Types of chemical bonds. Chemical bond Hcl what chemical bond
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Each atom has a number of electrons.
Entering into chemical reactions, atoms donate, acquire, or socialize electrons, reaching the most stable electronic configuration. The most stable is the configuration with the lowest energy (as in the atoms of noble gases). This pattern is called the "octet rule" (Figure 1).
Figure: one.
This rule applies to all types of links... Electronic bonds between atoms allow them to form stable structures, from the simplest crystals to complex biomolecules that ultimately form living systems. They differ from crystals by their continuous metabolism. Moreover, many chemical reactions proceed according to mechanisms electronic transfer, which play an essential role in the energy processes in the body.
A chemical bond is the force that holds two or more atoms, ions, molecules, or any combination of them together.
The nature of the chemical bond is universal: it is the electrostatic force of attraction between negatively charged electrons and positively charged nuclei, determined by the configuration of the electrons in the outer shell of atoms. The ability of an atom to form chemical bonds is called valence, or oxidation state... The concept of valence is associated with valence electrons - electrons that form chemical bonds, that is, those located in the highest energy orbitals. Accordingly, the outer shell of the atom containing these orbitals is called valence shell... At present, it is not enough to indicate the presence of a chemical bond, but it is necessary to clarify its type: ionic, covalent, dipole-dipole, metallic.
The first type of communication isionic connection
According to the electron theory of valence of Lewis and Kossel, atoms can achieve a stable electronic configuration in two ways: first, by losing electrons, turning into cations, secondly, acquiring them, turning into anions... As a result of electron transfer due to the electrostatic force of attraction between ions with charges of the opposite sign, a chemical bond is formed, called Kossel “ electrovalent"(Now it is called ionic).
In this case, anions and cations form a stable electronic configuration with a filled outer electron shell. Typical ionic bonds are formed from cations of T and II groups of the periodic table and anions of non-metallic elements of VI and VII groups (16 and 17 subgroups - respectively, chalcogenesand halogens). The bonds of ionic compounds are unsaturated and non-directional, so they retain the possibility of electrostatic interaction with other ions. In fig. Figures 2 and 3 show examples of ionic bonds corresponding to the Kossel electron transfer model.
Figure: 2.
Figure: 3. Ionic bond in sodium chloride molecule (NaCl)
Here it is appropriate to recall some of the properties that explain the behavior of substances in nature, in particular, to consider the concept of acidsand grounds.
Aqueous solutions of all these substances are electrolytes. They change color in different ways indicators... The mechanism of the indicators' action was discovered by F.V. Ostwald. He showed that the indicators are weak acids or bases, the color of which is different in the undissociated and dissociated states.
The bases are capable of neutralizing acids. Not all bases are soluble in water (for example, some organic compounds that do not contain OH-groups are insoluble, in particular, triethylamine N (C 2 H 5) 3); soluble bases are called alkalis.
Aqueous solutions of acids enter into characteristic reactions:
a) with metal oxides - with the formation of salt and water;
b) with metals - with the formation of salt and hydrogen;
c) with carbonates - with the formation of salt, CO 2 and H 2 O.
The properties of acids and bases are described by several theories. In accordance with the theory of S.A. Arrhenius, acid is a substance that dissociates to form ions H +, while the base forms ions IS HE -. This theory does not take into account the existence of organic bases that do not have hydroxyl groups.
According to protonby the theory of Bronsted and Lowry, an acid is a substance containing molecules or ions that donate protons ( donorsprotons), and the base is a substance consisting of molecules or ions that accept protons ( acceptorsprotons). Note that in aqueous solutions, hydrogen ions exist in a hydrated form, that is, in the form of hydronium ions H 3 O +. This theory describes reactions not only with water and hydroxide ions, but also carried out in the absence of a solvent or with a non-aqueous solvent.
For example, in the reaction between ammonia NH 3 (weak base) and hydrogen chloride in the gas phase forms solid ammonium chloride, and in an equilibrium mixture of two substances there are always 4 particles, two of which are acids, and the other two are bases:
This equilibrium mixture consists of two conjugated pairs of acids and bases:
1) NH 4 + and NH 3
2) HCland Сl ‑
Here, in each conjugate pair, the acid and base differ by one proton. Each acid has a base conjugated with it. A strong acid corresponds to a weak conjugated base, and a weak acid corresponds to a strong conjugate base.
