The concept of a chemical bond is of no small importance in various fields of chemistry as a science. This is due to the fact that it is with its help that individual atoms are able to combine into molecules, forming all kinds of substances, which, in turn, are the subject of chemical research.
The diversity of atoms and molecules is associated with the emergence of various types of bonds between them. Different classes of molecules are characterized by their own characteristics of electron distribution, and therefore their own types of bonds.
Basic Concepts
Chemical bond called a set of interactions that lead to the bonding of atoms with the formation of stable particles of a more complex structure (molecules, ions, radicals), as well as aggregates (crystals, glasses, etc.). The nature of these interactions is electrical in nature, and they arise during the distribution of valence electrons in approaching atoms.
Valence accepted name the ability of an atom to form a certain number of bonds with other atoms. In ionic compounds, the number of electrons given up or gained is taken as the valence value. In covalent compounds it is equal to the number of shared electron pairs.
Under the degree of oxidation is understood as a conditional the charge that could be on an atom if all polar covalent bonds were ionic in nature.
The multiplicity of a connection is called the number of shared electron pairs between the atoms under consideration.
The bonds considered in various branches of chemistry can be divided into two types of chemical bonds: those that lead to the formation of new substances (intramolecular) , And those that occur between molecules (intermolecular).
Basic communication characteristics
Energy of communication is the energy required to break all existing bonds in a molecule. It is also the energy released during bond formation.
Link length is the distance between neighboring nuclei of atoms in a molecule at which the forces of attraction and repulsion are balanced.
These two characteristics of a chemical bond between atoms are a measure of its strength: the shorter the length and the greater the energy, the stronger the bond.
Bond angle it is customary to call the angle between the represented lines passing in the direction of communication through the nuclei of atoms.
Methods for describing connections
The most common two approaches to explaining chemical bonding, borrowed from quantum mechanics:
Molecular orbital method. He views the molecule as a collection of electrons and atomic nuclei, with each individual electron moving in the field of action of all other electrons and nuclei. The molecule has an orbital structure, and all its electrons are distributed in these orbits. This method is also called MO LCAO, which stands for “molecular orbital - linear combination
Valence bond method. Represents a molecule as a system of two central molecular orbitals. Moreover, each of them corresponds to one bond between two neighboring atoms in the molecule. The method is based on the following provisions:
- The formation of a chemical bond is carried out by a pair of electrons having opposite spins, which are located between the two atoms in question. The electron pair formed belongs equally to the two atoms.
- The number of bonds formed by one or another atom is equal to the number of unpaired electrons in the ground and excited states.
- If electron pairs do not participate in the formation of a bond, then they are called lone pairs.
Electronegativity
The type of chemical bond in substances can be determined based on the difference in the electronegativity values of its constituent atoms. Under electronegativity understand the ability of atoms to attract shared electron pairs (electron cloud), which leads to bond polarization.
There are various ways to determine the electronegativity values of chemical elements. However, the most used is the scale based on thermodynamic data, which was proposed back in 1932 by L. Pauling.
The greater the difference in electronegativity of atoms, the more pronounced its ionicity. On the contrary, equal or similar electronegativity values indicate the covalent nature of the bond. In other words, it is possible to determine mathematically what chemical bond is observed in a particular molecule. To do this, you need to calculate ΔХ - the difference in electronegativity of atoms using the formula: ΔХ=|Х 1 -X 2 |.
- If ΔХ>1.7, then the bond is ionic.
- If 0.5≤ΔХ≤1.7, then the covalent bond is polar.
- If ΔХ=0 or close to it, then the bond is classified as covalent nonpolar.
Ionic bond
An ionic bond is a bond that appears between ions or due to the complete withdrawal of a common electron pair by one of the atoms. In substances, this type of chemical bond is carried out by forces of electrostatic attraction.
Ions are charged particles formed from atoms by gaining or losing electrons. If an atom accepts electrons, it acquires a negative charge and becomes an anion. If an atom gives up valence electrons, it becomes a positively charged particle called a cation.
