Patterns of changes in the properties of atoms. Changes in the properties of elements and their compounds in periods and main subgroups

in periods from left to right:

· the radius of atoms decreases;
· electronegativity of elements increases;
· the number of valence electrons increases from 1 to 8 (equal to the group number);
· the highest oxidation state increases (equal to the group number);
· the number of electronic layers of atoms does not change;
· metallic properties decrease;
· non-metallic properties of elements are increased.

Changing some element characteristics in a group from top to bottom:
· the charge of atomic nuclei increases;
· the radius of atoms increases;
· the number of energy levels (electronic layers) of atoms increases (equal to the period number);
· the number of electrons on the outer layer of atoms is the same (equal to the group number);
· the strength of the bond between the electrons of the outer layer and the nucleus decreases;
electronegativity decreases;
· metallicity of elements increases;
· non-metallicity of elements decreases.

Elements that are in the same subgroup are analogue elements, because they have some common properties (the same higher valency, the same forms of oxides and hydroxides, etc.). These general properties are explained by the structure of the outer electronic layer.

Read more about the patterns of changes in the properties of elements by periods and groups

The acid–base properties of hydroxides depend on which of the two bonds in the E–O–H chain is less strong.
If the E–O bond is less strong, then the hydroxide exhibits basic properties if O−H − acidic.
The weaker these bonds are, the greater the strength of the corresponding base or acid. The strength of the E–O and O–H bonds in the hydroxide depends on the distribution of electron density in the E–O–H chain. The latter is most strongly influenced by the oxidation state of the element and the ionic radius. An increase in the oxidation state of an element and a decrease in its ionic radius cause a shift in the electron density towards the atom
element in the chain E ← O ←N. This leads to a weakening of the O–H bond and strengthening of the E–O bond. Therefore, the basic properties of the hydroxide are weakened, and the acidic ones are enhanced.

Periodicity of properties of chemical elements

In modern science, D.I. Mendeleev’s table is called the periodic system of chemical elements, since general patterns in changes in the properties of atoms, simple and complex substances formed by chemical elements are repeated in this system at certain intervals - periods. Thus, all chemical elements existing in the world are subject to a single periodic law objectively operating in nature, the graphic representation of which is the periodic system of elements. This law and system are named after the great Russian chemist D.I. Mendeleev.

Periods- these are rows of elements located horizontally, with the same maximum value of the main quantum number of valence electrons. The period number corresponds to the number of energy levels in an element's atom. The periods consist of a certain number of elements: the first - of 2, the second and third - of 8, the fourth and fifth - of 18, the sixth period includes 32 elements. It depends on the number of electrons in the outer energy level. The seventh period is incomplete. All periods (with the exception of the first) begin with an alkali metal (s-element) and end with a noble gas. When a new energy level begins to fill, a new period begins. In a period with an increase in the atomic number of a chemical element from left to right, the metallic properties of simple substances decrease, and non-metallic properties increase.

Metallic properties- this is the ability of the atoms of an element to give up their electrons when forming a chemical bond, and non-metallic properties are the ability of the atoms of an element to attach electrons of other atoms when forming a chemical bond. In metals, the outer s-sublevel is filled with electrons, which confirms the metallic properties of the atom. The nonmetallic properties of simple substances manifest themselves during the formation and filling of the outer p-sublevel with electrons. The nonmetallic properties of the atom are enhanced by filling the p-sublevel (from 1 to 5) with electrons. Atoms with a completely filled outer electron layer (ns 2 np 6) form a group noble gases, which are chemically inert.

