An atom has two unpaired electrons in the ground state. How to determine the number of unpaired electrons

how to determine the number of unpaired electrons in an atom and got the best answer

Answer from Rafael ahmetov [guru]
Using the Klechkovsky rule, write an electronic formula. This is easily determined by an electronic formula. For example, the electronic formula of carbon is 1s2 2s2 2p2, we see that the s-orbitals have 2 electrons each, that is, they are paired. There are 2 electrons on p-orbitals, but there are three 2-p orbitals. So, according to Gund's rule, 2 electrons will occupy 2 different p-orbitals, and carbon will have 2 unpaired electrons. Arguing similarly, we see that the nitrogen atom 1s2 2s2 2p3 has 3 unpaired electrons. Oxygen 1s2 2s2 2p4 has 4 electrons on p-orbitals. 3 electrons are located one at a time in different p-orbitals, and the fourth has no separate place. Therefore, he paired to one of the three, and the two remain unpaired. Similarly, fluorine 1s2 2s2 2p5 has one unpaired electron, while neon 1s2 2s2 2p6 has no unpaired electrons.
The d- and f-orbitals should be considered in exactly the same way (if they are involved in the electronic formula, and do not forget that there are five d-orbitals, and seven f-orbitals.

Answer from Vadim Belenetsky[guru]
it is not necessary to paint any element and then it will be seen whether there are unpaired electrons or not. For example, aluminum has a charge of +13. and the distribution by levels is -2.8.3. It is already clear that the p-electron on the last layer is unpaired. And in the same way check for all elements.

Answer from Enat Lezgintsev[newbie]
Vadim, can I get more details?

Answer from Egor Ershov[newbie]
The number of unpaired electrons is equal to the number of the group in which the element is located

Answer from 3 answers[guru]

Hey! Here is a selection of topics with answers to your question: how to determine the number of unpaired electrons in an atom

Indicate the quantum numbers (n, l, m (l), m (s)) of the electron, which is the last in the order of filling, and determine the number not
what is there to think? the last will be the 5p electron.
n = 5 (main square number = level number)

CONTROL WORK No. 1 Option-1

Exercise 1.

1. An eight-electron outer shell has an ion: 1) Р 3+ 2) S 2- 3) С 4+ 4) Fe 2+
2. The number of electrons in the iron ion Fe 2+ equals: 1) 54 2) 28 3) 58 4) 24
3. In the ground state, three unpaired electrons have an atom
1) silicon 2) phosphorus 3) sulfur 4) chlorine
4. Electronic configuration Is 2 2s 2 2p 6 3s 2 3p 6 corresponds to ion: 1) Сl - 2) N3 - 3) Br - 4) О 2-
5. The same electronic configuration of the external level has Ca 2+ and
1) K + 2) Ar 3) Ba 4) F -
6. Element, which corresponds to the higher oxide of composition R 2 O 7 has an external level electronic configuration: 1) ns 2 np 3 2) ns 2 np 5 3) ns 2 np 1 4) ns 2 np 2

7. The atom has the largest radius: 1) tin 2) silicon 3) lead 4) carbon
8.The smallest radius has an atom: 1) bromine 2) arsenic 3) barium 4) tin
9.At a sulfur atom, the number of electrons at the external energy level and the charge of the nucleus are equal, respectively 1) 4 and + 16 2) 6 and + 32 3) 6 and + 16 4) 4 and + 32
10. Particles have the same electronic structure
1) Na 0 and Na + 2) Na 0 and K 0 3) Na + and F - 4) Cr 2+ and Cr 3+
Task 2.

