It is extremely rare that chemicals are made up of separate, unrelated atoms. chemical elements... Only a small number of gases called noble gases have such a structure under normal conditions: helium, neon, argon, krypton, xenon and radon. More often than not, chemical substances do not consist of scattered atoms, but of their combinations into various groups. Such associations of atoms can number several units, hundreds, thousands, or even more atoms. The force that keeps these atoms in the composition of such groups is called chemical bond.
In other words, we can say that a chemical bond is an interaction that provides a bond between individual atoms into more complex structures (molecules, ions, radicals, crystals, etc.).
The reason for the formation chemical bond is that the energy of more complex structures is less than the total energy of the individual atoms that form it.
So, in particular, if an XY molecule is formed during the interaction of X and Y atoms, this means that the internal energy of the molecules of this substance is lower than the internal energy of the individual atoms from which it was formed:
E (XY)< E(X) + E(Y)
For this reason, energy is released when chemical bonds are formed between individual atoms.
Electrons of the outer electron layer with the lowest binding energy with the nucleus, called valence... For example, in boron, these are electrons of 2 energy levels - 2 electrons for 2 s-orbitals and 1 by 2 p-orbitals:
When a chemical bond is formed, each atom seeks to obtain an electronic configuration of atoms noble gases, i.e. so that there are 8 electrons in its outer electron layer (2 for the elements of the first period). This phenomenon is called the octet rule.
Achievement of the electronic configuration of a noble gas by atoms is possible if initially single atoms make part of their valence electrons common to other atoms. In this case, common electron pairs are formed.
Depending on the degree of electron socialization, covalent, ionic and metallic bonds can be distinguished.
Covalent bond
A covalent bond occurs most often between the atoms of nonmetal elements. If the atoms of non-metals that form a covalent bond belong to different chemical elements, such a bond is called covalent polar. The reason for this name lies in the fact that the atoms of different elements also have a different ability to attract a common electron pair. Obviously, this leads to a shift of the common electron pair towards one of the atoms, as a result of which a partial negative charge is formed on it. In turn, a partial positive charge is formed on the other atom. For example, in a hydrogen chloride molecule, an electron pair is shifted from a hydrogen atom to a chlorine atom:
Examples of substances with a covalent polar bond:
СCl 4, H 2 S, CO 2, NH 3, SiO 2, etc.
A covalent non-polar bond is formed between the atoms of non-metals of the same chemical element. Since the atoms are identical, their ability to pull off shared electrons is the same. In this regard, no displacement of the electron pair is observed:
The above mechanism for the formation of a covalent bond, when both atoms provide electrons for the formation of common electron pairs, is called exchange.
There is also a donor-acceptor mechanism.
When a covalent bond is formed by the donor-acceptor mechanism, a common electron pair is formed due to the filled orbital of one atom (with two electrons) and the empty orbital of another atom. An atom providing a lone electron pair is called a donor, and an atom with a free orbital is called an acceptor. Atoms with paired electrons act as donors of electron pairs, for example, N, O, P, S.
For example, according to the donor-acceptor mechanism, the fourth covalent N-H bond is formed in the ammonium cation NH 4 +:
In addition to polarity, covalent bonds are also characterized by energy. Bond energy is the minimum energy required to break a bond between atoms.
The binding energy decreases with an increase in the radii of the bonded atoms. Since, as we know, atomic radii increase downward along subgroups, one can, for example, conclude that the strength of the halogen-hydrogen bond increases in the series:
HI< HBr < HCl < HF
Also, the bond energy depends on its multiplicity - the greater the bond multiplicity, the more its energy. The bond multiplicity refers to the number of common electron pairs between two atoms.
Ionic bond
The ionic bond can be considered as the limiting case of the covalent polar bond. If in a covalent-polar bond the total electron pair is partially displaced to one of the pair of atoms, then in the ionic it is almost completely "given" to one of the atoms. The atom that donated the electron (s) acquires a positive charge and becomes cation, and the atom that took the electrons from it acquires a negative charge and becomes anion.
