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

Properties of elements, as well as properties of the simple and complex bodies are in a periodic dependence on the values atomic weights elements.

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

Modern periodic table

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

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

This statement is now known as Moseley's law.

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

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

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

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

Periods

Main structural units periodic system there are periods and groups - natural aggregates into which chemical elements by electronic structures.

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

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

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

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

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

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

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

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

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

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

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

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

The gradual change in properties is characteristic not only for simple substances, but also for complex connections, as presented in Table 1.

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

Electronic family	s-elements		p-elements
Element symbol	Na	mg	Al	Si	P	S	Cl	Ar
The charge of the nucleus of an atom	+11	+12	+13	+14	+15	+16	+17	+18
External electronic configuration	3s 1	3s 2	3s 2 3p 1	3s 2 3p 2	3s 2 3p 3	3s 2 3p 4	3s 2 3p 5	3s 2 3p 6
Atomic radius, nm	0,189	0,160	0,143	0,118	0,110	0,102	0,099	0,054
Maximum valence	I	II	III	IV	V	VI	VII	—
Higher oxides and their properties	Na2O	MgO	Al2O3	SiO2	P2O5	SO 3	Cl2O7	—
	Basic properties		Amphoteric properties	Acid properties				—
Hydrates of oxides (bases or acids)	NaOH	Mg(OH)2	Al(OH)3	H2SiO3	H3PO4	H2SO4	HClO 4	—
	Base	Weak base	amphoteric hydroxide	Weak acid	medium strength acid	strong acid	strong acid	—
Compounds with hydrogen	NaH	MgH2	AlH 3	SiH4	PH 3	H 2 S	HCl	—
	Solid salty substances			Gaseous substances				—

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

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

Groups

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

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

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

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

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

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

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

period	Subgroup IA				Subgroup VIIA
	Element symbol	Core charge	Radius of an atom, nm		Element symbol	Core charge	Radius of an atom, nm	External electronic configuration
II	Li	+3	0,155	2 s 1	F	+9	0,064	2 s2 2 p5
III	Na	+11	0,189	3 s 1	Cl	+17	0,099	3 s2 3 p5
IV	K	+19	0,236	4 s 1	Br	35	0,114	4 s2 4 p5
V	Rb	+37	0,248	5 s 1	I	+53	0,133	5 s2 5 p5
VI	Cs	55	0,268	6 s 1	At	85	0,140	6 s2 6 p5
VII	Fr	+87	0,280	7 s 1	—	—	—	—

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

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

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

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

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

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

The periodic system of chemical elements is a classification of chemical elements based on certain features of the structure of atoms of chemical elements. It was compiled on the basis of the Periodic Law, discovered in 1869 by D. I. Mendeleev. At that time, the Periodic system included 63 chemical elements and differed in appearance from the modern one. Now the Periodic system includes about one hundred and twenty chemical elements.

The periodic system is compiled in the form of a table in which the chemical elements are arranged in a certain order: as their atomic masses increase. Now there are many types of images of the Periodic system. The most common is an image in the form of a table with the arrangement of elements from left to right.

All chemical elements in the Periodic system are grouped into periods and groups. The periodic system includes seven periods and eight groups. Periods are called horizontal rows of chemical elements, in which the properties of elements change from typical metallic to non-metallic. Vertical columns of chemical elements that contain elements with similar chemical properties form groups of chemical elements.

The first, second and third periods are called small because they contain a small number of elements (the first - two elements, the second and third - eight elements each). Elements of the second and third periods are called typical, their properties regularly change from a typical metal to an inert gas.

All other periods are called large (the fourth and fifth contain 18 elements each, the sixth - 32 and the seventh - 24 elements). A special similarity of properties is shown by elements located inside large periods, at the end of each even row. These are the so-called triads: Ferum - Cobalt - Nikol, which form the iron family, and two others: Ruthenium - Rhodium - Palladium and Osmium - Iridium - Platinum, which form the family of platinum metals (platinoids).

At the bottom of the table of D. I. Mendeleev are the chemical elements that form the lanthanide family and the actinide family. All these elements are formally included in the third group and come after the chemical elements lanthanum (number 57) and actinium (number 89).

The Periodic Table of the Elements contains ten rows. Small periods (first, second and third) consist of one row, large periods (fourth, fifth and sixth) contain two rows each. There is one row in the seventh period.

