Grouping of elements in the periodic table. Periodic table D

Periodic table chemical elements is a classification of chemical elements created by D. I. Mendeleev based on what he discovered in 1869. periodic law.

D. I. Mendeleev

According to the modern formulation of this law, in a continuous series of elements arranged in order of increasing magnitude of the positive charge of the nuclei of their atoms, elements with similar properties periodically repeat.

The periodic table of chemical elements, presented in table form, consists of periods, series and groups.

At the beginning of each period (except for the first), the element has pronounced metallic properties (alkali metal).

Symbols for the color table: 1 - chemical sign of the element; 2 - name; 3 - atomic mass (atomic weight); 4 - serial number; 5 - distribution of electrons across layers.

As you increase serial number element equal to the positive charge of the nucleus of its atom, metallic properties gradually weaken and non-metallic properties increase. The penultimate element in each period is an element with pronounced non-metallic properties (), and the last is an inert gas. In period I there are 2 elements, in II and III - 8 elements, in IV and V - 18, in VI - 32 and in VII (not completed period) - 17 elements.

The first three periods are called small periods, each of them consists of one horizontal row; the rest - in large periods, each of which (except for the VII period) consists of two horizontal rows - even (upper) and odd (lower). Only metals are found in even rows of large periods. The properties of the elements in these series change slightly with increasing ordinal number. The properties of elements in odd rows of large periods change. In period VI, lanthanum is followed by 14 elements, very similar in chemical properties. These elements, called lanthanides, are listed separately below the main table. Actinides, the elements following actinium, are presented similarly in the table.

The table has nine vertical groups. The group number, with rare exceptions, is equal to the highest positive valence of the elements of this group. Each group, excluding the zero and eighth, is divided into subgroups. - main (located to the right) and secondary. In the main subgroups, as the atomic number increases, the metallic properties of the elements become stronger and the non-metallic properties weaken.

Thus, the chemical and a number of physical properties of elements are determined by the place occupied this element in the periodic table.

Biogenic elements, i.e. elements that make up organisms and perform a certain biological role in it, occupy top part Periodic tables. Cells occupied by elements that make up the bulk (more than 99%) of living matter are colored blue, in pink- cells occupied by microelements (see).

The periodic table of chemical elements is the greatest achievement modern natural science and a vivid expression of the most general dialectical laws of nature.

Modern formulation of the periodic law is this:

“the properties of chemical elements (i.e., the properties and form of the compounds they form) are periodically dependent on the charge of the nucleus of the atoms of the chemical elements.”

While teaching chemistry, Mendeleev understood that remembering the individual properties of each element caused difficulties for students. He began to look for ways to create a systematic method to make it easier to remember the properties of elements. The result was natural table, later it became known as periodic.

Our modern table is very similar to the periodic table. Let's take a closer look at it.

Periodic table

Mendeleev's periodic table consists of 8 groups and 7 periods.

The vertical columns of a table are called groups . Elements, within each group, have similar chemical and physical properties. This is explained by the fact that elements of the same group have similar electronic configurations of the outer layer, the number of electrons on which is equal to the group number. In this case, the group is divided into main and secondary subgroups.

IN Main subgroups includes elements whose valence electrons are located on the outer ns- and np-sublevels. IN Side subgroups includes elements whose valence electrons are located on the outer ns-sublevel and the inner (n - 1) d-sublevel (or (n - 2) f-sublevel).

All elements in periodic table , depending on which sublevel (s-, p-, d- or f-) valence electrons are classified into: s-elements (elements of the main subgroups of groups I and II), p-elements (elements of the main subgroups III - VII groups), d-elements (elements of side subgroups), f-elements (lanthanides, actinides).

The highest valency of an element (with the exception of O, F, elements of the copper subgroup and group eight) is equal to the number of the group in which it is found.

For elements of the main and secondary 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 of groups I - III, and groups IV - VII form gaseous hydrogen compounds. Hydrogen compounds of type EN 4 are more neutral compounds, EN 3 are bases, H 2 E and NE are acids.