Thus, an ionic bond is a bond formed due to the electrostatic attraction of cations to anions.
The formation of this type of bond is characteristic of the interaction of atoms of typical metals and typical non-metals.
For example, potassium fluoride. The potassium cation is obtained as a result of the abstraction of one electron from the neutral atom, and the fluorine ion is formed when one electron is attached to the fluorine atom:
A force of electrostatic attraction arises between the resulting ions, as a result of which an ionic compound is formed.
During the formation of a chemical bond, electrons from the sodium atom passed to the chlorine atom and oppositely charged ions were formed, which have a complete external energy level.
It was found that the electrons from the metal atom are not completely detached, but only shifted towards the chlorine atom, as in a covalent bond.
Most binary compounds that contain metal atoms are ionic. For example, oxides, halides, sulfides, nitrides.
An ionic bond also occurs between simple cations and simple anions (F -, Cl -, S 2-), as well as between simple cations and complex anions (NO 3 -, SO 4 2-, PO 4 3-, OH -). Therefore, salts and bases (Na 2 SO 4, Cu (NO 3) 2, (NH 4) 2 SO 4), Ca (OH) 2, NaOH) are referred to ionic compounds.
Metal bond
This type of bond is formed in metals.
The atoms of all metals on the outer electron layer have electrons that have a low binding energy with the atomic nucleus. For most metals, the process of loss of external electrons is energetically favorable.
In view of such a weak interaction with the nucleus, these electrons in metals are very mobile, and the following process continuously occurs in each metal crystal:
M 0 - ne - \u003d M n +, where M 0 is a neutral metal atom, and M n + is a cation of the same metal. The figure below provides an illustration of the ongoing processes.
That is, electrons "carry" along the metal crystal, detaching from one metal atom, forming a cation from it, joining another cation, forming a neutral atom. This phenomenon was called "electronic wind", and the set of free electrons in a crystal of a non-metal atom was called "electron gas". This type of interaction between metal atoms was called a metal bond.
Hydrogen bond
If a hydrogen atom in any substance is associated with an element with high electronegativity (nitrogen, oxygen or fluorine), such a substance is characterized by such a phenomenon as a hydrogen bond.
Since a hydrogen atom is bonded to an electronegative atom, a partial positive charge is formed on the hydrogen atom and a partial negative charge on the electronegative atom. In this regard, it becomes possible electrostatic attraction between the partially positively charged hydrogen atom of one molecule and the electronegative atom of another. For example, a hydrogen bond is observed for water molecules:
It is the hydrogen bond that explains the abnormally high melting point of water. In addition to water, strong hydrogen bonds are also formed in substances such as hydrogen fluoride, ammonia, oxygen-containing acids, phenols, alcohols, and amines.
Chemical bond characteristics
The doctrine of chemical bonds forms the basis of all theoretical chemistry. A chemical bond is understood as an interaction of atoms that binds them into molecules, ions, radicals, crystals. There are four types of chemical bonds: ionic, covalent, metallic and hydrogen... Different types of bonds can be contained in the same substances.
1. In the bases: between the oxygen and hydrogen atoms in the hydroxo groups, the bond is polar covalent, and between the metal and the hydroxo group, it is ionic.
2. In the salts of oxygen-containing acids: between the non-metal atom and the oxygen of the acid residue - covalent polar, and between the metal and acid residue - ionic.
3. In salts of ammonium, methylammonium, etc. between nitrogen and hydrogen atoms - covalent polar, and between ammonium or methylammonium ions and acid residue - ionic.
4. In metal peroxides (for example, Na 2 O 2), the bond between oxygen atoms is covalent non-polar, and between metal and oxygen it is ionic, etc.
The reason for the unity of all types and types of chemical bonds is their identical chemical nature - electron-nuclear interaction. The formation of a chemical bond in any case is the result of the electron-nuclear interaction of atoms, accompanied by the release of energy.
Methods for the formation of a covalent bond
Covalent chemical bond- This is a bond that arises between atoms due to the formation of common electron pairs.
