The main pattern of this change is the strengthening of the metallic nature of the elements as Z increases. This pattern is especially pronounced in the IIIa-VIIa subgroups. For metals I A-III A-subgroups, an increase in chemical activity is observed. In the elements of IVA - VIIA subgroups, as Z increases, a weakening of the chemical activity of the elements is observed. For elements of b-subgroups, the change in chemical activity is more difficult.
Theory periodic system was developed by N. Bohr and other scientists in the 20s. 20th century and is based on a real scheme for the formation of electronic configurations of atoms. According to this theory, as Z increases, the filling of electron shells and subshells in the atoms of elements included in the periods of the periodic system occurs in the following sequence:
Period numbers
1 2 3 4 5 6 7
1s 2s2p 3s3p 4s3d4p 5s4d5p 6s4f5d6p 7s5f6d7p
Based on the theory of the periodic system, the following definition of a period can be given: a period is a collection of elements that begins with an element with a value of n. equal to the period number, and l=0 (s-elements) and ending with an element with the same value n and l = 1 (p-elements) (see Atom). The exception is the first period containing only 1s elements. The number of elements in periods follows from the theory of the periodic system: 2, 8, 8. 18, 18, 32 ...
In the figure, the symbols of elements of each type (s-, p-, d- and f-elements) are depicted on a certain color background: s-elements - on red, p-elements - on orange, d-elements - on blue, f-elements - on green. Each cell contains serial numbers and atomic masses elements, as well as the electronic configurations of the outer electron shells, which basically determine the chemical properties of the elements.
It follows from the theory of the periodic system that the a-subgroups include elements with and equal to the number of the period, and l = 0 and 1. The b-subgroups include those elements in whose atoms the shells that previously remained incomplete are completed. That is why the first, second and third periods do not contain elements of b-subgroups.
Structure of the periodic system chemical elements closely related to the structure of atoms of chemical elements. As Z increases, similar types of configuration of the outer electron shells are periodically repeated. Namely, they determine the main features of the chemical behavior of elements. These features manifest themselves differently for the elements of the A-subgroups (s- and p-elements), for the elements of the b-subgroups (transitional d-elements), and for the elements of the f-families - lanthanides and actinides. A special case is represented by the elements of the first period - hydrogen and helium. Hydrogen is characterized by high chemical activity, because its only b-electron is easily split off. At the same time, the configuration of helium (1st) is very stable, which causes its complete chemical inactivity.
The elements of the A-subgroups are filled with outer electron shells (with n equal to the number of the period); therefore, the properties of these elements change markedly as Z increases. Thus, in the second period, lithium (configuration 2s) is an active metal that easily loses a single valence electron; beryllium (2s~) is also a metal, but less active due to the fact that its outer electrons are more firmly bound to the nucleus. Further, boron (2s "p) has a weakly pronounced metallic character, and all subsequent elements of the second period, in which the construction of a 2p subshell occurs, are already non-metals. The eight-electron configuration of the outer electron shell neon (2s ~ p ~) - an inert gas - is very durable.
Chemical properties of the elements of the second period are explained by the desire of their atoms to acquire the electronic configuration of the nearest inert gas (helium configuration - for elements from lithium to carbon or neon configuration - for elements from carbon to fluorine). This is why, for example, oxygen cannot exhibit a higher oxidation state equal to the group number: after all, it is easier for it to achieve the neon configuration by acquiring additional electrons. The same nature of the change in properties is manifested in the elements of the third period and in the s- and p-elements of all subsequent periods. At the same time, the weakening of the strength of the bond between the outer electrons and the nucleus in A-subgroups as Z increases manifests itself in the properties of the corresponding elements. Thus, for s-elements, there is a noticeable increase in chemical activity as Z increases, and for p-elements, an increase in metallic properties.
In atoms of transitional d-elements, previously unfinished shells with the value of the main quantum number and one less than the period number are completed. With some exceptions, the configuration of the outer electron shells of transition element atoms is ns. Therefore, all d-elements are metals, and that is why the changes in the properties of 1-elements as Z increases are not as sharp as we saw with s and p-elements. In higher oxidation states, d-elements show a certain similarity with p-elements of the corresponding groups of the periodic system.
The features of the properties of the elements of triads (VIII b-subgroup) are explained by the fact that the d-subshells are close to completion. This is why iron, cobalt, nickel and platinum metals, as a rule, are not inclined to give compounds of higher oxidation states. The only exceptions are ruthenium and osmium, which give the oxides RuO4 and OsO4. For elements of I- and II B-subgroups, the d-subshell actually turns out to be complete. Therefore, they exhibit oxidation states equal to the group number.
In the atoms of lanthanides and actinides (all of them are metals), the completion of previously incomplete electron shells occurs with the value of the main quantum number and two units less than the period number. In the atoms of these elements, the configuration of the outer electron shell (ns2) remains unchanged. At the same time, f-electrons do not actually affect the chemical properties. That's why the lanthanides are so similar.
