The distribution is characterized by the following rules:

the Pauli principle;

Gund's rule;

the principle of least energy and the Klechkovsky rule.

By Pauli principle An atom cannot have two or more electrons with the same value of all four quantum numbers. Based on the Pauli principle, you can set the maximum capacity of each energy level and sublevel.

	Sublevel, ℓ	Sublevel designation	Magnetic quantum number, m	Spin quantum number,s
			3, -2, -1, 0, 1, 2, 3

Thus, maximum number of electrons per:

s -sublevel - 2,

p - sublevel - 6,

d -sublevel - 10,

f -sublevel - 14.

Within the quantum level n, an electron can take on the values ​​of 2n 2 different states, which was established empirically using spectral analysis.

Gund's rule : in each sublevel, electrons tend to occupy the maximum number of free energy cells so that the total spin has the greatest value.

For example:

right wrong wrong

3r 3:

s = +1/2+1/2+1/2=1.5 s =-1/2+1/2+1/2=0.5 s = -1/2+1/2-1/2 =-0.5

The principle of least energy and the Klechkovsky rule: electrons primarily populate quantum orbitals with minimum energy. Since the energy reserve in an atom is determined by the value of the sum of the main and orbital quantum numbers (n + ℓ), the electrons first populate the orbitals for which the sum (n + ℓ) is the smallest.

For example: the sum (n + ℓ) for the 3d sublevel is n = 3, l = 2, hence (n + ℓ) = 5; for the 4s sublevel: n = 4, ℓ = 0, hence (n + ℓ ) = 4. In this case, the 4s sublevel is filled first and only then the 3d sublevel.

If the total energy values ​​are equal, then the level that is closer to the nucleus is populated.

For example: for 3d: n=3, ℓ=2 , (n + ℓ) = 5 ;

for 4p: n = 4, ℓ = 1, (n + ℓ) = 5.

Since n = 3 < n = 4, 3d will be populated with electrons earlier than 4 p.

Thus, the sequence of filling levels and sublevels with electrons in atoms:

1 s 2 <2 s 2 <2 p 6 <3 s 2 <3 p 6 <4 s 2 <3 d 10 <4 p 6 <5 s 2 <4 d 10 <5 p 6 <6 s 2 <5 d 10 ≈ 4 f 14 <6 p 6 <7s 2 …..

Electronic formulas

An electronic formula is a graphic representation of the distribution of electrons over levels and sublevels in an atom. There are two types of formulas:

when writing, only two quantum numbers are used: n and ℓ. The main quantum number is indicated by a number before the letter designation of the sublevel. The orbital quantum number is indicated by the letter s, p, d, or f. The number of electrons is indicated by a number as an exponent.

For example: +1 H: 1s 1 ; +4 Be: 1s 2 2s 2 ;

2 He: 1s 2 ; +10 Ne: 1s 2 2s 2 2p 6 ;

3 Li: 1s 2 2s 1 ; +14 Si: 1s 2 2s 2 2p 6 3s 2 3p 6 .

That is, the sequence

1 s 2 <2 s 2 <2 p 6 <3 s 2 <3 p 6 <4 s 2 <3 d 10 <4 p 6 <5 s 2 <4 d 10 <5 p 6 <6 s 2 <5 d 10 ≈ 4 f 14 <6 p 6 <7s 2 …..

graphic electronic formula - all 4 quantum numbers are used - this is the distribution of electrons in quantum cells. The main quantum number is depicted on the left, the orbital - at the bottom with a letter, the magnetic - the number of cells, the spin - the direction of the arrows.

For example:

8 O:…2s 2 2p 4

The graphical formula is used to write only valence electrons.

Consider the compilation of electronic formulas for elements by periods.

The I period contains 2 elements, in which the I quantum level and the s-sublevel are completely populated with electrons (the maximum number of electrons per sublevel is 2):

2 He: n=1 1s 2

Elements in which the s-sublevel is filled last are assigned to s -family and call s -elements .

The elements of the II period are filling the II quantum level, the s- and p-sublevels (the maximum number of electrons in the p-sublevel is 8).

