What is the relationship between metals. Metal Bond: Mechanism of Formation and Examples

Metal connection. Properties of a metallic bond.

A metallic bond is a chemical bond due to the presence of relatively free electrons. It is characteristic both for pure metals and their alloys and intermetallic compounds.

Metal bond mechanism

Positive metal ions are located at all nodes of the crystal lattice. Between them randomly, like gas molecules, valence electrons move, unhooked from atoms during the formation of ions. These electrons play the role of cement, holding the positive ions together; otherwise, the lattice would disintegrate under the action of repulsive forces between the ions. At the same time, electrons are also held by ions within the crystal lattice and cannot leave it. Communication forces are not localized and not directed. For this reason, high coordination numbers (eg 12 or 8) appear in most cases. When two metal atoms approach each other, their outer shell orbitals overlap to form molecular orbitals. If a third atom comes up, its orbital overlaps with the orbitals of the first two atoms, giving one more molecular orbital. When there are many atoms, a huge number of three-dimensional molecular orbitals arise, extending in all directions. Due to the multiple overlapping of orbitals, the valence electrons of each atom are influenced by many atoms.

Characteristic crystal lattices

Most metals form one of the following highly symmetric close-packed lattices: body-centered cubic, face-centered cubic, and hexagonal.

In a cubic body-centered lattice (bcc), atoms are located at the vertices of the cube and one atom is located at the center of the volume of the cube. Metals have a cubic body-centered lattice: Pb, K, Na, Li, β-Ti, β-Zr, Ta, W, V, α-Fe, Cr, Nb, Ba, etc.

In a face-centered cubic lattice (fcc), atoms are located at the vertices of the cube and at the center of each face. Metals of this type have a lattice: α-Ca, Ce, α-Sr, Pb, Ni, Ag, Au, Pd, Pt, Rh, γ-Fe, Cu, α-Co, etc.

In a hexagonal lattice, atoms are located at the vertices and the center of the hexagonal bases of the prism, and three atoms are located in the middle plane of the prism. Metals have such a packing of atoms: Mg, α-Ti, Cd, Re, Os, Ru, Zn, β-Co, Be, β-Ca, etc.

Other properties

Freely moving electrons cause high electrical and thermal conductivity. Substances with a metallic bond often combine strength with ductility, since when atoms are displaced relative to each other, bonds do not break. Another important property is metallic aromaticity.

Metals conduct heat and electricity well, they are strong enough, they can be deformed without breaking. Some metals are malleable (they can be forged), some are malleable (they can be drawn into wire). These unique properties are explained by a special type chemical bond that connects metal atoms to each other - a metallic bond.

Metals in the solid state exist in the form of crystals of positive ions, as if “floating” in a sea of ​​electrons freely moving between them.

The metallic bond explains the properties of metals, in particular their strength. Under the action of a deforming force, the metal lattice can change its shape without cracking, unlike ionic crystals.

The high thermal conductivity of metals is explained by the fact that if you heat a piece of metal on one side, then the kinetic energy of electrons will increase. This increase in energy will propagate in the "electronic sea" throughout the sample at great speed.

The electrical conductivity of metals also becomes clear. If a potential difference is applied to the ends of a metal sample, then the cloud of delocalized electrons will shift in the direction of the positive potential: this flow of electrons moving in the same direction is the familiar electric current.

Metal connection. Properties of a metallic bond. - concept and types. Classification and features of the category "Metal bond. Metal bond properties." 2017, 2018.

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Each atom has a certain number of electrons.

Entering into chemical reactions, atoms donate, acquire, or socialize electrons, reaching the most stable electronic configuration. The configuration with the lowest energy is the most stable (as in noble gas atoms). This pattern is called the "octet rule" (Fig. 1).

Rice. one.

This rule applies to all connection types. Electronic bonds between atoms allow them to form stable structures, from the simplest crystals to complex biomolecules that eventually form living systems. They differ from crystals in their continuous metabolism. However, many chemical reactions proceed according to the mechanisms electronic transfer, which play an important role in the energy processes in the body.

A chemical bond is a force that holds together two or more atoms, ions, molecules, or any combination of them..

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 in the outer shell of atoms. The ability of an atom to form chemical bonds is called valence, or oxidation state. The concept of valence electrons- electrons that form chemical bonds, that is, those located in the most high-energy orbitals. Respectively, outer shell an atom containing these orbitals is called valence shell. At present, it is not enough to indicate the presence of a chemical bond, but it is necessary to clarify its type: ionic, covalent, dipole-dipole, metallic.