1. In ammonia and barium chloride, the chemical bond, respectively

1) ionic and covalent polar

2) covalent polar and ionic

3) covalent non-polar and metallic

4) covalent non-polar and ionic

2. Substances with only ionic bonds are listed in the series:

1) F 2, CCl 4, KS1

2) NaBr, Na 2 O, KI

3) SO 2, P 4, CaF 2

4) H 2 S, Br 2, K 2 S

3. In which row do all substances have a covalent polar bond?

1) HCl, NaCl, Cl 2

2) O 2, H 2 O, CO 2

3) H 2 O, NH 3, CH 4

4. A covalent non-polar bond is characteristic of

1) C1 2 2) SO3 3) CO 4) SiO 2

5. A substance with a covalent polar bond is

1) C1 2 2) NaBr 3) H 2 S 4) MgCl 2

6. A substance with a covalent non-polar bond has the formula

1) NH 3 2) Cu 3) H 2 S 4) I 2

7. Substances with a non-polar covalent bond are

1) water and diamond

2) hydrogen and chlorine

3) copper and nitrogen

4) bromine and methane

8.A chemical bond is formed between atoms with the same relative electronegativity

1) ionic

2) covalent polar

3) covalent non-polar

4) hydrogen

9. A chemical element in whose atom electrons are distributed over the layers as follows: 2, 8, 8, 2 forms a chemical bond with hydrogen

1) covalent polar

2) covalent non-polar

3) ionic

4) metal

10. Three common electron pairs form a covalent bond in the molecule

2) hydrogen sulfide

3) methane

4) chlorine

11.The compound has a molecular crystal lattice: 1) hydrogen sulfide; 2) sodium chloride; 3) quartz; 4) copper.

12. The hydrogen bond is not characteristic of the substance

1) Н 2 О 2) СН 4 3) NH 3 4) СНзОН

In substances: methane, fluorine. Determine the type of bond and the type of crystal lattice.

Task 3.

1.Choose substances that have an atomic crystal lattice.

1.Graphite 3.Diamond

2.Copper sulfate 4.Silicon oxide

2.Choose substances with an ionic crystal lattice:

1.silicon 2.sodium chloride 3.potassium hydroxide 4.aluminum sulfate

3.Atomic crystal lattice is characteristic for:

1.aluminum and graphite 2.sulfur and iodine

3.Silicon oxide and sodium chloride 4.Diamond and boron

4. Isotopes are:

1.ethane and ethene 2.O 16 and O 17

3.sodium and potassium 4.graphite and nitrogen

5. Substances with a metal crystal lattice, as a rule:

2.fusible and volatile
3. Solid and electrically conductive
4. Heat conductive and plastic

6.Install

NAME OF SUBSTANCE:	TYPE OF CHEMICAL BOND:
nitric oxide (II);	covalent non-polar;
B) sodium sulfide;	covalent polar;
	3) metal;
D) diamond
	5) hydrogen

CONTROL WORK No. 1 Option-2

Exercise 1.

1. An ion has a two-electron outer shell: 1) S 6+ 2) S 2- 3) Br 5+ 4) Sn 4+
2. Electronic configuration Is 2 2s 2 2p 6 3s 2 3p 6 corresponds to ion
1) Sn 2+ 2) S 2- 3) Cr 3+ 4) Fe 2
3. Element with electronic configuration of external level ... 3s 2 3p 3 forms a hydrogen compound of the composition: 1) EN 4 2) EN 3) EN 3 4) EN 2
2 2s 2 2p 6 corresponds to ion
1) А 3+ 2) Fe 3+ 3) Zn 2+ 4) Cr 3+
5. A metal atom, the higher oxide of which is Me 2 O 3 , has an electronic formula for the external energy level: 1) ns 2 pr 1 2) ns 2 pr 2 3) ns 2 np 3 4) ns 2 np
6. Higher oxide of composition R 2 O 7 forms a chemical element in the atom of which the filling of energy levels with electrons corresponds to a number of numbers:
1) 2, 8, 1 2) 2, 8, 7 3) 2, 8, 8, 1 4) 2, 5
7. In the series of chemical elements Na -> Mg -> Al -> Si
1) the number of valence electrons in atoms increases
2) the number of electronic layers in atoms decreases
3) the number of protons in the nuclei of atoms decreases
4) the radii of the atoms increase
8.Electronic configuration 1s 2 2s 2 2p 6 3.s 2 Zr 6 3d 1 has ion
1) Ca 2+ 2) A 3+ 3) K + 4) Sc 2+
9. The number of valence electrons in manganese is equal to: 1) 1 2) 3 3) 5 4) 7

10. What electronic configuration does the atom of the most active metal have?

Task 2.