In short periods, as the positive charge of atomic nuclei increases, the number of electrons in the outer level increases(from 1 to 2 - in the first period and from 1 to 8 - in the second and third periods), which explains the change in the properties of the elements: at the beginning of the period (except for the first period) there is an alkali metal, then the metallic properties gradually weaken and non-metallic properties increase. In long periods As the charge of nuclei increases, filling levels with electrons becomes more difficult, which also explains the more complex change in the properties of elements compared to elements of small periods. Thus, in even rows of long periods, with increasing charge, the number of electrons in the outer level remains constant and is equal to 2 or 1. Therefore, while the level next to the outer (second from the outside) is filled with electrons, the properties of the elements in the even rows change extremely slowly. Only in odd rows, when the number of electrons in the outer level increases with increasing nuclear charge (from 1 to 8), the properties of the elements begin to change in the same way as those of typical ones.

Groups- these are vertical columns of elements with the same number of valence electrons equal to the group number. There is a division into main and secondary subgroups. The main subgroups consist of elements of small and large periods. The valence electrons of these elements are located on the outer ns and np sublevels. Side subgroups consist of elements of large periods. Their valence electrons are located in the outer ns sublevel and the inner (n – 1) d sublevel (or (n – 2) f sublevel). Depending on which sublevel (s-, p-, d- or f-) is filled with valence electrons, elements are divided into:

1) s-elements - elements of the main subgroup of groups I and II;

2) p-elements - elements of the main subgroups of III-VII groups;

3) d-elements - elements of secondary subgroups;

4) f-elements - lanthanides, actinides.

Top down in the main subgroups, metallic properties increase, and non-metallic properties weaken. Elements of the main and secondary groups differ in properties. The group number indicates the highest valency of the element. The exceptions are oxygen, fluorine, elements of the copper subgroup and group eight. The formulas of higher oxides (and their hydrates) are common to the elements of the main and secondary subgroups. In higher oxides and their hydrates of elements of groups I-III (with the exception of boron), basic properties predominate; from IV to VIII - acidic properties. For elements of the main subgroups, the formulas for hydrogen compounds are common. Elements of groups I-III form solids - hydrides, since the oxidation state of hydrogen is -1. Elements of groups IV-VII are gaseous. Hydrogen compounds of elements of the main subgroups of group IV (EN 4) are neutral, group V (EN3) are bases, groups VI and VII (H 2 E and NE) are acids.

Atomic radii, their periodic changes in the system of chemical elements

The radius of an atom decreases with increasing charges of atomic nuclei in a period, because the attraction of the electron shells by the nucleus increases. A kind of “compression” occurs. From lithium to neon, the charge of the nucleus gradually increases (from 3 to 10), which causes an increase in the forces of attraction of electrons to the nucleus, and the sizes of atoms decrease. Therefore, at the beginning of the period there are elements with a small number of electrons in the outer electron layer and a large atomic radius. Electrons located further from the nucleus are easily separated from it, which is typical for metal elements.

In the same group, as the period number increases, the atomic radii increase, because increasing the charge of an atom has the opposite effect. From the point of view of the theory of atomic structure, whether elements belong to metals or non-metals is determined by the ability of their atoms to give up or gain electrons. Metal atoms give up electrons relatively easily and cannot add them to complete their outer electron layer.

D.I. Mendeleev formulated a periodic law in 1869, which sounds like this: the properties of chemical elements and the substances formed by them are periodically dependent on the relative atomic masses of the elements. Systematizing chemical elements based on their relative atomic masses, Mendeleev also paid great attention to the properties of the elements and the substances formed by them, distributing elements with similar properties into vertical columns - groups. In accordance with modern ideas about the structure of the atom, the basis for the classification of chemical elements is the charges of their atomic nuclei, and the modern formulation of the periodic law is as follows: the properties of chemical elements and the substances formed by them are periodically dependent on the charges of their atomic nuclei. The periodicity in changes in the properties of elements is explained by the periodic repetition in the structure of the external energy levels of their atoms. It is the number of energy levels, the total number of electrons located on them and the number of electrons on the outer level that reflect the symbolism adopted in the periodic table.

a) Regularities associated with metallic and non-metallic properties of elements.