It is characteristic of compounds formed by the interaction of atoms of typical metals with atoms of typical non-metals. The main reason for this process is the desire of atoms to acquire stable electronic configurations. And for this, typical metals and non-metals need to give or accept only 1-2 electrons, which they do with ease.
The mechanism of formation of an ionic chemical bond in a molecule is traditionally considered using the example of the interaction of sodium and chlorine. Alkali metal atoms easily give up an electron, drawn by a halogen atom. As a result, the Na + cation and the Cl - anion are formed, which are held together by electrostatic attraction.
There is no ideal ionic bond. Even in such compounds, which are often classified as ionic, the final transfer of electrons from atom to atom does not occur. The formed electron pair still remains in common use. Therefore, they talk about the degree of ionicity of a covalent bond.
An ionic bond is characterized by two main properties related to each other:
- non-directionality, i.e. the electric field around the ion has the shape of a sphere;
- unsaturation, i.e., the number of oppositely charged ions that can be placed around any ion, is determined by their sizes.
Covalent chemical bond
A bond formed by overlapping electron clouds of nonmetal atoms, that is, carried out by a common electron pair, is called a covalent bond. The number of shared electron pairs determines the multiplicity of the bond. Thus, hydrogen atoms are connected by a single H··H bond, and oxygen atoms form an O::O double bond.
There are two mechanisms for its formation:
- Exchange - each atom represents one electron to form a common pair: A· + ·B = A:B, while external atomic orbitals, on which one electron is located, participate in the bonding.
- Donor-acceptor - to form a bond, one of the atoms (donor) provides a pair of electrons, and the second (acceptor) provides a free orbital for its placement: A + : B = A: B.
The ways in which electron clouds overlap during the formation of a covalent chemical bond are also different.
- Direct. The region of cloud overlap lies on a straight imaginary line connecting the nuclei of the atoms in question. In this case, σ bonds are formed. The type of chemical bond that occurs in this case depends on the type of electron clouds that overlap: s-s, s-p, p-p, s-d or p-d σ bonds. In a particle (molecule or ion), only one σ bond is possible between two neighboring atoms.
- Lateral. It is carried out on both sides of the line connecting the nuclei of atoms. This is how a π bond is formed, and its varieties are also possible: p-p, p-d, d-d. A π bond is never formed separately from a σ bond; it can occur in molecules containing multiple (double and triple) bonds.
Properties of covalent bonds
They determine the chemical and physical properties of compounds. The main properties of any chemical bond in substances are its directionality, polarity and polarizability, as well as saturation.
Focus connections are determined by the features of the molecular structure of substances and the geometric shape of their molecules. Its essence is that the best overlap of electron clouds is possible at a certain orientation in space. The options for the formation of σ- and π-bonds have already been discussed above.
Under saturation understand the ability of atoms to form a certain number of chemical bonds in a molecule. The number of covalent bonds for each atom is limited by the number of outer orbitals.
Polarity bond depends on the difference in the electronegativity values of the atoms. The uniformity of the distribution of electrons between the nuclei of atoms depends on it. According to this characteristic, a covalent bond can be polar or nonpolar.
- If the common electron pair belongs equally to each of the atoms and is located at the same distance from their nuclei, then the covalent bond is non-polar.
- If a common pair of electrons is displaced towards the nucleus of one of the atoms, then a covalent polar chemical bond is formed.
Polarizability is expressed by the displacement of bond electrons under the influence of an external electric field, which may belong to another particle, neighboring bonds in the same molecule, or come from external sources of electromagnetic fields. Thus, a covalent bond under their influence can change its polarity.
Hybridization of orbitals is understood as a change in their shapes during a chemical bond. This is necessary to achieve the most effective overlap. The following types of hybridization exist:
- sp3. One s and three p orbitals form four “hybrid” orbitals of the same shape. Outwardly it resembles a tetrahedron with an angle between the axes of 109°.
- sp2. One s- and two p-orbitals form a flat triangle with an angle between the axes of 120°.