The Bronsted-Lowry theory makes it possible to explain the uniqueness of the role of water in the life of the biosphere. Water, depending on the substance interacting with it, can exhibit the properties of either an acid or a base. For example, in reactions with aqueous solutions of acetic acid, water is a base, and with aqueous solutions of ammonia, it is an acid.
1) CH 3 COOH + H 2 O ↔ H 3 O + + CH 3 COO -. Here, an acetic acid molecule donates a proton to a water molecule;
2) NH 3 + H 2 O ↔ NH 4 + + IS HE -. Here the ammonia molecule accepts a proton from a water molecule.
Thus, water can form two conjugated pairs:
1) H 2 O (acid) and IS HE - (conjugate base)
2) H 3 O + (acid) and H 2 O(conjugate base).
In the first case, water donates a proton, and in the second, it accepts it.
This property is called amphiprotonicity... Substances that can react as both acids and bases are called amphoteric... Such substances are often found in living nature. For example, amino acids are capable of forming salts with both acids and bases. Therefore, peptides easily form coordination compounds with the present metal ions.
Thus, a characteristic property of the ionic bond is the complete movement of the bunk of binding electrons to one of the nuclei. This means that there is a region between the ions where the electron density is almost zero.
The second type of communication iscovalent connection
Atoms can form stable electronic configurations by sharing electrons.
Such a bond is formed when a pair of electrons is socialized one by one from each atom. In this case, the socialized bond electrons are equally distributed between the atoms. Examples of covalent bonds include homonucleardiatomic molecules H 2 , N 2 , F 2. Allotropes have the same type of connection. O 2 and ozone O 3 and the polyatomic molecule S 8, as well as heteronuclear molecules hydrogen chloride Hcl, carbon dioxide CO 2, methane CH 4, ethanol FROM 2 H 5 IS HE, sulfur hexafluoride SF 6, acetylene FROM 2 H 2. All these molecules have the same electrons in common, and their bonds are saturated and directed in the same way (Fig. 4).
It is important for biologists that the covalent radii of atoms in double and triple bonds are reduced in comparison with a single bond.
Figure: four. Covalent bond in the Cl 2 molecule.
Ionic and covalent bond types are two limiting cases of many existing types of chemical bonds, and in practice, most bonds are intermediate.
Compounds of two elements located at opposite ends of one or different periods of the Mendeleev system predominantly form ionic bonds. As the elements approach each other within the period, the ionic character of their compounds decreases, and the covalent character increases. For example, halides and oxides of the elements on the left side of the periodic table form predominantly ionic bonds ( NaCl, AgBr, BaSO 4, CaCO 3, KNO 3, CaO, NaOH), and the same compounds of the elements on the right side of the table are covalent ( H 2 O, CO 2, NH 3, NO 2, CH 4, phenol C 6 H 5 OH, glucose C 6 H 12 O 6, ethanol C 2 H 5 OH).
The covalent bond, in turn, has another modification.
In polyatomic ions and in complex biological molecules, both electrons can only come from oneatom. It is called donorelectronic pair. An atom that socializes this pair of electrons with a donor is called acceptorelectronic pair. This kind of covalent bond is called coordination (donor-acceptor, ordative) communication(fig. 5). This type of bond is most important for biology and medicine, since the chemistry of the most important d-elements for metabolism is largely described by coordination bonds.
Fig. five.
As a rule, in a complex compound, a metal atom acts as an acceptor of an electron pair; on the contrary, in ionic and covalent bonds, the metal atom is an electron donor.
The essence of the covalent bond and its variety - the coordination bond - can be clarified using another theory of acids and bases proposed by GN. Lewis. He somewhat expanded the concept of the terms "acid" and "base" according to the Bronsted-Lowry theory. Lewis's theory explains the nature of the formation of complex ions and the participation of substances in nucleophilic substitution reactions, that is, in the formation of CS.