The horizontal rows of a table are called periods. The elements in the periods differ from each other, but what they have in common is that the last electrons are at the same energy level ( principal quantum numbern- the same ).

The first period differs from the others in that there are only 2 elements: hydrogen H and helium He.

In the second period there are 8 elements (Li - Ne). Lithium Li, an alkali metal, begins the period, and the noble gas neon Ne closes it.

In the third period, just like in the second, there are 8 elements (Na - Ar). The period begins with the alkali metal sodium Na, and the noble gas argon Ar closes it.

The fourth period contains 18 elements (K - Kr) - Mendeleev designated it as the first large period. It also begins with the alkali metal Potassium and ends with the inert gas krypton Kr. The composition of large periods includes transition elements (Sc - Zn) - d- elements.

In the fifth period, similar to the fourth, there are 18 elements (Rb - Xe) and its structure is similar to the fourth. It also begins with the alkali metal rubidium Rb, and ends with the inert gas xenon Xe. The composition of large periods includes transition elements (Y - Cd) - d- elements.

The sixth period consists of 32 elements (Cs - Rn). Except 10 d-elements (La, Hf - Hg) it contains a row of 14 f-elements (lanthanides) - Ce - Lu

The seventh period is not over. It begins with Franc Fr, it can be assumed that it will contain, like the sixth period, 32 elements that have already been found (up to the element with Z = 118).

Interactive periodic table

If you look at periodic table and draw an imaginary line starting at boron and ending between polonium and astatine, then all metals will be to the left of the line, and non-metals to the right. Elements immediately adjacent to this line will have the properties of both metals and non-metals. They are called metalloids or semimetals. These are boron, silicon, germanium, arsenic, antimony, tellurium and polonium.

Periodic law

Mendeleev gave the following formulation of the Periodic Law: “the properties of simple bodies, as well as the forms and properties of compounds of elements, and therefore the properties of the simple and complex bodies they form, are periodically dependent on their atomic weight.”
There are four main periodic patterns:

Octet rule states that all elements tend to gain or lose an electron in order to have the eight-electron configuration of the nearest noble gas. Because Since the outer s- and p-orbitals of noble gases are completely filled, they are the most stable elements.
Ionization energy is the amount of energy required to remove an electron from an atom. According to the octet rule, when moving across the periodic table from left to right, more energy is required to remove an electron. Therefore, elements on the left side of the table tend to lose an electron, and those on the right side tend to gain one. Inert gases have the highest ionization energy. The ionization energy decreases as you move down the group, because Electrons at low energy levels have the ability to repel electrons at higher energy levels. This phenomenon is called shielding effect. Due to this effect, the outer electrons are less tightly bound to the nucleus. Moving along the period, the ionization energy smoothly increases from left to right.

Electron affinity– the change in energy when an atom of a substance in a gaseous state acquires an additional electron. As one moves down the group, the electron affinity becomes less negative due to the screening effect.

Electronegativity- a measure of how strongly it tends to attract electrons from another atom associated with it. Electronegativity increases when moving in periodic table from left to right and from bottom to top. It must be remembered that noble gases do not have electronegativity. Thus, the most electronegative element is fluorine.

Based on these concepts, let us consider how the properties of atoms and their compounds change in periodic table.

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

Let us consider the change in the properties of atoms and their compounds depending on their position in periodic table of chemical elements.

The non-metallicity of the atom increases when moving in the periodic table left to right and bottom to top. Due to this the basic properties of the oxides decrease, and acidic properties increase in the same order - when moving from left to right and from bottom to top. In this case, the acidic properties of oxides are stronger, the more degree oxidation of its constituent element

By period from left to right basic properties hydroxides weaken; in the main subgroups, from top to bottom, the strength of the foundations increases. Moreover, if a metal can form several hydroxides, then with an increase in the oxidation state of the metal, basic properties hydroxides weaken.

By period from left to right the strength of oxygen-containing acids increases. When moving from top to bottom within one group, the strength of oxygen-containing acids decreases. In this case, the strength of the acid increases with increasing oxidation state of the acid-forming element.