Covalent compounds are usually gases, liquids, or relatively low melting solids. One of the rare exceptions is diamond, which melts above 3,500 ° C. This is due to the structure of diamond, which is a continuous lattice of covalently bonded carbon atoms, rather than a collection of individual molecules. In fact, any diamond crystal, regardless of its size, is one huge molecule.
A covalent bond occurs when the electrons of two nonmetal atoms combine. The resulting structure is called a molecule.
The mechanism for the formation of such a bond can be exchange and donor-acceptor.
In most cases, two covalently bonded atoms have different electronegativity and the shared electrons do not belong to two atoms equally. Most of the time they are closer to one atom than to another. In a molecule of hydrogen chloride, for example, the electrons forming a covalent bond are located closer to the chlorine atom, since its electronegativity is higher than that of hydrogen. However, the difference in the ability to attract electrons is not so great that a complete transfer of an electron from a hydrogen atom to a chlorine atom occurs. Therefore, the bond between hydrogen and chlorine atoms can be regarded as a cross between an ionic bond (complete electron transfer) and a non-polar covalent bond (symmetric arrangement of a pair of electrons between two atoms). Partial charge on atoms is denoted by the Greek letter δ. Such a bond is called a polar covalent bond, and a hydrogen chloride molecule is said to be polar, that is, it has a positively charged end (hydrogen atom) and a negatively charged end (chlorine atom).
1. The exchange mechanism operates when atoms form common electron pairs due to the combination of unpaired electrons.
1) H 2 - hydrogen.
The bond arises due to the formation of a common electron pair by s-electrons of hydrogen atoms (overlapping of s-orbitals).
2) HCl - hydrogen chloride.
The bond arises due to the formation of a common electron pair of s- and p-electrons (overlapping s-p-orbitals).
3) Cl 2: In the chlorine molecule covalent bond is formed by unpaired p-electrons (overlapping p-p-orbitals).
4) N \u200b\u200b2: In a nitrogen molecule, three common electron pairs are formed between the atoms.
Donor-acceptor mechanism of covalent bond formation
Donor has an electronic pair, acceptor- a free orbital that this pair can occupy. In the ammonium ion, all four bonds with hydrogen atoms are covalent: three were formed due to the creation of common electron pairs by the nitrogen atom and hydrogen atoms by the exchange mechanism, and one by the donor-acceptor mechanism. Covalent bonds are classified according to the method of overlapping electron orbitals, as well as their displacement to one of the bonded atoms. The chemical bonds formed by overlapping electron orbitals along the link are called σ -connections (sigma links). The sigma link is very strong.
p-orbitals can overlap in two regions, forming a covalent bond due to lateral overlap.
The chemical bonds formed as a result of the "lateral" overlap of electron orbitals outside the communication line, ie, in two regions, are called pi bonds.
According to the degree of displacement of common electron pairs to one of the atoms connected by them, a covalent bond can be polar and non-polar. A covalent chemical bond formed between atoms with the same electronegativity is called non-polar. Electron pairs are not displaced towards any of the atoms, since the atoms have the same electronegativity - the property of drawing valence electrons away from other atoms. For instance,
that is, molecules of simple non-metallic substances are formed through a covalent non-polar bond. A covalent chemical bond between atoms of elements whose electronegativities differ is called polar.
For example, NH 3 is ammonia. Nitrogen is more electronegative than hydrogen, so the common electron pairs are shifted towards its atom.
Covalent bond characteristics: bond length and energy
The characteristic properties of a covalent bond are its length and energy. The bond length is the distance between the nuclei of the atoms. The shorter its length, the stronger the chemical bond. However, a measure of bond strength is the bond energy, which is determined by the amount of energy required to break the bond. It is usually measured in kJ / mol. Thus, according to experimental data, the bond lengths of the H2, Cl 2 and N 2 molecules are, respectively, 0.074, 0.198, and 0.109 nm, and the bond energies are 436, 242, and 946 kJ / mol, respectively.
Jonah. Ionic bond
There are two main possibilities for an atom to obey the octet rule. The first is the formation of an ionic bond. (The second is the formation of a covalent bond, which will be discussed below). When an ionic bond is formed, a metal atom loses electrons, and a non-metal atom gains.
