How to use the periodic table? For an uninitiated person, reading the periodic table is the same as looking at the ancient runes of elves for a dwarf. And the periodic table, by the way, if used correctly, can tell a lot about the world. In addition to serving you in the exam, it is also simply indispensable for solving a huge number of chemical and physical problems. But how to read it? Fortunately, today everyone can learn this art. In this article we will tell you how to understand the periodic table.

The periodic system of chemical elements (Mendeleev's table) is a classification of chemical elements that establishes the dependence of various properties of elements on the charge of the atomic nucleus.

History of the creation of the Table

Dmitri Ivanovich Mendeleev was not a simple chemist, if someone thinks so. He was a chemist, physicist, geologist, metrologist, ecologist, economist, oilman, aeronaut, instrument maker and teacher. During his life, the scientist managed to conduct a lot of fundamental research in various fields of knowledge. For example, it is widely believed that it was Mendeleev who calculated the ideal strength of vodka - 40 degrees. We do not know how Mendeleev treated vodka, but it is known for sure that his dissertation on the topic “Discourse on the combination of alcohol with water” had nothing to do with vodka and considered alcohol concentrations from 70 degrees. With all the merits of the scientist, the discovery of the periodic law of chemical elements - one of the fundamental laws of nature, brought him the widest fame.

There is a legend according to which the scientist dreamed of the periodic system, after which he only had to finalize the idea that had appeared. But, if everything were so simple .. This version of the creation of the periodic table, apparently, is nothing more than a legend. When asked how the table was opened, Dmitry Ivanovich himself answered: “ I’ve been thinking about it for maybe twenty years, and you think: I sat and suddenly ... it’s ready. ”

In the middle of the nineteenth century, attempts to streamline the known chemical elements (63 elements were known) were simultaneously undertaken by several scientists. For example, in 1862 Alexandre Émile Chancourtois placed the elements along a helix and noted the cyclical repetition of chemical properties. Chemist and musician John Alexander Newlands proposed his version of the periodic table in 1866. An interesting fact is that in the arrangement of the elements the scientist tried to discover some mystical musical harmony. Among other attempts was the attempt of Mendeleev, which was crowned with success.

In 1869, the first scheme of the table was published, and the day of March 1, 1869 is considered the day of the discovery of the periodic law. The essence of Mendeleev's discovery was that the properties of elements with increasing atomic mass do not change monotonously, but periodically. The first version of the table contained only 63 elements, but Mendeleev made a number of very non-standard decisions. So, he guessed to leave a place in the table for yet undiscovered elements, and also changed the atomic masses of some elements. The fundamental correctness of the law derived by Mendeleev was confirmed very soon after the discovery of gallium, scandium and germanium, the existence of which was predicted by scientists.

Modern view of the periodic table

Below is the table itself.

Today, instead of atomic weight (atomic mass), the concept of atomic number (the number of protons in the nucleus) is used to order the elements. The table contains 120 elements, which are arranged from left to right in ascending order of atomic number (number of protons)

The columns of the table are so-called groups, and the rows are periods. There are 18 groups and 8 periods in the table.

• The metallic properties of elements decrease when moving along the period from left to right, and increase in the opposite direction.
• The dimensions of atoms decrease as they move from left to right along the periods.
• When moving from top to bottom in the group, the reducing metallic properties increase.
• Oxidizing and non-metallic properties increase along the period from left to right. I.

What do we learn about the element from the table? For example, let's take the third element in the table - lithium, and consider it in detail.

First of all, we see the symbol of the element itself and its name under it. In the upper left corner is the atomic number of the element, in the order in which the element is located in the table. atomic number, as already mentioned, is equal to the number protons in the nucleus. The number of positive protons is usually equal to the number of negative electrons in an atom (with the exception of isotopes).

Atomic mass is listed under atomic number (in this option tables). If we round the atomic mass to the nearest integer, we get the so-called mass number. The difference between the mass number and the atomic number gives the number of neutrons in the nucleus. Thus, the number of neutrons in a helium nucleus is two, and in lithium - four.

