Opening Dmitry Mendeleev Periodic Table chemical elements In March 1869, it became a real breakthrough in chemistry. The Russian scientist managed to systematize the knowledge of the chemical elements and submit them in the form of a table, which the schoolchildren in the lessons of chemistry are still being learned. The periodic table became the foundation for the rapid development of this complex and interesting science, and the history of its opening is shrouded in legends and myths. For all interested science, it will be interesting to learn the truth about how Mendeleev opened the table of periodic elements.

History of Mendeleev Table: how it all started

Attempts to classify and systematize well-known chemical elements made long before Dmitry Mendeleev. Its elements were offered such well-known scientists as Debaser, Newlends, Meyer and others. However, due to the lack of data on the chemical elements and their correct atomic masses, the proposed systems were not entirely reliable.

The opening history of the Mendeleev table begins in 1869, when the Russian scientist at a meeting of the Russian Chemical Society told his colleagues about the discovery made them. In the proposed table, the chemical elements were located depending on their properties, ensuring the magnitude of their molecular weight.

An interesting feature of the Mendeleev table was also the presence of empty cells, which in the future were filled with open chemical elements predicted by scientists (Germany, Gallium, Scandium). After opening a periodic table, adding and amendments were made in it many times. Together with the Scottish chemist William, Ramzay Mendeleev added a group of inert gases to the table (zero group).

In the future, the history of the periodic table of Mendeleev was directly related to discoveries in another science - physics. Work on the table of periodic elements continues until now, and modern scientists add new chemical elements as they are discovered. The value of the periodic system of Dmitry Mendeleev is difficult to overestimate, as due to it:

The knowledge of the properties of already open chemical elements was systematized;
The possibility of predicting the discovery of new chemical elements;
These sections of physics, like physics of the atom and physics of the nuclei, began to develop;

There are many variants of the image of chemical elements in accordance with the periodic law, however, the most famous and common option is familiar to each Table of Mendeleev.

Myths and facts about creating a periodic table

The most common misconception in the opening history of the Mendeleev table is that the scientist saw her in a dream. In fact, Dmitry Mendeleev himself denied this myth and stated that he was thinking over the periodic law over the years. To systematize the chemical elements, he discharged each of them into a separate card and many times combined them between themselves, arranging into the ranks depending on their similar properties.

The myth about the "things" of a scholar's dream can be explained by the fact that Mendeleev worked on the systematization of chemical elements by day, interrupting a short sleep. However, only the stubborn work and the natural talent of the scientist gave the long-awaited result and provided Dmitry Mendeleev worldwide fame.

Many students at school, and sometimes at the university, forcing or at least approximately navigate in the Mendeleev table. For this, a person should not only have a good memory, but also to think to think, linking elements into separate groups and classes. The study of the table is easiest to be given to those people who constantly maintain the brain in the tone, passing trainings on brainapps.

Periodic law D.I. Mendeleev and Periodic System of Chemical Elements It has great importance in the development of chemistry. I will plunge in 1871, when Professor of Chemistry D.I. Mendeleev, method of numerous samples and errors, came to the conclusion that "... properties of elements, and therefore the properties of them formed by them simple and complex bodies, stand in periodic dependence on their atomic weight." The frequency of changes in the properties of elements occurs due to the periodic repetition of the electronic configuration of the external electron layer with an increase in the charge of the kernel.

Modern formulation of periodic law Such is:

"The properties of chemical elements (that is, the properties and shape of the compounds formed) are in periodic dependence on the charge of the kernel of atoms of chemical elements."

Taking chemistry, Mendeleev understood that the memorization of the individual properties of each element causes difficulties from students. He began to look for ways to create a system method to facilitate memorizing the properties of the elements. As a result, appeared natural table, later she began to be called periodic.

Our modern table is very similar to Mendeleevskaya. Consider it in more detail.

Mendeleev table

Periodic table of Mendeleev consists of 8 groups and 7 periods.

Vertical columns table called groups . Elements, inside each group, have similar chemical and physical properties. This is explained by the fact that the elements of the same group have similar electronic configurations of the outer layer, the number of electrons on which is equal to the number of the group. At the same time, the group is divided into the main and side subgroups.

IN The main subgroups It includes elements in which valence electrons are located on external NS- and NP systems. IN Side subgroups It includes elements in which valence electrons are located on the external NS- pylon and internal (N - 1) D- pylon (or (n - 2) f-lines).