The first type of connection isionic connection

In accordance with electronic theory Lewis and Kossel valencies, atoms can achieve a stable electron 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 the opposite sign, a chemical bond is formed, called 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 T and II group cations periodic system and anions of non-metallic elements of groups VI and VII (16 and 17 subgroups - respectively, chalcogens And halogens). The bonds in ionic compounds are unsaturated and non-directional, so they retain the possibility of electrostatic interaction with other ions. On fig. 2 and 3 show examples of ionic bonds corresponding to the Kossel electron transfer model.

Rice. 2.

Rice. 3. Ionic bond in a molecule table salt(NaCl)

Here it is appropriate to recall some of the properties that explain the behavior of substances in nature, in particular, to consider the concept of acids And grounds.

Aqueous solutions of all these substances are electrolytes. They change color in different ways. indicators. The mechanism of action of indicators was discovered by F.V. Ostwald. He showed that the indicators are weak acids or bases, the color of which in the undissociated and dissociated states is different.

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 enter into characteristic reactions:

a) with metal oxides - with the formation of salt and water;

b) with metals - with the formation of salt and hydrogen;

c) with carbonates - with the formation of salt, CO 2 and H 2 O.

The properties of acids and bases are described by several theories. In accordance with the theory of S.A. Arrhenius, an acid is a substance that dissociates to form ions H+ , while the base forms ions IS HE- . This theory does not take into account the existence of organic bases that do not have hydroxyl groups.

In line with proton Bronsted and Lowry's theory, an acid is a substance containing molecules or ions that donate protons ( donors protons), and the base is a substance consisting of molecules or ions that accept protons ( acceptors protons). Note that in aqueous solutions, hydrogen ions exist in a hydrated form, that is, in the form of hydronium ions H3O+ . This theory describes reactions not only with water and hydroxide ions, but also carried out in the absence of a solvent or with a non-aqueous solvent.

For example, in the reaction between ammonia NH 3 (weak base) and hydrogen chloride in the gas phase, 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 conjugated pairs of acids and bases:

1)NH 4+ and NH 3

2) HCl And Cl ‑

Here, in each conjugated pair, the acid and base differ by one proton. Every acid has a conjugate base. A strong acid corresponds to a weak conjugate base, and weak acid is a strong conjugate base.

The Bronsted-Lowry theory makes it possible to 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 With acetic acid, water is a base, and with aqueous solutions of ammonia, it is an acid.

1) CH 3 COOH + H 2 O ↔ H 3 O + + CH 3 SOO- . Here the acetic acid molecule donates a proton to the water molecule;

2) NH3 + H 2 O ↔ NH4 + + IS HE- . Here the ammonia molecule accepts a proton from the water molecule.

Thus, water can form two conjugated pairs:

1) H 2 O(acid) and IS HE- (conjugate base)

2) H 3 O+ (acid) and H 2 O(conjugate base).

In the first case, water donates a proton, and in the second, it accepts it.

Such a property is called amphiprotonity. Substances that can react as both acids and bases are called amphoteric. Such substances are often found in nature. For example, amino acids can form salts with both acids and bases. Therefore, peptides readily form coordination compounds with the metal ions present.

In this way, characteristic property ionic bond - the complete movement of a bunch of binding electrons to one of the nuclei. This means that there is a region between the ions where the electron density is almost zero.

The second type of 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 each atom. In this case, the socialized bond electrons are distributed equally among the atoms. An example of a covalent bond is homonuclear diatomic H molecules 2 , N 2 , F 2. Allotropes have the same type of bond. 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 FROM 2 H 5 IS HE, sulfur hexafluoride SF 6, acetylene FROM 2 H 2. All these molecules have the same common electrons, and their bonds are saturated and directed in the same way (Fig. 4).

For biologists, it is important that double and triple bonds have covalent radii of atoms compared to single bond reduced.

Rice. 4. Covalent bond in the Cl 2 molecule.

Ionic and covalent types of bonds are two limiting cases of many existing types of chemical bonds, and in practice most of the bonds are intermediate.