Each big period consists of even and odd rows. Paired rows contain metal elements, in odd rows, the properties of the elements change in the same way as in typical elements, i.e. from metallic to pronounced non-metallic.

Each group of the table of D. I. Mendeleev consists of two subgroups: the main and the secondary. The composition of the main subgroups includes elements of both small and large periods, that is, the main subgroups begin either from the first or second period. The secondary subgroups include elements of only large periods, i.e. side subgroups begin only from the fourth period.

The ingenious Russian chemist D. I. Mendeleev was distinguished all his life by the desire to know the unknown. This desire, as well as the deepest and vast knowledge combined with unerring scientific intuition and allowed Dmitry Ivanovich to develop scientific classification chemical elements - Periodic system in the form of his famous table.

The periodic system of chemical elements of D. I. Mendeleev can be represented as big house, in which absolutely all chemical elements “live together”, known to man. To be able to use the Periodic system, it is necessary to study the chemical alphabet, that is, the signs of chemical elements.

With their help, you will learn how to write words - chemical formulas, and on their basis you can write sentences - equations of chemical reactions. Each chemical element is designated by its own chemical sign, or symbol, which, along with the name of the chemical element, is recorded in the table of D. I. Mendeleev. as symbols on offer Swedish chemist J. Berzelius, in most cases, the initial letters of the Latin names of chemical elements were accepted. So, hydrogen Latin name Hydrogenium - hydrogenium) is denoted by the letter H (read "ash"), oxygen (the Latin name Oxygenium - oxygen) - by the letter O (read "o"), carbon (the Latin name Carboneum - carboneum) - by the letter C (read "ce").

The Latin names of several more chemical elements begin with the letter C: calcium (

Calcium), copper (Cuprum), cobalt (Cobaltum), etc. To distinguish them, I. Berzelius proposed to initial letter Latin name to add one more of the subsequent letters of the name. So, chemical sign calcium is written with the symbol Ca (read "calcium"), copper - Cu (read "cuprum"), cobalt - Co (read "cobalt").

The names of some chemical elements reflect the most important properties elements, for example, hydrogen - giving birth to water, oxygen - giving birth to acids, phosphorus - carrying light (Fig. 20), etc.

Rice. twenty.
Etymology of the name of the element No. 15 of the Periodic system of D. I. Mendeleev

Other elements are named after celestial bodies or planets solar system- selenium and tellurium (Fig. 21) (from the Greek. Selena - Moon and Telluris - Earth), uranium, neptunium, plutonium.

Rice. 21.
Etymology of the name of the element No. 52 of the Periodic system of D. I. Mendeleev

Some names are borrowed from mythology (Fig. 22). For example, tantalum. That was the name of the beloved son of Zeus. For crimes against the gods, Tantalus was severely punished. It stood up to its neck in water, and branches with juicy, fragrant fruits hung over it. However, as soon as he wanted to get drunk, the water flowed away from him, he barely wanted to satisfy his hunger and stretched out his hand to the fruits - the branches deviated to the side. Trying to isolate tantalum from ores, chemists experienced no less torment.

Rice. 22.
Etymology of the name of the element No. 61 of the Periodic system of D. I. Mendeleev

Some elements were named after different states or parts of the world. For example, germanium, gallium (Gallium is the old name for France), polonium (in honor of Poland), scandium (in honor of Scandinavia), francium, ruthenium (Ruthenia is the Latin name for Russia), europium and americium. Here are the elements named after cities: hafnium (in honor of Copenhagen), lutetium (in the old days Paris was called Lutetium), berkelium (in honor of the city of Berkeley in the USA), yttrium, terbium, erbium, ytterbium (the names of these elements come from Ytterby - small town in Sweden, where a mineral containing these elements was first discovered), dubnium (Fig. 23).

Rice. 23.
Etymology of the name of the element No. 105 of the Periodic system of D. I. Mendeleev

Finally, the names of the elements immortalize the names of great scientists: curium, fermium, einsteinium, mendelevium (Fig. 24), lawrencium.