By period from left to right the strength of oxygen-free acids increases. When moving from top to bottom within one group, the strength of oxygen-free acids increases.

Categories,

The brilliant Russian chemist D.I. Mendeleev was distinguished throughout his life by the desire to understand the unknown. This desire, as well as the deepest and most extensive knowledge, combined with unmistakable scientific intuition, allowed Dmitry Ivanovich to develop scientific classification chemical elements - the periodic table in the form of its famous table.

D. I. Mendeleev’s periodic system of chemical elements can be imagined as a large house in which absolutely all chemical elements “live together”, known to man. To be able to use the Periodic Table, you need to study the chemical alphabet, i.e., the signs of chemical elements.

With their help, you will learn to write words - chemical formulas, and on their basis you will be able to 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 written in D.I. Mendeleev’s table. At the suggestion of the Swedish chemist J. Berzelius, the initial letters of the Latin names of chemical elements were adopted in most cases as symbols. Thus, hydrogen (Latin name Hydrogenium - hydrogenium) is denoted by the letter H (read "ash"), oxygen (Latin name Oxygenium - oxygenium) - by the letter O (read "o"), carbon (Latin name Сarboneum - carboneum) - by the letter C ( read "tse").

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 adding one of the subsequent letters of the name to the initial letter of the Latin name. Thus, the chemical sign for 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 of the elements, for example, hydrogen - which produces water, oxygen - which produces acids, phosphorus - which carries light (Fig. 20), etc.

Rice. 20.
Etymology of the name of element No. 15 of the Periodic Table of D. I. Mendeleev

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

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

Some names are borrowed from mythology (Fig. 22). For example, tantalum. This was the name of the beloved son of Zeus. For crimes against the gods, Tantalus was severely punished. He stood up to his neck in water, and branches with juicy, fragrant fruits hung over him. However, as soon as he wanted to drink, the water flowed away from him; as soon as he wanted to satisfy his hunger, he 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 element No. 61 of the Periodic Table of D. I. Mendeleev

Some elements were named after different states or parts of the world. For example, germanium, gallium (Gallium - old name France), polonium (in honor of Poland), scandium (in honor of Scandinavia), francium, ruthenium (Ruthenium is the Latin name for Russia), europium and americium. Here are the elements named after cities: hafnium (after Copenhagen), lutetium (in the old days Paris was called Lutetium), berkelium (after 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 element No. 105 of the Periodic Table 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 element No. 101 of the Periodic Table 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 with further study of chemistry. The number of floors of these “apartments” is also strictly distributed - the periods in which the elements “live”. Like the serial number of an element (the number of the “apartment”), the number of the period (“floor”) is fraught with vital information about the structure of atoms of chemical elements. Horizontally - “storeys” - the Periodic Table 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 each include two rows of elements; they are called large periods; The 4th and 5th periods contain 18 elements each, the 6th - 32 elements.

The 7th period is unfinished, so far it consists of only one row.

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

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

Each group consists of two subgroups - main and secondary. The subgroup, which includes elements of both short and long periods, is called the main subgroup or group A. The subgroup, which includes elements of only long periods, is called the secondary subgroup or group B. Thus, the main subgroup of group I (group IA) includes lithium , sodium, potassium, rubidium and francium are a subgroup of lithium Li; a side subgroup of this group (IB group) is formed by copper, silver and gold - this is a subgroup of Cu copper.

In addition to the form of D.I. Mendeleev’s table, which is called short-period (it is shown 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 different objects from the elements of the Lego game (see Fig. 10), so from chemical elements nature and man have created the variety of substances that surround us. Another model is even more clear: 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 laws of the formation of words - chemical formulas, and then the world of substances will open before you in all its colorful diversity.

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

Table 1
Names of some chemical elements

Key words and phrases

Periodic table of chemical elements (table) by D. I. Mendeleev.
Periods large and small.
Groups and subgroups - main (A group) and secondary (B group).
Symbols of chemical elements.