For actinides, the situation is much more complicated. In the range of nuclear charges Z = 90 - 95, the electrons bd and 5/ can take part in chemical interactions. And from this it follows that actinides exhibit a much wider range of oxidation states. For example, for neptunium, plutonium and americium, compounds are known where these elements act in a seven-valence state. Only for elements starting from curium (Z = 96) does the trivalent state become stable. Thus, the properties of the actinides differ significantly from those of the lanthanides, and therefore both families cannot be considered similar.
The actinide family ends with an element with Z = 103 (lawrencium). Grade chemical properties kurchatovium (Z = 104) and nilsborium (Z = 105) shows that these elements should be analogues of hafnium and tantalum, respectively. Therefore, scientists believe that after the family of actinides in atoms, the systematic filling of the 6d subshell begins.
The finite number of elements that the periodic system covers is unknown. The problem of its upper limit is, perhaps, the main riddle of the periodic system. The heaviest element found in nature is plutonium (Z = 94). The reached limit of artificial nuclear fusion is an element with the serial number 107. It remains open question: will it be possible to get elements with large ordinal numbers, which ones and how many? It cannot yet be answered with any certainty.
The properties of elements and their compounds are determined: 1 - charges of atomic nuclei, 2 - atomic radii.
Small periods. Consider the change in some properties of elements and their compounds using the example of period II (see Table 3). In the second period, with an increase in the positive charge of the atomic nuclei, there is a sequential increase in the number of electrons at the outer level, which is the most distant from the atomic nucleus and therefore easily deformed, which leads to a rapid decrease in the atomic radius. This explains the rapid weakening of the metallic and reducing properties of elements, the strengthening of non-metallic and oxidizing properties, an increase in the acidic properties of oxides and hydroxides and a decrease in basic properties. The period ends with a noble gas (Ne). In the third period, the properties of the elements and their compounds change in the same way as in the second, since the atoms of the elements of this period repeat the electronic structures of the atoms of the elements of the second period (3s- and 3p-sublevels)
Large periods (IV, V). In even rows of large periods (IV, V), starting from the third element, the number of electrons in the penultimate level increases sequentially, while the structure of the outer level remains unchanged. The penultimate level is located closer to the atomic nucleus and therefore deforms to a lesser extent. This leads to a slower decrease in the atomic radius. For example:
A consequence of a slow change in the radius of atoms and the same number of electrons at the outer level is also a slow decrease in the metallic and reducing properties of elements and their compounds. So, in the even row of IV period K - Mn - active metals Fe - Ni - metals average activity(compare with the elements of period II, where the third element, boron, is no longer a metal).
And starting from group III of an odd series, the properties of elements and their compounds change in the same way as in small periods, since the external level begins to build up. Thus, the structure of the energy level is decisive in the properties of elements and their compounds. Each period under consideration also ends with a noble gas.
Having considered the change in some properties of elements and their compounds in periods, we can draw the following conclusions:
1. Each period begins with an alkali metal and ends with a noble gas.
2. The properties of elements and their compounds are periodically repeated because the structures of energy levels are periodically repeated. In this physical meaning periodic law.
In the main subgroups, the number of energy levels increases, which leads to an increase in atomic radii. Therefore, in the main subgroups (from top to bottom), the electronegativity decreases, the megalithic and reducing properties of the elements increase, while the non-metallic and oxidizing properties decrease, the basic properties of oxides and hydroxides increase, and the acid properties decrease. For example, consider the main subgroup of group II.
Thus, the properties of an element and its compounds are intermediate between two elements adjacent to it in terms of period and subgroup.
According to the coordinates (period number and group number) of an element in the periodic system of D. I. Mendeleev, it is possible to determine the electronic structure of its atom, and, therefore, to foresee its main properties.
1. number of electronic levels in an atom defines period number The containing the corresponding element.
2. Total number of electrons, located in the s- and p-orbitals of the outer level (for elements of the main subgroups) and in the d-orbitals of the pre-outer and s-orbitals of the outer level (for elements of secondary subgroups; exceptions:
defines group number.
3. f-elements are located either in the side subgroup of group III (short-term variant), or between IIA- and IIIB-groups (long-term variant) - lanthanides(№ 57-70), actinides(№ 89-102).
4. atoms elements different periods, but one subgroup have the same structure of the outer and pre-outer electronic levels and therefore have similar chemical properties.
5. element's maximum oxidation number coincides with the number of the group in which the element is located. The nature of the oxides and hydroxides formed by the element depends on oxidizing number of elements in them. Oxides and hydroxides in which the element is in the oxidation state:
The higher the degree of oxidation of the acid-forming element, the more pronounced acid properties oxides and hydroxides.
Therefore: oxides and hydroxides of elements of groups I-III are predominantly amphoteric. Oxides and hydroxides of elements of groups IV-VII are predominantly acidic (at the maximum degree of oxidation). Oxides and hydroxides of the same elements, but with the lowest degree oxidation can be of a different nature.
6. Connections of elements with hydrogen can be subdivided into 3 major groups:
a) salt-like hydrides active metals(LiH - , CaH - and etc.);
b) covalent hydrogen compounds of p-elements (B 2 H 6 , CH 4 , NH 3 , H 2 O, HF, etc.);
c) metal-like phases formed by d- and f-elements; the latter are usually non-stoichiometric compounds and it is often difficult to decide whether to refer to them as individual compounds or solid solutions.
