Thus, it was shown that the periodicity of changes in the properties of chemical elements is explained by the existence of periodicity in the construction of electronic shells and subshells of atoms.

The periodic table covers more than 100 elements. Of these, all transuranium elements (Z = 93–110), as well as elements with Z = 43 (technetium), 61 (promethium), 85 (astatine), 87 (france) were obtained artificially. Over the entire history of the existence of the periodic system, a very large number (>500) of variants of its graphic representation have been proposed, mainly in the form of tables, but also in the form of various geometric figures (spatial and planar), analytical curves (spirals, etc.), etc. The most widespread are short, semi-long, long and ladder forms of tables. Currently, short form is preferred.

The fundamental principle of constructing the periodic table is its division into groups and periods. Mendeleev's concept of series of elements is not used today, since it is devoid of physical meaning. The groups, in turn, are divided into main (a) and secondary (b) subgroups. Each subgroup contains elements - chemical analogues. Elements of the a- and b-subgroups in most groups also show a certain similarity with each other, mainly in higher oxidation states, which, as a rule, are equal to the group number. A period is a collection of elements that begins with an alkali metal and ends with an inert gas (a special case is the first period). Each period contains a strictly defined number of elements. The periodic table consists of eight groups and seven periods, with the seventh period not yet completed.

Peculiarity first period is that it contains only 2 gaseous elements in free form: hydrogen and helium. The place of hydrogen in the system is ambiguous. Since it exhibits properties common to alkali metals and halogens, it is placed either in the 1a-, or in the Vlla-subgroup, or in both at the same time, enclosing the symbol in brackets in one of the subgroups. Helium is the first representative of the VIIIa‑subgroup. For a long time, helium and all inert gases were separated into an independent zero group. This position required revision after the synthesis of the chemical compounds krypton, xenon and radon. As a result, the noble gases and elements of the former Group VIII (iron, cobalt, nickel and platinum metals) were combined within one group.

Second the period contains 8 elements. It begins with the alkali metal lithium, whose only oxidation state is +1. Next comes beryllium (metal, oxidation state +2). Boron already exhibits a weakly expressed metallic character and is a non-metal (oxidation state +3). Next to boron, carbon is a typical nonmetal that exhibits both +4 and −4 oxidation states. Nitrogen, oxygen, fluorine and neon are all non-metals, with nitrogen having the highest oxidation state of +5 corresponding to the group number. Oxygen and fluorine are among the most active nonmetals. The inert gas neon ends the period.

Third period (sodium - argon) also contains 8 elements. The nature of the change in their properties is largely similar to that observed for elements of the second period. But there is also some specificity here. Thus, magnesium, unlike beryllium, is more metallic, as is aluminum compared to boron. Silicon, phosphorus, sulfur, chlorine, argon are all typical non-metals. And all of them, except argon, exhibit higher oxidation states equal to the group number.

As we can see, in both periods, as Z increases, there is a clear weakening of the metallic and strengthening of the nonmetallic properties of the elements. D.I. Mendeleev called the elements of the second and third periods (in his words, small) typical. Elements of small periods are among the most common in nature. Carbon, nitrogen and oxygen (along with hydrogen) are organogens, i.e. the main elements of organic matter.

All elements of the first - third periods are placed in a-subgroups.

Fourth period (potassium - krypton) contains 18 elements. According to Mendeleev, this is the first big period. After the alkali metal potassium and the alkaline earth metal calcium comes a series of elements consisting of 10 so-called transition metals (scandium - zinc). All of them are included in b-subgroups. Most transition metals exhibit higher oxidation states equal to the group number, except iron, cobalt and nickel. The elements, from gallium to krypton, belong to the a-subgroups. A number of chemical compounds are known for krypton.