3 Li: 1s 2 2s 1 ; 4 Be: 1s 2 2s 2 ;

5 B: 1s 2 2s 2 2p 1 ; 10 Ne: 1s 2 2s 2 2p 6

Elements in which the p-sublevel is filled last are assigned to p-family and call p-elements .

The elements of the III period begin to form the III quantum level. Na and Mg are populating the 3s sublevel with electrons. For elements from 13 Al to 18 Ar, the 3p sublevel is populated; The 3d sublevel remains empty, since it has a higher energy level than the 4s sublevel and is not filled for the elements of period III.

The 3d-sublevel begins to be filled at the elements of the IV period, and 4d - at the elements of the V period (in accordance with the sequence):

19 K: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 ; 20 Ca: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 ;

21 Sc: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 1 ; 25 Mn: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5 ;

33 As: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p3; 43 Tc: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p6 5s 2 4d 5

Elements in which the d-sublevel is filled last are assigned to d -family and call d -elements .

4f is filled in only after the 57th element of the VI period:

57 La: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 5 5s 2 4d 10 5p 6 6s 2 5d 1 ;

58 Ce: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 5 5s 2 4d 10 5p 6 6s 2 5d 1 4f 1 ;

The population of the V quantum level by electrons proceeds similarly to period IV. Thus, the previously shown sequence of population of levels and sublevels by electrons is observed:

6s 2 5d 10 4f 14 6p 6

the population of a new quantum level by electrons always starts from the s-sublevel. For elements of a given period, only the s and p sublevels of the outer quantum level are populated by electrons;

the population of the d-sublevel is delayed by period I; 3d-sublevel is filled in for elements of period IV, 4d - sublevel for elements of period V, etc.;

the electron population f of the sublevel is delayed by 2 periods; The 4f-sublevel is populated by the elements of period VI, the 5f sublevel is populated by elements of period VII, and so on.

The distribution of electrons over energy levels explains the metallic as well as non-metallic properties of any elements.

Electronic formula

There is a certain rule according to which free and paired negative particles are placed at levels and sublevels. Let us consider in more detail the distribution of electrons over energy levels.
There are only two electrons in the first energy level. The filling of the orbital with them is carried out as the energy supply increases. The distribution of electrons in an atom of a chemical element corresponds to an ordinal number. The energy levels with the minimum number have the most pronounced force of attraction of valence electrons to the nucleus.

An example of compiling an electronic formula

Consider the distribution of electrons over energy levels using the example of a carbon atom. Its serial number is 6, therefore, there are six positively charged protons inside the nucleus. Given that carbon is a representative of the second period, it is characterized by the presence of two energy levels. The first has two electrons, the second has four.
Hund's rule explains the location in one cell of only two electrons that have different spins. There are four electrons in the second energy level. As a result, the distribution of electrons in an atom of a chemical element has the following form: 1s22s22p2.
There are certain rules according to which the distribution of electrons into sublevels and levels occurs.

Pauli principle

This principle was formulated by Pauli in 1925. The scientist stipulated the possibility of placing in the atom only two electrons that have the same quantum numbers: n, l, m, s. Note that the distribution of electrons over energy levels occurs as the amount of free energy increases.

Klechkovsky's rule

The filling of energy orbitals is carried out according to the increase in quantum numbers n + l and is characterized by an increase in the energy reserve.
Consider the distribution of electrons in a calcium atom.
In the normal state, its electronic formula is as follows:
Ca 1s2 2s2 2p6 3s2 3p6 3d0 4s2.
For elements of similar subgroups related to d- and f-elements, there is a “failure” of an electron from an external sublevel, which has a lower energy reserve, to the previous d- or f-sublevel. A similar phenomenon is typical for copper, silver, platinum, gold.
The distribution of electrons in an atom involves the filling of sublevels with unpaired electrons that have the same spins.
Only after the complete filling of all free orbitals with single electrons, the quantum cells are supplemented with second negative particles endowed with opposite spins.
For example, in the unexcited state of nitrogen:
1s2 2s2 2p3.
The properties of substances are influenced by the electronic configuration of valence electrons. By their number, you can determine the highest and lowest valency, chemical activity. If the element is in the main subgroup of the periodic table, you can use the group number to compose the external energy level, determine its oxidation state. For example, phosphorus, which is in the fifth group (the main subgroup), contains five valence electrons, therefore, it is able to accept three electrons or give five particles to another atom.
All representatives of the secondary subgroups of the periodic table act as exceptions to this rule.