So our course "Mendeleev's Table for Dummies" has ended. In conclusion, we invite you to watch a thematic video, and we hope that the question of how to use the periodic table of Mendeleev has become clearer to you. We remind you that learning a new subject is always more effective not alone, but with the help of an experienced mentor. That is why, you should never forget about those who will gladly share their knowledge and experience with you.

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 the periodic system of Mendeleev 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 the periodic law created by Dmitry Ivanovich back in the third quarter of the 19th century (1869). It was in 1869 at a meeting of the Russian chemical community that Mendeleev's notice was read out about the creation of a certain structure by him. 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 of 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 valence is, 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. Ranking them in ascending order atomic masses, he nevertheless achieved periodicity in each of the series.

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 has been reflected in later editions. periodic system Mendeleev. 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 ideas about various compounds and simple substances Oh. 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 want 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 the main role in this process was played by the famous Russian chemist Dmitry Ivanovich Mendeleev - 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

By 1869, the main idea had already been formed by Mendeleev, and in a fairly short time, but he could not formalize it into any sort of ordered system that clearly displays what was what, for a long time he could not. 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 a 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 the right order. After that, the students even joked that 40° vodka was discovered in the same way. But there were still real prerequisites for the sleep story: 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, including 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, among them: 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 quantum mechanics appeared, the true meaning of the order of 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, we can cite as an example the ideas of an 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:

• Preparation- 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- the stage at which the intuitive solution is found. 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 of your plans!

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

This diagram contains all known to man elements, and they are grouped according to atomic mass and serial 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, the Latin pronunciation in Russian of which 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, then 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. In the fifth group there are elements such as nitrogen, phosphorus, vanadium, arsenic, niobium, antimony are located below, then bismuth tantalum comes and completes the dubnium group. 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 borium. The last group is the most numerous. It includes gases such as helium, neon, argon, krypton, xenon and radon. This group also includes the metals iron, cobalt, nickel, rhodium, palladium, ruthenium, osmium, iridium, platinum. Next come hannium and meitnerium. Separately located elements that form the actinide series and the 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 with different properties. How to determine whether an element belongs to a particular group, a conditional line will help, which must be drawn from boron to astatine. It should be remembered that such a line can only be drawn in full version tables. All elements that are above this line and are located in the main subgroups are considered non-metals. And which are lower, in the main subgroups - metals. Also, metals are substances that are in side subgroups. There are special pictures and photos on which you can get acquainted with the position of these elements in detail. 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 also 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 equally both basic and acid properties. The predominance of certain properties depends on the reaction conditions and the substances with which the amphoteric element reacts.

It should be noted that this scheme in the traditional execution of good quality is color. Wherein different colors for ease of orientation are marked main and secondary subgroups. And also elements are grouped depending on the similarity of their properties.
However, at present, along with the color scheme, the black-and-white periodic table of Mendeleev is very common. This form is used for black and white printing. Despite the apparent complexity, working with it is just as convenient, given some of the nuances. Yes, distinguish main subgroup from the side in this case, it is possible 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, the information indicated in each individual cell of the element will be enough.

The exam today is the main type of test at the end of school, which means that preparation for it must be given Special attention. Therefore, when choosing final exam in chemistry, you need to pay attention to the materials that can help in its delivery. 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 benefit in tests, 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 that you don't face any difficulties in the exam.

In addition to the main table characterizing the properties of elements and their dependence on atomic mass, there are other schemes that can help in the study of chemistry. For example, there are tables of solubility and electronegativity of substances. The first one can determine how soluble a particular compound is in water at ordinary 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 in 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 in normal conditions. In the presence of the letter "m" - the substance is slightly soluble, and in the presence of the letter "n" - it almost does not dissolve. 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 the 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 by increasing the degree of electrochemical potential. A series of stress metals begins with lithium, ends with gold. It is believed that the further to the left a metal occupies in this row, the more active it is in chemical reactions. Thus, the most active metal Lithium is considered to be an alkaline metal. Hydrogen is also present at the end of the list of elements. It is believed that the metals that are located after it are practically inactive. Among them are elements such as copper, mercury, silver, platinum and gold.

