Hydrogen bond (H-bond) is a bond formed by a protonated hydrogen atom with a highly electronegative atom of the same or another molecule. Under normal conditions, the valence of hydrogen is 1, and it is capable of sharing one electron pair with other atoms, forming a covalent bond: a hydrogen atom can attach an electron, forming a hydride ion H +.

The hydrogen atom has a feature that distinguishes it from all other atoms: giving up its electron, it remains in the form of a nucleus without electrons, i.e. in the form of a particle, the diameter of which is thousands of times smaller than the diameter of other atoms. In the absence of electrons, the H+ ion is not repelled by the electron shells of other atoms or ions, but, on the contrary, is attracted; it can come close to other atoms, interact with their electrons, and even penetrate their electron shells. In liquids, H + -ions for the most part are not stored as an independent particle, but are associated with molecules of two substances: in water with water molecules, forming the H 3 O + ion - hydronium ion; with an ammonia molecule – NH 4 + ammonium ion.

Being bound to an atom of one of the most electronegative elements: with an atom of fluorine, oxygen, chlorine and nitrogen, the hydrogen atom acquires a relatively high positive charge, not exceeding one. Since this charge is concentrated on an extremely small atomic core, it moves very close to another atom carrying a negative charge. This causes the formation of a fairly strong dipole-dipole bond with an energy of 20-30 kJ/mol or more. A hydrogen bond occurs as a result of the interdipole interaction of two highly polar bonds belonging to different molecules or the same molecule. It is weaker than a conventional covalent bond, the energy of which is approximately 125-420 kJ/mol and can be strengthened due to the mutual polarization of bonds caused by these features of the hydrogen atom. A hydrogen bond (H-bond) is designated X-H××××X.

The hydrogen atom involved in a hydrogen bond can be located exactly in the middle between two highly negative atoms—a symmetrical arrangement—or it can move closer to the one that has a higher electronegativity—an asymmetrical arrangement.

The energy of a hydrogen bond is sufficient to cause a noticeable dissociation of molecules at ordinary and low temperatures. Hydrogen fluoride, even near its boiling point, has average composition(HF)4. The association leads to abnormally high melting and boiling points of hydrogen fluoride. The existence of the H 2 F 2 dimer explains the formation of acid salts such as KHF 2 ×NaHF 2. The fact that hydrofluoric acid, in contrast to hydrochloric, hydrobromic and hydroiodic acid, is weak acid(K d = 7×10 -4) – is also a consequence of the association of HF molecules due to hydrogen bonds.

In the presence of an asymmetric hydrogen bond, which occurs in compounds of oxygen and nitrogen, the hydrogen is located slightly closer to one of the two neighboring atoms, here intermolecular H-bond. Each H2O molecule participates in the formation of two H-bonds, so that the oxygen atom is bonded to four hydrogen atoms. Associated water molecules form an openwork spatial structure, where each oxygen atom is located in the center of the tetrahedron, and hydrogen atoms are located in the corners.

Openwork spatial structure of water

The openwork structure of ice explains its lower density than water. When melting, some of the H-bonds break and the density of water increases, because molecules are more densely packed. X-ray research has shown that for most molecules in liquid water the tetrahedral environment is also preserved: the arrangement of neighboring molecules is almost the same as in an ice crystal, and is repeated in the next layer

some deviation from the specified order; the deviation increases with distance from the sample molecule. Water is characterized by the presence of “short-range order”, like other liquids, and to a lesser extent, compared to other liquids, the presence of “long-range order”. This explains the presence of a crystalline structure in water.

Properties of water such as high heat capacity and heat of evaporation, abnormally high melting and boiling points, high dielectric constant - due to the connection of water molecules by hydrogen bonds. Without H-bonds t melting water = -100 o C, t boiling water = -80 o C.

Hydrogen bonds are present in liquid ammonia. A hydrogen atom bonded to carbon can acquire the ability to form a hydrogen bond if the remaining carbon valences are saturated with strongly electronegative atoms or corresponding atomic groups, for example, chloroform (CHCl 3), pentachloroethane (CCl 3 -CHCl 2), i.e. the proximity of electronegative atoms can activate the formation of hydrogen bonds at the atoms of CH groups, although the electronegativity of the C and H atoms is almost the same. This explains the occurrence of H-bonds between molecules in liquid HCN, CHF 3, etc.

Hydrogen bonding is characteristic of any aggregate state of a substance. It is formed between identical and between different molecules, between different parts of the same molecule - intramolecular hydrogen bond. The most common is the H-bond between molecules containing hydroxyl groups OH - .

Ethers, even with a higher molar mass, are more volatile than alcohols, since in ethers all hydrogen atoms are bonded to carbon atoms and are not able to form H-bonds.