All elements B. periodic table Depending on which paragraph (S-, P-, D- or F-) are valented electrons are classified on: S- elements (elements of the main subgroup I and II groups), P- elements (elements of the main subgroups III - VII groups), D- elements (elements of side subgroups), F-elements (lantanoids, actinoids).

The highest valence of the element (except O, F, the elements of the subgroup of copper and the eighth group) is equal to the number of the group in which it is located.

For the elements of the main and side subgroups, the formulas of higher oxides (and their hydrates) are the same. In the main subgroups, the composition of hydrogen compounds is the same, for the elements in this group. Solid hydrides form elements of the main subgroups I - III groups, and IV - VII groups form and gaseous hydrogen compounds. Hydrogen compounds of the type EN 4 is neutrally compound, EN 3 - bases, H 2 E and NE - acids.

Horizontal rows of tables call periods. Elements in periods differ among themselves, but in general they have the fact that the latest electrons are in one energy level ( the main quantum numbern. - equally ).

The first period differs from other things that there are only 2 elements: Hydrogen H and Helium He.

In the second period there are 8 elements (Li - NE). Lithium Li-alkaline metal starts period, and it closes its noble neon NE gas.

In the third period, as well as in the second are 8 elements (NA - AR). It starts the period of alkaline metal sodium Na, and it closes its noble gas argon AR.

In the fourth period there are 18 elements (K - KR) - Mendeleev denoted him as the first long period. It also begins with an alkaline metal of potassium, and the Kripton Kr is ends with an inert gas. The larger periods include transition elements (SC - Zn) - d-elements.

In the fifth period, the fourth elements are located in the same way (RB - XE) and the structure of it is similar to the fourth. It also begins with an alkaline metal Rubidium RB, and ends with an inert gas xenon XE. The composition of large periods includes transitional elements (Y - CD) - d-elements.

The sixth period consists of 32 elements (CS - RN). Except 10. d.- elements (LA, HF - HG) in it is a number of 14 f.-Elements (Lantanoids) - CE - LU

The seventh period is not completed. It begins with FR FRENCE, it can be assumed that it will contain, as well as the sixth period, 32 elements that have already been found (to the element with Z \u003d 118).

Interactive table Mendeleev

If you look at periodic table of Mendeleev And to hold an imaginary trait starting at the boron and ending between polonium and astatom, then all metals will be left of the line, and non-metals - to the right. The elements directly adjacent to this line will possess the properties of both metals and non-metals. They are called metalloids or semimetal. This is boron, silicon, germanium, arsenic, antimony, tellurium and polonium.

Periodic law

Mendeleev gave the following formulation of the periodic law: "Properties of simple bodies, as well as the forms and properties of the compounds of elements, and therefore the properties of them forms of simple and complex bodies, stand in periodic dependence on their atomic weight."
There are four main periodic patterns:

OKTET rule It claims that all elements seek to acquire or lose an electron to have an eight-electron configuration of the nearest noble gas. Because External S- and P-orbitals of noble gases are completely filled, then they are the most stable elements.
Ionization energy - This is the amount of energy required for the separation of the electron from the atom. According to the octet rule, when moving along the periodic table from left to right for an electron separation, more energy is required. Therefore, the elements on the left side of the table seek to lose the electron, and on the right side - to purchase it. The highest ionization energy in inert gases. Ionization energy decreases when driving down the group, because The electrons of low energy levels have the ability to repel electrons with higher energy levels. This phenomenon is called effect shielding. Due to this effect, the external electrons are firmly connected to the nucleus. Moving through the period of ionization energy smoothly increases from left to right.

Error affinity- Change of energy when purchasing an additional electron by an atom of a substance in a gaseous state. When driving down the group, the gear of the electron becomes less negative due to the shielding effect.

Electricity - A measure of how much the electrons associated with him of the other atom are striving to attract. Electricity increases when driving in periodic table Left to right and bottom up. It should be remembered that noble gases do not have electronegability. Thus, the electronegative element is fluorine.

Based on these concepts, consider how the properties of atoms and their compounds change table Mendeleev.

So, in periodic dependence there are such properties of an atom that are associated with its electronic configuration: atomic radius, ionization energy, electronegativity.

Consider changing the properties of atoms and their compounds, depending on the position in periodic system of chemical elements.

