Fluorine is a chemical bond. Types of chemical bond

Task number 1

From the proposed list, select two compounds in which there is an ionic chemical bond.

• 1. Ca(ClO 2) 2
• 2. HClO 3
• 3.NH4Cl
• 4. HClO 4
• 5.Cl2O7

Answer: 13

In the vast majority of cases, the presence of an ionic type of bond in a compound can be determined by the fact that its structural units simultaneously include atoms of a typical metal and non-metal atoms.

On this basis, we establish that there is an ionic bond in compound number 1 - Ca(ClO 2) 2, because in its formula, one can see atoms of a typical calcium metal and atoms of non-metals - oxygen and chlorine.

However, there are no more compounds containing both metal and non-metal atoms in this list.

Among the compounds indicated in the assignment there is ammonium chloride, in which the ionic bond is realized between the ammonium cation NH 4 + and the chloride ion Cl − .

Task number 2

From the proposed list, select two compounds in which the type of chemical bond is the same as in the fluorine molecule.

1) oxygen

2) nitric oxide (II)

3) hydrogen bromide

4) sodium iodide

Write down the numbers of the selected connections in the answer field.

Answer: 15

The fluorine molecule (F 2) consists of two atoms of one non-metal chemical element, therefore the chemical bond in this molecule is covalent non-polar.

A covalent non-polar bond can only be realized between atoms of the same chemical element of a non-metal.

Of the proposed options, only oxygen and diamond have a covalent non-polar type of bond. The oxygen molecule is diatomic, consists of atoms of one chemical element of a non-metal. Diamond has an atomic structure and in its structure each carbon atom, which is a non-metal, is bonded to 4 other carbon atoms.

Nitric oxide (II) is a substance consisting of molecules formed by atoms of two different non-metals. Since the electronegativity of different atoms is always different, the shared electron pair in the molecule is shifted towards the more electronegative element, in this case oxygen. Thus, the bond in the NO molecule is covalent polar.

Hydrogen bromide also consists of diatomic molecules made up of hydrogen and bromine atoms. The shared electron pair forming the H-Br bond is shifted to the more electronegative bromine atom. The chemical bond in the HBr molecule is also covalent polar.

Sodium iodide is an ionic substance formed by a metal cation and an iodide anion. The bond in the NaI molecule is formed due to the transfer of an electron from 3 s-orbitals of the sodium atom (the sodium atom turns into a cation) to an underfilled 5 p-orbital of the iodine atom (the iodine atom turns into an anion). Such a chemical bond is called ionic.

Task number 3

From the proposed list, select two substances between the molecules of which hydrogen bonds are formed.

• 1. C 2 H 6
• 2.C2H5OH
• 3.H2O
• 4. CH 3 OCH 3
• 5. CH 3 COCH 3

Write down the numbers of the selected connections in the answer field.

Answer: 23

Explanation:

Hydrogen bonds take place in substances of a molecular structure, in which there are covalent bonds H-O, H-N, H-F. Those. covalent bonds of the hydrogen atom with the atoms of the three chemical elements with the highest electronegativity.

Thus, obviously, there are hydrogen bonds between molecules:

2) alcohols

3) phenols

4) carboxylic acids

5) ammonia

6) primary and secondary amines

7) hydrofluoric acid

Task number 4

From the proposed list, select two compounds with an ionic chemical bond.

• 1. PCl 3
• 2.CO2
• 3.NaCl
• 4. H 2 S
• 5. MgO

Write down the numbers of the selected connections in the answer field.

Answer: 35

Explanation:

In the overwhelming majority of cases, it can be concluded that there is an ionic type of bond in a compound by the fact that the composition of the structural units of a substance simultaneously includes atoms of a typical metal and non-metal atoms.

On this basis, we establish that there is an ionic bond in compound number 3 (NaCl) and 5 (MgO).

Note*

In addition to the above feature, the presence of an ionic bond in a compound can be said if its structural unit contains an ammonium cation (NH 4 +) or its organic analogs - alkyl ammonium RNH 3 +, dialkylammonium R 2 NH 2 +, trialkylammonium R 3 NH cations + or tetraalkylammonium R 4 N + , where R is some hydrocarbon radical. For example, the ionic type of bond takes place in the compound (CH 3) 4 NCl between the cation (CH 3) 4 + and the chloride ion Cl - .

Task number 5

From the proposed list, select two substances with the same type of structure.

4) table salt

Write down the numbers of the selected connections in the answer field.

Answer: 23

Task number 8

From the proposed list, select two substances of non-molecular structure.

2) oxygen

3) white phosphorus

5) silicon

Write down the numbers of the selected connections in the answer field.

Answer: 45

Task number 11

From the proposed list, select two substances in the molecules of which there is a double bond between carbon and oxygen atoms.

3) formaldehyde

4) acetic acid

5) glycerin

Write down the numbers of the selected connections in the answer field.

Answer: 34

Task number 14

From the proposed list, select two substances with an ionic bond.