Let's imagine that two atoms "meet": a metal atom of group I and a non-metal atom of group VII. The metal atom has a single electron on the external energy level, and the non-metal atom just lacks just one electron for its external level to be complete. The first atom will easily give the second its electron, which is far from the nucleus and weakly bound to it, and the second will give it a free space on its external electronic level. Then the atom, deprived of one of its negative charge, will become a positively charged particle, and the second will turn into a negatively charged particle due to the received electron. These particles are called ions.
This is a chemical bond that occurs between ions. The numbers showing the number of atoms or molecules are called coefficients, and the numbers showing the number of atoms or ions in a molecule are called indices.
Metal bond
Metals have specific properties that differ from those of other substances. Such properties are relatively high melting points, ability to reflect light, high thermal and electrical conductivity. These features are due to the existence in metals of a special type of bond - a metallic bond.
Metallic bond - a bond between positive ions in metal crystals, carried out due to the attraction of electrons freely moving around the crystal. The atoms of most metals on the outer level contain a small number of electrons - 1, 2, 3. These electrons easily come off, and the atoms turn into positive ions... Detached electrons move from one ion to another, linking them into a single whole. Connecting with ions, these electrons temporarily form atoms, then break off again and combine with another ion, etc. The process is endlessly going on, which can be schematically depicted as follows:
Consequently, in the bulk of the metal, atoms are continuously converted into ions and vice versa. The bond in metals between ions by means of shared electrons is called metallic. The metallic bond has some similarities with the covalent bond, since it is based on the sharing of external electrons. However, with a covalent bond, the external unpaired electrons of only two neighboring atoms are socialized, while with a metal bond, all atoms take part in the socialization of these electrons. That is why crystals with a covalent bond are fragile, while crystals with a metal bond are usually plastic, electrically conductive and have a metallic luster.
The metallic bond is characteristic both for pure metals and for mixtures of various metals - alloys in solid and liquid states. However, in the vapor state, the metal atoms are bound together by a covalent bond (for example, sodium vapor is used to fill yellow lamps to illuminate the streets of large cities). Metal pairs are composed of individual molecules (monoatomic and diatomic).
A metallic bond also differs from a covalent bond in strength: its energy is 3-4 times less than the energy of a covalent bond.
Bond energy is the energy required to break a chemical bond in all molecules that make up one mole of a substance. The energies of covalent and ionic bonds are usually high and are of the order of 100-800 kJ / mol.
Hydrogen bond
The chemical bond between positively polarized hydrogen atoms of one molecule (or part of it) and negatively polarized atoms of strongly electronegative elementshaving identical electron pairs (F, O, N and less often S and Cl), another molecule (or part of it) is called hydrogen. The mechanism of hydrogen bonding is partially electrostatic, partially d onorno-acceptor character.
Examples of intermolecular hydrogen bonds:
In the presence of such a bond, even low-molecular substances can, under normal conditions, be liquids (alcohol, water) or easily liquefied gases (ammonia, hydrogen fluoride). In biopolymers - proteins ( secondary structure) - there is an intramolecular hydrogen bond between carbonyl oxygen and hydrogen of the amino group:
Polynucleotide molecules - DNA (deoxyribonucleic acid) - are double helices in which two chains of nucleotides are linked to each other by hydrogen bonds. In this case, the principle of complementarity operates, i.e., these bonds are formed between certain pairs consisting of purine and pyrimidine bases: against the adenine nucleotide (A) there is thymine (T), and against the guanine (G) - cytosine (C).
Substances with hydrogen bonds have molecular crystal lattices.
Types (kinds) of connection of words in a phrase
In a subordinate phrase, one word is the main word, and the other is dependent (you can ask a question to it from the main word). There are three types of relationship between words in a phrase:
- Agreement - a type of connection in which the dependent word is similar in its form to the main word.
Examples: beautiful hat, about an interesting story.
- Control - a type of connection in which the dependent word is used in a certain form, depending on the lexical and grammatical meaning of the main word.