Nonmet atom increases When driving in a periodic table left right and bottom up. Concerning the main properties of oxides are reduced, And acidic properties increase in the same order - when moving from left to right and bottom up. At the same time, the acidic properties of oxides are the stronger than the greater the degree of oxidation of the forming item

Upon period from left to right basic properties hydroxidesweakens, according to the main subgroups from top to bottom, the base force increases. In this case, if the metal can form several hydroxides, then with an increase in the degree of metal oxidation, basic properties Hydroxides weaken.

By period from left to right The strength of oxygen-containing acids increases. When moving from top to bottom within the same group, the power of oxygen-containing acids decreases. In this case, the acid of acid increases with an increase in the degree of oxidation of the acid forming an acid.

By period from left to right Increases the strength of oxygenic acids. When moving from top to bottom within the same group, the strength of oxygenic acids increases.

Categories ,

In nature there are a lot of repetitive sequences:

seasons;
times of Day;
days of the week…

In the middle of the 19th century, D.I. Mendeleev noticed that the chemical properties of elements also have a certain sequence (they say that this idea came to him in a dream). The result of the wonderful dreams of the scientist became a periodic table of chemical elements in which D.I. Mendeleev built chemical elements ascending atomic mass. In the modern table, the chemical elements are built up to an increase in the atomic number of the element (the number of protons in the nucleus of the atom).

The atomic number is depicted above the symbol of the chemical element, under the symbol is its atomic mass (the sum of protons and neutrons). Please note that atomic weight in some elements is a neurochny! Remember about isotopes! Atomic mass is weighted from all isotopes of an element found in nature in natural conditions.

Under the table there are lanthanoids and actinoids.

Metals, non-metals, metalloids

Located in the periodic table to the left of the step diagonal line, which begins with boron (B) and ends with polonium (PO) (the exception is Germany (GE) and antimony (SB). It is not difficult to note that the metals occupy most of the periodic table. Main properties of metals : Solid (except mercury); shine; good electrical and thermal conductors; plastic; daring; easily give electrons.

Elements located to the right of the step diagonal B-Po are called nemmetallas. The properties of non-metals are directly opposite to the properties of metals: bad conduits of heat and electricity; fragile; uncommon; default; Usually make electrons.

Metalloids

Between metals and non-metals are located semimetal (metalloids). They are characterized by the properties of both metals and non-metals. The main use in industry semi-metals found in the production of semiconductors, without which no modern chip or microprocessor is unthinkable.

Periods and groups

As mentioned above, the periodic table consists of seven periods. In each period, the atomic numbers of the elements increase left to right.

Properties of elements in periods change sequentially: so sodium (Na) and magnesium (MG), which are at the beginning of the third period, give electrons (Na gives one electron: 1S 2 2S 2 2P 6 3S 1; Mg gives two electrons: 1s 2 2S 2 2p 6 3s 2). But chlorine (CL), located at the end of the period, receives one element: 1S 2 2S 2 2P 6 3S 2 3P 5.

In groups, on the contrary, all the elements possess the same properties. For example, in group Ia (1), all elements, starting from lithium (Li) and ending with Francium (FR), give one electron. And all elements of the group VIIA (17) take one element.

Some groups are so important that they received special names. These groups are discussed below.

Group IA (1). The atoms of the elements of this group have in the outer electronic layer of only one electron, therefore easily give one electron.

The most important alkali metals - sodium (Na) and potassium (k), because they play an important role in the process of human activity and are part of the salts.

Electronic configurations:

LI - 1s 2 2s 1;
Na. - 1s 2 2S 2 2P 6 3S 1;
K. - 1S 2 2S 2 2P 6 3S 2 3P 6 4S 1

Group IIa (2). Atoms of the elements of this group have two electron in the outer electron layer, which are also given during chemical reactions. Most important element - Calcium (CA) - the base of bones and teeth.

Electronic configurations:

BE. - 1s 2 2S 2;
MG. - 1S 2 2S 2 2P 6 3S 2;
CA. - 1S 2 2S 2 2P 6 3S 2 3P 6 4S 2

Group VIIA (17). Atoms of the elements of this group are usually obtained by one electron, because On the external electronic layer is five elements and to the "full set" just lacking one electron.

The most famous elements of this group: chlorine (CL) - part of salt and chlorine lime; iodine (I) is an element playing an important role in the activity of the thyroid gland of a person.

