> Periodic table

Characteristics and structure Mendeleev's periodic table of chemical elements a: the position of the elements, the distribution system, the atomic number of the element.

Periodic table- the arrangement of chemical elements based on their electronic configurations and recurring chemical characteristics.

Learning task

• Understand how the elements are arranged in the periodic table.

Key Points

• The periodic table is the main basis for characterizing the chemical behavior of elements.
• The table contains only those chemical elements that have a unique atomic number (the number of protons in the nucleus).
• The primacy of the publication of the first table is assigned to Dmitri Mendeleev.

Terms

• An element is any of the simplest chemicals that cannot be broken down by a chemical reaction or by a chemical agent.
• The Periodic Table is a diagram of the chemical elements arranged according to their atomic numbers.
• Atomic number - a number equal to the number of protons, characterizing the chemical properties (Z).

The Periodic Table is a list of chemical elements arranged based on their atomic numbers, electronic configurations, and overlapping chemical characteristics. Elements are presented according to atomic number in ascending order. What does the structure of the periodic table look like? The standard form of the table accommodates an 18 x 7 grid. It can be deconstructed into 4 rectangular blocks: s for the left, p for the right, d for the middle, and f for the bottom of the last one. Table rows are periods. Columns s-, d- and p- are called groups, some of which have their own names (for example, halogens or noble gases).

The periodic table accommodates recurring trends, so it can be used to establish relationships between the characteristics of the elements. This also makes it possible to predict elements that have not yet been discovered. As a result, it can be used to analyze chemical behavior.

The standard form of the periodic table, in which the colors represent the different categories of elements

Features of the periodic table

Let's analyze the properties and characteristics of the periodic table of chemical elements. All varieties of the periodic table contain only chemical elements. Each has a unique atomic number - the number of protons in the nucleus. Many elements have a different number of neutrons - isotopes. For example, carbon has three naturally occurring isotopes. All its atoms have six protons, most of which have six neutrons and about 1% - 7 neutrons. In the table, isotopes are never divided, as they are grouped under one element. If the elements are devoid of stable isotopes, then they are endowed with a mass belonging to the most stable (indicated in brackets).

Scientists have managed to detect or synthesize all elements of atomic numbers from 1 (hydrogen) to 118 (oganesson). But even beyond the last element, new ones continue to be created. There is still debate about whether new ones should be added to the table.

Despite the fact that earlier tables are also known, the first publication was the version of Dmitry Mendeleev in 1869. He created it in order to show periodic trends in the characteristics of certain elements. He also managed to predict the properties of those not yet found, which were recorded in the table after him. With the advent of new elements, it was expanded and supplemented.

Mendeleev's periodic table (1869) displays periods vertically and groups horizontally

Known for illuminating the periodic table of elements

IS THERE A LIMIT
PERIODIC TABLE
D.I.MENDELEEV?

UNLOCKING NEW ITEMS

P The problem of systematization of chemical elements attracted close attention in the middle of the 19th century, when it became clear that the variety of substances around us is the result of different combinations of a relatively small number of chemical elements.

In the chaos of elements and their compounds, the great Russian chemist D.I. Mendeleev was the first to put things in order by creating his own periodic table of elements.

March 1, 1869 is considered the day of the discovery of the periodic law, when Mendeleev informed the scientific community about it. The scientist placed the 63 elements known at that time in his table in such a way that the main properties of these elements and their compounds changed periodically as their atomic mass increased. The observed changes in element properties in the horizontal and vertical directions of the table followed strict rules. For example, the metallic (basic) character, pronounced in the elements of group Ia, decreased along the horizontal of the table and increased along the vertical with increasing atomic mass.

Based on the open law, Mendeleev predicted the properties of several yet undiscovered elements and their place in the periodic table. Already in 1875, "ekaaluminum" (gallium) was discovered, four years later - "ekabor" (scandium), and in 1886 - "ekasilicon" (germanium). In subsequent years, the periodic table served and still serves as a guide in the search for new elements and the prediction of their properties.