Working with a computer

Refer to the electronic application. Study the lesson material and complete the assigned tasks.
Find email addresses on the Internet that can serve as additional sources that reveal the content of keywords and phrases in the paragraph. Offer your help to the teacher in preparing a new lesson - send a message by keywords and phrases in the next paragraph.

Questions and tasks

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.
Explain how the names of the chemical elements titanium and vanadium reflect the influence of ancient Greek myths.
Why is the Latin name for gold Aurum (aurum) and silver - Argentum (argentum)?
Tell the story of the discovery of a chemical element of your choice and explain the etymology of its name.
Write down the “coordinates”, i.e. the position in the Periodic Table of D.I. Mendeleev (element number, period number and its type - large or small, group number and subgroup - main or minor), for the following chemical elements: calcium, zinc , antimony, tantalum, europium.
Distribute the chemical elements listed in Table 1 into three groups based on the “pronunciation of the chemical symbol.” Could doing this activity help you remember chemical symbols and pronounce element symbols?

A chemical element is a collective term that describes a collection of atoms of a simple substance, that is, one that cannot be divided into any simpler (according to the structure of their molecules) components. Imagine being given a piece of pure iron and being asked to separate it into its hypothetical constituents using any device or method ever invented by chemists. However, you can't do anything; the iron will never be divided into something simpler. A simple substance - iron - corresponds to the chemical element Fe.

Theoretical definition

The experimental fact noted above can be explained using the following definition: a chemical element is an abstract collection of atoms (not molecules!) of the corresponding simple substance, i.e. atoms of the same type. If there was a way to look at each of the individual atoms in the piece of pure iron mentioned above, then they would all be iron atoms. In contrast to this, chemical compound, for example, iron oxide, always contains at least two various types atoms: iron atoms and oxygen atoms.

Terms you should know

Atomic mass: The mass of protons, neutrons, and electrons that make up an atom of a chemical element.

Atomic number: The number of protons in the nucleus of an element's atom.

Chemical symbol: letter or pair Latin letters, representing the designation of this element.

Chemical compound: a substance that consists of two or more chemical elements combined with each other in a certain proportion.

Metal: An element that loses electrons in chemical reactions with other elements.

Metalloid: An element that reacts sometimes as a metal and sometimes as a non-metal.

Non-metal: an element that seeks to gain electrons in chemical reactions with other elements.

Periodic Table of Chemical Elements: A system of classifying chemical elements according to their atomic numbers.

Synthetic element: One that is produced artificially in a laboratory and is generally not found in nature.

Natural and synthetic elements

Ninety-two chemical elements occur naturally on Earth. The rest were obtained artificially in laboratories. A synthetic chemical element is usually a product nuclear reactions in particle accelerators (devices used to increase the speed of subatomic particles such as electrons and protons) or nuclear reactors(devices used to control the energy released during nuclear reactions). The first synthetic element with atomic number 43 was technetium, discovered in 1937 by Italian physicists C. Perrier and E. Segre. Apart from technetium and promethium, all synthetic elements have nuclei larger than uranium. The last synthetic chemical element to receive its name is livermorium (116), and before it was flerovium (114).

Two dozen common and important elements

Name	Symbol	Percentage of all atoms *				Properties of chemical elements (under normal room conditions)
Name	Symbol	In the universe	In the earth's crust	In sea water	In the human body
Aluminum	Al	-	6,3	-	-	Lightweight, silver metal
Calcium	Ca	-	2,1	-	0,02	Found in natural minerals, shells, bones
Carbon	WITH	-	-	-	10,7	The basis of all living organisms
Chlorine	Cl	-	-	0,3	-	Poisonous gas
Copper	Cu	-	-	-	-	Red metal only
Gold	Au	-	-	-	-	Yellow metal only
Helium	He	7,1	-	-	-	Very light gas
Hydrogen	N	92,8	2,9	66,2	60,6	The lightest of all elements; gas
Iodine	I	-	-	-	-	Non-metal; used as an antiseptic
Iron	Fe	-	2,1	-	-	Magnetic metal; used to produce iron and steel
Lead	Pb	-	-	-	-	Soft, heavy metal
Magnesium	Mg	-	2,0	-	-	Very light metal
Mercury	Hg	-	-	-	-	Liquid metal; one of two liquid elements
Nickel	Ni	-	-	-	-	Corrosion-resistant metal; used in coins
Nitrogen	N	-	-	-	2,4	Gas, the main component of air
Oxygen	ABOUT	-	60,1	33,1	25,7	Gas, the second important one air component
Phosphorus	R	-	-	-	0,1	Non-metal; important for plants
Potassium	TO	-	1.1	-	-	Metal; important for plants; usually called "potash"