Electronic configuration:

F. - 1s 2 2S 2 2p 5;
Cl. - 1S 2 2S 2 2P 6 3S 2 3P 5;
Br. - 1s 2 2S 2 2P 6 3S 2 3P 6 4S 2 3D 10 4P 5

Group VIII (18). Atoms of the elements of this group have a fully "equipped" external electronic layer. Therefore, they do not need electrons. And they "don't want to give them". From here - the elements of this group are very "reluctant" enter into chemical reactions. For a long time it was believed that they do not enter the reaction at all (hence the name "inert", i.e. "inactive"). But Chemik Neil Barlett discovered that some of these gases under certain conditions can still enter into reactions with other elements.

Electronic configurations:

Ne - 1s 2 2S 2 2p 6;
AR - 1S 2 2S 2 2P 6 3S 2 3P 6;
Kr. - 1S 2 2S 2 2P 6 3S 2 3P 6 4S 2 3D 10 4P 6

Valence elements in groups

It is easy to see that inside each group, elements are similar to each other with their valence electrons (electrons S and p-orbitals located at the external energy level).

Alkali metal - 1 valence electron:

LI - 1s 2 2s 1;
Na. - 1s 2 2S 2 2P 6 3S 1;
K. - 1S 2 2S 2 2P 6 3S 2 3P 6 4S 1

At alkaline earth metals - 2 valence electron:

BE. - 1s 2 2S 2;
MG. - 1S 2 2S 2 2P 6 3S 2;
CA. - 1S 2 2S 2 2P 6 3S 2 3P 6 4S 2

Halogen has 7 valence electrons:

F. - 1s 2 2S 2 2p 5;
Cl. - 1S 2 2S 2 2P 6 3S 2 3P 5;
Br. - 1s 2 2S 2 2P 6 3S 2 3P 6 4S 2 3D 10 4P 5

In the inert gases - 8 valence electrons:

Ne - 1s 2 2S 2 2p 6;
AR - 1S 2 2S 2 2P 6 3S 2 3P 6;
Kr. - 1S 2 2S 2 2P 6 3S 2 3P 6 4S 2 3D 10 4P 6

For more information, see Valence Article and in the table of electronic configurations of atoms of chemical elements by periods.

Reverse your attention to the elements located in groups with symbols IN. They are located in the center of the periodic table and are called transition metals.

A distinctive feature of these elements is the presence of electron atoms filling d-orbital:

SC - 1S 2 2S 2 2P 6 3S 2 3P 6 4S 2 3D 1;
TI - 1S 2 2S 2 2P 6 3S 2 3P 6 4S 2 3D 2

Separate from the main table are located lantanoids and aktinoids - this is the so-called domestic transition metals. In atoms of these elements, electrons fill f-orbital:

CE - 1S 2 2S 2 2P 6 3S 2 3P 6 4S 2 3D 10 4P 6 4D 10 5S 2 5P 6 4F 1 5D 1 6S 2;
TH. - 1S 2 2S 2 2P 6 3S 2 3P 6 4S 2 3D 10 4P 6 4D 10 5S 2 5P 6 4F 14 5D 10 6S 2 6P 6 6D 2 7S 2

How it all began?

Many famous famous chemists at the turn of the XIX-XX centuries have long noticed that the physical and chemical properties of many chemical elements are very similar to each other. So for example, potassium, lithium and sodium - are all active metalswhich when interacting with water form the active hydroxides of these metals; Chlorine, fluorine, bromine in its compounds with hydrogen exhibited the same valence equal to I and all these compounds are strong acids. From this similarity, it was suggested that all known chemical elements can be combined into groups, and so that the elements of each group had a certain set of physicochemical characteristics. However, often such groups were incorrectly compiled from various elements of various scientists and for a long time, many of the main characteristics of the elements were ignored by many of the main characteristics of the elements. It was ignored because it was and there are different from various elements, which means it could not use it as a parameter to combine into groups. The exception was only the FRAVO chemist Alexander Emil Chaccourto, he tried to arrange all the elements in a three-dimensional model on the screw line, but his work was not recognized by the scientific community, and the model turned out to be cumbersome and uncomfortable.