1) oxygen

3) carbon monoxide (IV)

4) sodium chloride

5) calcium oxide

Write down the numbers of the selected connections in the answer field.

Answer: 45

Task number 15

From the proposed list, select two substances with the same type of crystal lattice as diamond.

1) silica SiO 2

2) sodium oxide Na 2 O

3) carbon monoxide CO

4) white phosphorus P 4

5) silicon Si

Write down the numbers of the selected connections in the answer field.

Answer: 15

Task number 20

From the proposed list, select two substances in the molecules of which there is one triple bond.

• 1. HCOOH
• 2.HCOH
• 3. C 2 H 4
• 4. N 2
• 5.C2H2

Write down the numbers of the selected connections in the answer field.

Answer: 45

Explanation:

In order to find the correct answer, let's draw the structural formulas of the compounds from the list presented:

Thus, we see that the triple bond exists in the molecules of nitrogen and acetylene. Those. correct answers 45

Task number 21

From the proposed list, select two substances in the molecules of which there is a covalent non-polar bond.

The work selected tasks on chemical bonds.

Pugacheva Elena Vladimirovna

Development Description

6. A covalent non-polar bond is characteristic of

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

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

3) ionic 4) metallic

15. Three common electron pairs form a covalent bond in a molecule

16. Hydrogen bonds are formed between molecules

1) HI 2) HCl 3) HF 4) HBr

1) water and diamond 2) hydrogen and chlorine 3) copper and nitrogen 4) bromine and methane

19. Hydrogen bond not typical for substance

1) fluorine 2) chlorine 3) bromine 4) iodine

1) CF 4 2) CCl 4 3) CBr 4 4) CI 4

1) 1 2) 2 3) 3 4) 4

1) 1 2) 2 3) 3 4) 4

32. Atoms of chemical elements of the second period of the periodic system D.I. Mendeleev form compounds with an ionic chemical bond of composition 1) LiF 2) CO 2 3) Al 2 O 3 4) BaS

1) ionic 2) metallic

43. An ionic bond is formed by 1) H and S 2) P and C1 3) Cs and Br 4) Si and F

when interacting

1) ionic 2) metallic

1) ionic 2) metallic

NAME OF THE SUBSTANCE TYPE OF COMMUNICATION

1) zinc A) ionic

2) nitrogen B) metal

62. Match

TYPE OF COMMUNICATION CONNECTION

1) ionic A) H 2

2) metal B) Va

3) covalent polar B) HF

66. The strongest chemical bond takes place in the molecule 1) F 2 2) Cl 2 3) O 2 4) N 2

67. Bond strength increases in the series 1) Cl 2 -O 2 -N 2 2) O 2 - N 2- Cl 2 3) O 2 -Cl 2 -N 2 4) Cl 2 -N 2 -O 2

68. Indicate a series characterized by an increase in the length of a chemical bond

1) O 2, N 2, F 2, Cl 2 2) N 2, O 2, F 2, Cl 2 3) F 2, N 2, O 2, Cl 2 4) N 2, O 2, Cl 2, F2

Let's analyze tasks No. 3 from the USE options for 2016.

Tasks with solutions.

Task number 1.

Compounds with a covalent non-polar bond are located in the series:

1. O2, Cl2, H2

2. HCl, N2, F2

3. O3, P4, H2O

4.NH3, S8, NaF

Explanation: we need to find such a series in which there will be only simple substances, since a covalent non-polar bond is formed only between atoms of the same element. The correct answer is 1.

Task number 2.

Substances with a covalent polar bond are listed in the series:

1. CaF2, Na2S, N2

2. P4, FeCl2, NH3

3. SiF4, HF, H2S

4. NaCl, Li2O, SO2

Explanation: here you need to find a series in which only complex substances and, moreover, all non-metals. The correct answer is 3.

Task number 3.

The hydrogen bond is characteristic of

1. Alkanes 2. Arenes 3. Alcohols 4. Alkynes

Explanation: A hydrogen bond is formed between a hydrogen ion and an electronegative ion. Such a set, among those listed, is only for alcohols.

The correct answer is 3.

Task number 4.

Chemical bond between water molecules

1. Hydrogen

2. Ionic

3. Covalent polar

4. Covalent non-polar

Explanation: a covalent polar bond is formed between the O and H atoms in water, since these are two non-metals, but a hydrogen bond is formed between water molecules. The correct answer is 1.

Task number 5.

Only covalent bonds have each of the two substances:

1. CaO and C3H6

2. NaNO3 and CO

3. N2 and K2S

4.CH4 and SiO2

Explanation: compounds must consist only of non-metals, i.e. the correct answer is 4.

Task number 6.

A substance with a covalent polar bond is

1. O3 2. NaBr 3. NH3 4. MgCl2

Explanation: A polar covalent bond is formed between atoms of different non-metals. The correct answer is 3.

Task number 7.

A non-polar covalent bond is characteristic of each of the two substances:

1. Water and diamond

2. Hydrogen and chlorine

3. Copper and nitrogen

4. Bromine and methane

Explanation: a non-polar covalent bond is characteristic of the connection of atoms of the same non-metal element. The correct answer is 2.