Family Features

Depending on what structure the external energy level has, there is a division of all neutral atoms included in the periodic table into four families:

s-elements are in the first and second groups (main subgroups); the p-family is located in groups III-VIII (A subgroups); d-elements can be found in similar subgroups from groups I-VIII; the f-family consists of actinides and lanthanides.

All s-elements in the normal state have valence electrons in the s-sublevel. The p-elements are characterized by the presence of free electrons at the s- and p-sublevels.
The d-elements in the unexcited state have valence electrons both on the last s- and on the penultimate d-sublevel.

Conclusion

The state of any electron in an atom can be described using a set of basic numbers. Depending on the features of its structure, we can talk about a certain amount of energy. Using the rule of Hund, Klechkovsky, Pauli for any element included in the periodic table, you can make a configuration of a neutral atom.
The smallest energy reserve in the unexcited state is possessed by electrons located at the first levels. When a neutral atom is heated, the transition of electrons is observed, which is always accompanied by a change in the number of free electrons, leads to a significant change in the oxidation state of the element, a change in its chemical activity.

Since the nuclei of reacting atoms remain unchanged during chemical reactions, the chemical properties of atoms depend primarily on the structure of the electron shells of atoms. Therefore, we will dwell in more detail on the distribution of electrons in an atom, and mainly on those that determine the chemical properties of atoms (the so-called valence electrons), and, consequently, the periodicity in the properties of atoms and their compounds. We already know that the state of electrons can be described by a set of four quantum numbers, but to explain the structure of the electron shells of atoms, you need to know the following three main provisions: 1) the Pauli principle, 2) the principle of least energy, and 3) hit Hund. Pauli principle. In 1925, the Swiss physicist W. Pauli established a rule later called the Pauli principle (or the Pauli exclusion): there can be two electrons in the atom ve that have the same properties. Knowing that the properties of electrons are characterized by quantum numbers, the Pauli principle can also be formulated in this way: there cannot be two electrons in an atom, in which all four quantum numbers would be the same. At least one of the quantum numbers l, /, mt or m3 must necessarily differ. So, electrons with the same quantum - In what follows, we agree to graphically denote electrons having the values ​​s = + lj2> by the arrow T, and those having the values ​​J- ~ lj2 - by the arrow Two electrons having the same spins are often called electrons with parallel spins and are denoted by ft (or C). Two electrons having opposite spins are called electrons with aptiparallel spins and are denoted by | The J-th numbers l, I and mt must necessarily differ in spins. Therefore, in an atom there can be only two electrons with the same n, / and m, one with m = -1/2, the other with m = + 1/2. On the contrary, if the spins of two electrons are the same, one of the quantum numbers must differ: n, / or mh n= 1. Then /=0, mt-0 and t can have an arbitrary value: +1/2 or -1/2. We see that if n - 1, there can be only two such electrons. In the general case, for any given value of n, electrons primarily differ in the side quantum number /, which takes values ​​from 0 to n-1. For given whether/ there can be (2/+1) electrons with different values ​​of the magnetic quantum number m. This number must be doubled, since the given values ​​of l, /, and m( correspond to two different values ​​of the spin projection mx. Consequently, the maximum number of electrons with the same quantum number l is expressed by the sum. From this it is clear why there can be no more than 2 electrons on the first energy level, 8 on the second, 18 on the third, etc. Consider, for example, the hydrogen atom iH. There is one electron in the hydrogen atom iH, and the spin of this electron can be directed arbitrarily (i.e. ms ^ + ij2 or mt = -1 / 2), and the electron is in the s-co state at the first energy level with l- 1 (Recall once again that the first energy level consists of one sublevel - 15, the second energy level - of two sublevels - 2s and 2p, the third - of three sublevels - 3 *, Zru 3d, etc.). The sublevel, in turn, is divided into quantum cells * (energy states determined by the number of possible values ​​\u200b\u200bof m (, i.e. 2 / 4-1). It