Compounds of two elements located at opposite ends of the same or different periods of the Mendeleev system predominantly form ionic bonds. As the elements approach each other within a period, the ionic nature of their compounds decreases, while the covalent character increases. For example, the halides and oxides of the elements on the left side of the periodic table form predominantly ionic bonds ( NaCl, AgBr, BaSO 4 , CaCO 3 , KNO 3 , CaO, NaOH), and the same compounds of the elements on the right side of the table are covalent ( H 2 O, CO 2, NH 3, NO 2, CH 4, phenol C6H5OH, glucose C 6 H 12 O 6, ethanol C 2 H 5 OH).

The covalent bond, in turn, has another modification.

In polyatomic ions and in complex biological molecules, both electrons can only come from one atom. It is called donor electron pair. An atom that socializes 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 most important d-elements for metabolism is largely described by coordination bonds.

Pic. five.

As a rule, in a complex compound, a metal atom acts as an electron pair acceptor; 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. The Lewis 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 pair of electrons, which, by donating electrons, forms a covalent bond with Lewis acid.

That is, the Lewis 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 able to accept an electron pair.

Therefore, according to this theory, cations are Lewis acids and anions are Lewis bases. The following reactions are examples:

It was noted above that the subdivision of substances into ionic and covalent ones is relative, since there is no complete transfer of an electron from metal atoms to acceptor atoms in covalent molecules. In compounds with an ionic bond, 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; it is higher for anions than for cations. The highest polarizability among cations is for cations of larger charge and smaller size, for example, for Hg 2+ , Cd 2+ , Pb 2+ , Al 3+ , Tl 3+. Has a strong polarizing effect H+ . Since the effect of ion polarization is two-way, it significantly changes the properties of the compounds they form.

The third type of connection -dipole-dipole connection

In addition to the listed types of communication, there are also dipole-dipole intermolecular interactions, also known as 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 ( dispersion 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 debye(1D \u003d 3.338 × 10 -30 coulomb meters - C × m).

In biochemistry, another type of bond is distinguished - 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 a similar electronegativity (for example, with chlorine and sulfur), the hydrogen bond is much weaker. The hydrogen atom is distinguished by one essential feature: when the binding electrons are pulled away, its nucleus - the proton - is exposed and ceases to be screened 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, for stabilizing the structure of proteins in the form of an a-helix, or for the formation of a DNA double helix (Fig. 7).

Fig.7.

Hydrogen and van der Waals bonds are much weaker than ionic, covalent, and coordination bonds. The energy of intermolecular bonds is indicated in Table. one.

Table 1. Energy of intermolecular forces

Note: The degree of intermolecular interactions reflect the enthalpy of melting and evaporation (boiling). Ionic compounds require much more energy to separate ions than to separate molecules. The melting enthalpies of ionic compounds are much higher than those of molecular compounds.

The fourth type of connection -metallic bond

Finally, there is another type of intermolecular bonds - metal: connection of positive ions of the lattice of metals with free electrons. This type of connection does not occur in biological objects.

From a brief review of the types of bonds, one detail emerges: an important parameter of an atom or ion of a metal - 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, the ionic radii of metals, and the van der Waals radii of interacting molecules increase as their atomic number in the groups of the periodic system increases. 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.

The most important for biologists and physicians are coordination(donor-acceptor) bonds considered by coordination chemistry.

Medical bioinorganics. G.K. Barashkov

Atoms of most elements do not exist separately, as they can interact with each other. In this interaction, more complex particles are formed.

The nature of the chemical bond is the action of electrostatic forces, which are the forces of interaction between electric charges. Electrons and atomic nuclei have such charges.

Electrons located at the outer electronic levels (valence electrons), being farthest from the nucleus, interact with it the weakest, and therefore are able to break away from the nucleus. They are responsible for the binding of atoms to each other.

Types of interaction in chemistry

The types of chemical bond can be represented as the following table:

Ionic bond characteristic

The chemical interaction that is formed due to ion attraction having different charges is called ionic. This happens if the bonded atoms have a significant difference in electronegativity (that is, the ability to attract electrons) and the electron pair goes to a more electronegative element. The result of such a transition of electrons from one atom to another is the formation of charged particles - ions. There is an attraction between them.

have the lowest electronegativity typical metals, and the largest are typical non-metals. Ions are thus formed by interactions between typical metals and typical non-metals.

Metal atoms become positively charged ions (cations), donating electrons to external electronic levels, and non-metals accept electrons, thus turning into negatively charged ions (anions).

Atoms move into a more stable energy state, completing their electronic configurations.

The ionic bond is non-directional and not saturable, since the electrostatic interaction occurs in all directions, respectively, the ion can attract ions of the opposite sign in all directions.