According to Lewis, an acid is a substance capable of forming a covalent bond by accepting an electron pair from a base. Lewis base is a substance that has a lone electron pair, which, by donating electrons, forms a covalent bond with Lewisic acid.
That is, Lewis's theory expands the range of acid-base reactions to reactions in which protons do not participate at all. Moreover, the proton itself, according to this theory, is also an acid, since it is capable of accepting an electron pair.
Therefore, according to this theory, cations are Lewis acids, and anions are Lewis bases. An example is the following reactions:
It was noted above that the division of substances into ionic and covalent ones is relative, since the complete transition of an electron from metal atoms to acceptor atoms in covalent molecules does not occur. In compounds with ionic bonds, each ion is in the electric field of ions of the opposite sign, so they mutually polarize, and their shells are deformed.
Polarizabilitydetermined by the electronic structure, charge and size of the ion; it is higher for anions than for cations. The highest polarizability among cations is for cations with a larger charge and a smaller size, for example, for Hg 2+, Cd 2+, Pb 2+, Al 3+, Tl 3+... Has a strong polarizing effect H +. Since the influence of ion polarization is two-sided, it significantly changes the properties of the compounds formed by them.
The third type of connection isdipole-dipole connection
In addition to the listed types of communication, there are also dipole-dipole intermolecularinteractions, also called vanderwaals .
The strength of these interactions depends on the nature of the molecules.
There are three types of interactions: permanent dipole - permanent dipole ( dipole-dipole attraction); permanent dipole - induced dipole ( induction attraction); instantaneous dipole - induced dipole ( dispersive gravity, or London forces; fig. 6).
Figure: 6.
Only molecules with polar covalent bonds have a dipole-dipole moment ( HCl, NH 3, SO 2, H 2 O, C 6 H 5 Cl), and the bond strength is 1-2 debaya(1D \u003d 3.338 × 10 ‑30 coulomb meters - Cm × m).
In biochemistry, another type of bond is distinguished - hydrogen limiting bond dipole-dipole attraction. This bond is formed by the attraction between a hydrogen atom and a small electronegative atom, most often oxygen, fluorine and nitrogen. With large atoms that have a similar electronegativity (for example, with chlorine and sulfur), the hydrogen bond is much weaker. The hydrogen atom differs in one essential feature: when attracting electrons, its nucleus - a proton - is exposed and ceases to be screened by electrons.
Therefore, the atom turns into a large dipole.
The hydrogen bond, in contrast to the van der Waals bond, is formed not only during intermolecular interactions, but also within one molecule - intramolecularhydrogen bond. Hydrogen bonds play an important role in biochemistry, for example, to stabilize the structure of proteins in the form of an a-helix, or to form a DNA double helix (Fig. 7).
Fig. 7.
Hydrogen and van der Waals bonds are much weaker than ionic, covalent and coordination bonds. The energy of intermolecular bonds is indicated in table. one.
Table 1. Energy of intermolecular forces
Note: The degree of intermolecular interactions reflects the values \u200b\u200bof the enthalpy of melting and evaporation (boiling). Ionic compounds require significantly more energy to separate ions than to separate molecules. The enthalpies of melting of ionic compounds are much higher than that of molecular compounds.
The fourth type of connection ismetal bond
Finally, there is another type of intermolecular bonds - metal: connection of positive ions of the lattice of metals with free electrons. This type of connection does not occur in biological objects.
From a brief overview of the types of bonds, one detail becomes clear: an important parameter of an atom or metal ion - an electron donor, as well as an atom - an electron acceptor, is its the size.
Without going into details, we note that the covalent radii of atoms, ionic radii of metals, and van der Waals radii of interacting molecules increase as their ordinal number in the groups of the periodic system increases. In this case, the values \u200b\u200bof the radii of the ions are the smallest, and the values \u200b\u200bof the van der Waals radii are the greatest. As a rule, when moving down the group, the radii of all elements increase, both covalent and van der Waals.
Most important for biologists and physicians are coordinating(donor-acceptor) connections considered by coordination chemistry.