Fifth The period (rubidium - xenon) is similar in structure to the fourth. It also contains an insert of 10 transition metals (yttrium - cadmium). The elements of this period have their own characteristics. In the triad ruthenium - rhodium - palladium, compounds are known for ruthenium where it exhibits an oxidation state of +8. All elements of a-subgroups exhibit higher oxidation states equal to the group number. The features of changes in properties of elements of the fourth and fifth periods as Z increases are more complex in comparison with the second and third periods.

Sixth period (cesium - radon) includes 32 elements. This period, in addition to 10 transition metals (lanthanum, hafnium - mercury), also contains a set of 14 lanthanides - from cerium to lutetium. Elements from cerium to lutetium are chemically very similar, and for this reason they have long been included in the family of rare earth elements. In the short form of the periodic table, a series of lanthanides is included in the lanthanum cell, and the decoding of this series is given at the bottom of the table (see Lanthanides).

What is the specificity of the elements of the sixth period? In the triad osmium - iridium - platinum, the oxidation state of +8 is known for osmium. Astatine has a fairly pronounced metallic character. Radon has the greatest reactivity of all noble gases. Unfortunately, due to the fact that it is highly radioactive, its chemistry has been little studied (see Radioactive elements).

Seventh the period starts from France. Like the sixth, it should also contain 32 elements, but 24 of them are still known. Francium and radium are respectively elements of the Ia and IIa subgroups, actinium belongs to the IIIb subgroup. Next comes the actinide family, which includes elements from thorium to lawrencium and is placed similarly to the lanthanides. The decoding of this series of elements is also given at the bottom of the table.

Now let's see how the properties of chemical elements change in subgroups periodic system. The main pattern of this change is the strengthening of the metallic character of the elements as Z increases. This pattern is especially clearly manifested in the IIIa–VIIa subgroups. For metals of Ia–IIIa subgroups, an increase in chemical activity is observed. For elements of IVa–VIIa subgroups, as Z increases, a weakening of the chemical activity of the elements is observed. For b-subgroup elements, the nature of the change in chemical activity is more complex.

The theory of the periodic system was developed by N. Bohr and other scientists in the 20s. XX century and is based on a real scheme for the formation of electronic configurations of atoms (see Atom). According to this theory, as Z increases, the filling of electron shells and subshells in the atoms of elements included in the periods of the periodic table occurs in the following sequence:

Based on the theory of the periodic system, we can give the following definition of a period: a period is a set of elements starting with an element with a value n equal to the period number and l = 0 (s-elements) and ending with an element with the same value n and l = 1 (p-elements elements) (see Atom). The exception is the first period, which contains only 1s elements. From the theory of the periodic system, the numbers of elements in periods follow: 2, 8, 8, 18, 18, 32...

In the table, the symbols of elements of each type (s-, p-, d- and f-elements) are depicted on a specific color background: s-elements - on red, p-elements - on orange, d-elements - on blue, f-elements - on green. Each cell shows the atomic numbers and atomic masses of the elements, as well as the electronic configurations of the outer electron shells.

From the theory of the periodic system it follows that the a-subgroups include elements with n equal to the period number, and l = 0 and 1. The b-subgroups include those elements in the atoms of which the completion of shells that previously remained incomplete occurs. That is why the first, second and third periods do not contain elements of b-subgroups.

The structure of the periodic table of elements is closely related to the structure of atoms of chemical elements. As Z increases, similar types of configuration of the outer electron shells periodically repeat. Namely, they determine the main features of the chemical behavior of elements. These features manifest themselves differently for elements of the a-subgroups (s- and p-elements), for elements of the b-subgroups (transition d-elements) and elements of the f-families - lanthanides and actinides. A special case is represented by the elements of the first period - hydrogen and helium. Hydrogen is characterized by high chemical activity because its only 1s electron is easily removed. At the same time, the configuration of helium (1s 2) is very stable, which determines its chemical inactivity.