However, neither Mendeleev himself nor his contemporaries could answer the question, what are the reasons for the periodicity of the properties of elements, whether and where the boundary of the periodic system exists. Mendeleev foresaw that the reason for the relationship he presented between the properties and atomic mass of elements lies in the complexity of the atoms themselves.

Only many years after the creation of the periodic system of chemical elements in the works of E. Rutherford, N. Bohr and other scientists, the complex structure of the atom was proved. Subsequent achievements in atomic physics made it possible to solve many obscure problems of the periodic table of chemical elements. First of all, it turned out that the place of an element in the periodic table is determined not by the atomic mass, but by the charge of the nucleus. The nature of the periodicity of the chemical properties of elements and their compounds became clear.

The atom began to be considered as a system in the center of which there is a positively charged nucleus, and negatively charged electrons revolve around it. In this case, the electrons are grouped in the circumnuclear space and move along certain orbits included in the electron shells.

All the electrons of an atom are usually denoted by numbers and letters. According to this designation, the main quantum numbers 1, 2, 3, 4, 5, 6, 7 refer to electron shells, and the letters s, p, d, f, g– to subshells (orbits) of each shell. The first shell (counting from the kernel) has only s-electrons, the second can have s- and p- electrons, the third - s-, p- and d- electrons, the fourth - s-,
p-, d- and f- electrons, etc.

Each shell can accommodate a very certain number of electrons: the first - 2, the second - 8, the third - 18, the fourth and fifth - 32 each. This determines the number of elements in the periods of the periodic table. The chemical properties of elements are determined by the structure of the outer and pre-outer electron shells of atoms, i.e. how many electrons they contain.

The nucleus of an atom consists of positively charged particles - protons and electrically neutral particles - neutrons, often referred to in one word - nucleons. The ordinal number of an element (its place in the periodic table) is determined by the number of protons in the nucleus of an atom of a given element. Mass number BUT element atom is equal to the sum of the numbers of protons Z and neutrons N in the kernel: A = Z + N. Atoms of the same element with a different number of neutrons in the nucleus are its isotopes.

The chemical properties of different isotopes of the same element do not differ from each other, while the nuclear properties vary widely. This manifests itself primarily in the stability (or instability) of isotopes, which essentially depends on the ratio of the number of protons and neutrons in the nucleus. Light stable isotopes of elements usually have an equal number of protons and neutrons. With an increase in the charge of the nucleus, i.e., the ordinal number of the element in the table, this ratio changes. Stable heavy nuclei have almost one and a half times more neutrons than protons.

Like atomic electrons, nucleons also form shells. With an increase in the number of particles in the nucleus, proton and neutron shells are successively filled. Nuclei with completely filled shells are the most stable. For example, the lead isotope Pb-208 is characterized by a very stable nuclear structure, which has filled proton shells ( Z= 82) and neutrons ( N = 126).

Such filled nuclear shells are similar to the filled electron shells of inert gas atoms, which represent a separate group in the periodic table. Stable nuclei of atoms with completely filled proton or neutron shells contain certain "magic" numbers of protons or neutrons: 2, 8, 20, 28, 50, 82, 114, 126, 184. properties, the periodicity of nuclear properties is also inherent. Among the different combinations of the number of protons and neutrons in the nuclei of isotopes (even-even; even-odd; odd-even; odd-odd), it is the nuclei containing an even number of protons and an even number of neutrons that are most stable.

The nature of the forces holding protons and neutrons in the nucleus is still not clear enough. It is believed that very large gravitational forces of attraction act between nucleons, which contribute to an increase in the stability of nuclei.