Medical bioinorganics. G.K. Barashkov
Task number 1
From the proposed list, select two compounds in which an ionic chemical bond is present.
- 1. Ca (ClO 2) 2
- 2. HClO 3
- 3. NH 4 Cl
- 4. HClO 4
- 5. Cl 2 O 7
Answer: 13
In the overwhelming majority of cases, it is possible to determine the presence of an ionic type of bond in a compound by the fact that atoms of a typical metal and atoms of a non-metal are simultaneously included in its structural units.
On this basis, we establish that there is an ionic bond in the compound under number 1 - Ca (ClO 2) 2, since in its formula you can see the atoms of a typical metal calcium 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 specified in the task 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 list provided, 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
A fluorine molecule (F 2) consists of two atoms of one chemical element of a non-metal, therefore, the chemical bond in this molecule is covalent non-polar.
A covalent non-polar bond can be realized only between atoms of the same chemical element of a non-metal.
Of the proposed options, only oxygen and diamond have a covalent non-polar bond. The oxygen molecule is diatomic, it 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 electronegativities of different atoms are always different, the total electron pair in the molecule is shifted towards a more electronegative element, in this case oxygen. Thus, the bond in the NO molecule is covalent polar.
Hydrogen bromide also consists of diatomic molecules composed of hydrogen and bromine atoms. The total electron pair forming the H-Br bond is shifted towards 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 transition of an electron from 3 s-orbital of the sodium atom (the sodium atom turns into a cation) to the underfilled 5 p-orbital of the iodine atom (the iodine atom turns into an anion). This 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.C 2 H 5 OH
- 3. H 2 O
- 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 molecular structure, in which covalent bonds H-O, H-N, H-F are present. Those. covalent bonds of a hydrogen atom with the atoms of three chemical elements with the highest electronegativity.
Thus, obviously, there are hydrogen bonds between the molecules:
2) alcohols
3) phenols
4) carboxylic acids
5) ammonia
6) primary and secondary amines
7) hydrofluoric acid
Task number 4
Select two compounds with ionic chemical bonds from the list.
- 1.PCl 3
- 2.CO 2
- 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 is possible to draw a conclusion about the presence of an ionic type of bond in a compound by the fact that atoms of a typical metal and atoms of a non-metal are simultaneously included in the structural units of a substance.
On this basis, we establish that there is an ionic bond in the compound numbered 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 - alkylammonium cations RNH 3 +, dialkylammonium R 2 NH 2 +, trialkylammonium R 3 NH + 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
Select two substances of non-molecular structure from the proposed list.
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.C 2 H 2
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 compounds from the list presented:
Thus, we see that there is a triple bond in nitrogen and acetylene molecules. 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.
1.Alkaline earth metals are5) to s– elements
6) to p - elements
7) to d - elements
8) to f - elements
2. How many electrons do the atoms of alkaline earth metals contain at the external energy level?
1) One 2) two 3) three 4) four
3. In chemical reactions, aluminum atoms exhibit
3) Oxidizing properties 2) acidic properties
4) 3) reducing properties 4) basic properties
4. The interaction of calcium with chlorine refers to reactions
1) Decompositions 2) compounds 3) substitutions 4) exchange
5. The molecular weight of sodium bicarbonate is:
1) 84 2) 87 3) 85 4) 86
3. Which atom is heavier - iron or silicon - and how many times?4. Determine the relative molecular weights of simple substances: hydrogen, oxygen, chlorine, copper, diamond (carbon). Remember which of them are made up of diatomic molecules and which are made up of atoms.
5.Calculate the relative molecular weights of the following compounds of carbon dioxide CO2 sulfuric acid H2SO4 sugar C12H22O11 ethyl alcohol C2H6O marble CaCPO3
6. In hydrogen peroxide, there is one hydrogen atom for one oxygen atom. Determine the formula for hydrogen peroxide, if you know that its relative molecular weight is 34. What is the mass ratio of hydrogen and oxygen in this compound?
7. How many times is a carbon dioxide molecule heavier than an oxygen molecule?
Help pozhzhzhzhzhaluysta, grade 8 assignment.