Unlike many scientists, D.I. Mendeleev took the atomic mass (in those days another "atomic weight") as a key parameter when classifying elements. In its version, Dmitry Ivanovich placed elements to increase their atomic weights and here it was marked here that, after certain intervals of the elements, their properties are periodically repeated. True, exceptions had to do: some elements were changed in places and did not correspond to the increase in atomic masses (for example, tellurium and iodine), but they corresponded to the properties of elements. Further development Atomic molecular teachings acquitted such movements and showed the justice of this arrangement. You can read more about this in the article "What is the opening of Mendeleev"

As we can see, the location of the elements in this embodiment is not at all as we see in the modern form. First, groups and periods are changed in places: horizontal groups, vertical periods, and secondly, the groups themselves are somehow more and nineteen, instead of the eighteen adopted today.

However, just a year later, in the 1870s, Mendeleev formed new option Tables that are more recognized by us: similar elements are built vertically, forming groups, and 6 periods are horizontally. It is especially noteworthy that in the first and in the second version of the table can be seen. significant achievements, which had no predecessors from his predecessors: the table was carefully left to the elements that, in Mendeleev's opinion, still had to open. The corresponding vacant places are marked with a question mark and you can see them in the figure above. In the future, the corresponding elements were really open: Gary, Germany, Scandium. Thus, Dmitry Ivanovich not only systemed the elements in groups and periods, but also predicted the discovery of new, not yet known, elements.

In the future, after the resolution of many current puzzles of chemistry of the time - the opening of new elements, the allocation of a group of noble gases together with the participation of William Ramzaya, establishing the fact that didimius is not at all an independent element, but is a mixture of two others - all new and new and New table options, sometimes having even at all and not a tabular view. But we will not give them everything here, but we only give the final option formed during the lifetime of the Great Scientist.

Transition from atomic weights to the chore charge.

Unfortunately, Dmitry Ivanovich did not live to the planetary theory of the buildings of the atom and did not see the triumph of Reforda's experiments, although it was with his discoveries a new epoch in the development of the periodic law and the entire periodic system begins. Let me remind you from experiments conducted by Ernest Rutherford, therefore, the atoms of elements consist of positively charged atomic nucleus and accessing the kernel of negatively charged electrons. After determining the charges of atomic nuclei of all known at that time, it turned out that in the periodic system they are arranged in accordance with the charge of the kernel. BUT periodic law I purchased a new meaning, now he began to sound like this:

"Properties of chemical elements, as well as forms and properties formed by them simple substances and compounds are in periodic dependence on the values \u200b\u200bof the nuclei of their atoms "

Now it became clear why some more easily elements were set by Mendeleev behind their more heavy predecessors, the thing is that they are in order of charges of their kernel. For example, televour is heavier than iodine, however, it is in the table before it, for the charge of the nucleus of its atom and the number of electrons is 52, and the iodine - 53 can look at the table and make sure that herself.

After the opening of the structure of the atom and the atomic nucleus, the periodic system has undergone a few more changes, until finally reached the view already familiar to us from the school, the short-period version of the Mendeleev table.

In this table, everything is already familiar to us: 7 periods, 10 rows, side and main subgroups. Also, over time, the opening of new elements and filling the tables, I had to endure elements such as acts and lanthanas in some rows, all of them were called actinoids and lanthanoids. This version of the system existed for a very long time - in the global scientific community to almost the end of the 80s, the beginning of the 90s, and in our country and that longer - until the 10th century.

Modern variant of the Mendeleev table.

However, the option that many of us passed at school in practice is very confusing, and the confusion is expressed in the division of subgroups on the main and side and memorization of the logic of the properties of the elements becomes quite complex. Of course, despite this, many studied on him, became doctors of chemical sciences, but still, in modern times, he came to replace a new version - a long-period. I note that it is this option that is approved by IUPAC (the international alliance of theoretical and applied chemistry). Let's take a look at him.

Eighteen came to replace eighteen, among which there are no separation on top and side, and all groups are dictated by the location of electrons in the atomic shell. At the same time got rid of the two-row and single-row periods, now all periods contain only one row. What is the convenient such option? Now the frequency of the properties of the elements is visible more clearly. The number of the group, in fact, denotes the number of electrons at the external level, and therefore all the main subgroups of the old version are located in the first, second and thirteenth to the eighteenth group, and all the "former side" groups are located in the middle of the table. Thus, now from the table, it is clear that if this is the first group - then these are alkali metals and no copper or silver to you, and it can be seen that all transit metals well demonstrate the similarity of their properties in connection with the filling of D-suicide, to a lesser extent affecting External properties, as well as lanthanoids and actinoids, show similar properties due to different only F-sublevels. Thus, the entire table is broken into the following blocks: the S-block, which is filled with S-electrons, D-block, P-block and F-unit, with filling D, P, and F electrons, respectively.