- sp. One s- and one p-orbital form two “hybrid” orbitals with an angle between their axes of 180°.
A special feature of the structure of metal atoms is their rather large radius and the presence of a small number of electrons in outer orbitals. As a result, in such chemical elements the bond between the nucleus and valence electrons is relatively weak and is easily broken.
Metal A bond is an interaction between metal atoms and ions that occurs with the help of delocalized electrons.
In metal particles, valence electrons can easily leave the outer orbitals, as well as occupy vacant positions on them. Thus, at different moments of time the same particle can be an atom and an ion. The electrons detached from them move freely throughout the entire volume of the crystal lattice and carry out a chemical bond.
This type of bond has similarities with ionic and covalent bonds. Just like ionic bonds, metallic bonds require ions to exist. But if cations and anions are needed to carry out electrostatic interaction in the first case, then in the second the role of negatively charged particles is played by electrons. When comparing a metallic bond with a covalent bond, both require shared electrons to form. However, unlike polar chemical bonds, they are not localized between two atoms, but belong to all metal particles in the crystal lattice.
Metallic bonding is responsible for the special properties of almost all metals:
- plasticity is present due to the possibility of displacement of layers of atoms in a crystal lattice held by an electron gas;
- metallic luster, which is observed due to the reflection of light rays from electrons (in the powder state there is no crystal lattice and, therefore, electrons moving through it);
- electrical conductivity, which is carried out by a flow of charged particles, and in this case small electrons move freely among large metal ions;
- thermal conductivity is observed due to the ability of electrons to transfer heat.
This type of chemical bond is sometimes called intermediate between covalent and intermolecular interactions. If a hydrogen atom has a bond with one of the highly electronegative elements (such as phosphorus, oxygen, chlorine, nitrogen), then it is capable of forming an additional bond, called a hydrogen bond.
It is much weaker than all the types of bonds discussed above (energy no more than 40 kJ/mol), but it cannot be neglected. This is why a hydrogen chemical bond appears as a dotted line in the diagram.
The occurrence of a hydrogen bond is possible due to the simultaneous donor-acceptor electrostatic interaction. A large difference in electronegativity values leads to the appearance of excess electron density on the O, N, F and other atoms, as well as to its deficiency on the hydrogen atom. In the event that there is no existing chemical bond between such atoms, when they are close enough, attractive forces are activated. In this case, the proton is the acceptor of the electron pair, and the second atom is the donor.
Hydrogen bonds can occur both between neighboring molecules, for example, water, carboxylic acids, alcohols, ammonia, and within a molecule, for example, salicylic acid.
The presence of hydrogen bonds between water molecules explains a number of its unique physical properties:
- The values of its heat capacity, dielectric constant, boiling and melting points, in accordance with calculations, should be significantly less than real ones, which is explained by the connectivity of molecules and the need to expend energy on breaking intermolecular hydrogen bonds.
- Unlike other substances, the volume of water increases as the temperature decreases. This occurs due to the fact that the molecules occupy a certain position in the crystal structure of ice and move away from each other by the length of the hydrogen bond.
This connection plays a special role for living organisms, since its presence in protein molecules determines their special structure, and therefore their properties. In addition, nucleic acids, making up the double helix of DNA, are also connected by hydrogen bonds.
Bonds in crystals
The vast majority of solids have a crystal lattice - a special relative arrangement of the particles that form them. In this case, three-dimensional periodicity is observed, and atoms, molecules or ions are located at the nodes, which are connected by imaginary lines. Depending on the nature of these particles and the connections between them, all crystalline structures are divided into atomic, molecular, ionic and metallic.
The nodes of the ionic crystal lattice contain cations and anions. Moreover, each of them is surrounded by a strictly defined number of ions with only the opposite charge. A typical example is sodium chloride (NaCl). They tend to have high melting points and hardness because they require a lot of energy to break down.