The role of H-bonds in biochemical systems is great. The properties of proteins and nucleic acids are largely determined by the presence of hydrogen bonds. H-bonding plays an important role in dissolution processes. Hydrogen bonds are especially common in molecules of proteins, nucleic acids and other biologically important compounds, so these bonds play important role in the chemistry of life processes.

Link length - internuclear distance. The shorter this distance, the stronger the chemical bond. The length of a bond depends on the radii of the atoms forming it: the smaller the atoms, the shorter the bond between them. For example, link length N-O less than the H-N bond length (due to less oxygen atom exchange).

An ionic bond is extreme case polar covalent bond.

Metal connection.

The prerequisite for the formation of this type of connection is:

1) availability on external levels atoms have a relatively small number of electrons;

2) the presence of empty (vacant orbitals) on the outer levels of metal atoms

3) relatively low ionization energy.

Consider education metal connection using sodium as an example. The valence electron of sodium, which is located on the 3s sublevel, can relatively easily move through the empty orbitals of the outer layer: along 3p and 3d. When atoms come closer together as a result of the formation of a crystal lattice, the valence orbitals of neighboring atoms overlap, due to which electrons move freely from one orbital to another, establishing a bond between ALL atoms of the metal crystal.

At the nodes of the crystal lattice there are positively charged ions and atoms of metals, and between them there are electrons that can move freely throughout the crystal lattice. These electrons become common to all atoms and ions of the metal and are called " electron gas" The bond between all positively charged metal ions and free electrons in the metal crystal lattice is called metal bond.

The presence of a metal bond is due to physical properties metals and alloys: hardness, electrical conductivity, thermal conductivity, malleability, ductility, metallic luster. Free electrons can transfer heat and electricity, so they are the reason for the main physical properties that distinguish metals from non-metals - high electrical and thermal conductivity.

Hydrogen bond.

Hydrogen bond occurs between molecules that contain hydrogen and atoms with high EO (oxygen, fluorine, nitrogen). Covalent H-O bonds, H-F, H-N are highly polar, due to which an excess positive charge accumulates on the hydrogen atom, and an excess charge on the opposite poles negative charge. Between oppositely charged poles, forces of electrostatic attraction arise - hydrogen bonds.

Hydrogen bonds can be either intermolecular or intramolecular. The energy of a hydrogen bond is approximately ten times less than the energy of a conventional covalent bond, but nevertheless, hydrogen bonds play an important role in many physicochemical and biological processes. In particular, DNA molecules are double helices in which two chains of nucleotides are linked by hydrogen bonds. Intermolecular hydrogen bonds between water and hydrogen fluoride molecules can be depicted (by dots) as follows:

Substances with hydrogen bonds have molecular crystal lattices. The presence of a hydrogen bond leads to the formation of molecular associates and, as a consequence, to an increase in the melting and boiling points.

In addition to the listed main types of chemical bonds, there are also universal forces of interaction between any molecules that do not lead to the breaking or formation of new chemical bonds. These interactions are called van der Waals forces. They determine the attraction of molecules of a given substance (or various substances) to each other in liquid and solid states of aggregation.

Various types of chemical bonds determine the existence various types crystal lattices (table).

Substances consisting of molecules have molecular structure . These substances include all gases, liquids, as well as solids with molecular crystal lattice, for example iodine. Solids with an atomic, ionic or metal lattice have non-molecular structure , they have no molecules.

Table

Feature of the crystal lattice	Lattice type
Molecular	Ionic	Nuclear	Metal
Particles at lattice nodes	Molecules	Cations and anions	Atoms	Metal cations and atoms
The nature of the connection between particles	Powers intermolecular interaction(including hydrogen bonds)	Ionic bonds	Covalent bonds	Metal connection
Bond strength	Weak	Durable	Very durable	Various strengths
Distinctive physical properties of substances	Low-melting or sublimating, low hardness, many soluble in water	Refractory, hard, brittle, many soluble in water. Solutions and melts conduct electric current	Very refractory, very hard, practically insoluble in water	High electrical and thermal conductivity, metallic luster, ductility.
Examples of substances	Simple substances - non-metals (in solid state): Cl 2, F 2, Br 2, O 2, O 3, P 4, sulfur, iodine (except silicon, diamond, graphite); complex substances, consisting of non-metal atoms (except ammonium salts): water, dry ice, acids, non-metal halides: PCl 3, SiF 4, CBr 4, SF 6, organic matter: hydrocarbons, alcohols, phenols, aldehydes, etc.	Salts: sodium chloride, barium nitrate, etc.; alkalis: potassium hydroxide, calcium hydroxide, ammonium salts: NH 4 Cl, NH 4 NO 3, etc., metal oxides, nitrides, hydrides, etc. (compounds of metals with non-metals)	Diamond, graphite, silicon, boron, germanium, silicon oxide (IV) - silica, SiC (carborundum), black phosphorus (P).	Copper, potassium, zinc, iron and other metals
Comparison of substances by melting and boiling points.
	Because of weak forces intermolecular interactions, such substances have the most low temperatures melting and boiling. Moreover, the more molecular weight substances, the higher t 0 pl. it has. Exceptions are substances whose molecules can form hydrogen bonds. For example, HF has a higher t0 pl. than HCl.	Substances have high t 0 pl., but lower than substances with atomic lattice. The higher the charges of the ions that are located at lattice sites and the shorter the distance between them, the more high temperature melting has a substance. For example, t 0 pl. CaF 2 is higher than t 0 pl. KF.	They have the highest t 0 pl. The stronger the bond between the atoms in the lattice, the higher the t 0 pl. has substance. For example, Si has a lower t0 pl. than C.	Metals have different t0 pl.: from -37 0 C for mercury to 3360 0 C for tungsten.