* If the value is not specified, then the element is less than 0.1 percent.

The Big Bang as the root cause of matter formation

What chemical element was the very first in the Universe? Scientists believe the answer to this question lies in stars and the processes by which stars are formed. The universe is believed to have come into being at some point in time between 12 and 15 billion years ago. Until this moment, nothing existing except energy is thought of. But something happened that turned this energy into a huge explosion (the so-called Big Bang). In the next seconds after big bang matter began to form.

The first simplest forms of matter to appear were protons and electrons. Some of them combine to form hydrogen atoms. The latter consists of one proton and one electron; it is the simplest atom that can exist.

Slowly, over long periods of time, hydrogen atoms began to cluster together in certain areas of space, forming dense clouds. The hydrogen in these clouds was pulled into compact formations by gravitational forces. Eventually these clouds of hydrogen became dense enough to form stars.

Stars as chemical reactors of new elements

A star is simply a mass of matter that generates energy from nuclear reactions. The most common of these reactions involves the combination of four hydrogen atoms forming one helium atom. Once stars began to form, helium became the second element to appear in the Universe.

As stars get older, they switch from hydrogen-helium nuclear reactions to other types. In them, helium atoms form carbon atoms. Later, carbon atoms form oxygen, neon, sodium and magnesium. Later still, neon and oxygen combine with each other to form magnesium. As these reactions continue, more and more chemical elements are formed.

The first systems of chemical elements

More than 200 years ago, chemists began to look for ways to classify them. In the mid-nineteenth century, about 50 chemical elements were known. One of the questions that chemists sought to resolve. boiled down to the following: is a chemical element a substance completely different from any other element? Or some elements related to others in some way? Is there common law, uniting them?

Chemists suggested various systems chemical elements. For example, the English chemist William Prout in 1815 suggested that the atomic masses of all elements are multiples of the mass of the hydrogen atom, if we take it equal to unity, i.e. they must be integers. At that time, the atomic masses of many elements had already been calculated by J. Dalton in relation to the mass of hydrogen. However, if this is approximately the case for carbon, nitrogen, and oxygen, then chlorine with a mass of 35.5 did not fit into this scheme.

The German chemist Johann Wolfgang Dobereiner (1780 – 1849) showed in 1829 that three elements from the so-called halogen group (chlorine, bromine and iodine) could be classified according to their relative atomic masses. The atomic weight of bromine (79.9) turned out to be almost exactly the average of the atomic weights of chlorine (35.5) and iodine (127), namely 35.5 + 127 ÷ 2 = 81.25 (close to 79.9). This was the first approach to constructing one of the groups of chemical elements. Dobereiner discovered two more such triads of elements, but he was unable to formulate a general periodic law.

How did the periodic table of chemical elements appear?

Most of the early classification schemes were not very successful. Then, around 1869, almost the same discovery was made by two chemists at almost the same time. Russian chemist Dmitry Mendeleev (1834-1907) and German chemist Julius Lothar Meyer (1830-1895) proposed organizing elements that have similar physical and chemical properties into an ordered system of groups, series and periods. At the same time, Mendeleev and Meyer pointed out that the properties of chemical elements periodically repeat depending on their atomic weights.

Today, Mendeleev is generally considered the discoverer of the periodic law because he took one step that Meyer did not. When all the elements were arranged in the periodic table, some gaps appeared. Mendeleev predicted that these were places for elements that had not yet been discovered.