Rice. 24.
Etymology of the name of the element No. 101 of the Periodic system of D. I. Mendeleev

Each chemical element is assigned in the periodic table, in the common "house" of all elements, its own "apartment" - a cell with a strictly defined number. deep meaning This number will be revealed to you in the further study of chemistry. The number of storeys of these "apartments" is also strictly distributed - the periods in which the elements "live". Like the serial number of the element (number of the "apartment"), the number of the period ("floor") is fraught with essential information about the structure of atoms of chemical elements. Horizontally - "number of floors" - the Periodic system is divided into seven periods:

• The 1st period includes two elements: hydrogen H and helium He;
• the 2nd period begins with lithium Li and ends with neon Ne (8 elements);
• The 3rd period begins with sodium Na and ends with argon Ar (8 elements).

The first three periods, each consisting of one row, are called small periods.

Periods 4, 5 and 6 include two rows of elements each, they are called large periods; The 4th and 5th periods contain 18 elements each, the 6th - 32 elements.

7th period - unfinished, so far consists of only one row.

Pay attention to the "basement floors" of the Periodic system - 14 twin elements "live" there, similar in their properties, some to lanthanum La, others to actinium Ac, which represent them on the upper "floors" of the table: in the 6th and 7th -m periods.

Vertically, chemical elements “living” in “apartments” of similar properties are located one below the other in vertical columns - groups, of which there are eight in the table of D. I. Mendeleev.

Each group consists of two subgroups - main and secondary. A subgroup that includes elements of both small and large periods is called the main subgroup or group A. A subgroup that includes elements of only large periods is called a side subgroup or group B. So, in main subgroup Group I (IA group) includes lithium, sodium, potassium, rubidium and francium - this is a subgroup of lithium Li; secondary subgroup this group (IB group) is formed by copper, silver and gold - this is a subgroup of copper Si.

In addition to the form of D. I. Mendeleev’s table, which is called short-period (it is given on the flyleaf of the textbook), there are many other forms, for example, the long-period version.

Just as a child can construct a huge number of elements from the Lego game various items(see Fig. 10), and from chemical elements, nature and man created the variety of substances that surround us. Another model is even clearer: just as 33 letters of the Russian alphabet form various combinations, tens of thousands of words, so 114 chemical elements in various combinations create more than 20 million different substances.

Try to learn the patterns of word formation - chemical formulas, and then the world of substances will open before you in all its colorful diversity.

But for this, first learn the letters - symbols of chemical elements (Table 1).

Table 1
Names of some chemical elements

Keywords and phrases

1. Periodic system of chemical elements (table) D. I. Mendeleev.
2. periods large and small.
3. Groups and subgroups - main (A group) and secondary (B group).
4. Symbols of chemical elements.

Work with computer

1. Please refer to the electronic application. Study the material of the lesson and complete the suggested tasks.
2. Search online email addresses, which can serve additional sources, revealing the content of the keywords and phrases of the paragraph. Offer the teacher your help in preparing a new lesson - make a message on keywords and phrases in the next paragraph.

Questions and tasks

1. Using dictionaries (etymological, encyclopedic and chemical terms), name the most important properties that are reflected in the names of chemical elements: bromine Br, nitrogen N, fluorine F.
2. Explain how the name of the chemical elements titanium and vanadium reflects the influence of ancient Greek myths.
3. Why is the Latin name for gold Aurum (aurum), and silver - Argentum (argentum)?
4. Tell the story of the discovery of any (of your choice) chemical element and explain the etymology of its name.
5. Write down the "coordinates", i.e. the position in the Periodic system of D. I. Mendeleev (element number, period number and its type - large or small, group number and subgroup - main or secondary), for the following chemical elements: calcium, zinc , antimony, tantalum, europium.
6. Distribute the chemical elements listed in Table 1 into three groups according to the "pronunciation of the chemical symbol" feature. Can this activity help you remember chemical symbols and the pronunciation of the symbols of the elements?

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 in solving problems. huge amount chemical and physical tasks. 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 a relationship various properties elements from 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 the most different areas 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 it were that easy... This version about 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 own version 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 undertook a number of very non-standard solutions. 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, to order the elements, instead of atomic weight (atomic mass), the concept is used atomic number(the number of protons in the nucleus). 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 in reverse direction- increase.
• 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).

The atomic mass is indicated under the atomic number (in this version of the table). If we round the atomic mass to the nearest integer, we get the so-called mass number. Difference mass number and 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. Reminder to study new item 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 properties of chemical elements allow them to be combined into appropriate groups. On this principle, a periodic system was created that changed the idea of ​​existing substances and made it possible to assume the existence of new, previously unknown elements.