CONNECTION

COMMUNICATION, -and, about communication, in connection and in connection, w.

1. (in connection). A relationship of mutual dependence, conditionality, commonality between something. C. theory and practice. Causal p.

2. (in connection). Close communication between someone or something. Friendly village Strengthen international relations.

3. (in connection and in connection). Love relationships, cohabitation. Lyubovnaya s. To be in touch with someone.

4. pl. h. Close acquaintance with someone, providing support, patronage, benefit. Have connections in influential circles. Great connections.

5. (in connection). Communication with someone, as well as means that make it possible to communicate, to communicate. Kosmicheskaya village Live s.(via contacts). Air village Intercity telephone s.

6. (in connection). Industry national economy, relating to the means of such communication (mail, telegraph, telephone, radio), as well as the totality of such means concentrated in the relevant institutions. Communication service. Communication workers.

7. (in connection), usually plural. h. Part of a building structure connecting its main elements (special).

Due to how, preposition with TV. n. as a result of something, because of something, being conditioned by something. Late due to skidding.

Due to the fact that, union for the reason that, on the basis of the fact that. I inquired because accurate information was needed.

CONNECTION what is this CONNECTION, meaning of the word CONNECTION, synonyms for CONNECTION, origin (etymology) CONNECTION, CONNECTION stress, word forms in other dictionaries

+ CONNECTION- T.F. Efremova New dictionary Russian language. Explanatory and word-formative

COMMUNICATION is

connection

and.

A) Mutual relationship between smb., sth.

b) Community, mutual understanding, internal unity.

a) Communication with someone.

b) Love relationships, cohabitation.

3) Relationships between someone that create mutual dependence, conditionality.

4) Consistency, coherence, harmony (in thoughts, presentation, etc.).

5) The ability to communicate with someone or something. at a distance.

6) Means by which communication is carried out at a distance.

7) A set of institutions that provide means of communication at a distance (telegraph, mail, telephone, radio).

a) Connection, fastening of something.

b) Clutch, mutual attraction(molecules, atoms, electrons, etc.).

+ CONNECTION- Modern explanatory dictionary ed. "Big Soviet Encyclopedia»

COMMUNICATION is

CONNECTION

1) transmission and reception of information using various technical means. In accordance with the nature of the means of communication used, it is divided into postal (see Mail) and electric (see Telecommunications). 2) The branch of the national economy that ensures the transmission and reception of postal, telephone, telegraph, radio and other messages. In the USSR in 1986 there were 92 thousand communications enterprises; 8.5 billion letters, 50.3 billion newspapers and magazines, 248 million parcels, 449 million telegrams were sent; the number of telephone sets on the general telephone network amounted to 33.0 million. 60s in the USSR, the Unified Automated Communications Network (EASC) is being introduced. 3) Military communications are provided by the Signal Corps. --- in philosophy - the interdependence of the existence of phenomena separated in space and time. Connections are classified according to objects of cognition, according to forms of determinism (unambiguous, probabilistic and correlational), according to their strength (rigid and corpuscular), according to the nature of the result that the connection gives (connection of generation, connection of transformation), according to the direction of action (direct and reverse), by the type of processes that define this connection (functioning connection, development connection, control connection), by the content that is the subject of the connection (connection that ensures the transfer of matter, energy or information).

+ CONNECTION- Small academic dictionary Russian language

COMMUNICATION is

connection

AND, sentence about communication, in connection and in connection, and.

Mutual relationship between someone or something.

Link between industry and agriculture. Connection between science and production. Trade connections. Economic connections between regions. Family connections.

Mutual dependence, conditionality.

Causality.