- Contiguity - a type of connection, in which the dependence of a word is expressed lexically, by word order and intonation, without the use of official words or morphological changes.
Examples: sing beautifully, lie trembling.
Classification of phrases by the main word
Classification of phrases by composition (by structure)
- Simple phrases, as a rule, consist of two significant words.
Examples: new home, man with gray hair (\u003d gray-haired man).
- Complex phrases are formed on the basis of simple phrases.
Examples: fun walks in the evenings, relax in the summer in the south.
The academic classification of phrases by composition is more complicated. Besides simple and complex phrases also highlight combined... The main criterion for this classification is the way in which words are connected within a phrase.
Classification of phrases according to the degree of fusion of components
According to the degree of merging of the components, phrases are distinguished:
- syntactically free
Examples: high house, go to school.
- syntactically (or phraseologically) not freeforming an indecomposable syntactic unity and acting as one member in a sentence:
Examples: three sisters, pansies, bang.
Notes
Links
see also
- Syntagma (speech)
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A word combination is a combination of two or more words related in meaning and grammatical, serving to delineate a single concept (object, quality of an object, action, etc.). The phrase is considered as a unit ... ... Wikipedia
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A sentence (in a language) is the minimum unit of human speech, which is a grammatically organized combination of words (or a word) with semantic and intonational completeness. ("Modern Russian language" Valgin N.S.) ... Wikipedia
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Subordination, or subordinate relationship, the relation of syntactic inequality between words in a phrase and a sentence, as well as between predicative parts complex sentence... In this connection, one of the components (words or sentences) ... ... Wikipedia
Crystals.
There are four types of chemical bonds: ionic, covalent, metallic and hydrogen.
Ionic chemical bond
Ionic chemical bond is a bond formed due to the electrostatic attraction of cations to anions.
As you know, the most stable is the electronic configuration of atoms in which there will be 8 electrons on the external electronic level, like the atoms of noble gases (or for the first energy level - 2). In chemical interactions, atoms tend to acquire just such a stable electronic configuration and often achieve this either as a result of the addition of valence electrons from other atoms (reduction process), or as a result of the return of their valence electrons (oxidation process). Atoms that have attached "foreign" electrons turn into negative ions, or anions. Atoms that donate their electrons turn into positive ions, or cations. It is clear that the forces of electrostatic attraction arise between the anions and cations, which will hold them near each other, thereby realizing an ionic chemical bond.
Since cations form mainly metal atoms, and anions form nonmetal atoms, it is logical to conclude that this type of bond is characteristic of compounds of typical metals (elements of the main subgroups of groups I and II, except for magnesium and beryllium Be) with typical nonmetals (elements of the main subgroup VII group). A classic example is the formation of alkali metal halides (fluorides, chlorides, etc.). For example, consider the scheme for the formation of an ionic bond in sodium chloride:
Two oppositely charged ions, bound by attractive forces, do not lose the ability to interact with oppositely charged ions, as a result of which compounds with an ionic crystal lattice are formed. Ionic compounds are solid, strong, refractory substances with a high melting point.
Solutions and melts of most ionic compounds are electrolytes. This type of bond is characteristic of typical metal hydroxides and many salts of oxygen-containing acids. However, when an ionic bond is formed, an ideal (complete) transition of electrons does not occur. The ionic bond is an extreme case of the covalent polar bond.
In an ionic compound, ions are represented as if in the form of electric charges with spherical symmetry electric field, equally decreasing with increasing distance from the center of the charge (ion) in any direction. Therefore, the interaction of ions does not depend on the direction, that is, the ionic bond, in contrast to the covalent bond, will be non-directional.
The ionic bond also exists in ammonium salts, where there are no metal atoms (their role is played by the ammonium cation).
Covalent chemical bond
A covalent chemical bond is a bond that occurs between atoms due to the formation of common electron pairs.
Its description is also based on the idea that atoms of chemical elements acquire an energetically favorable and stable electronic configuration of eight electrons (for a hydrogen atom of two). This configuration is obtained by atoms not through the donation or attachment of electrons, as in the case of ionic bonds, but through the formation of common electron pairs. The mechanism for the formation of such a bond can be exchange or donor-acceptor.