Task number 8.

What chemical bond is formed between atoms of elements with serial numbers 9 and 19?

1. Ionic

2. Metal

3. Covalent polar

4. Covalent non-polar

Explanation: these are elements - fluorine and potassium, that is, a non-metal and a metal, respectively, only an ionic bond can form between such elements. The correct answer is 1.

Task number 9.

A substance with an ionic bond type corresponds to the formula

1. NH3 2. HBr 3. CCl4 4. KCl

Explanation: an ionic bond is formed between a metal atom and a nonmetal atom, that is the correct answer is 4.

Task number 10.

The same type of chemical bond have hydrogen chloride and

1. Ammonia

2. Bromine

3. Sodium chloride

4. Magnesium oxide

Explanation: Hydrogen chloride has a covalent polar bond, that is, we need to find a substance consisting of two different non-metals - this is ammonia.

The correct answer is 1.

Tasks for independent decision.

1. Hydrogen bonds form between molecules

1. Hydrofluoric acid

2. Chloromethane

3. Dimethyl ether

4. Ethylene

2. A compound with a covalent bond corresponds to the formula

1. Na2O 2. MgCl2 3. CaBr2 4. HF

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

1. H2O 2. Br2 3. CH4 4. N2O5

4. A substance with an ionic bond is

1. CaF2 2. Cl2 3. NH3 4. SO2

5. Hydrogen bonds form between molecules

1. Methanol

3. Acetylene

4. Methyl formate

6. A covalent non-polar bond is characteristic of each of the two substances:

1. Nitrogen and ozone

2. Water and ammonia

3. Copper and nitrogen

4. Bromine and methane

7. A covalent polar bond is characteristic of a substance

1. KI 2. CaO 3. Na2S 4. CH4

8. A covalent non-polar bond is characteristic of

1. I2 2. NO 3. CO 4. SiO2

9. A substance with a covalent polar bond is

1. Cl2 2. NaBr 3. H2S 4. MgCl2

10. A covalent non-polar bond is characteristic of each of the two substances:

1. Hydrogen and chlorine

2. Water and diamond

3. Copper and nitrogen

4. Bromine and methane

This note used assignments from the USE collection of 2016, edited by A.A. Kaverina.

A4 Chemical bond.

Chemical bond: covalent (polar and non-polar), ionic, metallic, hydrogen. Methods for the formation of a covalent bond. Characteristics of a covalent bond: bond length and energy. Formation of an ionic bond.

Option 1 - 1,5,9,13,17,21,25,29,33,37,41,45,49,53,57,61,65

Option 2 - 2,6,10,14,18,22,26,30,34,38,42,46,50,54,58,62,66

Option 3 - 3,7,11,15,19,23,27,31,35,39,43,47,51,55,59,63,67

Option 4 - 4,8,12,16,20,24,28,32,36,40,44,48,52,56,60,64,68

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, KCl 2) NaBr, Na 2 O, KI 3) SO 2 .P 4 .CaF 2 4) H 2 S, Br 2 , K 2 S

3. A compound with an ionic bond is formed by interaction

1) CH 4 and O 2 2) SO 3 and H 2 O 3) C 2 H 6 and HNO 3 4) NH 3 and HCI

4. In what series 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) NaBr, HBr, CO

5. In which row are the formulas of substances written only with a covalent polar bond?

1) Cl 2, NO 2, HCl 2) HBr, NO, Br 2 3) H 2 S, H 2 O, Se 4) HI, H 2 O, PH 3

6. A covalent non-polar bond is characteristic of

1) Cl 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 bond is

1) CaCl 2 2) MgS 3) H 2 S 4) NaBr

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

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

10. Substances with a non-polar covalent bond are

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

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

12. A covalent polar bond is characteristic of

1) KCl 2) HBr 3) P 4 4) CaCl 2

13. A chemical element in the atom of which the 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) metallic

14. In a molecule of what substance is the bond length between carbon atoms the longest?

1) acetylene 2) ethane 3) ethene 4) benzene

15. Three common electron pairs form a covalent bond in a molecule

1) nitrogen 2) hydrogen sulfide 3) methane 4) chlorine

16. Hydrogen bonds are formed between molecules

1) dimethyl ether 2) methanol 3) ethylene 4) ethyl acetate

17. The polarity of the bond is most pronounced in the molecule

1) HI 2) HCl 3) HF 4) HBr

18. Substances with a non-polar covalent bond are

1) water and diamond 2) hydrogen and chlorine 3) copper and nitrogen 4) bromine and methane

19. Hydrogen bond not typical for substance

1) H 2 O 2) CH 4 3) NH 3 4) CH3OH

20. A covalent polar bond is characteristic of 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

21. The least strong chemical bond in a molecule

22. In the molecule of which substance is the length of the chemical bond the longest?

1) fluorine 2) chlorine 3) bromine 4) iodine

23. 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, CCl 4

24. 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

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

1) C 3 H 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, CCl 4

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

1) C 3 H a, NO 2, NaF 2) KCl, CH 3 Cl, C 6 H 12 0 6 3) P 2 O 5, NaHSO 4, Ba 4) C 2 H 5 NH 2, P 4, CH 3 Oh