1) dimethyl ether

2) methanol

3) ethylene

4) ethyl acetate

2.1) HI 2) HC1 3) HF 4) HBr

3. A covalent polar bond is characteristic for each of the two substances, the formulas of which

1) KI and H 2 O

2) CO 2 and K 2 O

3) H 2 S and Na 2 S

4) CS 2 and PC1 5

1) C 4 H 10, NO 2, NaCl

2) CO, CuO, CH 3 Cl

3) BaS, C 6 H 6, H 2

4) C 6 H 5 NO 2, F 2, CC1 4

5. Each of the substances indicated in the series has a covalent bond:

1) CaO, C 3 H 6, S 8

2) Fe.NaNO 3, CO

3) N 2, CuCO 3, K 2 S

4) C 6 H 5 N0 2, SO 2, CHC1 3

6. Each of the substances indicated in the series has a covalent bond:

1) С 3 Н 4, NO, Na 2 O

2) CO, CH 3 C1, PBr 3

3) P 2 Oz, NaHSO 4, Cu

4) C 6 H 5 NO 2, NaF, CC1 4

7. Substances of molecular structure are characterized by

1) high melting point 2) low melting point 3) hardness

4) electrical conductivity.

8. In which row are the formulas of substances with only covalent polar
communication? 1) C1 2, NO 2, HC1 2) HBr, NO, Br 2 3) H 2 S, H 2 O, Se 4) HI, H 2 O, PH 3

9. A substance with an ionic bond is: 1) Ca 2) MgS 3) H 2 S 4) NH 3

10. Each of two substances has an atomic crystal lattice:

2) diamond and silicon

3) chlorine and iodine

11. Compounds with a covalent polar and covalent non-polar bond are, respectively:

1) water and hydrogen sulfide

2) potassium bromide and nitrogen

3) ammonia and hydrogen

4) oxygen and methane

12. A chemical element in whose atom electrons are distributed over the layers as follows: 2, 8, 1 forms a chemical bond with hydrogen

13. Make diagrams of the formation of connections in substances: sodium nitride, oxygen. Determine the type of bond and the type of crystal lattice.

Task 3.

2 .In the sites of different crystal lattices can be

1.atoms 2.electrons 3.protons 4.ions 5.molecules

3. Allotropy is called:

1.existence of several stable isotopes for atoms of the same element

2.the ability of the atoms of an element to form several complex substances with the atoms of another element

3.the existence of several complex substances, the molecules of which have the same composition, but different chemical structure

4.the existence of several simple substances formed by atoms of the same element

1.molecular 2.atomic

3.ionic 4.metallic

1.Refractory and highly soluble in water

6.Installcorrespondence between the name of a substance and the type of chemical bond in it.

NAME OF SUBSTANCE:	TYPE OF CHEMICAL BOND:
A) ammonium sulfate;	covalent non-polar;
B) aluminum;	covalent polar;
B) ammonia;	3) metal;
D) graphite.
	5) hydrogen

7. Are the following judgments about the structure and properties of substances in the solid state true?

A. Both ammonium chloride and carbon (II) oxide have an ionic crystal lattice.

B. Substances with molecular crystal lattices are characterized by high hardness.

Only A is true; 3) both judgments are correct;

only B is true; 4) both judgments are wrong.

CONTROL WORK No. 1 Option-3

Exercise 1.