Hydrogen compounds of elements of group IV (CH 4 -methane, SiH 4 - silane) do not interact with acids and bases, practically do not dissolve in water.
Hydrogen compounds of the elements of group V (NH 3 -ammonia) when dissolved in water form bases.
Hydrogen compounds of elements of groups VI and VII (H 2 S, HF) form acids when dissolved in water.
7. elements of the second period, in the atoms of which the 2nd electron layer is filled, are very different from all other elements. This is explained by the fact that the energy of electrons in the second layer is much lower than the energy of electrons in subsequent layers, and that the second layer cannot contain more than eight electrons.
8. d-elements of the same period differ less from each other than the elements of the main subgroups, in which the outer electronic layers are built up.
9. Differences in the properties of lanthanides, in the atoms of which the f-shell, which belongs to the third layer from the outside, is built up, are insignificant.
Every period(except for the first) begins with a typical metal and ends with a noble gas preceded by a typical non-metal.
Changing the properties of elements within a period:
1) weakening of metallic properties;
2) decrease in the radius of the atom;
3) strengthening of oxidizing properties;
4) the ionization energy increases;
5) electron affinity increases;
6) electronegativity increases;
7) acidic properties of oxides and hydroxides increase;
8) starting from group IV (for p-elements), stability increases hydrogen compounds and their acidic properties are enhanced.
Changing the properties of elements within a group:
1) metallic properties increase;
2) the radius of the atom increases;
3) strengthening of reducing properties;
4) the ionization energy decreases;
5) electron affinity decreases;
6) electronegativity decreases;
7) the main properties of oxides and hydroxides increase;
8) starting from group IV (for p-elements), the stability of hydrogen compounds decreases, their acidic and oxidizing properties increase.
VALENCE- the ability of the atoms of elements to form chemical bonds. Quantitatively, valence is determined by the number of unpaired electrons.
In 1852, the English chemist Edward Frankland introduced the concept of connecting force. This property of atoms was later called valency.
valency is 2, because there are 2 unpaired electrons.
OXIDATION DEGREE- the conditional charge of the atom, which is calculated based on the assumption that the molecule consists only of ions.
Unlike valency, the oxidation state has a sign.
positive oxidation stateis equal to the number of drawn (given) electrons from a given atom. An atom can donate all unpaired electrons.
negative degree oxidationis equal to the number of attracted (attached) electrons to a given atom; only non-metals show it. Atoms of non-metals attach such a number of electrons that is necessary to form a stable eight-electron configuration of the outer level.
For example: N -3 ; S-2; Cl-; C -4 .
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);
· highest degree oxidation increases (equal to the group number);
the number of electron layers of atoms does not change;
the metallic properties are reduced;
· the non-metallic properties of the elements are increased.
Changing some characteristics of elements in a group from top to bottom:
the charge of the nuclei of atoms increases;
the radius of the atoms increases;
the number of energy levels (electronic layers) of atoms increases (equal to the number of the period);
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;
The electronegativity decreases
the metallicity of the elements increases;
the non-metallicity of the elements decreases.
Elements that are in the same subgroup are analogue elements, because they have some general 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.
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 main properties if О−Н − acid.
The weaker these bonds, 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 electron density distribution in the E–O– H chain. The latter is most strongly affected 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 to the atom
element in the chain E ← O ←N. This leads to weakening of the O–H bond and strengthening of the E–O bond. Therefore, the basic properties of the hydroxide are weakened, and the acid properties are enhanced.
1. What does computer science study?
Computer techologies
information is intangible
process.
smell
sound
human speech
taste
Photo
encryption
transmission of information
data storage
list sorting
database search
6. What is coding?
information retrieval tool
distortion of information
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
the relationship of phenomena in nature
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 does not yet know
process.
smell
sound
human speech
taste
Photo
4. Select processes that can be called information processing.
encryption
transmission of information
data storage
list sorting
database search
5. Mark all correct statements.
information can only exist together with the carrier
storage of information 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 information is written, the properties of the media change
6. What is coding?
information retrieval tool
recording information in another system of signs
distortion of information
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?
_______________________________________________________________
yourself?
_______________________________________________________________
systems?
_______________________________________________________________
7. What phrase can serve as a definition of sorting?
selection of required elements
arrange the elements of a list in a given order
alphabetical arrangement of strings
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, which are facts, laws,
principles?
_______________________________________________________________
10. What is the name of the knowledge that is the algorithms
solving some problems?
_______________________________________________________________
11. What is the name of a person's ideas about nature, society and himself
yourself?
_______________________________________________________________
12. Mark all correct statements.
the information received depends on the knowledge of the recipient
the received information depends only on the received message
getting information always increases knowledge
knowledge increases only when the received information is partially known
the same information can be presented in different forms
13. What is the name of 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, e a, c, e b, gb
8 9 10 11 12 13 signal declarative procedural knowledge a, d, e data