is customary to graphically represent a cell as a rectangle, the direction of the electron spin is arrows. Therefore, the state of an electron in an atom hydrogen iH can be represented as Ijt1, or, what is the same, By “quantum cell” you mean * an orbital characterized by the same set of values ​​of quantum numbers n, I and m * in each cell a maximum of two electrons with ayati-parallel spins can be placed, which is denoted by ti - The distribution of electrons in atoms In the helium atom 2He, the quantum numbers n-1, / \u003d 0 and m (-0) are the same for both of its electrons, and the quantum number m3 is different. Helium electron spin projections can be mt \u003d + V2 and ms \u003d - V2 The structure of the electron shell of the helium atom 2He can be represented as Is-2 or, which is the same, 1S AND Let us depict the structure of the electron shells of five atoms of the elements of the second period of the periodic table: The electron shells 6C, 7N, and VO must be filled in exactly this way, it is not obvious in advance. The given arrangement of spins is determined by the so-called Hund's rule (first formulated in 1927 by the German physicist F. Gund). Gund's rule. For a given value of I (that is, within a certain sublevel), the electrons are arranged in such a way that the total hundred * is maximum. If, for example, it is necessary to distribute three electrons in three / ^-cells of the nitrogen atom, then they will each be located in a separate cell, i.e., placed on three different p-orbitals: In this case, the total spin is 3/2, since its projection is m3 - 4-1/2 + A/2 + 1/2 = 3/2 * The same three electrons cannot be arranged in this way: 2p NI because then the projection of the total spin is mm = + 1/2 - 1/2+ + 1/2=1/2. For this reason, exactly as above, the electrons are located in the atoms of carbon, nitrogen and oxygen. Let us further consider the electronic configurations of atoms of the next third period. Starting with sodium uNa, the third energy level with the main quantum number n-3 is filled. The atoms of the first eight elements of the third period have the following electronic configurations: Consider now the electronic configuration of the first atom of the fourth period of potassium 19K. The first 18 electrons fill the following orbitals: ls12s22p63s23p6. Seemingly; that the nineteenth electron of the potassium atom must fall on the 3d sublevel, which corresponds to n = 3 and 1=2. However, in fact, the valence electron of the potassium atom is located in the 4s orbital. Further filling of the shells after the 18th element does not occur in the same sequence as in the first two periods. Electrons in atoms are arranged in accordance with the Pauli principle and Hund's rule, but in such a way that their energy is the smallest. The principle of least energy (the greatest contribution to the development of this principle was made by the domestic scientist V. M. Klechkovsky) - in an atom, each electron is located so that its energy is minimal (which corresponds to its greatest connection with the nucleus). The energy of an electron is mainly determined by the main quantum number n and the side quantum number /, therefore, those sublevels for which the sum of the values ​​of quantum numbers pi / is the smallest are filled first. For example, the energy of an electron at the 4s sublevel is less than at the 3d sublevel, since in the first case n+/=4+0=4, and in the second n+/=3+2= 5; at sublevel 5* (n+ /=5+0=5) the energy is less than at Ad (l + /=4+ 4-2=6); by 5p (l+/=5 +1 = 6) the energy is less than by 4/(l-f/= =4+3=7), etc. It was V. M. Klechkovsky who first in 1961 formulated a general proposition that an electron in the ground state occupies a level not with the minimum possible value of n, but with the smallest value of the sum n + / « In the case when the sums of the values ​​of pi / are equal for two sublevels, the sublevel with a lower value n. For example, at the sublevels 3d, Ap, 5s, the sum of the values ​​of pi/ is equal to 5. In this case, the sublevels with smaller values ​​of n are first filled, i.e., 3dAp-5s, etc. In Mendeleev’s periodic system of elements, the sequence of filling with electrons levels and sublevels is as follows (Fig. 2.4). Distribution of electrons in atoms. Scheme of filling energy levels and sublevels with electrons Therefore, according to the principle of least energy, in many cases it is energetically more profitable for an electron to occupy the sublevel of the “overlying” level, although the sublevel of the “lower” level is not filled: That is why in the fourth period the sublevel 4s is filled first and only after that the sublevel 3d .