At the nodes of the molecular crystal lattice there are molecules of substances formed by covalent bonds (for example, I 2). They are connected to each other by a weak van der Waals interaction, and therefore such a structure is easy to destroy. Such compounds have low boiling and melting points.
The atomic crystal lattice is formed by atoms of chemical elements with high valency values. They are connected by strong covalent bonds, which means that the substances have high boiling and melting points and high hardness. An example is a diamond.
Thus, all types of bonds present in chemical substances have their own characteristics, which explain the subtleties of the interaction of particles in molecules and substances. The properties of the compounds depend on them. They determine all processes occurring in the environment.
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Each atom has a certain number of electrons.
When entering into chemical reactions, atoms donate, gain, or share electrons, achieving the most stable electronic configuration. The configuration with the lowest energy (as in noble gas atoms) turns out to be the most stable. This pattern is called the “octet rule” (Fig. 1).
Rice. 1.
This rule applies to everyone types of connections. Electronic connections between atoms allow them to form stable structures, from the simplest crystals to complex biomolecules that ultimately form living systems. They differ from crystals in their continuous metabolism. At the same time, many chemical reactions proceed according to the mechanisms electronic transfer, which play a critical role in energy processes in the body.
A chemical bond is the force that holds together two or more atoms, ions, molecules, or any combination of these.
The nature of the chemical bond is universal: it is an electrostatic force of attraction between negatively charged electrons and positively charged nuclei, determined by the configuration of the electrons of the outer shell of atoms. The ability of an atom to form chemical bonds is called valence, or oxidation state. The concept of valence electrons- electrons that form chemical bonds, that is, located in the highest energy orbitals. Accordingly, the outer shell of the atom containing these orbitals is called valence shell. Currently, 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 connection isionic connection
According to Lewis and Kossel's electronic valence theory, atoms can achieve a stable electronic configuration in two ways: first, by losing electrons, becoming 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 opposite signs, a chemical bond is formed, called by Kossel “ electrovalent"(now 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 T and II groups of the periodic system and anions of non-metallic elements of groups VI and VII (16 and 17 subgroups, respectively, chalcogens And 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 model of electron transfer.
Rice. 2.
Rice. 3. Ionic bond in a molecule of table salt (NaCl)
Here it is appropriate to recall some properties that explain the behavior of substances in nature, in particular, consider the idea of acids And reasons.
Aqueous solutions of all these substances are electrolytes. They change color differently indicators. The mechanism of action of indicators was discovered by F.V. Ostwald. He showed that indicators are weak acids or bases, the color of which differs in the undissociated and dissociated states.
Bases can neutralize 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 undergo 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 N 2 O.
The properties of acids and bases are described by several theories. In accordance with the theory of S.A. Arrhenius, an acid is a substance that dissociates to form ions N+ , while the base forms ions HE- . This theory does not take into account the existence of organic bases that do not have hydroxyl groups.
In accordance with proton According to the theory of Brønsted and Lowry, an acid is a substance containing molecules or ions that donate protons ( donors protons), and a base is a substance consisting of molecules or ions that accept protons ( acceptors protons). Note that in aqueous solutions, hydrogen ions exist in hydrated form, that is, in the form of hydronium ions H3O+ . This theory describes reactions not only with water and hydroxide ions, but also those carried out in the absence of a solvent or with a non-aqueous solvent.
For example, in the reaction between ammonia N.H. 3 (weak base) and hydrogen chloride in the gas phase, solid ammonium chloride is formed, 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 conjugate pairs of acids and bases:
1)N.H. 4+ and N.H. 3
2) HCl And Cl ‑
Here, in each conjugate pair, the acid and base differ by one proton. Every acid has a conjugate base. A strong acid has a weak conjugate base, and a weak acid has a strong conjugate base.
The Brønsted-Lowry theory helps explain the unique role of water for 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 in reactions with aqueous solutions of ammonia, it is an acid.
1) CH 3 COOH + H2O ↔ H3O + + CH 3 COO- . Here, an acetic acid molecule donates a proton to a water molecule;
2) NH 3 + H2O ↔ NH 4 + + HE- . Here, an ammonia molecule accepts a proton from a water molecule.