The arrangement of ions is such that around each is a certain number of oppositely charged ions. The concept of "molecule" for ionic compounds doesn't make sense.

Examples of Education

The formation of a bond in sodium chloride (nacl) is due to the transfer of an electron from the Na atom to the Cl atom with the formation of the corresponding ions:

Na 0 - 1 e \u003d Na + (cation)

Cl 0 + 1 e \u003d Cl - (anion)

In sodium chloride, there are six chloride anions around the sodium cations, and six sodium ions around each chloride ion.

When an interaction is formed between atoms in barium sulfide, the following processes occur:

Ba 0 - 2 e \u003d Ba 2+

S 0 + 2 e \u003d S 2-

Ba donates its two electrons to sulfur, resulting in the formation of sulfur anions S 2- and barium cations Ba 2+ .

metal chemical bond

The number of electrons in the outer energy levels of metals is small; they easily break away from the nucleus. As a result of this detachment, metal ions and free electrons are formed. These electrons are called "electron gas". Electrons move freely throughout the volume of the metal and are constantly bound and detached from atoms.

The structure of the metal substance is as follows: the crystal lattice is the backbone of the substance, and electrons can move freely between its nodes.

The following examples can be given:

Mg - 2e<->Mg2+

Cs-e<->Cs +

Ca-2e<->Ca2+

Fe-3e<->Fe3+

Covalent: polar and non-polar

The most common type of chemical interaction is a covalent bond. The electronegativity values ​​of the interacting elements do not differ sharply, in connection with this, only a shift of the common electron pair to a more electronegative atom occurs.

Covalent interaction can be formed by the exchange mechanism or by the donor-acceptor mechanism.

The exchange mechanism is realized if each of the atoms has unpaired electrons in the outer electronic levels and the overlap of atomic orbitals leads to the appearance of a pair of electrons that already belongs to both atoms. When one of the atoms has a pair of electrons at the outer electronic level, and the other has a free orbital, then when the atomic orbitals overlap, the electron pair is socialized and the interaction occurs according to the donor-acceptor mechanism.

Covalent are divided by multiplicity into:

• simple or single;
• double;
• triple.

Doubles provide the socialization of two pairs of electrons at once, and triples - three.

According to the distribution of electron density (polarity) between the bonded atoms, the covalent bond is divided into:

• non-polar;
• polar.

A non-polar bond is formed by the same atoms, and a polar bond is formed by electronegativity different.

The interaction of atoms with similar electronegativity is called a non-polar bond. The common pair of electrons in such a molecule is not attracted to any of the atoms, but belongs equally to both.

The interaction of elements differing in electronegativity leads to the formation of polar bonds. Common electron pairs with this type of interaction are attracted by a more electronegative element, but do not completely transfer to it (that is, the formation of ions does not occur). As a result of such a shift in the electron density, partial charges appear on the atoms: on the more electronegative - a negative charge, and on the less - positive.

Properties and characteristics of covalence

The main characteristics of a covalent bond:

• The length is determined by the distance between the nuclei of the interacting atoms.
• Polarity is determined by the displacement of the electron cloud to one of the atoms.
• Orientation - the property to form space-oriented bonds and, accordingly, molecules that have certain geometric shapes.
• Saturation is determined by the ability to form a limited number of bonds.
• Polarizability is determined by the ability to change polarity under the influence of an external electric field.
• The energy required to break a bond, which determines its strength.

Molecules of hydrogen (H2), chlorine (Cl2), oxygen (O2), nitrogen (N2) and many others can be an example of a covalent non-polar interaction.

H+ + H → H-H molecule has a single non-polar bond,

O: + :O → O=O the molecule has a double nonpolar,

Ṅ: + Ṅ: → N≡N the molecule has a triple non-polar.

As an example of a covalent bond chemical elements you can bring molecules of carbon dioxide (CO2) and carbon monoxide (CO) gas, hydrogen sulfide (H2S), of hydrochloric acid(HCL), water (H2O), methane (CH4), sulfur oxide (SO2) and many others.

In the CO2 molecule, the relationship between carbon and oxygen atoms is covalent polar, since the more electronegative hydrogen attracts electron density to itself. Oxygen has two unpaired electrons at the outer level, while carbon can provide four valence electrons to form an interaction. As a result, double bonds are formed and the molecule looks like this: O=C=O.