To in the mid-thirties of the last century, the periodic table was developed so much that it already showed the position of 92 elements. Under the serial number 92 was uranium - the last of the natural heavy elements found on Earth back in 1789. Of the 92 elements of the table, only elements with serial numbers 43, 61, 85 and 87 were not accurately identified in the thirties. They were discovered and studied later. A rare earth element with atomic number 61, promethium, was found in small quantities in ores as a product of the spontaneous decay of uranium. An analysis of the atomic nuclei of the missing elements showed that they are all radioactive, and because of their short half-lives, they cannot exist on Earth in appreciable concentrations.

Due to the fact that the last heavy element found on Earth was element with atomic number 92, one could assume that it is the natural limit of Mendeleev's periodic table. However, the achievements of atomic physics indicated the path along which it turned out to be possible to step over the boundary of the periodic table set by nature.

Elements with b about Larger atomic numbers than uranium are called transuranium. By their origin, these elements are artificial (synthetic). They are obtained by nuclear transformation reactions of elements found in nature.

The first attempt, although not entirely successful, to discover the transuranium region of the periodic table was made by the Italian physicist Enrico Fermi in Rome shortly after the existence of neutrons was proved. But only in 1940-1941. success in the discovery of the first two transuranium elements, namely neptunium (atomic number 93) and plutonium (atomic number 94), was achieved by American scientists from the University of California at Berkeley.

Several types of nuclear reactions underlie the methods for obtaining transuranium elements.

The first type is neutron fusion. In this method, in the nuclei of heavy atoms irradiated with neutrons, one of the neutrons is converted into a proton. The reaction is accompanied by the so-called electronic decay (--decay) - the formation and ejection from the nucleus with a huge kinetic energy of a negatively charged - particle (electron). The reaction is possible with an excess of neutrons in the nucleus.

The opposite reaction is the transformation of a proton into a neutron with the emission of a positively charged + -particle (positron). A similar positron decay (+ -decay) is observed when there is a shortage of neutrons in the nuclei and leads to a decrease in the nuclear charge, i.e. to decrease the atomic number of an element by one. A similar effect is achieved when a proton is converted into a neutron by capturing a nearby orbital electron.

New transuranium elements were first obtained from uranium by neutron fusion in nuclear reactors (as products of nuclear bomb explosions), and later synthesized using particle accelerators - cyclotrons.

The second type is the reactions between the nuclei of atoms of the initial element (“target”) and the nuclei of atoms of light elements (isotopes of hydrogen, helium, nitrogen, oxygen, and others) used as bombarding particles. The protons in the "target" and "projectile" nuclei have a positive electric charge and experience a strong repulsion when approaching each other. To overcome the repulsive forces, to form a compound nucleus, it is necessary to provide the atoms of the "projectile" with a very large kinetic energy. Such enormous energy of bombarding particles is stored in cyclotrons. The resulting intermediate compound nucleus has a rather large excess energy, which must be released to stabilize the new nucleus. In the case of heavy transuranium elements, this excess energy, when no nuclear fission occurs, is dissipated by emitting γ-rays (high energy electromagnetic radiation) and "evaporating" neutrons from the excited nuclei. The atomic nuclei of the new element are radioactive. They seek to achieve higher stability by changing the internal structure through radioactive electronic - -decay or -decay and spontaneous fission. Such nuclear reactions are inherent in the heaviest atoms of elements with serial numbers above 98.

The reaction of spontaneous, spontaneous fission of the nuclei of atoms of radioactive elements was discovered by our compatriot G.N. Flerov and Czech K.A. Petrzhak at the Joint Institute for Nuclear Research (JINR, Dubna) in experiments with uranium-238. An increase in the serial number leads to a rapid decrease in the half-life of the nuclei of atoms of radioactive elements.

In connection with this fact, the outstanding American scientist G.T. Seaborg, Nobel Prize winner, who participated in the discovery of nine transuranium elements, believed that the discovery of new elements would probably end approximately at the element with serial number 110 (similar in properties to platinum). This idea about the boundary of the periodic table was expressed in the 60s of the last century with a caveat: unless new methods for the synthesis of elements and the existence of still unknown regions of stability of the heaviest elements are discovered. Some of these possibilities have been identified.