27. Bond polarity is most pronounced in molecules

1) hydrogen sulfide 2) chlorine 3) phosphine 4) hydrogen chloride

28. In the molecule of what substance are chemical bonds the strongest?

1) CF 4 2) CCl 4 3) CBr 4 4) CI 4

29. Among the substances NH 4 Cl, CsCl, NaNO 3, PH 3, HNO 3 - the number of compounds with an ionic bond is

1) 1 2) 2 3) 3 4) 4

30. Among the substances (NH 4) 2 SO 4, Na 2 SO 4, CaI 2, I 2, CO 2 - the number of compounds with a covalent bond is

1) 1 2) 2 3) 3 4) 4

31. In substances formed by combining identical atoms, a chemical bond

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

32. Atoms of chemical elements of the second period of the periodic system D.I. Mendeleev form compounds with an ionic chemical bond of composition 1) LiF 2) CO 2 3) Al 2 O 3 4) BaS

33. Compounds with covalent polar and covalent non-polar bonds are respectively 1) water and hydrogen sulfide 2) potassium bromide and nitrogen 3) ammonia and hydrogen 4) oxygen and methane

34. A covalent non-polar bond is characteristic of 1) water 2) ammonia 3) nitrogen 4) methane

35. Chemical bond in a hydrogen fluoride molecule

1) covalent polar 3) ionic

2) covalent non-polar 4) hydrogen

36. Choose a pair of substances, all bonds in which are covalent:

1) NaCl, Hcl 2) CO 2, BaO 3) CH 3 Cl, CH 3 Na 4) SO 2, NO 2

37. In potassium iodide, a chemical bond

1) covalent non-polar 3) metallic

2) covalent polar 4) ionic

38. In carbon disulfide CS 2 chemical bond

1) ionic 2) metallic

3) covalent polar 4) covalent non-polar

39. A covalent non-polar bond is realized in a compound

1) CrO 3 2) P 2 O 5 3) SO 2 4) F 2

40. A substance with a covalent polar bond has the formula 1) KCl 2) HBr 3) P 4 4) CaCl 2

41. Connection with the ionic nature of the chemical bond

1) phosphorus chloride 2) potassium bromide 3) nitric oxide (II) 4) barium

42. 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

43. An ionic bond is formed by 1) H and S 2) P and C1 3) Cs and Br 4) Si and F

44. What type of bond is in the H 2 molecule?

1) Ionic 2) Hydrogen 3) Covalent non-polar 4) Donor-acceptor

45. A substance with a covalent polar bond is

1) sulfur oxide (IV) 2) oxygen 3) calcium hydride 4) diamond

46. ​​In a fluorine molecule, a chemical bond

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

47. In which series are substances listed only with a covalent polar bond:

1) CH 4 H 2 Cl 2 2) NH 3 HBr CO 2 3) PCl 3 KCl CCl 4 4) H 2 S SO 2 LiF

48. In what series 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) KBr, HBr, CO

49. In which row are listed substances only with an ionic type of bond:

1) F 2 O LiF SF 4 2) PCl 3 NaCl CO 2 3) KF Li 2 O BaCl 2 4) CaF 2 CH 4 CCl 4

50. A compound with an ionic bond is formed when interacting

1) CH 4 and O 2 2) NH 3 and HCl 3) C 2 H 6 and HNO 3 4) SO 3 and H 2 O

51. A hydrogen bond is formed between the molecules of 1) ethane 2) benzene 3) hydrogen 4) ethanol

52. What substance has hydrogen bonds? 1) Hydrogen sulfide 2) Ice 3) Hydrogen bromide 4) Benzene

53. Relationship formed between elements with serial numbers 15 and 53

1) ionic 2) metallic

3) covalent non-polar 4) covalent polar

54. Relationship formed between elements with serial numbers 16 and 20

1) ionic 2) metallic

3) covalent polar 4) hydrogen

55. A bond arises between the atoms of elements with serial numbers 11 and 17

1) metallic 2) ionic 3) covalent 4) donor-acceptor

56. Hydrogen bonds are formed between molecules

1) hydrogen 2) formaldehyde 3) acetic acid 4) hydrogen sulfide

57. In which row are the formulas of substances written only with a covalent polar bond?

1) Cl 2, NH 3, HCl 2) HBr, NO, Br 2 3) H 2 S, H 2 O, S 8 4) NI, H 2 O, PH 3

58. In what substance are there both ionic and covalent chemical bonds?

1) Sodium chloride 2) Hydrogen chloride 3) Sodium sulfate 4) Phosphoric acid

59. A chemical bond in a molecule has a more pronounced ionic character.

1) lithium bromide 2) copper chloride 3) calcium carbide 4) potassium fluoride

60. In what substance are all chemical bonds - covalent non-polar?

1) Diamond 2) Carbon monoxide (IV) 3) Gold 4) Methane

61. Establish a correspondence between the substance and the type of bond of atoms in this substance.

NAME OF THE SUBSTANCE TYPE OF COMMUNICATION

1) zinc A) ionic

2) nitrogen B) metal

3) ammonia B) covalent polar

4) calcium chloride D) covalent non-polar

62. Match

TYPE OF COMMUNICATION CONNECTION

1) ionic A) H 2

2) metal B) Va

3) covalent polar B) HF

4) covalent non-polar D) BaF 2

63. In what compound is the covalent bond between atoms formed by the donor-acceptor mechanism? 1) KCl 2) CCl 4 3) NH 4 Cl 4) CaCl 2