Thus, water can form two conjugate pairs:
1) H2O(acid) and HE- (conjugate base)
2) H 3 O+ (acid) and H2O(conjugate base).
In the first case, water donates a proton, and in the second, it accepts it.
This property is called amphiprotonism. Substances that can react as both acids and bases are called amphoteric. Such substances are often found in living nature. For example, amino acids can form salts with both acids and bases. Therefore, peptides easily form coordination compounds with the metal ions present.
Thus, a characteristic property of an ionic bond is the complete movement of the bonding electrons to one of the nuclei. This means that between the ions there is a region where the electron density is almost zero.
The second type of connection iscovalent connection
Atoms can form stable electronic configurations by sharing electrons.
Such a bond is formed when a pair of electrons is shared one at a time from everyone atom. In this case, the shared bond electrons are distributed equally between the atoms. Examples of covalent bonds include homonuclear diatomic molecules H 2 , N 2 , F 2. The same type of connection is found in allotropes O 2 and ozone O 3 and for a polyatomic molecule S 8 and also heteronuclear molecules hydrogen chloride HCl, carbon dioxide CO 2, methane CH 4, ethanol WITH 2 N 5 HE, sulfur hexafluoride SF 6, acetylene WITH 2 N 2. All these molecules share the same electrons, and their bonds are saturated and directed in the same way (Fig. 4).
It is important for biologists that double and triple bonds have reduced covalent atomic radii compared to a single bond.
Rice. 4. Covalent bond in a Cl 2 molecule.
Ionic and covalent types of bonds are two extreme cases of the many existing types of chemical bonds, and in practice most bonds are intermediate.
Compounds of two elements located at opposite ends of the same or different periods of the periodic system predominantly form ionic bonds. As elements move closer together within a period, the ionic nature of their compounds decreases, and the covalent character increases. For example, the halides and oxides of 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 elements on the right side of the table are covalent ( H 2 O, CO 2, NH 3, NO 2, CH 4, phenol C6H5OH, glucose C 6 H 12 O 6, ethanol C 2 H 5 OH).
The covalent bond, in turn, has one more modification.
In polyatomic ions and in complex biological molecules, both electrons can only come from one atom. It is called donor electron pair. An atom that shares this pair of electrons with a donor is called acceptor electron pair. This type 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 d-elements most important for metabolism is largely described by coordination bonds.
Fig. 5.
As a rule, in a complex compound the 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 with the help of another theory of acids and bases proposed by GN. Lewis. He somewhat expanded the semantic 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. A Lewis base is a substance that has a lone electron pair, which, by donating electrons, forms a covalent bond with Lewis acid.
That is, Lewis's theory expands the range of acid-base reactions also 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, the cations are Lewis acids and the anions are Lewis bases. An example would be the following reactions:
It was noted above that the division of substances into ionic and covalent is relative, since complete electron transfer from metal atoms to acceptor atoms does not occur in covalent molecules. In compounds with ionic bonds, each ion is in the electric field of ions of the opposite sign, so they are mutually polarized, and their shells are deformed.
Polarizability determined by the electronic structure, charge and size of the ion; for anions it is higher than for cations. The highest polarizability among cations is for cations of greater charge and smaller size, for example, Hg 2+, Cd 2+, Pb 2+, Al 3+, Tl 3+. Has a strong polarizing effect N+ . Since the influence of ion polarization is two-way, it significantly changes the properties of the compounds they form.
The third type of connection isdipole-dipole connection
In addition to the listed types of communication, there are also dipole-dipole intermolecular interactions, also called van der Waals .
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 attraction, or London forces; rice. 6).
Rice. 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 = 3.338 × 10‑30 coulomb meters - C × m).
In biochemistry, there is another type of connection - hydrogen connection, which is a limiting case 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 similar electronegativity (such as chlorine and sulfur), the hydrogen bond is much weaker. The hydrogen atom is distinguished by one significant feature: when the bonding electrons are pulled away, its nucleus - the proton - is exposed and is no longer shielded by electrons.