When moving FROM RIGHT TO LEFT along PERIOD METAL properties of p-elements INCREASED. In the opposite direction, non-metallic ones increase. This is explained by the fact that to the right are elements whose electronic shells are closer to the octet. Elements on the right side of the period are less likely to give up their electrons to form metallic bonds and in chemical reactions in general.
For example, carbon is a more pronounced nonmetallic than its period neighbor boron, and nitrogen has even more pronounced nonmetallic properties than carbon. From left to right in a period, the nuclear charge also increases. Consequently, the attraction of valence electrons to the nucleus increases and their release becomes more difficult. On the contrary, the s-elements on the left side of the table have few electrons in the outer shell and a lower nuclear charge, which promotes the formation of a metallic bond. With the obvious exception of hydrogen and helium (their shells are close to complete or complete!), all s-elements are metals; p-elements can be both metals and non-metals, depending on whether they are on the left or right side of the table.
The d- and f-elements, as we know, have “reserve” electrons from the “penultimate” shells, which complicate the simple picture characteristic of the s- and p-elements. In general, d- and f-elements exhibit metallic properties much more readily.
The overwhelming number of elements are metals and only 22 elements are classified as non-metals: H, B, C, Si, N, P, As, O, S, Se, Te, as well as all halogens and inert gases. Some elements, due to the fact that they can exhibit only weak metallic properties, are classified as semimetals. What are semimetals? If you select p-elements from the Periodic Table and write them in a separate “block” (this is done in the “long” form of the table), you will find a pattern shown in The lower left part of the block contains typical metals, top right - typical nonmetals. Elements that occupy places on the border between metals and non-metals are called semimetals.
Semimetals are located approximately along the diagonal running through the p-elements from the upper left to the lower right corner of the Periodic Table
Semimetals have a covalent crystal lattice with metallic conductivity (electrical conductivity). They either have insufficient valence electrons to form a full-fledged “octet” covalent bond (as in boron), or they are not held tightly enough (as in tellurium or polonium) due to the large size of the atom. Therefore, the bond in covalent crystals of these elements is partially metallic in nature. Some semimetals (silicon, germanium) are semiconductors. The semiconducting properties of these elements are explained by many complex reasons, but one of them is the significantly lower (although not zero) electrical conductivity, explained by the weak metallic bond. The role of semiconductors in electronic technology is extremely important.
When moving TOP DOWN along the groups METAL IS REINFORCED properties of elements. This is due to the fact that lower in the groups there are elements that already have quite a lot of filled electron shells. Their outer shells are further from the core. They are separated from the nucleus by a thicker “coat” of lower electron shells, and the electrons of the outer levels are held less tightly.

b) Regularities associated with redox properties. Changes in electronegativity of elements.

The reasons listed above explain why FROM LEFT TO RIGHT OXIDATING INCREASES properties, and when moving TOP TO DOWN - RESTORATIVE properties of elements.
The latter pattern even applies to such unusual elements as inert gases. From the “heavy” noble gases krypton and xenon, which are in the lower part of the group, it is possible to “select” electrons and form their compounds with strong oxidizing agents (fluorine and oxygen), but for the “light” helium, neon and argon this cannot be done.
In the upper right corner of the table is the most active non-metal oxidizing agent fluorine (F), and in the lower left corner is the most active reducing metal cesium (Cs). The element francium (Fr) should be an even more active reducing agent, but its chemical properties are extremely difficult to study due to its rapid radioactive decay.
For the same reason as the oxidizing properties of elements, their ELECTRONEGATIVITY INCREASES Same FROM LEFT TO RIGHT, reaching a maximum for halogens. Not the least role in this is played by the degree of completeness of the valence shell, its proximity to the octet.
When moving TOP DOWN by groups ELECTRONEGATIVITY DECREASES. This is due to an increase in the number of electron shells, on the last of which electrons are attracted to the nucleus weaker and weaker.
c) Regularities associated with the sizes of atoms.
Atomic sizes (ATOMIC RADIUS) when moving FROM LEFT TO RIGHT along the period REDUCED. Electrons are increasingly attracted to the nucleus as the nuclear charge increases. Even an increase in the number of electrons in the outer shell (for example, in fluorine compared to oxygen) does not lead to an increase in the size of the atom. On the contrary, the size of a fluorine atom is smaller than that of an oxygen atom.
When moving FROM TOP TO DOWN ATOMIC RADIUS elements GROWING, because more electron shells are filled.

d) Regularities associated with the valence of elements.