We only want to say --- that all sciences are in harmony with each other. close connection and that the lasting acquisitions of one science should not remain fruitless for others. Chernyshevsky, Grammar notes. V. Klassovsky.

The connection between Petrov-Vodkin’s work and the traditions of ancient Russian painting is obvious.

L. Mochalov, The uniqueness of talent.

Coherence, harmony, consistency (in connecting thoughts, in presentation, in speech).

Thoughts were confused in his head, and words had no connection. Pushkin, Dubrovsky.

There is not enough consistency in my thoughts, and when I put them on paper, it always seems to me that I have lost my sense of their organic connection. Chekhov, A boring story.

Closeness with someone, inner unity.

That invisible connection grew between them, which was not expressed in words, but only felt. Mamin-Sibiryak, Privalovsky millions.

When a writer deeply feels his blood connection with the people, it gives him beauty and strength. M. Gorky, Letter to D.N. Mamin-Sibiryak, October 18. 1912.

Communication (friendly or business), relations with someone or something.

Keep in touch with smb. Make connections in the literary world.

(Ivan Ivanovich and Ivan Nikiforovich) broke off all ties, while previously they were known as the most inseparable friends! Gogol, The story of how Ivan Ivanovich quarreled with Ivan Nikiforovich.

Drozdov’s connections were established with one of revolutionary organizations, arrests have been made. M. Gorky, Story about a hero.

Love relationships; cohabitation.

(Matvey) entered into a relationship with a bourgeois woman and had a child with her. Chekhov, Murder.

(Sophia:) What right do you have to talk about my infidelity?.. You had dozens of relationships. M. Gorky, The Last.

|| pl. h.(connections, -ey).

Close acquaintance with influential persons who can provide support and patronage.

Good B. decided to find a home for his stepfather. He already had great connections and immediately began to ask and recommend his poor comrade. Dostoevsky, Netochka Nezvanova.

Thanks to the connections of my late engineer father, I was enrolled in the Mikhailovsky School. Pertsov, From autobiography.

Communication, communication with someone or something. using various means.

In the cabin, using a speaking tube, the commander could communicate with the bridge, and by telephone with any department of the ship. Novikov-Priboy, Captain 1st Rank.

Morozka was among the cavalry assigned to communicate with the platoons during the battle. Fadeev, Defeat.

Now there was only one way of communication left - through the Volga. Simonov, Days and Nights.

|| Those.

Transmitting and receiving information using special means.

5. usually with a definition.

The means by which communication and transmission of information are carried out.

Radiotelephone communication. Telegraph communication. Dispatcher communication.

Signalmen at night artillery regiment managed to establish a telephone connection to the tank. V. Kozhevnikov, Seven days.

The set of institutions serving technical means communication at a distance (telegraph, mail, telephone, radio).

Communication workers.

|| Military

A service that provides communication between military units (using telephone, radio, messengers, etc.).

Arkhip Khromkov became the head of intelligence and communications. Markov, Strogovs.

A liaison officer arrived from army headquarters with an urgent package. Popovkin, Rubanyuk Family.

Connection, fastening of something.

Bonding stones and bricks with clay.

In the Trinity Cathedral, he introduces iron into the masonry of the building to connect the corners. Pilyavsky, Works of V.P. Stasov in Leningrad.

Cohesion, mutual attraction (molecules, atoms, electrons, etc.).

The connection of electrons with the nucleus.

A device that binds or fastens parts of something. buildings or structures; clamp.

It was a huge decorative workshop - a dome intertwined at the top with iron rafters and ties. A. N. Tolstoy, Egor Abozov. logic, coherence, continuity, foldability, sequence, harmony, interaction, connection, articulation, concatenation, cohesion, communication, means of communication, intercourse, communication, contact, association, relation, relationship, dependence, binding, ties, romance, connecting link, union, causation, public relations, tomba, intimate relationships, intrigue, ratio, duplex, umbilical cord, intercourse, bonding, religion, cohabitation, parataxis, binding thread, continuity, adhesion, interconnectedness, correlation, conditionality, connection, kinship, putty, bond, cupids, affair, synapse, context, love, thread, mail, message, quadruplex. Ant. fragmentation

CONNECTION

Synonyms:

consistency, coherence, continuity, foldability, sequence, harmony, interaction, connection, articulation, concatenation, coupling, communication, means of communication, intercourse, communication, contact, association, relation, relationship, dependence, binding, ties, romance, connecting link, union, causation, public relations, tomba, intimate relationships, intrigue, correlation, duplex, umbilical cord, intercourse, bonding, religion, cohabitation, parataxis, connecting thread, continuity, adhesion, interconnectedness, correlation, conditionality, connection, kinship, putty, bond , cupids, affair, synapse, context, love, thread, mail, message, quadruplex. Ant. fragmentation