Therefore, the atom turns into a large dipole.
A hydrogen bond, unlike a van der Waals bond, is formed not only during intermolecular interactions, but also within one molecule - intramolecular hydrogen 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 for the formation of a double helix of DNA (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. 1.
Table 1. Energy of intermolecular forces
Note: The degree of intermolecular interactions is reflected by the enthalpy of melting and evaporation (boiling). Ionic compounds require significantly more energy to separate ions than to separate molecules. The enthalpy of melting of ionic compounds is much higher than that of molecular compounds.
The fourth type of connection ismetal connection
Finally, there is another type of intermolecular bonds - metal: connection of positive ions of a metal lattice with free electrons. This type of connection does not occur in biological objects.
From a brief review of bond types, one detail becomes clear: an important parameter of a metal atom or ion - an electron donor, as well as an atom - an electron acceptor, is its 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 atomic number increases in groups of the periodic system. In this case, the values of the ion radii are the smallest, and the van der Waals radii are the largest. As a rule, when moving down the group, the radii of all elements increase, both covalent and van der Waals.
Of greatest importance for biologists and physicians are coordination(donor-acceptor) bonds considered by coordination chemistry.
Medical bioinorganics. G.K. Barashkov
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A phrase is the building material of a sentence. This is the smallest syntactic unit that has its own connection methods. If we know how to determine the types of connections between words in, then we will learn to parse more complex syntactic units - sentences.
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Words are combined in a subordinating way. This means that they are unequal: one is the main thing, the other is dependent. The function of such a connection is to describe the concept (object, sign, action) in more detail.
Important! Not every combination of words can become a phrase.
What types of word combinations do not belong to phrases:
- The grammatical basis is subject and predicate: dad has arrived, the window is open, the problem has been solved.
- Homogeneous members of the sentence. They are connected by coordinating conjunctions: kind and cheerful; sometimes sad, sometimes funny; not only smart, but also beautiful.
- Complex future tense: I will read, we will laugh.
- Comparative degree: fastest, less high.
- with independent: over time, near the river, towards the wind.
- Phraseologisms. In meaning, they are equivalent to the words: hang up (get upset), reluctantly (reluctantly).
The words in the phrase are connected:
- by meaning (from the main element a semantic question is asked: write (what?) a book, go (where?) home);
- grammatically: using endings: yellow jacket, or using endings and prepositions: to catch on a branch.
To better understand what a dependent word is, let’s see what semantic relationships occur:
- Definitive. The attribute of an object is called: fruit (what kind?) is delicious.
- Object. The object of action, place, direction is indicated: come (to whom?) to a friend, turn (where?) to the right.
- Circumstantial. A sign of action is indicated: run (how?) quickly.
Submission and its methods
There is a semantic connection in all constructions, but a grammatical one - not. The main types of phrases are determined by the form of their constituent elements. We look at whether these are parts of speech that can be changed or not, what type they have, what means of connecting words in a construction. To quickly determine the type of connection, you need to be able to change word forms by and by person.
There are 3 types of grammatical connections between words in minimal syntactic units. Let's look at each of them in detail.
A method of combination in which the dependent word takes the form of the main word: the hat (what?) is beautiful. Both members have the same case, gender, and number.
Attention! When the main component changes, the secondary component also changes: hats Ouch handsome Ouch, hats ami handsome them oh hats Oh handsome s.
Both elements in such constructions are variable parts of speech. Therefore, the means of connecting words in combinations of this type are meaning and grammatical form.
| Main | Dependent | Examples |
| Noun and those word forms that can perform its function | Adjective | Something (what?) beautiful, the sky is (what?) blue, the dining room (which one?) is clean |
| Student (what?) reading, river (what?) frozen |
||
| Numeral | House (which?) second, in the cities of (how many?) three, with (how many?) both hands |
|
| Some kind of person (what?) no sense (what?) plate (whose?) is mine |
||
| Noun (application) | Girl (what?) Olya, eyes (what?) beads (beady eyes) |
The main word controls the dependent, puts it in the necessary form: came (with whom?) with a friend - the verb indicates the form of the noun etc. If you change the word form of the leading element, the driven element will remain in the same case. For example: come at with a friend ohm, came And with a friend ohm, coming no with a friend ohm.