However, he went even further. Mendeleev predicted the properties of these not yet discovered elements. He knew where they were located on the periodic table, so he could predict their properties. Remarkably, every chemical element Mendeleev predicted, gallium, scandium, and germanium, was discovered less than ten years after he published his periodic law.

Short form of the periodic table

There have been attempts to count how many options for the graphic representation of the periodic table were proposed by different scientists. It turned out that there were more than 500. Moreover, 80% total number options are tables, and the rest is geometric shapes, mathematical curves, etc. As a result practical application found four types of tables: short, half-long, long and ladder (pyramidal). The latter was proposed by the great physicist N. Bohr.

The picture below shows the short form.

In it, chemical elements are arranged in ascending order of their atomic numbers from left to right and from top to bottom. Thus, the first chemical element of the periodic table, hydrogen, has atomic number 1 because the nuclei of hydrogen atoms contain one and only one proton. Likewise, oxygen has atomic number 8 since the nuclei of all oxygen atoms contain 8 protons (see figure below).

The main structural fragments of the periodic system are periods and groups of elements. In six periods, all cells are filled, the seventh is not yet completed (elements 113, 115, 117 and 118, although synthesized in laboratories, have not yet been officially registered and do not have names).

The groups are divided into main (A) and secondary (B) subgroups. Elements of the first three periods, each containing one row, are included exclusively in the A-subgroups. The remaining four periods include two rows.

Chemical elements in the same group tend to have similar chemical properties. Thus, the first group consists of alkali metals, the second - alkaline earth metals. Elements in the same period have properties that slowly change from an alkali metal to a noble gas. The figure below shows how one of the properties, atomic radius, changes for individual elements in the table.

Long period form of the periodic table

It is shown in the figure below and is divided in two directions, by rows and by columns. There are seven period rows, as in the short form, and 18 columns, called groups or families. In fact, the increase in the number of groups from 8 in the short form to 18 in the long form is obtained by placing all the elements in periods, starting from the 4th, not in two, but in one line.

Two different numbering systems are used for groups, as shown at the top of the table. The Roman numeral system (IA, IIA, IIB, IVB, etc.) has traditionally been popular in the United States. Another system (1, 2, 3, 4, etc.) is traditionally used in Europe and was recommended for use in the USA several years ago.

The appearance of the periodic tables in the figures above is a little misleading, as with any such published table. The reason for this is that the two groups of elements shown at the bottom of the tables should actually be located within them. The lanthanides, for example, belong to period 6 between barium (56) and hafnium (72). Additionally, actinides belong to period 7 between radium (88) and rutherfordium (104). If they were inserted into a table, it would become too wide to fit on a piece of paper or wall chart. Therefore, it is customary to place these elements at the bottom of the table.

Based on the Periodic Law of D.I. Mendeleev created Periodic table chemical elements, which consisted of 7 periods and 8 groups ( short period version of the table). Currently, the long-period version of the Periodic System is more often used (7 periods, 18 groups, the elements lanthanides and actinides are shown separately).

Periods- these are horizontal rows of the table, they are divided into small and large. In small periods there are 2 elements (1st period) or 8 elements (2nd, 3rd periods), in large periods there are 18 elements (4th, 5th periods) or 32 elements (6th, 5th periods) 7th period). Each period starts with typical metal, and ends non-metal(halogen) and noble gas.

Groups- these are vertical sequences of elements, they are numbered with Roman numerals from I to VIII and Russian letters A and B. The short-period version of the Periodic System included subgroups elements ( home And side).

Subgroup- this is a set of elements that are unconditional chemical analogues; often elements of a subgroup have the highest oxidation state corresponding to the group number.

In A-groups, the chemical properties of elements can vary over a wide range from non-metallic to metallic (for example, in the main subgroup of group V nitrogen- non-metal, but bismuth- metal).

In the Periodic Table, typical metals are located in group IA (Li-Fr), IIA (Mg-Ra) and IIIA (In, Tl). Non-metals are located in groups VIIA (F-Al), VIA (O-Te), VA (N-As), IVA (C, Si) and IIIA (B). Some elements of A-groups ( beryllium Ve, aluminum Al, germanium Ge, antimony Sb, polonium Po and others), as well as many elements of B-groups exhibit and metal, And non-metallic properties (phenomenon amphotericity).