The third type of nuclear reactions for the synthesis of new elements is the reaction between high-energy ions with an average atomic mass (calcium, titanium, chromium, nickel) as bombarding particles and atoms of stable elements (lead, bismuth) as a "target" instead of heavy radioactive isotopes. This way of obtaining heavier elements was proposed in 1973 by our scientist Yu.Ts. Oganesyan from JINR and successfully used in other countries. The main advantage of the proposed synthesis method was the formation of less "hot" compound nuclei during the fusion of the "projectile" and "target" nuclei. The release of excess energy of compound nuclei in this case occurred as a result of the "evaporation" of a significantly smaller number of neutrons (one or two instead of four or five).

An unusual nuclear reaction between ions of the rare Ca-48 isotope accelerated in a cyclotron
U-400, and atoms of the actinoid element curium Cm-248 with the formation of element-114 (“ekaslead”) was discovered in Dubna in 1979. It was found that this reaction produces a “cold” nucleus that does not “evaporate” a single neutron , and all excess energy is carried away by one -particle. This means that for the synthesis of new elements, one can also implement fourth kind nuclear reactions between accelerated ions of atoms with average mass numbers and atoms of heavy transuranium elements.

AT The development of the theory of the periodic system of chemical elements played an important role in the comparison of the chemical properties and structure of the electron shells of lanthanides with serial numbers 58–71 and actinides with serial numbers 90–103. It was shown that the similarity of the chemical properties of lanthanides and actinides is due to the similarity of their electronic structures. Both groups of elements are an example of an internal transition series with sequential filling 4 f- or 5 f-electron shells, respectively, after filling the outer s- and R-electronic orbitals.

Elements with atomic numbers in the periodic table of 110 and above were called superheavy. Progress towards the discovery of these elements becomes more and more difficult and long, because. it is not enough to synthesize a new element, it is necessary to identify it and prove that the new element has only its inherent properties. Difficulties are caused by the fact that a small number of atoms is available for studying the properties of new elements. The time during which a new element can be studied before radioactive decay occurs is usually very short. In these cases, even when only one atom of a new element has been obtained, the method of radioactive tracers is used to detect it and preliminary study some of its characteristics.

Element-109, meitnerium, is the last element on the periodic table found in most chemistry textbooks. Element-110, which belongs to the same group of the periodic table as platinum, was first synthesized in Darmstadt (Germany) in 1994 using a powerful heavy ion accelerator according to the reaction:

The half-life of the resulting isotope is extremely short. In August 2003, the 42nd IUPAC General Assembly and the IUPAC (International Union for Pure and Applied Chemistry) Council officially approved the name and symbol for element-110: darmstadtium, Ds.

In the same place, in Darmstadt, in 1994, element-111 was first obtained by the action of a beam of 64 28 Ni isotope ions on 209 83 Bi atoms as a “target”. By its decision in 2004, IUPAC recognized the discovery and approved the proposal to name the element-111 roentgenium, Rg, in honor of the outstanding German physicist W.K. Roentgen, who discovered X-rays, to which he gave such a name because of the uncertainty of their nature.

According to information received from JINR, in the Laboratory of Nuclear Reactions. G.N. Flerova synthesized elements with serial numbers 110–118 (with the exception of element-117).

As a result of synthesis according to the reaction:

in Darmstadt in 1996, several atoms of the new element-112 were obtained, which decays with the release of -particles. The half-life of this isotope was only 240 microseconds. A little later, at JINR, the search for new isotopes of element-112 was carried out by irradiating U-235 atoms with Ca-48 ions.