In order to determine the type of bond in a particular molecule, it is enough to consider its constituent atoms. Simple substances metals form metallic, metals with non-metals - ionic, simple substances non-metals - covalent non-polar, and molecules consisting of different non-metals are formed through a covalent polar bond.

You learned how atoms of metal and non-metal elements interact with each other (electrons pass from the first to the second), as well as atoms of non-metal elements with each other (unpaired electrons of the outer electronic layers of their atoms combine into common electron pairs). Now we will get acquainted with how the atoms of metal elements interact with each other. Metals do not usually exist as isolated atoms, but as an ingot or piece of metal. What holds metal atoms together?

The atoms of most metal elements at the outer level contain a small number of electrons - 1, 2, 3. These electrons are easily detached, and the atoms turn into positive ions. The detached electrons move from one ion to another, binding them into a single whole.

It is simply impossible to figure out which electron belonged to which atom. All detached electrons became common. Connecting with ions, these electrons temporarily form atoms, then break off again and combine with another ion, etc. A process occurs endlessly, which can be represented by a diagram:

Consequently, in the volume of the metal, atoms are continuously converted into ions and vice versa. They are called atom-ions.

Figure 41 schematically shows the structure of a sodium metal fragment. Each sodium atom is surrounded by eight neighboring atoms.

Rice. 41.
Scheme of the structure of a fragment of crystalline sodium

The detached outer electrons freely move from one formed ion to another, connecting, as if gluing together, the ionic backbone of sodium into one giant metal crystal (Fig. 42).

Rice. 42.
Diagram of a metallic bond

The metallic bond has some similarities with the covalent bond, as it is based on the socialization of external electrons. However, in the formation of a covalent bond, the outer unpaired electrons of only two neighboring atoms are socialized, while in the formation of a metallic bond, all atoms participate in the socialization of these electrons. That is why crystals with a covalent bond are brittle, while those with a metal bond are, as a rule, ductile, electrically conductive, and have a metallic sheen.

Figure 43 shows an ancient golden figurine of a deer, which is already more than 3.5 thousand years old, but it has not lost its noble metallic luster, which is characteristic of gold - this most plastic of metals.

rice. 43. Golden deer. 6th century BC e.

A metallic bond is characteristic of both pure metals and mixtures of various metals - alloys that are in solid and liquid states. However, in the vapor state, metal atoms are interconnected by a covalent bond (for example, yellow light lamps are filled with sodium vapor to illuminate the streets of large cities). Metal pairs consist of individual molecules (monatomic and diatomic).

The question of chemical bonds is the central question of the science of chemistry. You got acquainted with the initial ideas about the types of chemical bonds. In the future, you will learn a lot of interesting things about the nature of the chemical bond. For example, that in most metals, in addition to the metallic bond, there is also a covalent bond, that there are other types of chemical bonds.

Keywords and phrases

1. Metal connection.
2. Atom ions.
3. Shared electrons.

Work with computer

1. Talk to electronic application. Study the material of the lesson and complete the suggested tasks.
2. Search the Internet for email addresses that can serve as additional sources, revealing the content of the keywords and phrases of the paragraph. Offer the teacher your help in preparing a new lesson - make a message on keywords and phrases in the next paragraph.

Questions and tasks

1. A metallic bond has similarities with a covalent bond. Compare these chemical bonds with each other.
2. The metallic bond has similarities with the ionic bond. Compare these chemical bonds with each other.
3. How can the hardness of metals and alloys be increased?
4. According to the formulas of substances, determine the type of chemical bond in them: Ba, BaBr 2, HBr, Br 2.

A metallic bond is a bond formed between atoms under conditions of strongly pronounced delocalization (the spread of valence electrons along several chemical bonds in a compound) and a shortage of electrons in an atom (crystal). It is unsaturated and spatially non-directional.

The delocalization of valence electrons in metals is a consequence of the multicenter nature of the metallic bond. The multicenter nature of the metallic bond ensures high electrical and thermal conductivity of metals.

Saturability determined by the number of valence orbitals involved in the formation of chemical. connections. Quantitative characteristic - valency. Valence - the number of bonds that one atom can form with others; - is determined by the number of valence orbitals involved in the formation of bonds by the exchange and donor-acceptor mechanism.

Orientation – the connection is formed in the direction of maximum overlap of electron clouds; - determines the chemical and crystal-chemical structure of a substance (how the atoms are connected in the crystal lattice).