Elements of the same SUBGROUPS have a similar configuration of outer electron shells and, therefore, the same valence in compounds with other elements.
s-Elements have valences that match their group number.
p-Elements have the highest possible valence for them, equal to the group number. In addition, they can have a valency equal to the difference between the number 8 (octet) and their group number (the number of electrons in the outer shell).
d-Elements exhibit many different valencies that cannot be accurately predicted by group number.
Not only elements, but also many of their compounds - oxides, hydrides, compounds with halogens - exhibit periodicity. For each GROUPS elements, you can write formulas for compounds that periodically “repeat” (that is, they can be written in the form of a generalized formula).

So, let’s summarize the patterns of changes in properties manifested within periods:

Changes in some characteristics of elements in periods from left to right:

the radius of the atoms decreases;
the electronegativity of the elements increases;
the number of valence electrons increases from 1 to 8 (equal to the group number);
the highest oxidation state increases (equal to the group number);
the number of electronic layers of atoms does not change;
metallic properties are reduced;
the non-metallic properties of the elements increases.

Changing some characteristics of elements in a group from top to bottom:

the charge of atomic nuclei increases;
the radius of the atoms increases;
the number of energy levels (electronic layers) of atoms increases (equal to the period number);
the number of electrons on the outer layer of atoms is the same (equal to the group number);
the strength of the connection between the electrons of the outer layer and the nucleus decreases;
electronegativity decreases;
the metallicity of elements increases;
the non-metallicity of elements decreases.

Z is the serial number, equal to the number of protons; R is the radius of the atom; EO - electronegativity; Val e - number of valence electrons; OK. St. — oxidizing properties; Vos. St. — restorative properties; En. ur. — energy levels; Me - metallic properties; NeMe - non-metallic properties; HCO - highest oxidation state

Reference material for taking the test:

Mendeleev table

Solubility table

1. What does computer science study?

Computer techologies

information is intangible

process.
smell
sound
human speech
taste
photos

encryption
transfer of information
data storage
list sorting
database search

6. What is coding?
information search tool

misrepresentation
changing the type of information

Test on the topic: “Information and information processes”
1. What does computer science study?
any processes and phenomena related to information
computer programming
relationship between natural phenomena
Computer techologies
mathematical methods for solving problems
2. Mark all correct statements.
information is intangible
information is a reflection of the real world
information characterizes diversity
when receiving information, the uncertainty of knowledge decreases
there is a strict definition of information
3. Mark the types of information that the computer cannot yet do.
process.
smell
sound
human speech
taste
photos
4. Select processes that can be called information processing.
encryption
transfer of information
data storage
list sorting
database search
5. Mark all correct statements.
information can only exist together with the carrier
information storage is one of the information processes
in order to extract information from a message, a person uses knowledge
information processing is a change in its content
When recording information, the properties of the media change
6. What is coding?
information search tool
recording information in another sign system
misrepresentation
changing the type of information
change in the amount of information

selection of required elements

changing the order of elements
removing unnecessary elements

to convey information?

principles?
_______________________________________________________________

solving some problems?
_______________________________________________________________

to yourself?
_______________________________________________________________

systems?
_______________________________________________________________
7. What phrase can serve as a definition of sorting?
selection of required elements
arranging list elements in a given order
alphabetical ordering of lines
changing the order of elements
removing unnecessary elements
8. What is the name of the change in media properties that is used
to convey information?
_______________________________________________________________
9. What is the name of knowledge that represents facts, laws,
principles?
_______________________________________________________________
10. What is the name of the knowledge that represents algorithms?
solving some problems?
_______________________________________________________________
11. What are people’s ideas about nature, society and themselves called?
to yourself?
_______________________________________________________________
12. Check all the correct statements.
the information received depends on the knowledge of the recipient
the information received depends only on the received message
obtaining information always increases knowledge
knowledge increases only when the information received is partially known
the same information can be presented in different forms
13. What is the name for information recorded (encoded) in some form, in particular, in computer information
systems?
_______________________________________________________________