In February 2004, reports appeared in prestigious scientific journals about the discovery at JINR by our scientists, together with American researchers from the Lawrence Berkeley National Laboratory (USA), of two new elements with numbers 115 and 113. This group of scientists in experiments carried out in July– In August 2003, at the U-400 cyclotron with a gas-filled separator, in the reaction between Am-243 atoms and ions of the Ca-48 isotope, 1 atom of the element-115 isotope with a mass number of 287 and 3 atoms with a mass number of 288 were synthesized. All four atoms of the element -115 rapidly decayed with the release of -particles and the formation of isotopes of element-113 with mass numbers 282 and 284. The most stable isotope 284 113 had a half-life of about 0.48 s. It collapsed with the emission of -particles and turned into the X-ray isotope 280 Rg.

In September 2004, a group of Japanese scientists from the Physicochemical Research Institute, led by Kosuki Morita (Kosuke Morita) stated that they synthesized element-113 by the reaction:

During its decay with the release of -particles, the x-ray isotope 274 Rg was obtained. Since this is the first artificial element obtained by Japanese scientists, they felt that they had the right to make a proposal to call it "Japan".

The unusual synthesis of the element-114 isotope with a mass number of 288 from curium has already been noted above. In 1999, a report appeared on the production at JINR of the same isotope of element-114 by bombarding plutonium atoms with a mass number of 244 with Ca-48 ions.

The discovery of elements with serial numbers 118 and 116 was also announced as a result of long-term joint studies of nuclear reactions of californium Cf-249 and curium Cm-245 isotopes with a Ca-48 heavy ion beam, carried out by Russian and American scientists in the period 2002-2005. at JINR. Element-118 closes the 7th period of the periodic table, in its properties it is an analogue of the noble gas radon. Element-116 must have some properties in common with polonium.

According to the established tradition, the discovery of new chemical elements and their identification must be confirmed by the IUPAC decision, but the right to propose names for the elements is granted to the discoverers. Like a map of the Earth, the periodic table reflected the names of territories, countries, cities and scientific centers where elements and their compounds were discovered and studied, immortalized the names of famous scientists who made a great contribution to the development of the periodic system of chemical elements. And it is no coincidence that element-101 is named after D.I. Mendeleev.

To answer the question of where the border of the periodic table can pass, at one time an assessment was made of the electrostatic forces of attraction of the inner electrons of atoms to a positively charged nucleus. The higher the element's serial number, the stronger the electron "fur coat" around the nucleus is compressed, the stronger the internal electrons are attracted to the nucleus. There must come a moment when the electrons begin to be captured by the nucleus. As a result of such a capture and a decrease in the charge of the nucleus, the existence of very heavy elements becomes impossible. A similar catastrophic situation should arise when the ordinal number of the element is 170–180.

This hypothesis was refuted and it was shown that there are no restrictions for the existence of very heavy elements in terms of ideas about the structure of electron shells. Limitations arise as a result of the instability of the nuclei themselves.

However, it must be said that the lifetime of elements decreases irregularly with increasing atomic number. The next expected region of stability of superheavy elements, due to the appearance of closed neutron or proton shells of the nucleus, should lie in the vicinity of a doubly magic nucleus with 164 protons and 308 neutrons. The possibility of opening such elements is not yet clear.

Thus, the question of the boundary of the periodic table of elements still remains. Based on the rules for filling electron shells with an increase in the atomic number of an element, the predicted 8th period of the periodic table should contain superactinoid elements. The place allotted to them in the periodic table of D.I. Mendeleev corresponds to the III group of elements, similar to the already known rare earth and actinide transuranium 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 can tell a lot about the world.

In addition to serving you in the exam, it is also simply indispensable for solving a huge number of chemical and physical problems. But how to read it? Fortunately, today everyone can learn this art. In this article we will tell you how to understand the periodic table.

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

History of the creation of the Table

Dmitri Ivanovich Mendeleev was not a simple chemist, if someone thinks so. He was a chemist, physicist, geologist, metrologist, ecologist, economist, oilman, aeronaut, instrument maker and teacher. During his life, the scientist managed to conduct a lot of fundamental research in various fields of knowledge. For example, it is widely believed that it was Mendeleev who calculated the ideal strength of vodka - 40 degrees.