1. The number of energy layers and the number of electrons in the outer energy layer of arsenic atoms are equal, respectively: 1) 4, 6 2) 2, 5 3) 3, 7 4) 4, 5
2. What electronic configuration does the atom of the most active metal have?
1) 1s 2 2s 2 2p 1 2) 1s 2 2s 2 2p 6 3s 1 3) 1s 2 2s 2 4) 1s 2 2s 2 2p 6 3s 2 3p 1
3. The number of electrons in an atom is determined
1) the number of protons 2) the number of neutrons 3) the number of energy levels 4) the value of the relative atomic mass
4. The nucleus of the atom 81 Br contains: 1) 81p and 35n 2) 35p and 46n 3) 46p and 81n 4) 46p and 35n
5. Ion, which contains 16 protons and 18 electrons, has a charge
1) +4 2) -2 3) +2 4) -4
6. External energy level of an atom of an element that forms a higher oxide of the composition EO s , has the formula 1) ns 2 np 1 2) ns 2 nр 2 3) nз 2 nр 3 4) ns 2 nр 4
7. Configuration of the outer electron layer of the sulfur atom in the unexcited state
1) 4s 2 2) 3s 2 3p 6 3) 3s 2 3p 4 4) 4s 2 4p 4
8. Electronic configuration Is 2 2s 2 2p 6 3s 2 3p 6 4s 1 has an atom in the ground state
1) lithium 2) sodium 3) potassium 4) calcium
9. The number of protons and neutrons contained in the nucleus of an isotope atom 40 K, is equal respectively: 1) 19 and 40 2) 21 and 19 3) 20 and 40 4) 19 and 21
10. A chemical element, one of the isotopes of which has a mass number of 44 and contains 24 neutrons in its nucleus, is: 1) chromium 2) calcium 3) ruthenium 4) scandium

Task 2.

1. In ammonia and barium chloride, the chemical bond, respectively

2. The polarity of the bond is most pronounced in the molecule: 1) HI 2) HC1 3) HF 4) HBr

3. Substances with only ionic bonds are listed in the series:

1) F 2, CCl 4, KS1

2) NaBr, Na 2 O, KI

3) SO 2, P 4, CaF 2

4) H 2 S, Br 2, K 2 S

4. Each of the substances indicated in the series has covalent bonds:

1) C 4 H 10, NO 2, NaCl

2) CO, CuO, CH 3 Cl

3) BaS, C 6 H 6, H 2

4) C 6 H 5 NO 2, F 2, CC1 4

5. In which row do all substances have a covalent polar bond?

1) HCl, NaCl, Cl 2

2) O 2, H 2 O, CO 2

3) H 2 O, NH 3, CH 4

6. A covalent non-polar bond is characteristic for: 1) C1 2 2) SO3 3) CO 4) SiO 2

7. A substance with a covalent polar bond is: 1) C1 2 2) NaBr 3) H 2 S 4) MgCl 2

8. A substance with a covalent non-polar bond has the formula: 1) NH 3 2) Cu 3) H 2 S 4) I 2

9. Hydrogen bonds are formed between molecules

1) dimethyl ether

2) methanol

3) ethylene

4) ethyl acetate

10. Each of two substances has a molecular crystal lattice:

1) silicon oxide (IV) and carbon monoxide (IV)

2) ethanol and methane

3) chlorine and iodine

4) potassium chloride and iron (III) fluoride

11. Compounds with covalent non-polar and covalent polar bonds are, respectively:

1) water and hydrogen sulfide

2) potassium bromide and nitrogen

3) ammonia and hydrogen

4) oxygen and methane

12. A chemical element in whose atom electrons are distributed over the layers as follows:

2, 8,8,1 forms a chemical bond with hydrogen

1) covalent polar 2) covalent non-polar 3) ionic 4) metallic

13. Make diagrams of the formation of connections in substances: sodium oxide, oxygen. Determine the type of bond and the type of crystal lattice.