Unfortunately, in our country, this option was included in school textbooks only in the last 2-3 years, and then not in everything. And very in vain. What is it connected with? Well, firstly, with stagnant times in the dashing 90s, when there was no development in the country, not to mention the field of education, namely, in the 90s, the global chemical community was transferred to this option. Secondly, with light inertness and the severity of perception of the whole new, because our teachers are habit the old, short-screen version of the table, despite the fact that when studying chemistry it is much more difficult and less convenient.

Advanced version of the periodic system.

But time does not stand still, science and technology too. The 118 element of the periodic system is already open, which means it will soon have to open the next, eighth period of the table. In addition, a new energy sublayer will appear: G-suits. The elements of its constituents will have to make a down table, like lanthanoids or actinoids, or expand this table another twice, so that it will stop being placed on the A4 sheet. Here I will give only a link to Wikipedia (see Extended Periodic System) and I will not once again repeat the description of this option. To whom it becomes interesting - will be able to go through the link and familiarize yourself.

In this embodiment, no F-elements (lanthanoids and actinoids) nor G-elements ("Elements of the Future" with No. 121-128) are not taken separately, but make the table wider on 32 cells. Also, the element of helium is placed in the second group, as it enters the S-block.

In general, it is hardly future chemists will use this option, most likely one of the alternatives will be replaced by the Mendeleev table, which are already put forward by bold scientists: the Benfhey system, the "chemical galaxy" of Stoutärt or another option. But it will be only after reaching the second island of the stability of chemical elements and, most likely, it will be more for clarity in nuclear physics than in chemistry, well, we still have enough old good periodic system Dmitry Ivanovich.

Instruction

Periodic system represents a multi-storey "house" in which it is located a large number of apartments. Each "residents" or in its own apartment under a specific number, which is constant. In addition, the element has the "surname" or name, for example oxygen, boron or nitrogen. In addition to these data in each "apartment" or indicate such information as the relative atomic mass, which can have accurate or rounded values.

As in any house, there are "entrances", namely, groups. And in groups, elements are located on the left and right, forming. Depending on which side, they are more, the main thing is called. Another subgroup, respectively, will be side. Also in the table there are "floors" or periods. Moreover, periods can be as large (consist of two rows) and small (only one row).

The table can show the structure of an element atom, each of which has a positively charged kernel consisting of protons and neutrons, as well as negative electrons rotating around it. The number of protons and electrons numerically coincides and is defined in the table by the sequence number of the element. For example, a sulfur chemical element has No. 16, therefore will have 16 protons and 16 electrons.

To determine the number of neutrons (neutral particles, also located in the kernel), deduct from the relative atomic mass of the element of its sequence number. For example, iron has a relative atomic mass equal to 56 and sequence number 26. Therefore, 56 - 26 \u003d 30 protons in iron.

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

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

Also, on the table, you can analyze the properties of the elements. From left to right, metal, and non-metallic amplifies. This is clearly visible in the example of 2 periods: it starts with an alkaline metal, then alkaline earth metal magnesium, after it is an aluminum element, then non-metals of silicon, phosphorus, sulfur and ends with a period of gaseous substances - chlorine and argon. In the next period, a similar dependence is observed.

A regularity is also observed from top to bottom - metal properties are enhanced, and non-metallic weakens. That is, for example, cesium is much more actively compared to sodium.

Helpful advice

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

Opening of the Periodic Law and the creation of an ordered system of chemical elements D.I. Mendeleev became an apogee of the development of chemistry in the XIX century. The scientist was generalized and systematized extensive material knowledge of the properties of elements.

Instruction

In the XIX century there were no ideas about the structure of the atom. Opening D.I. Mendeleev was only a generalization of experienced facts, but their physical meaning remained incomprehensible for a long time. When the first data on the structure of the core and the distribution of electrons in atoms appeared, it looks at the law and the system of elements in a new way. Table D.I. Mendeleeva makes it possible to visually trace the properties of elements found in.

Each element in the table is assigned a certain sequence number (H - 1, Li - 2, BE - 3, etc.). This number corresponds to the nucleus (the number of protons in the kernel) and the number of electrons rotating around the kernel. The number of protons is thus equal to the number of electrons, and this suggests that under normal conditions an atom electrically.