Answer:
1 2 3 4 5 6 7
a, b, ha, b, c, ha, ha, d, d a, c, d b, gb
8 9 10 11 12 13 signal declarative procedural knowledge a, d, e data

Explanatory note Thematic test "Patterns of changes in the chemical properties of elements and their compounds by periods and groups"is intended to prepare students for the Unified State Exam in Chemistry. Target audience - 11th grade. The wording of the test tasks corresponds to the demo version of the 2018 test and measurement materials in chemistry.

The tasks are compiled by analogy with the tests published in the Unified State Examination manual. Chemistry: standard exam options: 30 options / ed. A.A. Kaverina", published by the publishing house "National Education" (Moscow, 2017)

Patterns of changes in the chemical properties of elements and their compounds by periods and groups

1) Cl

2)K

3) Si

4) S

5) O

From the chemical elements indicated in the series, select three elements that are in the Periodic Table of Chemical Elements D.I. Mendeleev are in the same period. Arrange the selected elements in order of decreasing electronegativity.
Write down the numbers of the selected elements in the required sequence in the answer field.

Answer:

From the chemical elements indicated in the series, select three elements that are in the Periodic Table of Chemical Elements D.I. Mendeleev are in the same group. Arrange the selected elements in order of increasing acidic properties of their hydrogen compounds.

From the chemical elements indicated in the series, select three elements that are in the Periodic Table of Chemical Elements D.I. Mendeleev are in the same period. Arrange the selected elements in order of increasing acidic properties of their higher hydroxides.

From the chemical elements indicated in the series, select three elements that are in the Periodic Table of Chemical Elements D.I. Mendeleev are in the same group. Arrange the selected elements in order of enhancing the basic properties of the oxides they form.

Select three metals from the chemical elements listed in the series. Arrange the selected elements in order of decreasing reducing properties.

From the chemical elements indicated in the series, select three elements that are in the Periodic Table of Chemical Elements D.I. Mendeleev are in the same group.
Arrange these elements in order of increasing strength of attraction of valence electrons.

Answers

Question 1

Question 2

Question 3

The periodic law of changes in the properties of chemical elements was discovered in 1869 by the great Russian scientist D.I. Mendeleev and in the original formulation sounded as follows:

“... the properties of the elements, and therefore the properties of the simple and complex bodies they form, are periodically dependent on their atomic weight.”

At that time, atomic weight was the name given to the atomic mass of a chemical element. It should be noted that at that time nothing was known about the real structure of the atom and the idea of its indivisibility prevailed, and therefore D.I. Mendeleev formulated his law of periodic changes in the properties of chemical elements and the compounds formed by them based on the mass of atoms. Later, after the structure of the atom was established, the law was formulated in the following formulation, which is still relevant at the present time.

The properties of atoms of chemical elements and the simple substances formed by them are periodically dependent on the charges of the nuclei of their atoms.

Graphic representation of the periodic law of D.I. Mendeleev can be considered a periodic table of chemical elements, first constructed by the great chemist himself, but somewhat improved and finalized by subsequent researchers. In fact, the currently used version of the D.I. table Mendeleev reflects modern ideas and specific knowledge about the structure of atoms of various chemical elements.

Let us consider in more detail the modern version of the periodic table of chemical elements:

In the table D.I. Mendeleev you can see lines called periods; There are seven of them in total. In fact, the period number reflects the number of energy levels at which electrons are located in an atom of a chemical element. For example, elements such as phosphorus, sulfur, and chlorine, symbolized by the symbols P, S, and Cl, are found in the third period. This suggests that the electrons in these atoms are located at three energy levels or, more simply, form a three-layer electron shell around the nuclei.