For some groups, group names are used: IA (Li-Fr) - alkali metals , IIA (Ca-Ra) - alkaline earth metals, VIA (O-Po) - chalcogens, VIIA (F-At) - halogens, VIIIА (He-Rn) - noble gases:

The form of the Periodic Table proposed by D.I. Mendeleev, was called short period or classic. Currently, another form of the Periodic Table is used more - long-period.

Periodic law D.I. Mendeleev and the Periodic Table of Chemical Elements became the basis of modern chemistry.

The periodic law was formulated by D.I. Mendeleev in the following form (1871): “the properties of simple bodies, as well as the forms and properties of compounds of elements, and therefore the properties of the simple and complex bodies they form, are periodically dependent on their atomic weight”.

With the development of atomic physics and quantum chemistry, the Periodic Law received a strict theoretical justification. Thanks to the classic works of J. Rydberg (1897), A. Van den Broek (1911), G. Moseley (1913), the physical meaning of the serial (atomic) number of an element was revealed. Later, a quantum

a mechanical model of periodic changes in the electronic structure of atoms of chemical elements as the charges of their nuclei increase (N. Bohr, W. Pauli, E. Schrödinger, W. Heisenberg, etc.).

Currently, D. I. Mendeleev’s Periodic Law has the following formulation: “properties of chemical elements, as well as the forms and properties of the elements formed by them simple substances and compounds are periodically dependent on the magnitude of the charges of the nuclei of their atoms".

The peculiarity of the Periodic Law among other fundamental laws is that it does not have an expression in the form of a mathematical equation. The graphic (tabular) expression of the law is the Periodic Table of Elements developed by Mendeleev.

The periodic law is universal for the Universe: as the famous Russian chemist N.D. Zelinsky figuratively noted, the periodic law was “the discovery of the mutual connection of all atoms in the universe.”

Investigating the change in the chemical properties of elements depending on the value of their relative atomic mass(atomic weight), D. I. Mendeleev discovered in 1869 law of periodicity these properties: “The properties of the elements, and therefore the properties of the simple and complex bodies they form, are periodically dependent on the atomic weights of the elements.”

Physical basis The periodic law was established in 1922 by N. Bohr. Since chemical properties are determined by the structure of the electron shells of the atom, periodic table of mendeleev is a natural classification of elements based on the electronic structures of their atoms. The simplest basis for this classification is the number of electrons in a neutral atom, which is equal to the charge of the nucleus. But when a chemical bond is formed, electrons can be redistributed between atoms, but the charge of the nucleus remains unchanged, therefore the modern formulation of the periodic law states: “The properties of elements are periodically dependent on the charges of the nuclei of their atoms”.

This circumstance is reflected in the periodic system in the form of horizontal and vertical rows - periods and groups.

Period– horizontal row having the same number of electronic layers, the period number coincides with the value of the main quantum number n external level (layer); There are seven such periods in the periodic table. The second and subsequent periods begin with an alkaline element ( ns 1) and ends with a noble gas ( ns 2 n.p. 6).

Vertical The periodic table is divided into eight groups, which are divided into main ones - A , consisting of s- And p-elements, and side – B-subgroups containing d-elements. Subgroup III B, except d-elements, contains 14 4 f- and 5 f-elements (4 f- and 5 f-families). The main subgroups contain the same number of electrons in the outer electron layer, which is equal to the group number.

In the main subgroups, valence electrons (electrons capable of forming chemical bonds) are located on s- And p-orbitals of the outer energy level, in side orbitals - on s-orbitals of the outer and d-orbitals of the pre-outer layer. For f-valence elements are ( n – 2)f- (n – 1)d- And ns-electrons.

The similarity of elements within each group is the most important pattern in the periodic table. In addition, it should be noted that diagonal similarity in pairs of elements Li and Mg, Be and Al, B and Si, etc. This pattern is due to the tendency for properties to change vertically (in groups) and their changes horizontally (in periods).