The grammatical means in these constructions are meaning and case form. Only when managing can a pretext be used between parts: to think O stars, shout on neighbor, fly towards wind.
When controlling, secondary words are variable parts of speech, as they are connected using case endings and/or prepositions.
| Main | Dependent | Examples |
| Verb, gerund, noun, participle, adjective, numeral, pronoun. |
Noun | Come (to whom?) to a friend, recording (what?) a lecture, read (by whom?) by a boy, memory (of what?) of the past, three (who?) sisters, no one (who?) needs it. |
| Pronoun | I asked (who?) someone saw (what?) something a gift (to whom?) for him |
|
| Adjective naming an object | Find out (about whom?) about the unknown, brought (what?) hot |
|
| Participle naming an object | Many (who?) gathered, greet (who?) vacationers |
It is necessary to differentiate! The numeral in the nominative and accusative cases commands the noun. This is management: five dogs, three boys. If the numeral is in other cases, then this is an agreement: with five dogs, about five dogs, with three boys, about three boys.
The main component is accompanied by an unchangeable part of speech: go (where?) forward. There is only one means of connection here - meaning, because the driven word cannot take on a different form. We can highlight additional means of connection in such constructions - word order and intonation.
Dependent components in adjacency are immutable, so there is no means of grammatical connection. A leading word is any part of speech.
| Main | Dependent | Examples |
| Verb, noun, adjective, participle, participle, pronoun |
Adverb | Arrived (when?) yesterday, house (what?) opposite, quickly (to what extent?) very |
| Participle | Spoke (how?) stuttering | |
| Infinitive | The dream (what?) is to get married, came (for what purpose?) to talk |
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| Immutable adjective | Color (what?) khaki | |
| Comparative degree of an adjective | The news (what?) is more important, someone (who?) more interesting |
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| Possessive pronouns (his, her, theirs) | His apartment (whose?) child (whose?) them |
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| Noun (inconsistent application) | Play (what?) “Dowry”, novel (which?) “War and Peace” |
How to determine the connection type
Write down the necessary structures from the proposal - this will make it easier to disassemble. Please note that not all connections are suitable. When the correct units have been found, we determine the methods of subordinating communication. Try following the algorithm:
Sample parsing:
- Let's take this example: I'll see you soon.
- We ask the question: see you (when?) soon. See you - the main element, soon - the secondary one.
- Let's change: I'll see you soon, you'll see soon. Only the main component was transformed, which means this cannot be a coordination. There remain those types of syntactic connections in a phrase in which only one component is changed.
- There is no excuse.
- "Soon" is an adverb. The adverb does not change, which means there is no grammatical device in our case.
- This is an adjacency.
Connection of words in a phrase
Task 6. Word combination
Conclusion
At parsing convenient to build a diagram. We denote the main part with a cross, emphasize formal means (prepositions and endings), and name the parts of speech of the members of the construction. Using the diagram and algorithm, it is easy to parse any examples of phrases.
It is extremely rare that chemical substances consist of individual, unrelated atoms of chemical elements. Under normal conditions, only a small number of gases called noble gases have this structure: helium, neon, argon, krypton, xenon and radon. Most often, chemical substances do not consist of isolated atoms, but of their combinations into various groups. Such associations of atoms can number a few, hundreds, thousands, or even more atoms. The force that holds these atoms in such groups is called chemical bond.
In other words, we can say that a chemical bond is an interaction that provides the connection of individual atoms into more complex structures (molecules, ions, radicals, crystals, etc.).
The reason for the formation of a 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 the interaction of atoms X and Y produces a molecule XY, 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, when chemical bonds are formed between individual atoms, energy is released.