Task 3.

1.The crystal lattice of both sulfur (IV) oxide and sulfur (VI) oxide in the solid state:

ionic; 3) molecular;

metal; 4) atomic.

2.The formula of a substance with a molecular crystal lattice in the solid state:

1) Li; 2) NaCl; 3) Si; 4) CH 3 OH.

3. Each of two substances has an ionic crystal lattice, the formulas of which are:

H 2 S and HC1; 3) CO 2 and O 2;

KBr and NH 4 NO 3; 4) N 2 and NH 3.

4. The metal crystal lattice has:

graphite; 3) aluminum;

silicon; 4) iodine.

5.Installcorrespondence between the name of a substance and the type of chemical bond in it.

NAME OF SUBSTANCE:	TYPE OF CHEMICAL BOND:
A) potassium tetrohydroxoaluminate;	covalent non-polar;
B) aluminum;	covalent polar;
	3) metal;
D) graphite.
	5) hydrogen

6. Are the following judgments about the structure and properties of substances in the solid state true?

A. Both bromine and magnesium are non-molecular substances.

B. Substances with an atomic crystal lattice are characterized by high hardness.

Only A is true; 3) both judgments are correct;

only true B; 4) both judgments are wrong.

7. Substance having a non-molecular structure:

hydrogen sulfide; 3) sulfur oxide (IV);

potassium bromide; 4) rhombic sulfur.

CONTROL WORK No. 1 Option-4

Exercise 1.

1. Substance formed by ionic bond:

1) ammonia; 3) nitrogen;

2) lithium nitride; 4) nitric oxide (IV).

2. Formula of a substance formed by a covalent non-polar bond:

1) Br 2; 2) KS1; 3) SO 3; 4) Ca.

3. Formula of a substance formed by a covalent polar bond:

1) NaI; 2) SO 2; 3) Al; 4) R 4.

4. Formula of a substance formed by a metal bond:

1) About 3; 2) S 8; 3) C; 4) Ca.

5. Substance, between the molecules of whichnot formed hydrogen bond:

ethanol;

acetic acid;

Compounds with covalent non-polar and covalent polar bonds are, respectively:

1) methane and chloromethane; 3) methane and graphite;

2) nitrogen and ammonia; 4) diamond and graphite.

Compounds with ionic and covalent polar bonds are, respectively:

calcium fluoride and barium oxide;
potassium bromide and hydrogen sulfide;
sodium iodide and iodine;
carbon monoxide (II) and sodium sulfide.

Each of the substances is formed by a covalent polar bond, the formulas of which are:

H 2, O 2, S 8; 3) NaCl, CaS, K 2 O;
CO 2, SiCl 4, HBr; 4) HCl, NaCl, PH 3.

Each of two substances is formed by ionic bond:

hydrogen bromide and carbon monoxide (IV);
barium and cobalt;
magnesium nitride and barium sulfide;
sodium chloride and phosphine.

A hydrogen bond is characteristic for each of two substances, the formulas of which are:

CO 2 and H 2 S; 3) H 2 O and C 6 H 6;
C 2 H 6 and HCHO; 4) HF and CH 3 OH.

Chemical bond in the combination of bromine with an element, the electronic formula of the outer electron layer of which is 4 s 2 4 p 5 :

covalent non-polar;
covalent polar;
metal.

Chemical bond in the combination of carbon with an element, the electronic formula of the outer electron layer of which is 3 s 2 3 p 5 :

metal;
covalent non-polar;
covalent polar.

13. The most pronounced character of the ionic bond:

in calcium chloride;

in calcium fluoride;

in calcium bromide;

in calcium iodide.

Task 3.