We do not know how Mendeleev treated vodka, but it is known for sure that his dissertation on the topic “Discourse on the combination of alcohol with water” had nothing to do with vodka and considered alcohol concentrations from 70 degrees. With all the merits of the scientist, the discovery of the periodic law of chemical elements - one of the fundamental laws of nature, brought him the widest fame.

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

In the middle of the nineteenth century, attempts to streamline the known chemical elements (63 elements were known) were simultaneously undertaken by several scientists. For example, in 1862 Alexandre Émile Chancourtois placed the elements along a helix and noted the cyclical repetition of chemical properties.

Chemist and musician John Alexander Newlands proposed his version of the periodic table in 1866. An interesting fact is that in the arrangement of the elements the scientist tried to discover some mystical musical harmony. Among other attempts was the attempt of Mendeleev, which was crowned with success.

In 1869, the first scheme of the table was published, and the day of March 1, 1869 is considered the day of the discovery of the periodic law. The essence of Mendeleev's discovery was that the properties of elements with increasing atomic mass do not change monotonously, but periodically.

The first version of the table contained only 63 elements, but Mendeleev made a number of very non-standard decisions. So, he guessed to leave a place in the table for yet undiscovered elements, and also changed the atomic masses of some elements. The fundamental correctness of the law derived by Mendeleev was confirmed very soon, after the discovery of gallium, scandium and germanium, the existence of which was predicted by scientists.

Modern view of the periodic table

Below is the table itself.

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

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

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

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. The atomic number, as already mentioned, is equal to the number of 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. The difference between the mass number and the atomic number gives the number of neutrons in the nucleus. Thus, the number of neutrons in a helium nucleus is two, and in lithium - four.

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

In nature, there are a lot of repeating 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 miraculous dreams of the scientist was the Periodic Table of Chemical Elements, in which D.I. Mendeleev arranged the chemical elements in order of increasing atomic mass. In the modern table, the chemical elements are arranged in ascending order of the atomic number of the element (the number of protons in the nucleus of an atom).

The atomic number is shown above the symbol of a chemical element, below the symbol is its atomic mass (the sum of protons and neutrons). Note that the atomic mass of some elements is a non-integer! Remember isotopes! Atomic mass is the weighted average of all the isotopes of an element that occur naturally under natural conditions.

Below the table are the lanthanides and actinides.

Metals, non-metals, metalloids

They are located in the Periodic Table to the left of the stepped diagonal line that starts with Boron (B) and ends with polonium (Po) (the exceptions are germanium (Ge) and antimony (Sb). It is easy to see that metals occupy most of the Periodic Table. The main properties of metals : solid (except mercury); shiny; good electrical and thermal conductors; ductile; malleable; easily donate electrons.

The elements to the right of the stepped diagonal B-Po are called non-metals. The properties of non-metals are directly opposite to the properties of metals: poor conductors of heat and electricity; fragile; non-forged; non-plastic; usually accept electrons.

Metalloids

Between metals and non-metals are semimetals(metalloids). They are characterized by the properties of both metals and non-metals. Semimetals have found their main industrial application in the production of semiconductors, without which no modern microcircuit or microprocessor is inconceivable.

Periods and groups

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

The properties of elements in periods change sequentially: so sodium (Na) and magnesium (Mg), which are at the beginning of the third period, give up electrons (Na gives up one electron: 1s 2 2s 2 2p 6 3s 1; Mg gives up two electrons: 1s 2 2s 2 2p 6 3s 2). But chlorine (Cl), located at the end of the period, takes one element: 1s 2 2s 2 2p 6 3s 2 3p 5.

In groups, on the contrary, all elements have the same properties. For example, in the IA(1) group, all elements from lithium (Li) to francium (Fr) donate one electron. And all elements of group VIIA(17) take one element.