The division by seven periods is due to the number of energy levels of the atom. Atoms of the first period have a single-level electronic shell, the second - two-level, third - three-level, etc. When filling out a new energy level, a new period begins.

The first elements of any period are characterized by atoms having one electron at the external level, are alkali metal atoms. Periods of noble gas atoms that have fully filled with electrons external energy levels are completed: in the first period, the inert gases have 2 electrons, in the following - 8. It is because of the similar structure of the electronic shells of the group of elements that have similar physico-.

Table D.I. Mendeleev present 8 main subgroups. This amount is due to the maximum possible number of electrons at the energy level.

At the bottom of the periodic system allocated lanthanoids and actinoids as independent rows.

Using Table D.I. Mendeleev can be observed the frequency of the following properties of the elements: the radius of the atom, the volume of the atom; the potential of ionization; Electron affinity forces; Electricity atom; ; physical properties of potential compounds.

Clearly traceable frequency of location of elements in Table D.I. Mendeleeva is rationally due to the consistent character of filling with electrons of energy levels.

Sources:

Mendeleev table

Periodic law, which is the basis of modern chemistry and explaining the patterns of changing the properties of chemical elements, D.I. Mendeleev in 1869. The physical meaning of this law is revealed when studying the complex structure of the atom.

In the XIX century it was believed that atomic mass is the main characteristic Element, therefore, it was used to classify substances. Now atoms are determined and identified by the magnitude of the charge of their kernel (the number and sequence number in the Mendeleev table). However, the atomic mass of elements for some exceptions (for example, atomic mass is less than the atomic mass of argon) increases in proportion to their chore charge.

With an increase in atomic mass, there is a periodic change in the properties of the elements and their connections. This is the metallicity and non-metallium atoms, atomic radius, ionization potential, electron affinity, electronegativity, oxidation degree, compounds (boiling, melting, density temperature), their basicity, amphoteriness or acidity.

How many elements in the modern Mendeleev table

The Mendeleev table graphically expresses the law outdoor. The modern periodic system contains 112 chemical elements (the latter - recesses, Darmstadtion, Rentgesies and Copernation). According to the latest data, the following 8 elements are open (up to 120 inclusive), but not all of them received their names, and these elements are still small in which prints are present.

Each element occupies a certain cell in the periodic system and has its own sequence number corresponding to the charge of the kernel of its atom.

How to build a periodic system

The structure of the periodic system is represented by seven periods, ten rows and eight groups. Each period begins alkaline metal and ends with noble gas. Exceptions are the first period, beginning with hydrogen, and the seventh incomplete period.

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

In the sixth period of the table after (sequence number 57) there are 14 elements similar to the properties for Lantane - Lantanoids. They are put into the lower part of the table with a separate line. The same applies to actinoids, located after Actinia (with number 89) and in many respects repetitive properties.

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

Elements in groups exhibit the same highest in oxides and other compounds, and this valence corresponds to the group number. The main components of the elements of small and large periods - only large. Top down intensify, non-metallic - weaken. All atoms of side subgroups are metals.

Tip 4: Selenium as a chemical element of the Mendeleev table

The chemical element is selenged to the VI group of the periodic Mendeleev system, it is a chalcogen. Natural selenium consists of six stable isotopes. Also 16 radioactive isotopes of Selena are also known.

Instruction

Selenium is considered a very rare and scattered element, in the biosphere he migrates vigorously, forming more than 50 minerals. The most famous of them are: bercelianit, naughty, native selenium and chalcomat.

Selenium is contained in volcanic sulfur, galena, pyrite, bismutin and other sulphides. It is extracted from lead, copper, nickel and other ores in which it is in a scattered state.

In the tissues of most living beings, it is contained from 0.001 to 1 mg / kg, some plants, marine organisms and mushrooms are concentrated. For a row of plants, selenium is a necessary element. The need for man and animals at is 50-100 μg / kg of food, this element has antioxidant properties, affects many enzymatic reactions and increases the susceptibility of the retina to the light.

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

When you heated any modification of this chemical element above 220 ° C and a subsequent cooling is formed a glassy selenium, it is fragile and has a glass glitter.