1. In ammonia and barium chloride, the chemical bond, respectively

1) ionic and covalent polar

2) covalent polar and ionic

3) covalent non-polar and metallic

4) covalent non-polar and ionic

2. The polarity of the bond is most pronounced in the molecule: 1) HI 2) HC1 3) HF 4) HBr

3. Substances with only ionic bonds are listed in the series:

1) F 2, CCl 4, KS1

2) NaBr, Na 2 O, KI

3) SO 2, P 4, CaF 2

4) H 2 S, Br 2, K 2 S

4. If a substance is readily soluble in water, has a high melting point, and is electrically conductive, then its crystal lattice:

1.molecular 2.atomic

3.ionic 4.metallic

5. Substances with a molecular crystal lattice, as a rule:

1.Refractory and highly soluble in water
2. fusible and volatile 3. Solid and electrically conductive

6.Installcorrespondence between the name of a substance and the type of chemical bond in it.

NAME OF SUBSTANCE:	TYPE OF CHEMICAL BOND:
A) ammonium sulfate;	covalent non-polar;
B) aluminum;	covalent polar;
B) ammonia;	3) metal;
D) graphite.
	5) hydrogen

7. Are the following judgments about the composition, structure and properties of substances in the solid state correct?

A. Substances with atomic crystal lattices can be both simple and complex.

B. Substances with an ionic crystal lattice are characterized by low melting points.

Only A is true; 3) both judgments are correct;
only B is true; 4) both judgments are wrong.

For the correct answer for each of the tasks 1-8, 12-16, 20, 21, 27-29, 1 point is given.

Tasks 9-11, 17-19, 22-26 are considered completed correctly if the sequence of numbers is indicated correctly. For a complete correct answer in tasks 9–11, 17–19, 22–26, 2 points are given; if one mistake was made - 1 point; for an incorrect answer (more than one mistake) or its absence - 0 points.

Theory on assignment:

1) F 2) S 3) I 4) Na 5) Mg

Determine which atoms of the indicated elements in the ground state until the completion of the outer electron layer lacks one electron.

The eight-electron shell corresponds to the shell of an inert gas. For each of the substances in the period in which they are located, an inert gas corresponds, for fluorine neon, for sulfur argon, for iodine xenon, for sodium and magnesium argon, but of the listed elements, only fluorine and iodine lack one electron to the eight-electron shell, since they are in the seventh group.

To complete the task, use the following series of chemical elements. The answer in the task is a sequence of three numbers, under which the chemical elements in this row are indicated.

1) Be 2) H 3) N 4) K 5) C

Determine which atoms of these elements in the ground state contain the same number of unpaired electrons.

4 Be Beryllium: 1s 2 2s 2

7 N Nitrogen: 1s 2 2s 2 2p 3

Number of unpaired electrons - 1

6 C Carbon: 1s 2 2s 2 2p 2

1s 2	2s 2	2p 3
↓	↓

The number of unpaired electrons - 2

Hence, it is obvious that for hydrogen and for potassium the number of unpaired electrons is the same.

To complete the task, use the following series of chemical elements. The answer in the task is a sequence of three numbers, under which the chemical elements in this row are indicated.

1) Ge 2) Fe 3) Sn 4) Pb 5) Mn

Determine which atoms of the indicated in the series of elements valence electrons are located both on s- and d-sublevels.

To solve this task, it is necessary to paint the upper electronic level of the elements:

32 Ge Germanium: 3d 10 4s 2 4p 2
26 Fe Iron: 3d 6 4s 2
50 Sn Tin: 4d 10 5s 2 5p 2
82 Pb Lead: 4f 14 5d 10 6s 2 6p 2
25 Mn Manganese: 3d 5 4s 2

In iron and manganese, valence electrons are at the s and d sublevels.

To complete the task, use the following series of chemical elements. The answer in the task is a sequence of three numbers, under which the chemical elements in this row are indicated.