Some groups are so important that they have been given special names. These groups are discussed below.

Group IA(1). The atoms of the elements of this group have only one electron in the outer electron layer, so they easily donate one electron.

The most important alkali metals are sodium (Na) and potassium (K), since they play an important role in the process of human life and are part of 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). The atoms of the elements of this group have two electrons in the outer electron layer, which also give up during chemical reactions. The most important element is calcium (Ca) - the basis 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 usually receive one electron each, because. on the outer electronic layer there are five elements each, and one electron is just missing to the "complete set".

The most famous elements of this group are: chlorine (Cl) - is part of salt and bleach; iodine (I) is an element that plays an important role in the activity of the human thyroid gland.

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 "staffed" outer electron layer. Therefore, they "do not need" to accept electrons. And they don't want to give them away. Hence - the elements of this group are very "reluctant" to enter into chemical reactions. For a long time it was believed that they do not react at all (hence the name "inert", i.e. "inactive"). But chemist Neil Barlett discovered that some of these gases, under certain conditions, can still react 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 within each group, the elements are similar to each other in their valence electrons (electrons of s and p orbitals located on the outer energy level).

Alkali metals have 1 valence electron each:

• 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

Alkaline earth metals have 2 valence electrons:

• 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

Halogens have 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

Inert gases have 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 the article Valence and the Table of electronic configurations of atoms of chemical elements by periods.

Let us now turn our attention to the elements located in groups with symbols AT. 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 electrons in atoms that fill d-orbitals:

1. sc- 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 1 ;
2. Ti- 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 2

Separate from the main table are located lanthanides and actinides are the so-called internal transition metals. In the atoms of these elements, electrons fill f-orbitals:

1. 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 ;
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

In this lesson, you will learn about the Periodic Law of Mendeleev, which describes the change in the properties of simple bodies, as well as the shape and properties of compounds of elements, depending on the magnitude of their atomic masses. Consider how a chemical element can be described by its position in the Periodic Table.

Topic: Periodic law andPeriodic system of chemical elements of D. I. Mendeleev

Lesson: Description of an element by position in the Periodic system of elements of D. I. Mendeleev

In 1869, D.I. Mendeleev, based on the data accumulated on chemical elements, formulated his periodic law. Then it sounded like this: "The properties of simple bodies, as well as the forms and properties of the compounds of elements, are in a periodic dependence on the magnitude of the atomic masses of the elements." For a very long time, the physical meaning of DIMendeleev's law was incomprehensible. Everything fell into place after the discovery of the structure of the atom in the 20th century.

Modern formulation of the periodic law:"The properties of simple substances, as well as the forms and properties of compounds of elements, are in a periodic dependence on the magnitude of the charge of the atomic nucleus."

The charge of the nucleus of an atom is equal to the number of protons in the nucleus. The number of protons is balanced by the number of electrons in the atom. Thus, the atom is electrically neutral.

The charge of the nucleus of an atom in the periodic table is the ordinal number of the element.

Period number shows the number of energy levels, on which the electrons revolve.

Group number shows the number of valence electrons. For elements of the main subgroups, the number of valence electrons is equal to the number of electrons in the outer energy level. It is the valence electrons that are responsible for the formation of the chemical bonds of an element.

Chemical elements of the 8th group - inert gases have 8 electrons on the outer electron shell. Such an electron shell is energetically favorable. All atoms tend to fill their outer electron shell with up to 8 electrons.

What characteristics of an atom change periodically in the Periodic system?

The structure of the external electronic level is repeated.

The radius of an atom changes periodically. In a group radius increases with an increase in the period number, since the number of energy levels increases. In a period from left to right the growth of the atomic nucleus will occur, but the attraction to the nucleus will be greater and therefore the radius of the atom decreases.