First way: Electrons can easily be distributed into sublevels based on some rules. First, you need a color table. Let's imagine each element as one new electron, Each period is the corresponding level, s.p-electrons are always in their period, d-electrons one level lower (3 d-electrons are away in the 4th period), f-electrons are 2 levels lower . We just take a table and read based on the color of the element, for s, p-elements, the level number corresponds to the period number, if we reach the d-element, we write the level one less than the number of the period in which this element is located (if the element is in the 4th period, therefore 3 d). We also act with the f-element, only the level is indicated less than the period number by 2 values ​​(if the element is in the 6th period, therefore, 4 f).

Second way: It is necessary to display all sublevels in the form of one cell, and the levels should be arranged symmetrically under each other, sublevel under sublevel. In each cell, write the maximum number of electrons of a given sublevel. And the last step is to string the sublevels diagonally (from the top corner to the bottom) with an arrow. Read sublevels from top to bottom towards the tip of the arrow, up to the number of electrons of the desired atom.

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Master class on the topic:"The order in which electrons fill the energy levels of atoms".

Purpose of the lesson: Consider options for a faster form of writing a short electronic configuration of an atom.

Depending on which sublevel in the atom is filled last, all chemical elements are divided into 4 electronic families: s-, p-, d-, f-elements. The elements whose atoms have the s-sublevel of the outer level filled last are called s-elements. In s-elements, the valence electrons are the s-electrons of the outer energy level. For p-elements, the p-sublevel of the outer level is filled last. They have valence electrons located in the p- and s-sublevels of the outer level. For d-elements, the d-sublevel of the preexternal level is filled last, and the s-electrons of the external and d-electrons of the preexternal energy levels are valence. For f-elements, the f-sublevel of the third energy level from the outside is filled last.

The electronic configuration of an atom can also be depicted in the form of electron placement schemes in quantum cells, which are a graphical representation of the atomic orbital. Each quantum cell can contain no more than two electrons with oppositely directed spins ↓ . The order of placement of electrons within one sublevel is determined by the rule Hunda: within a sublevel, electrons are arranged so that their total spin is maximum. In other words, the orbitals of a given sublevel are filled first by one electron with the same spins, and then by the second electron with opposite spins.

There are several ways to write the electronic configuration of an atom.

First way:

For the selected element, according to its location in the periodic table of chemical elements of D.I. Mendeleev, you can write down the matrix of the structure of the electron shell of the atom corresponding to this period.

For example, the element iodine: 127 53 I 1s2s2p3s3p3d4s4p4d4f5s5p5d5f

According to the table, sequentially moving from element to element, you can fill in the matrix in accordance with the serial number of the element and the order in which the sublevels are filled:

127 53 I 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 4f 0 5s 2 5p 5 5d 0 5f 0

But, the sublevels are filled in the sequence s-f-d-p, and when using this method, we do not observe the sequence in filling the electron shells.

Second way:

It is possible to consider the order of filling levels and sublevels with electrons, using the concepts of the basic principle - the principle of the least energy reserve: the most stable state of an atom is in which its electrons have the lowest energy.

Those. based onPauli Ban, Hund Rules and Kleczkowski

Pauli ban : an atom cannot have two electrons whose four quantum numbers are the same (that is, each atomic orbital cannot be filled with more than two electrons, and with antiparallel spins.)

Hund's rule : electrons are located in identical orbitals in such a way that their total spin number is maximum, i.e. the most stable state of the atom corresponds to the maximum possible number of unpaired electrons with the same spins.

Rules of Klechkovsky: A) The filling of electron layers with electrons starts from the levels and sublevels with the lowest values ​​of n and l, and proceeds in ascending order n+l;

B) If for two orbitals the sum n + l turns out to be the same, then the orbital with a smaller value of n is filled first with electrons.

The first case does not show the sequence of filling sublevels, and the second one takes time to build a table.

Table number 2

The order in which electrons fill the energy levels of atoms.

quantum numbers		Sum of quantum numbers n+l	Orbital to be filled

In the distribution of electrons in an atom To in accordance with the Klechkovsky rule, 4s orbitals are preferred

Therefore, for an atom potassium the distribution of electrons in orbitals (electron-graphic formula) has the form

Scandium refers to d-elements, and its atom is characterized by the following distribution of electrons in orbitals:

Based on the Klechkovsky rule, we see the order of successive filling of sublevels. The first case does not show the sequence of filling sublevels, and the second one takes time to build a table. Therefore, I offer you more acceptable options for the sequential filling of orbitals.