1) Br 2) Si 3) Mg 4) C 5) Al

Determine which atoms of the indicated in the series of elements in the excited state have the electronic formula of the external energy level ns 1 np 3

For an unexcited state, the electronic formula ns 1 np 3 will represent ns 2 np 2, it is the elements of such a configuration that we need. Let's write down the upper electronic level of the elements (or simply find the elements of the fourth group):

35 Br Bromine: 3d 10 4s 2 4p 5
14 Si Silicon: 3s 2 3p 2
12 Mg Magnesium: 3s 2
6 C Carbon: 1s 2 2s 2 2p 2
13 Al Aluminum: 3s 2 3p 1

For silicon and carbon, the upper energy level coincides with the desired

To complete the task, use the following series of chemical elements. The answer in the task is a sequence of three numbers, under which the chemical elements in this row are indicated.

1) Si 2) F 3) Al 4) S 5) Li

Paired electrons

If there is one electron in the orbital, then it is called unpaired and if two - then this paired electrons.

Four quantum numbers n, l, m, m s fully characterize the energy state of an electron in an atom.

Considering the structure of the electron shell of many-electron atoms of various elements, it is necessary to take into account three main points:

· Pauli's principle,

The principle of least energy,

Gund's rule.

According to Pauli principle an atom cannot have two electrons with the same values of all four quantum numbers.

Pauli's principle determines the maximum number of electrons in one orbital, level and sublevel. Since AO is characterized by three quantum numbers n, l, m, then the electrons of a given orbital can differ only in the spin quantum number m s... But the spin quantum number m s can only have two values + 1/2 and - 1/2. Consequently, in one orbital there can be no more than two electrons with different values of the spin quantum numbers.

Rice. 4.6. The maximum capacity of one orbital is 2 electrons.

The maximum number of electrons at the energy level is defined as 2 n 2, and on the sublevel - as 2 (2 l+ 1). The maximum number of electrons located at different levels and sublevels is given in table. 4.1.

Table 4.1.

Maximum number of electrons at quantum levels and sublevels

Energy level	Energy sublevel	Possible values of the magnetic quantum number m	The number of orbitals per	The maximum number of electrons per
sublevel	level	sublevel	level
K (n=1)	s (l=0)
L (n=2)	s (l=0) p (l=1)	–1, 0, 1
M (n=3)	s (l=0) p (l=1) d (l=2)	–1, 0, 1 –2, –1, 0, 1, 2
N (n=4)	s (l=0) p (l=1) d (l=2) f (l=3)	–1, 0, 1 –2, –1, 0, 1, 2 –3, –2, –1, 0, 1, 2, 3

The sequence of filling the orbitals with electrons is carried out in accordance with the principle of least energy .

According to the principle of least energy, electrons fill the orbitals in order of increasing energy.

The order of filling the orbitals is determined the Klechkovsky rule: the increase in energy and, accordingly, the filling of the orbitals occurs in the increasing order of the sum of the principal and orbital quantum numbers (n + l), and for an equal sum (n + l) - in the increasing order of the principal quantum number n.

For example, the energy of an electron at the 4s sublevel is less than at the 3 d, since in the first case the sum n+ l = 4 + 0 = 4 (recall that for s-sublevel value of the orbital quantum number l= = 0), and in the second n+ l = 3 + 2 = 5 ( d- sublevel, l= 2). Therefore, sublevel 4 is first filled s and then 3 d(see figure 4.8).

On sublevels 3 d (n = 3, l = 2) , 4R (n = 4, l= 1) and 5 s (n = 5, l= 0) the sum of the values NS and l are the same and equal to 5. In the case of equality of the values of the sums n and l first the sublevel with the minimum value is filled n, i.e. sublevel 3 d.

In accordance with the Klechkovsky rule, the energy of atomic orbitals increases in the following order:

1s < 2s < 2R < 3s < 3R < 4s < 3d < 4R < 5s < 4d < 5p < 6s < 5d »

"4 f < 6p < 7s….