Periodic table pictures in good quality

This scheme is one of the greatest achievements in the field of chemistry. Wherein There are many types of this table.- a short version, a long one, as well as an extra long one. The most common is the short table, and the long version of the schema is also common. It is worth noting that the short version of the scheme is not currently recommended by IUPAC for use.
Total was more than a hundred types of tables have been developed, which differ in presentation, shape, and graphical representation. They are used in various fields of science, or not used at all. Currently, new circuit configurations continue to be developed by researchers. As the main option, either a short or a long circuit in excellent quality is used.

How it all began?

Many well-known eminent chemists on turn of XIX-XX centuries have long been noticed that the physical and Chemical properties many chemical elements are very similar to each other. For example, Potassium, Lithium and Sodium are all active metals, which, when interacting with water, form active hydroxides of these metals; Chlorine, Fluorine, Bromine in their compounds with hydrogen showed the same valence equal to I and all these compounds are strong acids. From this similarity, the conclusion has long been suggested that all known chemical elements can be combined into groups, and so that the elements of each group have a certain set of physicochemical characteristics. However, such groups were often incorrectly composed of different elements various scientists and for a long time many ignored one of the main characteristics of the elements - this is their atomic mass. It was ignored because there was and is a different various elements, which means it could not be used as a parameter for grouping. The only exception was the French chemist Alexander Emile Chancourtua, he tried to arrange all the elements in a three-dimensional model along a helix, but his work was not recognized by the scientific community, and the model turned out to be cumbersome and inconvenient.

Unlike many scientists, D.I. Mendeleev took atomic mass (at that time still "Atomic weight") as a key parameter in the classification of elements. In his version, Dmitry Ivanovich arranged the elements in ascending order of their atomic weights, and here a pattern emerged that at certain intervals of the elements, their properties are periodically repeated. True, exceptions had to be made: some elements were swapped and did not correspond to the increase in atomic masses (for example, tellurium and iodine), but they corresponded to the properties of the elements. Further development atomic and molecular theory justified such advances and showed the validity of this arrangement. You can read more about this in the article "What is the discovery of Mendeleev"

As we can see, the layout of the elements in this version is not at all the same as we see in the modern form. Firstly, groups and periods are reversed: groups horizontally, periods vertically, and secondly, there are a bit too many groups in it - nineteen, instead of eighteen accepted today.

However, just a year later, in 1870, Mendeleev formed a new version of the table, which is already more recognizable to us: similar elements are lined up vertically, forming groups, and 6 periods are arranged horizontally. It is especially noteworthy that in both the first and second versions the tables are visible significant achievements that his predecessors did not have: places were carefully left in the table for elements that, according to Mendeleev, had yet to be discovered. The corresponding vacancies are indicated by him with a question mark and you can see them in the picture above. Subsequently, the corresponding elements were indeed discovered: Galium, Germanium, Scandium. Thus, Dmitry Ivanovich not only systematized the elements into groups and periods, but also predicted the discovery of new, not yet known, elements.

Later, after resolving many of the topical mysteries of chemistry of that time - the discovery of new elements, the isolation of a group of noble gases together with the participation of William Ramsay, the establishment of the fact that Didymium is not an independent element at all, but is a mixture of two others - more and more new and new versions of the table, sometimes even having a non-table view at all. But we will not give them all here, but we will give only the final version, which was formed during the life of the great scientist.

Transition from atomic weights to nuclear charge.

Unfortunately, Dmitry Ivanovich did not live to see the planetary theory of the structure of the atom and did not see the triumph of Rutherford's experiments, although it was with his discoveries that the new era in the development of the periodic law and the entire periodic system. Let me remind you that from the experiments conducted by Ernest Rutherford, it followed that the atoms of the elements consist of a positively charged atomic nucleus and negatively charged electrons revolving around the nucleus. After determining the charges of the atomic nuclei of all the elements known at that time, it turned out that in the periodic system they are located in accordance with the charge of the nucleus. And the periodic law has acquired a new meaning, now it began to sound like this:

"The properties of chemical elements, as well as the forms and properties of the simple substances and compounds they form, are in a periodic dependence on the magnitude of the charges of the nuclei of their atoms"

Now it became clear why some of the lighter elements were put by Mendeleev behind their heavier predecessors - the whole point is that this is how they stand in the order of the charges of their nucleus. For example, tellurium is heavier than iodine, but it is earlier in the table, because the charge of the nucleus of its atom and the number of electrons is 52, while iodine has 53. You can look at the table and see for yourself.