Electrons of the outer electron layer with the lowest binding energy with the nucleus, called valence. For example, in boron these are electrons of the 2nd energy level - 2 electrons per 2 s- orbitals and 1 by 2 p-orbitals:
When a chemical bond is formed, each atom tends to obtain the electronic configuration of noble gas atoms, i.e. so that there are 8 electrons in its outer electron layer (2 for elements of the first period). This phenomenon is called the octet rule.
It is possible for atoms to achieve the electron configuration of a noble gas if initially single atoms share some of their valence electrons with other atoms. In this case, common electron pairs are formed.
Depending on the degree of electron sharing, covalent, ionic and metallic bonds can be distinguished.
Covalent bond
Covalent bonds most often occur between atoms of nonmetal elements. If the nonmetal atoms forming a covalent bond belong to different chemical elements, such a bond is called a polar covalent bond. The reason for this name lies in the fact that atoms of different elements also have different abilities to attract a common electron pair. Obviously, this leads to a displacement 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 the electron pair is shifted from the hydrogen atom to the chlorine atom:
Examples of substances with polar covalent bonds:
CCl 4, H 2 S, CO 2, NH 3, SiO 2, etc.
A covalent nonpolar bond is formed between nonmetal atoms of the same chemical element. Since the atoms are identical, their ability to attract shared electrons is also 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 to form 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 shared electron pair is formed due to the filled orbital of one atom (with two electrons) and the empty orbital of another atom. An atom that provides a lone pair of electrons is called a donor, and an atom with a vacant orbital is called an acceptor. Atoms that have paired electrons, for example N, O, P, S, act as donors of electron pairs.
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 increasing radii of bonded atoms. Since we know that atomic radii increase down the subgroups, we 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 greater its energy. Bond multiplicity refers to the number of shared electron pairs between two atoms.
Ionic bond
An ionic bond can be considered as an extreme case of a polar covalent bond. If in a covalent-polar bond the common electron pair is partially shifted to one of the pair of atoms, then in an ionic bond it is almost completely “given” to one of the atoms. The atom that donates electron(s) acquires a positive charge and becomes cation, and the atom that has taken electrons from it acquires a negative charge and becomes anion.
Thus, an ionic bond is a bond formed by the electrostatic attraction of cations to anions.
The formation of this type of bond is typical during the interaction of atoms of typical metals and typical non-metals.
For example, potassium fluoride. The potassium cation is formed by the removal of one electron from a neutral atom, and the fluorine ion is formed by the addition of one electron to the fluorine atom:
An electrostatic attraction force arises between the resulting ions, resulting in the formation of an ionic compound.
When a chemical bond was formed, electrons from the sodium atom passed to the chlorine atom and oppositely charged ions were formed, which have a completed external energy level.
It has been established that electrons from the metal atom are not completely detached, but are 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.
Ionic bonding 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, ionic compounds include salts and bases (Na 2 SO 4, Cu(NO 3) 2, (NH 4) 2 SO 4), Ca(OH) 2, NaOH).
Metal connection
This type of bond is formed in metals.
Atoms of all metals have electrons in their outer electron layer that have a low binding energy with the nucleus of the atom. For most metals, the process of losing outer electrons is energetically favorable.
Due to 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 - = 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 processes taking place.
That is, electrons “rush” across a metal crystal, detaching from one metal atom, forming a cation from it, joining another cation, forming a neutral atom. This phenomenon was called “electron wind,” and the collection of free electrons in a crystal of a nonmetal atom was called “electron gas.” This type of interaction between metal atoms is called a metallic bond.
Hydrogen bond
If a hydrogen atom in a substance is bonded to an element with high electronegativity (nitrogen, oxygen, or fluorine), that substance is characterized by a phenomenon called hydrogen bonding.
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 is formed on the atom of the electronegative element. In this regard, electrostatic attraction becomes possible between a partially positively charged hydrogen atom of one molecule and an electronegative atom of another. For example, hydrogen bonding 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.