For elements of the a-subgroups, the outer electron shells of the atoms are filled (with n equal to the period number), so the properties of these elements change noticeably as Z increases. Thus, in the second period, lithium (2s configuration) is an active metal that easily loses its only valence electron ; beryllium (2s 2) is also a metal, but less active due to the fact that its outer electrons are more tightly bound to the nucleus. Further, boron (2s 2 p) has a weakly expressed metallic character, and all subsequent elements of the second period, in which the 2p subshell is built, are already non-metals. The eight-electron configuration of the outer electron shell of neon (2s 2 p 6) - an inert gas - is very strong.

The chemical properties of elements of the second period are explained by the desire of their atoms to acquire the electronic configuration of the nearest inert gas (helium configuration for elements from lithium to carbon or neon configuration for elements from carbon to fluorine). This is why, for example, oxygen cannot exhibit a higher oxidation state equal to its group number: it is easier for it to achieve the neon configuration by acquiring additional electrons. The same nature of changes in properties manifests itself in the elements of the third period and in the s- and p-elements of all subsequent periods. At the same time, the weakening of the strength of the bond between outer electrons and the nucleus in a-subgroups as Z increases is manifested in the properties of the corresponding elements. Thus, for s‑elements there is a noticeable increase in chemical activity as Z increases, and for p‑elements there is an increase in metallic properties.

In the atoms of transition d‑elements, previously incomplete shells are completed with the value of the main quantum number n, one less than the period number. With a few exceptions, the configuration of the outer electron shells of the atoms of transition elements is ns 2. Therefore, all d-elements are metals, and that is why the changes in the properties of d-elements as Z increases are not as dramatic as those observed for s- and p-elements. In higher oxidation states, d-elements show a certain similarity with p-elements of the corresponding groups of the periodic table.

The peculiarities of the properties of the elements of triads (VIIIb-subgroup) are explained by the fact that the b-subshells are close to completion. This is why iron, cobalt, nickel and platinum metals, as a rule, do not tend to produce compounds in higher oxidation states. The only exceptions are ruthenium and osmium, which give the oxides RuO 4 and OsO 4 . For elements of subgroups Ib and IIb, the d-subshell is actually complete. Therefore, they exhibit oxidation states equal to the group number.

In the atoms of lanthanides and actinides (all of them are metals), previously incomplete electron shells are completed with the value of the main quantum number n being two units less than the period number. In the atoms of these elements, the configuration of the outer electron shell (ns 2) remains unchanged, and the third outer N‑shell is filled with 4f‑electrons. This is why the lanthanides are so similar.

For actinides the situation is more complicated. In atoms of elements with Z = 90–95, the 6d and 5f electrons can take part in chemical interactions. Therefore, actinides have many more oxidation states. For example, for neptunium, plutonium and americium, compounds are known where these elements appear in the heptavalent state. Only for elements, starting with curium (Z = 96), the trivalent state becomes stable, but this also has its own characteristics. Thus, the properties of the actinides differ significantly from the properties of the lanthanides, and the two families therefore cannot be considered similar.

The actinide family ends with the element with Z = 103 (lawrencium). An assessment of the chemical properties of kurchatovium (Z = 104) and nilsborium (Z = 105) shows that these elements should be analogues of hafnium and tantalum, respectively. Therefore, scientists believe that after the actinide family in atoms, the systematic filling of the 6d subshell begins. The chemical nature of elements with Z = 106–110 has not been assessed experimentally.

The final number of elements that the periodic table covers is unknown. The problem of its upper limit is perhaps the main mystery of the periodic table. The heaviest element that has been discovered in nature is plutonium (Z = 94). The limit of artificial nuclear fusion has been reached - an element with atomic number 110. The question remains open: will it be possible to obtain elements with large atomic numbers, which ones and how many? This cannot yet be answered with any certainty.