In contact with

Periodic system of Mendeleev

The Periodic Table of Chemical Elements was compiled by D. I. Mendeleev in the second half of the 19th century. What is it, and why is it needed? It combines all the chemical elements in order of increasing atomic weight, and all of them are arranged so that their properties change in a periodic manner.

Periodic system of Mendeleev brought into single system all existing elements, previously considered to be simply separate substances.

On the basis of its study, new chemical substances. The significance of this discovery for science cannot be overestimated., it was far ahead of its time and gave impetus to the development of chemistry for many decades.

There are three most common table options, which are conventionally referred to as "short", "long" and "extra long". ». The main table is considered to be a long table, it approved officially. The difference between them is the layout of the elements and the length of the periods.

What is a period

The system contains 7 periods. They are represented graphically as horizontal lines. In this case, the period can have one or two lines, called rows. Each subsequent element differs from the previous one by increasing the nuclear charge (the number of electrons) by one.

If you do not complicate, the period is horizontal line periodic table. Each of them begins with a metal and ends with an inert gas. Actually, this creates periodicity - the properties of elements change within one period, repeating again in the next. The first, second and third periods are incomplete, they are called small and contain 2, 8 and 8 elements, respectively. The rest are complete, they have 18 elements each.

What is a group

Group is a vertical column, containing elements with the same electronic structure or, to put it simply, with the same higher . The officially approved long table contains 18 groups that start with alkali metals and end with inert gases.

Each group has its own name, which makes it easier to find or classify elements. The metallic properties are enhanced regardless of the element in the direction from top to bottom. This is due to an increase in the number atomic orbits- the more of them, the weaker electronic communications, which makes the crystal lattice more pronounced.

Metals in the periodic table

Metals in the table Mendeleev have a predominant number, their list is quite extensive. They are characterized common features, according to their properties, they are heterogeneous and are divided into groups. Some of them have little in common with metals in physical sense, while others can exist only for fractions of a second and are absolutely not found in nature (according to at least, on the planet), because they were created, more precisely, calculated and confirmed in the laboratory, artificially. Each group has own signs , the name is quite noticeably different from the others. This difference is especially pronounced in the first group.

The position of the metals

What is the position of metals in the periodic table? Elements are arranged by increasing atomic mass, or the number of electrons and protons. Their properties change periodically, so there is no neat one-to-one placement in the table. How to determine metals, and is it possible to do this according to the periodic table? In order to simplify the question, a special technique was invented: conditionally, at the points of connection of elements, diagonal line from Bor to Polonius (or to Astatus). Those on the left are metals, those on the right are non-metals. It would be very simple and great, but there are exceptions - Germanium and Antimony.

Such a “method” is a kind of cheat sheet, it was invented only to simplify the memorization process. For a more accurate representation, remember that the list of non-metals is only 22 elements, therefore, answering the question of how many metals are contained in the periodic table

In the figure, you can clearly see which elements are non-metals and how they are arranged in the table by groups and periods.

General physical properties

There are general physical properties metals. These include:

• Plastic.
• characteristic brilliance.
• Electrical conductivity.
• High thermal conductivity.
• Everything except mercury is in a solid state.

It should be understood that the properties of metals vary greatly with respect to their chemical or physical essence. Some of them bear little resemblance to metals in the ordinary sense of the term. For example, mercury occupies a special position. She is at normal conditions is in liquid state, does not have crystal lattice, to the presence of which other metals owe their properties. The properties of the latter in this case are conditional, mercury is related to them in more chemical characteristics.

Interesting! Elements of the first group, alkali metals, in pure do not occur, being part of various compounds.

The softest metal that exists in nature - cesium - belongs to this group. He, like other alkaline similar substances, has little in common with more typical metals. Some sources claim that in fact, the softest metal is potassium, which is difficult to dispute or confirm, since neither one nor the other element exists on its own - being released as a result of a chemical reaction, they quickly oxidize or react.

The second group of metals - alkaline earth - is much closer to the main groups. The name "alkaline earth" comes from ancient times, when oxides were called "earths" because they have a loose crumbly structure. More or less familiar (in the everyday sense) properties are possessed by metals starting from the 3rd group. As the group number increases, the amount of metals decreases.