All of the above confirms that the structure of the electronic shell of the atoms of an element changes periodically with increasing atomic number of the element. On the other hand, the properties are determined by the structure of the electron shell and, therefore, are periodically dependent on the charge of the atomic nucleus. Next, some periodic properties of elements are considered.

Communication between electronic structure elements and their position in the periodic table are presented in table. 2.2.

First period (n = 1, l= 0) consists of two elements H (1 s 1) and He (1 s 2).

In the second period (n = 2, l= 0, 1) are filled in s- And p-orbitals from Li to Ne. The elements are named accordingly s- And p-elements.

In the third period five appear d-orbitals ( n = 3, l= 0, 1, 2). While they are vacant, and the third period, like the second, contains eight p-elements of elements from Na to Ar.

Potassium and calcium, next to argon, have 4 at the outer level s-electrons ( fourth period). Appearance 4 s-electrons in the presence of free 3 d-orbitals is due to the shielding of the nucleus by dense 3 s 2 3p 6-electronic layer. Due to the repulsion from this layer of external electrons for potassium and calcium, 4 s 1 - and 4 s 2 states. The similarity of K and Ca with Na and Mg, respectively, in addition to a purely “chemical” justification, is also confirmed by electronic spectra.

With a further increase in the charge of scandium 3, next to calcium d-the state becomes energetically more favorable than 4 p, that's why 3 is populated d-orbital (Fig. 2.3). From an analysis of the dependence of electron energy on the atomic number of an element, V. M. Klechkovsky formulated a rule according to which the energy of atomic orbitals increases as the sum increases ( n + l). If the amounts are equal, the level with the smaller one is filled first. n and big l and then with more n and smaller l. So for K and Ca 4 is filled s-orbital (4 + 0 = 4), and then Sc is filled with 3 d-orbital (3 + 2 = 5).

The above reasoning is confirmed by experimental data on energy changes s-, p-, d-And f-orbitals depending on the atomic number of the element. As follows from Fig. 1.3, the energy values of various states depend on the charge of the nucleus Z, and the more Z, the less these states differ in energy. The nature of this difference is such that the curves expressing the change in energy intersect. So for the elements K and Ca ( Z= 19 and 20) energy 3 d-orbitals higher than 4 p, and for elements with Z≥ 21 energy 3 d-orbitals lower than 4 p. Starting with scandium ( Z= 21) filled in with 3 d-orbital, and remain in the outer layer4 s-electrons. Therefore, in the fourth period in the series from Sc to Zn, all ten 3 d-elements – metals with the lowest oxidation state, usually 2, due to external 4 s-electrons. General electronic formula these elements are 3 d 1–10 4s 1–2. For chromium and copper, electron leakage (or failure) is observed by d-level: Cr –3 d 5 4s 1, Cu – 3 d 10 4s 1. Such a breakthrough with ns- on ( n – 1)d-level is also observed in Mo, Ag, Au, Pt and other elements and is explained by the proximity of energies ns- And ( n – 1)d-levels and stability of half and completely filled levels.

Formation of cations d-elements is associated with the loss primarily of external ns- and only then ( n – 1)d-electrons. For example:

Fifth period repeats the fourth - it also has 18 elements, and 4 d-elements, like 3 d form an inserted decade (4 d 1–10 5s 0–2).

In the sixth period after lanthanum (5 d 1 6s 2) – analogues of scandium and yttrium follow 14 4 f-elements – lanthanides. The properties of these elements are very close, since the deep-lying ( n – 2)f-sublevel. General formula of lanthanides 4 f 2–14 5d 0–1 6s 2 .

Ions of 4f elements are formed as follows:

After 4 f-elements are filled in 5 d- and 6 p-orbitals.

Seventh period partially repeats the sixth. 5 f-elements are called actinides. Their general formula 5f 2–14 6d 0–1 7s 2. This is followed by 6 more artificially obtained 6 d-elements of the incomplete seventh period.