The exchange mechanism works when atoms form common electron pairs by combining unpaired electrons. For instance:
1) H2 - hydrogen:
The bond arises due to the formation of a common electron pair by s-electrons of hydrogen atoms (overlapping of s-orbitals): 
The bond arises due to the formation of a common electron pair of s- and p-electrons (overlapping s-p-orbitals): 
Let us consider the donor-acceptor mechanism of the formation of a covalent bond using the classical example of the formation of the ammonium ion NH4 +:
The donor has an electron pair, the acceptor has a free orbital pair, which this pair can occupy. In the ammonium ion, all four bonds with hydrogen atoms are covalent: three were formed due to the creation of common electron pairs by the nitrogen atom and hydrogen atoms by the exchange mechanism, one was formed by the donor-acceptor mechanism. All four bonds N-H in the ammonium cation are equivalent.
The donor-acceptor bond in the methylammonium ion [CH3NH3] + is formed similarly.
Covalent bonds are classified not only by the mechanism of formation of common electron pairs connecting atoms, but also by the method of overlapping electron orbits, by the number of common electron pairs, as well as by their displacement to one of the bonded atoms.
According to the method of overlapping electron orbitals, covalent bonds of sigma and pi are distinguished.
In a nitrogen molecule, one common electron pair is formed due to the sigma bond (the electron density is in one region located on the line connecting the nuclei of the atoms; the bond is strong).
Two other common electron pairs are formed due to n-bonds, that is, lateral overlap of p-orbitals in two regions; The pi bond is less strong than the sigma bond. 
In a nitrogen molecule, there is one sigma bond between the atoms and two pi bonds, which are in mutually perpendicular planes (since 3 unpaired p-electrons of each atom interact).
Therefore, o-bonds can be formed due to the overlapping of electron orbitals:
and also due to the overlap of "pure" and hybrid orbitals:
sp 2 -sp 2 (C2H4), etc.
By the number of common electron pairs connecting atoms, that is, by the multiplicity, they are distinguished covalent bonds:
1) single: 
2) double:
CO,
carbon monoxide (IV)
3) triple:
C2H2
HC \u003d -CH acetylene
According to the degree of displacement of common electron pairs to one of the atoms connected by them, a covalent bond can be non-polar and polar. With a non-polar covalent bond, common electron pairs are not displaced to any of the atoms, since these atoms have the same electronegativity (EO) - the property to pull valence electrons away from other atoms.
A covalent chemical bond formed between atoms with the same electronegativity is called non-polar.
Through a covalent non-polar bond, molecules of simple non-metal substances are formed.
The values \u200b\u200bof the relative electronegativity of phosphorus and hydrogen are practically the same: EO (H) \u003d 2.1; EO (P) \u003d \u003d 2.1, therefore, in the phosphine molecule PH3, the bonds between the phosphorus atom and the hydrogen atoms are covalent non-polar.
A covalent chemical bond between atoms of elements whose electronegativities differ is called polar
For instance:
NH3
ammonia
Nitrogen is a more electronegative element than hydrogen, so the common electron pairs shift towards its atom. 
A distinction should be made between the polarity of the molecule and the polarity of the bond. The polarity of a bond depends on the values \u200b\u200bof the electronegativity of the linked atoms, and the polarity of the molecule depends on both the polarity of the bond and the geometry of the molecule. For example, the bonds in the CO2 molecule will be polar, and the molecule will not be polar, since it has a linear structure.
The H2O water molecule is polar, as it is formed by two covalent polar bonds H-\u003e 0 and has an angular shape. The HOH bond angle is 104.5 °, therefore, a negative pole of the molecule is formed for an oxygen atom with a partial negative charge of 6 and two lone electron pairs, and a positive pole for hydrogen atoms with a charge of 6+. The water molecule is a dipole.