64. Indicate the molecule in which the binding energy is the highest: 1) N≡N 2) H-H 3) O=O 4) H-F

65. Indicate the molecule in which the chemical bond is the strongest: 1) HF 2) HCl 3) HBr 4) HI

Topics of the USE codifier: Covalent chemical bond, its varieties and mechanisms of formation. Characteristics of a covalent bond (polarity and bond energy). Ionic bond. Metal connection. hydrogen bond

Intramolecular chemical bonds

Let us first consider the bonds that arise between particles within molecules. Such connections are called intramolecular.

chemical bond between atoms of chemical elements has an electrostatic nature and is formed due to interactions of external (valence) electrons, in more or less degree held by positively charged nuclei bonded atoms.

The key concept here is ELECTRONEGNATIVITY. It is she who determines the type of chemical bond between atoms and the properties of this bond.

is the ability of an atom to attract (hold) external(valence) electrons. Electronegativity is determined by the degree of attraction of external electrons to the nucleus and depends mainly on the radius of the atom and the charge of the nucleus.

Electronegativity is difficult to determine unambiguously. L. Pauling compiled a table of relative electronegativity (based on the bond energies of diatomic molecules). The most electronegative element is fluorine with meaning 4 .

It is important to note that in different sources you can find different scales and tables of electronegativity values. This should not be frightened, since the formation of a chemical bond plays a role atoms, and it is approximately the same in any system.

If one of the atoms in the chemical bond A:B attracts electrons more strongly, then the electron pair is shifted towards it. The more electronegativity difference atoms, the more the electron pair is displaced.

If the electronegativity values ​​of the interacting atoms are equal or approximately equal: EO(A)≈EO(V), then the shared electron pair is not displaced to any of the atoms: A: B. Such a connection is called covalent non-polar.

If the electronegativity of the interacting atoms differ, but not much (the difference in electronegativity is approximately from 0.4 to 2: 0,4<ΔЭО<2 ), then the electron pair is shifted to one of the atoms. Such a connection is called covalent polar .

If the electronegativity of the interacting atoms differ significantly (the difference in electronegativity is greater than 2: ΔEO>2), then one of the electrons almost completely passes to another atom, with the formation ions. Such a connection is called ionic.

The main types of chemical bonds are − covalent, ionic And metallic connections. Let's consider them in more detail.

covalent chemical bond

covalent bond – it's a chemical bond formed by formation of a common electron pair A:B . In this case, two atoms overlap atomic orbitals. A covalent bond is formed by the interaction of atoms with a small difference in electronegativity (as a rule, between two non-metals) or atoms of one element.

Basic properties of covalent bonds

• orientation,
• saturability,
• polarity,
• polarizability.

These bond properties affect the chemical and physical properties of substances.

Direction of communication characterizes the chemical structure and form of substances. The angles between two bonds are called bond angles. For example, in a water molecule, the H-O-H bond angle is 104.45 o, so the water molecule is polar, and in the methane molecule, the H-C-H bond angle is 108 o 28 ′.

Saturability is the ability of atoms to form a limited number of covalent chemical bonds. The number of bonds that an atom can form is called.

Polarity bonds arise due to the uneven distribution of electron density between two atoms with different electronegativity. Covalent bonds are divided into polar and non-polar.

Polarizability connections are the ability of bond electrons to be displaced by an external electric field(in particular, the electric field of another particle). The polarizability depends on the electron mobility. The farther the electron is from the nucleus, the more mobile it is, and, accordingly, the molecule is more polarizable.

Covalent non-polar chemical bond

There are 2 types of covalent bonding - POLAR And NON-POLAR .

Example . Consider the structure of the hydrogen molecule H 2 . Each hydrogen atom carries 1 unpaired electron in its outer energy level. To display an atom, we use the Lewis structure - this is a diagram of the structure of the external energy level of an atom, when electrons are denoted by dots. Lewis point structure models are a good help when working with elements of the second period.

H. + . H=H:H

Thus, the hydrogen molecule has one common electron pair and one H–H chemical bond. This electron pair is not displaced to any of the hydrogen atoms, because the electronegativity of hydrogen atoms is the same. Such a connection is called covalent non-polar .

Covalent non-polar (symmetrical) bond - this is a covalent bond formed by atoms with equal electronegativity (as a rule, the same non-metals) and, therefore, with a uniform distribution of electron density between the nuclei of atoms.