Depending on which sublevel in the atom is filled in the last turn, all chemical elements are divided into 4 electronic families : s-, p-, d-, f-elements.

4 4d

3 4s

1 2s

Sublevel levels

Rice. 4.8. Energy of atomic orbitals.

The elements in whose atoms the s-sublevel of the outer level is last filled are called s-elements ... Have s valence elements are s-electrons of the external energy level.

Have p-elements the last is the p-sublevel of the external level. Their valence electrons are located on p- and s-sub-levels of the external level. Have d-elements are last filled in d-sublevel of the pre-external level and valence are s-electrons of the external and d- electrons of pre-external energy levels.

Have f-elements the last to be filled f-sublevel of the third energy level outside.

The order of placement of electrons within one sublevel is determined Gund's rule:

within the sublevel, electrons are placed in such a way that the sum of their spin quantum numbers would have a maximum value in absolute value.

In other words, the orbitals of this sublevel are filled first by one electron with the same value of the spin quantum number, and then by the second electron with the opposite value.

For example, if it is necessary to distribute 3 electrons in three quantum cells, then each of them will be located in a separate cell, i.e. occupy a separate orbital:

∑m s= ½ – ½ + ½ = ½.

The order of distribution of electrons over energy levels and sublevels in the shell of an atom is called its electronic configuration, or electronic formula. Making up electronic configuration room energy level (principal quantum number) are designated by numbers 1, 2, 3, 4 ..., sublevel (orbital quantum number) - by letters s, p, d, f... The number of electrons on a sublevel is indicated by a number that is written at the top of the symbol for the sublevel.

The electronic configuration of an atom can be depicted in the form of the so-called electronic-graphic formula... This is a diagram of the arrangement of electrons in quantum cells, which are a graphical representation of an atomic orbital. Each quantum cell can contain no more than two electrons with different values of the spin quantum numbers.

To draw up an electronic or electronic-graphic formula for any element, you should know:

1. The ordinal number of the element, i.e. the charge of its nucleus and the corresponding number of electrons in the atom.

2. The number of the period, which determines the number of energy levels of the atom.

3. Quantum numbers and the relationship between them.

So, for example, a hydrogen atom with serial number 1 has 1 electron. Hydrogen is an element of the first period, therefore the only electron is located at the first energy level s-orbital having the lowest energy. The electronic formula of the hydrogen atom will be:

1 H 1 s 1 .

The electronic-graphical formula of hydrogen will be as follows:

Electronic and electron-graphic formulas of the helium atom:

2 Not 1 s 2

2 Not 1 s

reflect the completeness of the electronic shell, which determines its stability. Helium is a noble gas characterized by high chemical resistance (inertness).

The lithium atom 3 Li has 3 electrons, this is an element of the II period, which means that the electrons are located at 2 energy levels. Two electrons fill s- sublevel of the first energy level and the 3rd electron is located on s- sublevel of the second energy level:

3 Li 1 s 2 2s 1

Valence I

A lithium atom has an electron located at 2 s-sublevel, is less strongly bound to the nucleus than electrons of the first energy level, therefore, in chemical reactions, a lithium atom can easily donate this electron, turning into an Li + ion ( and he -electrically charged particle ). In this case, the lithium ion acquires a stable complete shell of the noble gas helium:

3 Li + 1 s 2 .

It should be noted that, the number of unpaired (single) electrons determines element valence , i.e. its ability to form chemical bonds with other elements.

So, a lithium atom has one unpaired electron, which determines its valency equal to one.

The electronic formula of the beryllium atom is:

4 Be 1s 2 2s 2.

Electron-graphic formula of the beryllium atom:

2 Valence is mainly

State is 0

Beryllium loses electrons of sublevel 2 more easily than others. s 2, forming the Be +2 ion:

It can be noted that the helium atom and lithium ions 3 Li + and beryllium 4 Be +2 have the same electronic structure, i.e. characterized by isoelectronic structure.