Substances with a covalent bond are characterized by a crystal lattice of two types:
atomic - very durable (diamond, graphite, quartz); molecular - under normal conditions these are gases, volatile liquids and solid, but low-melting or sublimating substances (Cl2, H20, iodine I2, “dry ice” CO2, etc.).
The intramolecular covalent bond is strong, but the intermolecular interaction is very weak, as a result of which the molecular crystal lattice is fragile.
Metal bond
The bond in metals and alloys, which is carried out by relatively free electrons between metal ions in a metallic crystal lattice, is called metallic.
Such a bond is undirected, unsaturated, characterized by a small number of valence electrons and a large number of free orbitals, which is typical for metal atoms. Formation diagram of a metal bond (M - metal):
_
M 0 - ne<-> M n +
The presence of a metal bond is due to physical properties metals and alloys: hardness, electrical and thermal conductivity, malleability, ductility, metallic luster. Substances with a metallic bond have a metallic crystal lattice. Its nodes contain metal ions or atoms, between which electrons move freely (within the crystal) ("electron gas").
Hydrogen bond
The chemical bond between positively polarized hydrogen atoms of one molecule (or part of it) and negatively polarized atoms of strongly electronegative elements that have lone electron pairs of another molecule (or part of it) is called hydrogen.
The mechanism of hydrogen bond formation is partially electrostatic and partially donor-acceptor. In the presence of such a bond, even low-molecular substances can, under normal conditions, be liquids (alcohol, water) or easily liquefied gases (ammonia, hydrogen fluoride).
In biopolymers - proteins (secondary structure) there is an intramolecular hydrogen bond between the carbonyl oxygen and the amino hydrogen.
Polynucleotide molecules - DNA (deoxyribonucleic acid) are double helices in which two chains of nucleotides are hydrogen bonded to each other. In this case, the principle of complementarity works, that is, these bonds are formed between certain pairs consisting of purine and pyrimidine bases: against the adenine nucleotide (A) there is thymine (T), and against the guanine (G) - cytosine (C).
Substances with hydrogen bonds have molecular crystal lattices.
The uniform nature of the chemical bond
The division of chemical bonds into types is conditional, since they are all characterized by a certain unity.
The ionic bond can be considered as the limiting case of the covalent polar bond.
The metallic bond combines the covalent interaction of atoms with the help of shared electrons and the electrostatic attraction between these electrons and metal ions.
In substances, there are often no extreme cases of chemical bonds (or "pure" chemical bonds).
For example, lithium fluoride 1lK is referred to as ionic compounds. In fact, the bond in it is 80% ionic and 20% covalent. Therefore, it is more correct to speak about the degree of polarity (ionicity) of a chemical bond.
In the series of hydrogen halides HF - HCl - HBr - HI - HAt, the degree of bond polarity decreases, because the difference in the values \u200b\u200bof electronegativity of halogen and hydrogen atoms decreases, and in hydrogen astate the bond becomes almost non-polar (EO (H) \u003d 2.1; EO (Ar) \u003d 2.2).
Different types of bonds can be contained in the same substances, for example:
1) in the bases - between the oxygen and hydrogen atoms in the hydroxyl groups, the bond is covalent polar, and between the metal and the hydroxyl group - ionic;
2) in salts of oxygen-containing acids - between the atoms of the non-metal and the oxygen of the acid residue - covalent polar, and between the metal and the acid residue - ionic;
3) in salts of ammonium, methylammonium, etc. - between nitrogen and hydrogen atoms - covalent polar, and between ammonium or methylammonium ions and acid residue - ionic;
4) in metal peroxides (for example, Na 2 O 2) - the bond between oxygen atoms is covalent non-polar, and between metal and oxygen - ionic, etc.
Various types of links can transform one into another:
During electrolytic dissociation of covalent compounds in water, the covalent polar bond transforms into an ionic one;
When metals evaporate, the metal bond turns into a covalent non-polar, etc.
The reason for the unity of all types and types of chemical bonds is their identical physical nature - electron-nuclear interaction. The formation of a chemical bond in any case is the result of the electron-nuclear interaction of atoms, accompanied by the release of energy (Table 7).