The dipole moment of nonpolar bonds is 0.

Examples: H 2 (H-H), O 2 (O=O), S 8 .

Covalent polar chemical bond

covalent polar bond is a covalent bond that occurs between atoms with different electronegativity (usually, different non-metals) and is characterized displacement common electron pair to a more electronegative atom (polarization).

The electron density is shifted to a more electronegative atom - therefore, a partial negative charge (δ-) arises on it, and a partial positive charge arises on a less electronegative atom (δ+, delta +).

The greater the difference in the electronegativity of atoms, the higher polarity connections and even more dipole moment . Between neighboring molecules and charges opposite in sign, additional attractive forces act, which increases strength connections.

Bond polarity affects the physical and chemical properties of compounds. The reaction mechanisms and even the reactivity of neighboring bonds depend on the polarity of the bond. The polarity of a bond often determines polarity of the molecule and thus directly affects such physical properties as boiling point and melting point, solubility in polar solvents.

Examples: HCl, CO 2 , NH 3 .

Mechanisms for the formation of a covalent bond

A covalent chemical bond can occur by 2 mechanisms:

1. exchange mechanism the formation of a covalent chemical bond is when each particle provides one unpaired electron for the formation of a common electron pair:

BUT . + . B= A:B

2. The formation of a covalent bond is such a mechanism in which one of the particles provides an unshared electron pair, and the other particle provides a vacant orbital for this electron pair:

BUT: + B= A:B

In this case, one of the atoms provides an unshared electron pair ( donor), and the other atom provides a vacant orbital for this pair ( acceptor). As a result of the formation of a bond, both electron energy decreases, i.e. this is beneficial for the atoms.

A covalent bond formed by the donor-acceptor mechanism, is not different by properties from other covalent bonds formed by the exchange mechanism. The formation of a covalent bond by the donor-acceptor mechanism is typical for atoms either with a large number of electrons in the external energy level (electron donors), or vice versa, with a very small number of electrons (electron acceptors). The valence possibilities of atoms are considered in more detail in the corresponding.

A covalent bond is formed by the donor-acceptor mechanism:

- in a molecule carbon monoxide CO(the bond in the molecule is triple, 2 bonds are formed by the exchange mechanism, one by the donor-acceptor mechanism): C≡O;

- in ammonium ion NH 4 +, in ions organic amines, for example, in the methylammonium ion CH 3 -NH 2 + ;

- in complex compounds, a chemical bond between the central atom and groups of ligands, for example, in sodium tetrahydroxoaluminate Na the bond between aluminum and hydroxide ions;

- in nitric acid and its salts- nitrates: HNO 3 , NaNO 3 , in some other nitrogen compounds;

- in a molecule ozone O 3 .

Main characteristics of a covalent bond

A covalent bond, as a rule, is formed between the atoms of non-metals. The main characteristics of a covalent bond are length, energy, multiplicity and directivity.

Chemical bond multiplicity

Chemical bond multiplicity - this the number of shared electron pairs between two atoms in a compound. The multiplicity of the bond can be quite easily determined from the value of the atoms that form the molecule.

For example , in the hydrogen molecule H 2 the bond multiplicity is 1, because each hydrogen has only 1 unpaired electron in the outer energy level, therefore, one common electron pair is formed.

In the oxygen molecule O 2, the bond multiplicity is 2, because each atom has 2 unpaired electrons in its outer energy level: O=O.

In the nitrogen molecule N 2, the bond multiplicity is 3, because between each atom there are 3 unpaired electrons in the outer energy level, and the atoms form 3 common electron pairs N≡N.

Covalent bond length

Chemical bond length is the distance between the centers of the nuclei of atoms that form a bond. It is determined by experimental physical methods. The bond length can be estimated approximately, according to the additivity rule, according to which the bond length in the AB molecule is approximately equal to half the sum of the bond lengths in the A 2 and B 2 molecules:

The length of a chemical bond can be roughly estimated along the radii of atoms, forming a bond, or by the multiplicity of communication if the radii of the atoms are not very different.

With an increase in the radii of the atoms forming a bond, the bond length will increase.

For example

With an increase in the multiplicity of bonds between atoms (whose atomic radii do not differ, or differ slightly), the bond length will decrease.

For example . In the series: C–C, C=C, C≡C, the bond length decreases.

Bond energy

A measure of the strength of a chemical bond is the bond energy. Bond energy is determined by the energy required to break the bond and remove the atoms that form this bond to an infinite distance from each other.

The covalent bond is very durable. Its energy ranges from several tens to several hundreds of kJ/mol. The greater the bond energy, the greater the bond strength, and vice versa.

The strength of a chemical bond depends on the bond length, bond polarity, and bond multiplicity. The longer the chemical bond, the easier it is to break, and the lower the bond energy, the lower its strength. The shorter the chemical bond, the stronger it is, and the greater the bond energy.

For example, in the series of compounds HF, HCl, HBr from left to right the strength of the chemical bond decreases, because the length of the bond increases.