Using complex calculations performed on electronic computers, scientists tried to determine the structure of atoms and evaluate the most important properties of “superelements,” right down to huge serial numbers (Z = 172 and even Z = 184). The results obtained were quite unexpected. For example, in an atom of an element with Z = 121, an 8p electron is expected to appear; this is after the formation of the 8s subshell has completed in atoms with Z = 119 and 120. But the appearance of p-electrons after s-electrons is observed only in atoms of elements of the second and third periods. Calculations also show that in elements of the hypothetical eighth period, the filling of the electron shells and sub-shells of atoms occurs in a very complex and unique sequence. Therefore, assessing the properties of the corresponding elements is a very difficult problem. It would seem that the eighth period should contain 50 elements (Z = 119–168), but, according to calculations, it should end at the element with Z = 164, i.e. 4 serial numbers earlier. And the “exotic” ninth period, it turns out, should consist of 8 elements. Here is his “electronic” entry: 9s 2 8p 4 9p 2. In other words, it would contain only 8 elements, like the second and third periods.

It is difficult to say how true the calculations made using a computer would be. However, if they were confirmed, then it would be necessary to seriously reconsider the patterns underlying the periodic table of elements and its structure.

The periodic table has played and continues to play a huge role in the development of various fields of natural science. It was the most important achievement of atomic-molecular science, contributed to the emergence of the modern concept of “chemical element” and clarification of concepts about simple substances and compounds.

The regularities revealed by the periodic system had a significant impact on the development of the theory of atomic structure, the discovery of isotopes, and the emergence of ideas about nuclear periodicity. The periodic system is associated with a strictly scientific formulation of the problem of forecasting in chemistry. This was manifested in the prediction of the existence and properties of unknown elements and new features of the chemical behavior of elements already discovered. Nowadays, the periodic system represents the foundation of chemistry, primarily inorganic, significantly helping to solve the problem of chemical synthesis of substances with predetermined properties, the development of new semiconductor materials, the selection of specific catalysts for various chemical processes, etc. And finally, the periodic system is the basis of teaching chemistry.

Element 115 of the periodic table, moscovium, is a superheavy synthetic element with the symbol Mc and atomic number 115. It was first obtained in 2003 by a joint team of Russian and American scientists at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia. In December 2015, it was recognized as one of the four new elements by the Joint Working Group of International Scientific Organizations IUPAC/IUPAP. On November 28, 2016, it was officially named in honor of the Moscow region, where JINR is located.

Characteristic

Element 115 of the periodic table is an extremely radioactive substance: its most stable known isotope, moscovium-290, has a half-life of just 0.8 seconds. Scientists classify moscovium as a non-transition metal, with a number of characteristics similar to bismuth. In the periodic table, it belongs to the transactinide elements of the p-block of the 7th period and is placed in group 15 as the heaviest pnictogen (nitrogen subgroup element), although it has not been confirmed to behave like a heavier homologue of bismuth.

According to calculations, the element has some properties similar to lighter homologues: nitrogen, phosphorus, arsenic, antimony and bismuth. At the same time, it demonstrates several significant differences from them. To date, about 100 moscovium atoms have been synthesized, which have mass numbers from 287 to 290.

Physical properties

The valence electrons of element 115 of the periodic table, moscovium, are divided into three subshells: 7s (two electrons), 7p 1/2 (two electrons), and 7p 3/2 (one electron). The first two of them are relativistically stabilized and, therefore, behave like noble gases, while the latter are relativistically destabilized and can easily participate in chemical interactions. Thus, the primary ionization potential of moscovium should be about 5.58 eV. According to calculations, moscovium should be a dense metal due to its high atomic weight with a density of about 13.5 g/cm 3 .

Estimated design characteristics:

• Phase: solid.
• Melting point: 400°C (670°K, 750°F).
• Boiling point: 1100°C (1400°K, 2000°F).
• Specific heat of fusion: 5.90-5.98 kJ/mol.
• Specific heat of vaporization and condensation: 138 kJ/mol.