After the discovery of the structure of the atom and the atomic nucleus, the periodic system underwent several more changes, until, finally, it reached the form already familiar to us from school, the short-period version of the periodic table.

In this table, we already know everything: 7 periods, 10 series, side and main subgroups. Also, with the time of the discovery of new elements and the filling of the table with them, elements like Actinium and Lanthanum had to be placed in separate rows, all of them were respectively named Actinides and Lanthanides. This version of the system existed for a very long time - in the world scientific community almost until the end of the 80s, the beginning of the 90s, and in our country even longer - until the 10s of this century.

A modern version of the periodic table.

However, the option that many of us went through at school actually turns out to be very confusing, and the confusion is expressed in the division of subgroups into main and secondary ones, and remembering the logic of displaying the properties of elements becomes quite difficult. Of course, despite this, many studied it, became doctors of chemical sciences, but still in modern times a new version has come to replace it - a long-period one. I note that this particular option is approved by IUPAC ( international union theoretical and applied chemistry). Let's take a look at it.

Eight groups were replaced by eighteen, among which there is no longer any division into main and secondary, and all groups are dictated by the arrangement of electrons in the atomic shell. At the same time, they got rid of two-row and single-row periods, now all periods contain only one row. How convenient is this option? Now the periodicity of the properties of elements is viewed more clearly. The group number, in fact, indicates the number of electrons in the outer level, and therefore all the main subgroups of the old version are located in the first, second and thirteenth to eighteenth groups, and all the "former side" groups are located in the middle of the table. Thus, it is now clearly seen from the table that if this is the first group, then these are alkali metals and no copper or silver for you, and it is clear that all transit metals demonstrate well the similarity of their properties due to the filling of the d-sublevel, which affects to a lesser extent external properties, as well as lanthanides and actinides, exhibit similar properties due to only the f-sublevel being different. Thus, the whole table is divided into the following blocks: s-block, on which s-electrons are filled, d-block, p-block and f-block, with filling of d, p, and f-electrons, respectively.

Unfortunately, in our country this option is included in school textbooks only in the last 2-3 years, and even then not in all. And very wrong. What is it connected with? Well, firstly, with stagnant times in the dashing 90s, when there was no development at all in the country, not to mention the education sector, namely in the 90s, the world chemical community switched to this option. Secondly, with a slight inertia and difficulty in perceiving everything new, because our teachers are accustomed to the old, short-term version of the table, despite the fact that it is much more difficult and less convenient when studying chemistry.

Expanded version of the periodic system.

But time does not stand still, science and technology too. The 118th element of the periodic system has already been discovered, which means that the next, eighth, period of the table will soon have to be discovered. In addition, a new energy sublevel will appear: the g-sublevel. The elements of its constituents will have to be moved down the table, like lanthanides or actinides, or this table will be expanded twice more, so that it will no longer fit on an A4 sheet. Here I will give only a link to Wikipedia (see Extended Periodic System) and will not repeat the description of this option once again. Anyone who is interested can follow the link and have a look.

In this version, neither f-elements (lanthanides and actinides) nor g-elements ("elements of the future" from Nos. 121-128) are listed separately, but make the table wider by 32 cells. Also, the element Helium is placed in the second group, since it is included in the s-block.

In general, it is unlikely that future chemists will use this option, most likely the periodic table will be replaced by one of the alternatives that are already put forward by brave scientists: the Benfey system, Stewart's "Chemical Galaxy" or another option. But this will be only after the achievement of the second island of stability of chemical elements and, most likely, it will be necessary more for clarity in nuclear physics than in chemistry, but for now, the good old Dmitry Ivanovich's periodic system will suffice.