The most resistant thermally hexagonal gray selenium, the grill of which is built from the spiral chains located in parallel to each other. It is obtained by heating other forms of selenium to melting and slow cooling to 180-210 ° C. Inside the chains of hexagonal selenium atoms are associated covalently.

Seleni resistant to air, it does not work on it: oxygen, water, diluted sulfur and hydrochloric acidHowever, it is well dissolved in nitric acid. Interacting with metals, selenium forms selenides. There are many complex compounds of Selena, all of them are poisonous.

Get selenium from waste paper or production, using electrolytic refining copper. In the sludge, this element is present with heavy and metals, gray and tellurium. To extract it, the slots are filtered, then heated with concentrated sulfuric acid or subjected to oxidative firing at a temperature of 700 ° C.

Selenium used in the production of rectifier semiconductor diodes and other converter equipment. In metallurgy, with its help, a fine-grained structure is given, and also improve its mechanical properties. In the chemical industry is selenged as a catalyst.

Sources:

Chemik.ru, selenium

Calcium is a chemical element related to a second subgroup of a periodic table with a symbolic designation of Ca and a atomic mass of 40.078 g / mol. It is a rather soft and chemically active alkaline earth metal with silver color.

Instruction

From the Latin language "" translates as "lime" or "soft stone", and he is obliged to the Englishman Humphrey Davy, which in 1808 was able to single out calcium electrolytic method. The scientist then took a mixture of a wet hazed to lime, "seasoned" oxide of mercury, and subjected it to the electrolysis process on the platinum plate appearing in the experiment as an anode. The cathode was the same wire, which the chemist was immersed in liquid mercury. It is also interesting that such calcium compounds, as limestone, marble and gypsum, as well as lime, were known to humanity in many centuries before the Davie experiment, during which scientists believed some of them simple and independent bodies. Only in 1789, the French Lavoisier published the work in which he suggested that lime, silica, barite and alumina are complex substances.

Calcium has a high degree of chemical activity, due to which in its pure form in nature is practically not found. But scientists calculated that about 3.38% of the total mass of the whole earthly crust occur to the share of this element, which makes calcium fifth in the prevalence after oxygen, silicon, aluminum and iron. There is this element in seawater - about 400 mg per liter. Calcium includes silicates of various rocks (for example, granite and gneiss). Much of it in a field swop, mel and limestones consisting of a calcite mineral with a Saco3 formula. Crystal calcium form is marble. In general difficulty by migrating this element in earth Kore It forms 385 minerals.

TO physical properties Calcium relates its ability to exercise valuable semiconductor abilities, although it does not become a semiconductor and metal in the traditional sense of the word. This situation changes with a gradual increase in pressure when calcium is reported to the metallic state and the ability of superconducting properties. Calcium with oxygen, air moisture and carbon dioxide, which is, in laboratories for work, this chemical element is stored in tightly closed and chemist John Alexander Newland - however science community ignored his achievement. Newland's proposal did not take seriously because of his search for harmony and the relationship between music and chemistry.

Dmitry Mendeleev first published his periodic table in 1869 on the pages of the magazine of Russian Chemical Society. The scientist also sent out the notice of his opening to all the leading world chemists, after which he repeatedly improved and modified the table until she became what she knew her today. The essence of the discovery of Dmitry Mendeleev was in a periodic, not monotonous change chemical properties Elements with increasing atomic mass. The final unification of the theory in the periodic law occurred in 1871.

Legends about Mendeleev

The most common legend is the opening table of Mendeleev in a dream. The scientist himself has repeatedly raised this myth, claiming that he came up with a table for many years. On another legend, Dmitry Mendeleev vodka - she appeared after defending the dissertation scientists "The reasoning about the connection of alcohol with water".

Mendeleev still many consider the discoverer, who himself liked to create under the aqueous-alcohol solution. The contemporaries of the scientist often laughed at Mendeleev's laboratory, which he equipped in a hupe of a giant oak.

A separate occasion for jokes for rumors was the passion of Dmitry Mendeleev to weaving suitcases, which the scientist was engaged in living in Simferopol. In the future, he mastered the cardboard for the needs of his laboratory, for which he was vividly called the master of suitcase cases.

Mendeleev Table, In addition to streamlining chemical elements in unified system, allowed to predict the opening of many new elements. However, at the same time, some of them scientists were recognized as non-existent because they were incompatible with the concept. Most famous history At that time, the discovery of such new elements as Koronia and Nebulia was.