Chemical properties

Element 115 of the periodic table is third in the 7p series of chemical elements and is the heaviest member of group 15 in the periodic table, ranking below bismuth. The chemical interaction of moscovium in an aqueous solution is determined by the characteristics of the Mc + and Mc 3+ ions. The former are presumably easily hydrolyzed and form ionic bonds with halogens, cyanides and ammonia. Muscovy(I) hydroxide (McOH), carbonate (Mc 2 CO 3), oxalate (Mc 2 C 2 O 4) and fluoride (McF) must be dissolved in water. The sulfide (Mc 2 S) must be insoluble. Chloride (McCl), bromide (McBr), iodide (McI) and thiocyanate (McSCN) are slightly soluble compounds.

Moscovium(III) fluoride (McF 3) and thiosonide (McS 3) are presumably insoluble in water (similar to the corresponding bismuth compounds). While chloride (III) (McCl 3), bromide (McBr 3) and iodide (McI 3) should be readily soluble and easily hydrolyzed to form oxohalides such as McOCl and McOBr (also similar to bismuth). Moscovium(I) and (III) oxides have similar oxidation states, and their relative stability depends largely on which elements they react with.

Uncertainty

Due to the fact that element 115 of the periodic table is synthesized experimentally only once, its exact characteristics are problematic. Scientists have to rely on theoretical calculations and compare them with more stable elements with similar properties.

In 2011, experiments were carried out to create isotopes of nihonium, flerovium and moscovium in reactions between “accelerators” (calcium-48) and “targets” (american-243 and plutonium-244) to study their properties. However, the “targets” included impurities of lead and bismuth and, therefore, some isotopes of bismuth and polonium were obtained in nucleon transfer reactions, which complicated the experiment. Meanwhile, the data obtained will help scientists in the future study in more detail heavy homologues of bismuth and polonium, such as moscovium and livermorium.

Opening

The first successful synthesis of element 115 of the periodic table was a joint work of Russian and American scientists in August 2003 at JINR in Dubna. The team led by nuclear physicist Yuri Oganesyan, in addition to domestic specialists, included colleagues from Lawrence Livermore National Laboratory. Researchers published information in the Physical Review on February 2, 2004 that they bombarded americium-243 with calcium-48 ions at the U-400 cyclotron and obtained four atoms of the new substance (one 287 Mc nucleus and three 288 Mc nuclei). These atoms decay (decay) by emitting alpha particles to the element nihonium in about 100 milliseconds. Two heavier isotopes of moscovium, 289 Mc and 290 Mc, were discovered in 2009–2010.

Initially, IUPAC could not approve the discovery of the new element. Confirmation from other sources was required. Over the next few years, the later experiments were further evaluated, and the Dubna team's claim to have discovered element 115 was once again put forward.

In August 2013, a team of researchers from Lund University and the Heavy Ion Institute in Darmstadt (Germany) announced that they had repeated the 2004 experiment, confirming the results obtained in Dubna. Further confirmation was published by a team of scientists working at Berkeley in 2015. In December 2015, the joint IUPAC/IUPAP working group recognized the discovery of this element and gave priority to the Russian-American team of researchers in the discovery.

Name

In 1979, according to the IUPAC recommendation, it was decided to name element 115 of the periodic table “ununpentium” and denote it with the corresponding symbol UUP. Although the name has since been widely used to refer to the undiscovered (but theoretically predicted) element, it has not caught on within the physics community. Most often, the substance was called that way - element No. 115 or E115.

On December 30, 2015, the discovery of a new element was recognized by the International Union of Pure and Applied Chemistry. According to the new rules, discoverers have the right to propose their own name for a new substance. At first it was planned to name element 115 of the periodic table “langevinium” in honor of the physicist Paul Langevin. Later, a team of scientists from Dubna, as an option, proposed the name “Moscow” in honor of the Moscow region, where the discovery was made. In June 2016, IUPAC approved the initiative and officially approved the name "moscovium" on November 28, 2016.