Ionic chemical bond

Ionic bond is a chemical bond based on electrostatic attraction of ions.

ions are formed in the process of accepting or giving away electrons by atoms. For example, the atoms of all metals weakly hold the electrons of the outer energy level. Therefore, metal atoms are characterized restorative properties the ability to donate electrons.

Example. The sodium atom contains 1 electron at the 3rd energy level. Easily giving it away, the sodium atom forms a much more stable Na + ion, with the electron configuration of the noble neon gas Ne. The sodium ion contains 11 protons and only 10 electrons, so the total charge of the ion is -10+11 = +1:

+11Na) 2 ) 8 ) 1 - 1e = +11 Na +) 2 ) 8

Example. The chlorine atom has 7 electrons in its outer energy level. To acquire the configuration of a stable inert argon atom Ar, chlorine needs to attach 1 electron. After the attachment of an electron, a stable chlorine ion is formed, consisting of electrons. The total charge of the ion is -1:

+17Cl) 2 ) 8 ) 7 + 1e = +17 Cl — ) 2 ) 8 ) 8

Note:

• The properties of ions are different from the properties of atoms!
• Stable ions can form not only atoms, but also groups of atoms. For example: ammonium ion NH 4 +, sulfate ion SO 4 2-, etc. Chemical bonds formed by such ions are also considered ionic;
• Ionic bonds are usually formed between metals And nonmetals(groups of non-metals);

The resulting ions are attracted due to electrical attraction: Na + Cl -, Na 2 + SO 4 2-.

Let us visually generalize difference between covalent and ionic bond types:

metal chemical bond

metal connection is the relationship that is formed relatively free electrons between metal ions forming a crystal lattice.

The atoms of metals on the outer energy level usually have one to three electrons. The radii of metal atoms, as a rule, are large - therefore, metal atoms, unlike non-metals, quite easily donate outer electrons, i.e. are strong reducing agents

Intermolecular interactions

Separately, it is worth considering the interactions that occur between individual molecules in a substance - intermolecular interactions . Intermolecular interactions are a type of interaction between neutral atoms in which new covalent bonds do not appear. The forces of interaction between molecules were discovered by van der Waals in 1869 and named after him. Van dar Waals forces. Van der Waals forces are divided into orientation, induction And dispersion . The energy of intermolecular interactions is much less than the energy of a chemical bond.

Orientation forces of attraction arise between polar molecules (dipole-dipole interaction). These forces arise between polar molecules. Inductive interactions is the interaction between a polar molecule and a non-polar one. A non-polar molecule is polarized due to the action of a polar one, which generates an additional electrostatic attraction.

A special type of intermolecular interaction is hydrogen bonds. - these are intermolecular (or intramolecular) chemical bonds that arise between molecules in which there are strongly polar covalent bonds - H-F, H-O or H-N. If there are such bonds in the molecule, then between the molecules there will be additional forces of attraction .

Mechanism of education The hydrogen bond is partly electrostatic and partly donor-acceptor. In this case, an atom of a strongly electronegative element (F, O, N) acts as an electron pair donor, and hydrogen atoms connected to these atoms act as an acceptor. Hydrogen bonds are characterized orientation in space and saturation .

The hydrogen bond can be denoted by dots: H ··· O. The greater the electronegativity of an atom connected to hydrogen, and the smaller its size, the stronger the hydrogen bond. It is primarily characteristic of compounds fluorine with hydrogen , as well as to oxygen with hydrogen , less nitrogen with hydrogen .

Hydrogen bonds occur between the following substances:

— hydrogen fluoride HF(gas, solution of hydrogen fluoride in water - hydrofluoric acid), water H 2 O (steam, ice, liquid water):

— solution of ammonia and organic amines- between ammonia and water molecules;

— organic compounds in which O-H or N-H bonds: alcohols, carboxylic acids, amines, amino acids, phenols, aniline and its derivatives, proteins, solutions of carbohydrates - monosaccharides and disaccharides.

The hydrogen bond affects the physical and chemical properties of substances. Thus, the additional attraction between molecules makes it difficult for substances to boil. Substances with hydrogen bonds exhibit an abnormal increase in the boiling point.

For example As a rule, with an increase in molecular weight, an increase in the boiling point of substances is observed. However, in a number of substances H 2 O-H 2 S-H 2 Se-H 2 Te we do not observe a linear change in boiling points.

Namely, at boiling point of water is abnormally high - not less than -61 o C, as the straight line shows us, but much more, +100 o C. This anomaly is explained by the presence of hydrogen bonds between water molecules. Therefore, under normal conditions (0-20 o C), water is liquid by phase state.

Chemical properties

The most active non-metal, it violently interacts with almost all substances (rare exceptions are fluoroplasts), and with most of them - with combustion and explosion. The contact of fluorine with hydrogen leads to ignition and explosion even at very low temperatures (up to −252°C). Even water and platinum: uranium for the nuclear industry burn in a fluorine atmosphere.
chlorine trifluoride ClF 3 - a fluorinating agent and a powerful rocket fuel oxidizer
sulfur hexafluoride SF 6 - gaseous insulator in the electrical industry
metal fluorides (such as W and V), which have some beneficial properties
freons are good refrigerants
teflon - chemically inert polymers
sodium hexafluoroaluminate - for the subsequent production of aluminum by electrolysis
various fluorine compounds

Missile technology

Application in medicine

Fluorine compounds are widely used in medicine as blood substitutes.