Each atom tends to complete the last energy level of the elements of the 1st group on the last layer 1 electron. Therefore, it is easier for them to give it away. And it is easier for the elements of the 7th group to attract 1 electron missing to the octet. In a group, the ability to donate electrons will increase from top to bottom, since the radius of the atom increases and the attraction to the nucleus is less. In a period from left to right, the ability to donate electrons decreases because the radius of the atom decreases.

The easier an element gives off electrons from the external level, the more metallic properties it has, and its oxides and hydroxides have more basic properties. This means that the metallic properties in groups increase from top to bottom, and in periods from right to left. With non-metallic properties, the opposite is true.

Rice. 1. The position of magnesium in the table

In the group, magnesium is adjacent to beryllium and calcium. Fig.1. Magnesium ranks lower than beryllium but higher than calcium in the group. Magnesium has more metallic properties than beryllium, but less than calcium. The basic properties of its oxides and hydroxides also change. In a period, sodium is to the left, and aluminum is to the right of magnesium. Sodium will exhibit more metallic properties than magnesium, and magnesium more than aluminum. Thus, any element can be compared with its neighbors by group and period.

Acid and non-metallic properties change opposite to basic and metallic properties.

Characteristics of chlorine according to its position in the periodic system of D.I. Mendeleev.

Rice. 4. Position of chlorine in the table

. The value of the serial number 17 indicates the number of protons17 and electrons17 in the atom. Fig.4. An atomic mass of 35 will help calculate the number of neutrons (35-17 = 18). Chlorine is in the third period, which means the number of energy levels in the atom is 3. It is in the 7-A group, it belongs to the p-elements. It's non-metal. Compare chlorine with its neighbors by group and by period. The non-metallic properties of chlorine are greater than those of sulfur, but less than those of argon. Chlorine ob-la-yes-is less non-metal-li-che-ski-mi properties than fluorine and more than bromine. Let's distribute the electrons over the energy levels and write the electronic formula. The general distribution of electrons will look like this. See Fig. 5

Rice. 5. Distribution of electrons of the chlorine atom over energy levels

Determine the highest and lowest oxidation state of chlorine. The highest oxidation state is +7, since it can donate 7 electrons from the last electron layer. The lowest oxidation state is -1 because chlorine needs 1 electron to complete. The formula of the highest oxide is Cl 2 O 7 (acid oxide), the hydrogen compound HCl.

In the process of donating or gaining electrons, an atom acquires conditional charge. This conditional charge is called .

- Simple substances have an oxidation state equal to zero.

Elements can show maximum oxidation state and minimum. Maximum An element shows its oxidation state when gives back all its valence electrons from the outer electronic level. If the number of valence electrons is equal to the group number, then the maximum oxidation state is equal to the group number.

Rice. 2. Position of arsenic in the table

Minimum the oxidation state of an element will show when it will accept all possible electrons to complete the electron layer.

Consider, using the example of element No. 33, the values ​​of oxidation states.

This is arsenic As. It is in the fifth main subgroup. Fig. 2. It has five electrons in its last electron level. So, giving them away, it will have an oxidation state of +5. Before the completion of the electron layer, the As atom lacks 3 electrons. By attracting them, it will have an oxidation state of -3.

The position of the elements of metals and non-metals in the Periodic system of D.I. Mendeleev.

Rice. 3. The position of metals and non-metals in the table

AT side effects subgroups are all metals . If you mentally carry out diagonal from boron to astatine , then higher this diagonal in the main subgroups will be all nonmetals , a below this diagonal - all metals . Fig.3.

1. No. 1-4 (p. 125) Rudzitis G.E. Inorganic and organic chemistry. Grade 8: textbook for educational institutions: basic level / G. E. Rudzitis, F.G. Feldman. M.: Enlightenment. 2011 176 pp.: ill.

2. What characteristics of an atom change with periodicity?

3. Give a description of the chemical element oxygen according to its position in the Periodic system of D.I. Mendeleev.