First way : Electrons can easily be distributed into sublevels based on some rules. First, you need a color table. Let's imagine each element as one new electron, Each period is the corresponding level, s.p-electrons are always in their period, d-electrons one level lower (3 d-electrons are away in the 4th period), f-electrons are 2 levels lower . We just take a table and read based on the color of the element, for s, p-elements, the level number corresponds to the period number, if we reach the d-element, we write the level one less than the number of the period in which this element is located (if the element is in the 4th period, therefore 3 d). We also act with the f-element, only the level is indicated less than the period number by 2 values ​​(if the element is in the 6th period, therefore, 4 f).

Second way : It is necessary to display all sublevels in the form of one cell, and the levels should be arranged symmetrically under each other, sublevel under sublevel. In each cell, write the maximum number of electrons of a given sublevel. And the last step is to string the sublevels diagonally (from the top corner to the bottom) with an arrow. Read sublevels from top to bottom towards the tip of the arrow, up to the number of electrons of the desired atom.

The energy state and arrangement of electrons in shells or layers of atoms is determined by four numbers, which are called quantum numbers and are usually denoted by the symbols n, l, s and j; quantum numbers have a discontinuous or discrete character, i.e., they can only receive individual, discrete, values, integer or half-integer.

In relation to the quantum numbers n, l, s and j, it is also necessary to keep in mind the following:

1. Quantum number n is called principal; it is common to all electrons that make up the same electron shell; in other words, each of the electron shells of an atom corresponds to a certain value of the main quantum number, namely: for the electron shells K, L, M, N, O, P and Q, the main quantum numbers are respectively 1, 2, 3, 4, 5, 6 and 7. In the case of a single-electron atom (hydrogen atom), the principal quantum number serves to determine the orbit of the electron and, at the same time, the energy of the atom in the stationary state.

2. Quantum number I is called side, or orbital, and determines the moment of momentum of the electron, caused by its rotation around the atomic nucleus. The side quantum number can have the values ​​0, 1, 2, 3, . . . , and in general it is denoted by the symbols s, p, d, f, . . . Electrons having the same side quantum number form a subgroup, or, as is often said, are on the same energy sublevel.

3. The quantum number s is often called the spin number, since it determines the angular momentum of an electron caused by its own rotation (spin momentum).

4. The quantum number j is called internal and is determined by the sum of the vectors l and s.

Distribution of electrons in atoms(atomic shells) also follows some general provisions, of which it is necessary to indicate:

1. The Pauli principle, according to which an atom cannot have more than one electron with the same values ​​of all four quantum numbers, that is, two electrons in the same atom must differ in the value of at least one quantum number.

2. The energy principle, according to which in the ground state of an atom all its electrons must be at the lowest energy levels.

3. The principle of the number (number) of electrons in shells, according to which the limiting number of electrons in shells cannot exceed 2n 2, where n is the main quantum number of a given shell. If the number of electrons in some shell reaches the limit value, then the shell is filled and a new electron shell begins to form in the next elements.

In accordance with what was said, the table below gives: 1) letter designations of electron shells; 2) the corresponding values ​​of the main and side quantum numbers; 3) symbols of subgroups; 4) theoretically calculated maximum number of electrons both in individual subgroups and in shells as a whole. It must be pointed out that in the K, L, and M shells, the number of electrons and their distribution over subgroups, determined from experience, fully correspond to theoretical calculations, but significant discrepancies are observed in the following shells: the number of electrons in the f subgroup reaches the limit value only in the N shell, in the next shell, it decreases, and then the entire subgroup f disappears.

Shell

Subgroup

Number of electrons in a subgroup

Number of electrons in the shell (2n 2)

The table gives the number of electrons in shells and their distribution by subgroups for all chemical elements, including transuranic ones. The numerical data of this table were established as a result of very careful spectroscopic studies.

1st period
2nd period
3rd period
4th period
5th period
6th period
7th period

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A source of information: BRIEF PHYSICAL AND TECHNICAL HANDBOOK / Volume 1, - M .: 1960.