Biological and physiological role

Fluorine is a vital element for the body. In the human body, fluorine is mainly found in tooth enamel as part of fluorapatite - Ca 5 F (PO 4) 3 . With insufficient (less than 0.5 mg / liter of drinking water) or excessive (more than 1 mg / liter) fluoride intake by the body, dental diseases can develop: caries and fluorosis (mottled enamel) and osteosarcoma, respectively.

To prevent caries, it is recommended to use toothpastes with fluoride additives or drink fluoridated water (up to a concentration of 1 mg / l), or apply local applications with a 1-2% solution of sodium fluoride or stannous fluoride. Such actions can reduce the likelihood of caries by 30-50%.

The maximum allowable concentration of bound fluorine in the air of industrial premises is 0.0005 mg/liter.

Additional Information

Fluorine, Fluorum, F(9)
Fluorine (Fluorine, French and German Fluor) was obtained in a free state in 1886, but its compounds have been known for a long time and were widely used in metallurgy and glass production. The first mention of fluorite (CaP,) under the name fluorspar (Fliisspat) dates back to the 16th century. One of the works attributed to the legendary Vasily Valentin mentions stones painted in various colors - fluxes (Fliisse from Latin fluere - flow, pour), which were used as fluxes in the smelting of metals. Agricola and Libavius ​​write about the same. The latter introduces special names for this flux - fluorspar (Flusspat) and mineral melt. Many authors of chemical and technical writings of the 17th and 18th centuries. describe different types of fluorspar. In Russia, these stones were called plavik, spalt, spat; Lomonosov classified these stones as selenites and called them spar or flux (crystal flux). Russian masters, as well as collectors of mineral collections (for example, in the 18th century, Prince P.F. Golitsyn) knew that some types of spars glow in the dark when heated (for example, in hot water). However, even Leibniz in his history of phosphorus (1710) mentions in this connection thermophosphorus (Thermophosphorus).

Apparently, chemists and artisan chemists became acquainted with hydrofluoric acid no later than the 17th century. In 1670, the Nuremberg craftsman Schwanhard used fluorspar mixed with sulfuric acid to etch designs on glass goblets. However, at that time the nature of fluorspar and hydrofluoric acid was completely unknown. It was believed, for example, that silicic acid has an etching effect in the Schwanhard process. This erroneous opinion was eliminated by Scheele, proving that when fluorspar interacts with sulfuric acid, silicic acid is obtained as a result of the erosion of the glass retort by the resulting hydrofluoric acid. In addition, Scheele established (1771) that fluorspar is a combination of calcareous earth with a special acid, which was called "Swedish acid".

Lavoisier recognized the hydrofluoric acid radical (radical fluorique) as a simple body and included it in his table of simple bodies. More or less pure hydrofluoric acid was obtained in 1809. Gay-Lussac and Tenard by distilling fluorspar with sulfuric acid in a lead or silver retort. During this operation, both researchers were poisoned. The true nature of hydrofluoric acid was established in 1810 by Ampère. He rejected Lavoisier's opinion that hydrofluoric acid must contain oxygen, and proved the analogy of this acid with hydrochloric acid. Ampère reported his findings to Davy, who shortly before that had established the elemental nature of chlorine. Davy fully agreed with Ampere's arguments and spent a lot of effort on obtaining free fluorine by electrolysis of hydrofluoric acid and in other ways. Taking into account the strong corrosive effect of hydrofluoric acid on glass, as well as on plant and animal tissues, Ampere suggested calling the element contained in it fluorine (Greek - destruction, death, pestilence, plague, etc.). However, Davy did not accept this name and proposed another - fluorine (Fluorine), by analogy with the then name of chlorine - chlorine (Chlorine), both names are still used in English. In Russian, the name given by Ampere has been preserved.

Numerous attempts to isolate free fluorine in the 19th century did not lead to successful results. Only in 1886 did Moissan manage to do this and obtain free fluorine in the form of a yellow-green gas. Since fluorine is an unusually aggressive gas, Moissan had to overcome many difficulties before he found a material suitable for the apparatus in experiments with fluorine. The U-tube for electrolysis of hydrofluoric acid at 55°C (cooled with liquid methyl chloride) was made of platinum with fluorspar plugs. After the chemical and physical properties of free fluorine were investigated, it found wide application. Today, fluorine is one of the most important components in the synthesis of a wide range of organofluorine compounds. Russian literature of the early 19th century. fluorine was called differently: the base of hydrofluoric acid, fluorine (Dvigubsky, 1824), fluorine (Iovsky), fluor (Shcheglov, 1830), fluor, fluorine, fluorine. Hess from 1831 introduced the name fluorine.