Each period of the table, except the first, begins with an alkali metal and ends with a noble (inert) gas.

All alkali metals have the electronic configuration of the outer electron layer ns1, and the noble gases have ns 2 np 6, where n is the number of the period in which the particular element is located. An exception to the noble gases is helium (He) with the electron configuration 1s 2 .

You can also notice that in addition to periods, the table is divided into vertical columns - groups, of which there are eight. Most chemical elements have a number of valence electrons equal to their group number. Let us recall that valence electrons in an atom are those electrons that take part in the formation of chemical bonds.

In turn, each group in the table is divided into two subgroups - main and secondary.

For main group elements, the number of valence electrons is always equal to the group number. For example, the chlorine atom, located in the third period in the main subgroup of group VII, has seven valence electrons:

Elements of side groups have electrons of the outer level or often electrons of the d-sublevel of the previous level as valence electrons. For example, chromium, which is in the side subgroup of group VI, has six valence electrons - 1 electron in the 4s sublevel and 5 electrons in the 3d sublevel:

The total number of electrons in an atom of a chemical element is equal to its atomic number. In other words, the total number of electrons in an atom increases with element number. However, the number of valence electrons in an atom does not change monotonically, but periodically - from 1 for alkali metal atoms to 8 for noble gases.

In other words, the reason for periodic changes in any properties of chemical elements is associated with periodic changes in the structure of electronic shells.

When moving down a subgroup, the atomic radii of chemical elements increase due to an increase in the number of electronic layers. However, when moving along one row from left to right, that is, with an increase in the number of electrons for elements located in the same row, the radius of the atom decreases. This effect is explained by the fact that when one electron shell of an atom is sequentially filled, its charge, like the charge of the nucleus, increases, which leads to an increase in the mutual attraction of electrons, as a result of which the electron shell is “pushed” towards the nucleus:

At the same time, within one period, as the number of electrons increases, the radius of the atom decreases, and the binding energy of each electron of the outer level with the nucleus increases. This means that, for example, the nucleus of a chlorine atom will hold onto the electrons of its outer level much more strongly than the nucleus of a sodium atom will hold onto the single electron of its outer electron level. Moreover, in the collision of a sodium atom and a chlorine atom, chlorine will “take away” the only electron from the sodium atom, that is, the electron shell of chlorine will become the same as that of the noble gas argon, and that of sodium will be the same as that of the noble gas neon. The ability of an atom of a chemical element to attract “foreign” electrons when colliding with atoms of another chemical element is called electronegativity. Electronegativity will be discussed in more detail in the chapter on chemical bonds, but it should be noted that electronegativity, like many other parameters of chemical elements, also obeys the periodic law of D.I. Mendeleev. Within one subgroup of chemical elements, electronegativity decreases, and when moving along the series of one period to the right, electronegativity increases.

You should learn one useful mnemonic technique that allows you to recall in your memory how certain properties of a chemical element change. It consists in the following. Let's imagine the dial of an ordinary round watch. If its center is placed in the lower right corner of the D.I. Mendeleev, then the properties of chemical elements will change uniformly when moving along it up and to the right (clockwise) and oppositely down and to the left (counterclockwise):

Let's try to apply this technique to the size of an atom. Let's say that you remember exactly that when moving down a subgroup in the table D.I. The Mendeleev radius of an atom increases as the number of electron shells increases, but they completely forgot how the radius changes when moving left and right.

Then you need to proceed as follows. Place your right thumb in the lower right corner of the table. The movement down the subgroup will coincide with the movement of the index finger counterclockwise, as well as the movement to the left along the period, that is, the radius of the atom when moving to the left along the period, as well as when moving down the subgroup, increases.

The same is true for other properties of chemical elements. Knowing exactly how this or that property of an element changes when moving up and down, thanks to this method you can restore in memory how the same property changes when moving left or right in the table.