Table 7 Types of chemical bonds
1. The expression is often encountered: "The molecules of noble gases are monoatomic." How does it correspond to the truth?
2. Why, unlike most non-metallic elements, their brightest representatives - halogens - do not form allotropic modifications?
3. Give the most complete characterization of the chemical bond in the nitrogen molecule using the following features: EO of bonded atoms, the mechanism of formation, the method of overlapping electron orbitals, the multiplicity of the bond.
4. Determine the type of chemical bond and consider the schemes of its formation in substances with the formulas: Ca, CaF2, F2, OF2.
5. Write the structural formulas of substances: CO, CaC2, CS2, FeS2. Determine the oxidation state of the elements and their valence (if possible) in these substances.
6. Prove that all types of chemical bonds have a common nature.
7. Why are the N2, CO and C2H2 molecules called isoelectronic?
Basic and additional textbooks
Word combination.
With the help of the site, you can easily learn to determine the type of subordinate relationship.
Submissive relationship Is a connection that unites sentences or words, one of which is the main (subordinate), and the other is dependent (subordinate).
Collocation - This is a combination of two or more significant words related to each other in meaning and grammar.
green eyes, writing letters, difficult to convey.
In the phrase, the main (from which the question is asked) and dependent (to which the question is asked) word is highlighted:
Blue ball. Rest outside the city. Ball and rest are the main words.
Trap!
Are not subordinate phrases:
1. Combination of an independent word with an official one: near the house, before the storm, let him sing;
2. Combinations of words in phraseological units: beat goofs, play the fool, headlong;
3. Subject and predicate: night has come;
4. Compound word forms : lighter, will walk;
5. Groups of words united by a compositional link: Fathers and Sons.
Videos about types of subordinate relationships
If you like the video format, you can watch it.
There are three types of subordinate relationships:
| communication type | what part of speech can the dependent word be | what question is asked for the dependent word |
| agreement (when changing the main word, the dependent changes): seashore reading youth, first snow, my home |
adjective, participle, ordinal, some categories of pronouns | which one? Questions can change by case! |
| control (when changing the main word, the dependent does not change): | noun or pronoun in the indirect case with or without a preposition | questions of indirect cases (who? what? - about whom? about what?) Remember! The prepositional-case form of a noun can be a circumstance, therefore, circumstances are asked to these forms (see below) |
| contiguity (dependent word is an unchangeable part of speech!): listen carefully, go without looking back, soft-boiled egg |
1.infinitive 2. verbal participle 3.adverb 4. possessive pronouns (him, her, them) |
1. what to do? what to do? 2. what to do? what having done? 3. How? Where? where? where from? when? what for? why? |
Distinguish!
Her coat is adjoining (whose), to see her is control (whom).
In the categories of pronouns, two homonymous (identical in sound and spelling, but different in meaning) are distinguished. The personal pronoun answers the questions of indirect cases, and it participates in a subordinate connection - control, and the possessive answers the question whose? and is immutable, it participates in contiguity.
Go to the garden - management, go there - adjoining.
Distinguish between prepositional and adverbial forms. They may have the same questions! If there is a preposition between the main word and the dependent, then you have control.
Algorithm of actions №1.
1) Determine the main word by asking a question from one word to another.
2) Determine the part of speech of the dependent word.
3) Pay attention to the question you are asking about the dependent word.
4) On the basis of the identified signs, determine the type of connection.
Analysis of the task.
What type of connection is used in the phrase FINE MECHANICALLY.
We define the main word and ask a question from him: to catch (how?) mechanically; catch -the main word, mechanically -dependent. Determine the part of speech of the dependent word: mechanicallyIs an adverb. If the dependent word answers the question as? and is an adverb, then the connection is used in the phrase adjoining.
Algorithm of actions №2.
1. It is easier for you to find the dependent word in the text first.
2. If you need agreement, look for a word that answers the question which one? whose?
3. If you need control, look for a noun or pronoun not in the nominative case.
4. If you need to find a contiguity, look for an unchangeable word (infinitive, participle, adverb or possessive pronoun).
5. Establish from which word you can ask a question to the dependent word.