When a covalent bond is formed, the electron density is concentrated between the interacting atoms (drawing from a notebook). In the case of a metallic bond, the electron density is delocalized over the entire crystal. (drawing from a notebook)

(example from notebook)

Due to the unsaturation and non-directional nature of the metallic bond, metallic bodies (crystals) are highly symmetrical and highly coordinated. The overwhelming majority of crystalline structures of a metal correspond to 3 types of atom packing in crystals:

1. HCC– Grenet-centered cubic close-packed structure. Packing density - 74.05%, coordination number = 12.

2. GPU– hexagonal close-packed structure, packing density = 74.05%, c.h. = 12.

3. BCC– volume is centered, packing density = 68.1%, k.ch. = 8.

A metallic bond does not preclude some degree of covalence. Metal bond in its pure form is typical only for alkali and alkaline earth metals.

A pure metallic bond is characterized by an energy of the order of 100/150/200 kJ/mol, which is 4 times weaker than the covalent one.

36. Chlorine and its properties. B \u003d 1 (III, IV, V and VII) oxidation state \u003d 7, 6, 5, 4, 3, 1, −1

greenish-yellow gas with a pungent, irritating odor. Chlorine occurs in nature only in the form of compounds. In nature, in the form of potassium chloride, magnesium, nitrium, formed as a result of the evaporation of former seas and lakes. Receipt.prom: 2NaCl + 2H2O \u003d 2NaOH + H2 + Cl2, by electrolysis of waters of chlorides Me.\2KMnO4 + 16HCl \u003d 2MnCl2 + 2KCl + 8H2O + 5Cl2 / Chemically, chlorine is very active, directly combines with almost all Me, and with non-metals (except carbon, nitrogen, oxygen, inert gases), replaces hydrogen in the pre-HC and joins unsaturated compounds, displaces bromine and iodine from their compounds. Phosphorus ignites in an atmosphere of chlorine PCl3, and with further chlorination - PCl5; sulfur with chlorine = S2Cl2, SCl2 and other SnClm. A mixture of chlorine and hydrogen burns. With oxygen, chlorine forms oxides: Cl2O, ClO2, Cl2O6, Cl2O7, Cl2O8, as well as hypochlorites (salts of hypochlorous acid), chlorites, chlorates and perchlorates. All oxygen compounds of chlorine form explosive mixtures with easily oxidized substances. Chlorine oxides are unstable and can explode spontaneously, hypochlorites decompose slowly during storage, chlorates and perchlorates can explode under the influence of initiators. in water - hypochlorous and salt: Сl2 + Н2О = НClО + НCl. When chlorinating aqueous solutions of alkalis in the cold, hypochlorites and chlorides are formed: 2NaOH + Cl2 \u003d NaClO + NaCl + H2O, and when heated - chlorates. When ammonia reacts with chlorine, nitrogen trichloride is formed. with other halogens interhalogen compounds. Fluorides СlF, СlF3, СlF5 are very reactive; for example, in a ClF3 atmosphere, glass wool ignites spontaneously. Known compounds of chlorine with oxygen to fluorine are chlorine oxyfluorides: ClO3F, ClO2F3, ClOF, ClOF3 and fluorine perchlorate FClO4. Application: production of chemical compounds, water purification, synthesis in food, farm prom-ti-bactericide, antiseptic, whitening of papers, fabrics, pyrotechnics, matches, destroys weeds in SH.

Biological role: biogenic component of plant and animal tissues. 100g the main osmotically active substance of blood plasma, lymph, cerebrospinal fluid and some tissues. Sodium chloride daily requirement = 6-9g-bread, meat and dairy products. Plays a role in water-salt metabolism, contributing to the retention of water by tissues. The regulation of acid-base balance in tissues is carried out along with other processes by changing the distribution of chlorine between the blood and other tissues, chlorine is involved in energy exchange in plants, activating both oxidative phosphorylation and photophosphorylation. Chlorine has a positive effect on the absorption of oxygen by the roots, a component of the iron juice.

37. Hydrogen, water. B \u003d 1; st.oxide \u003d + 1-1 The hydrogen ion is completely devoid of electron shells; it can approach very close distances and be introduced into electron shells.

The most common element in the universe. It makes up the bulk of the Sun, stars and other cosmic bodies. It is relatively rare in the free state on Earth - it is found in petroleum and combustible gases, is present as inclusions in some minerals, and most of it is in the composition of water. Receipt: 1. Laboratory Zn+2HCl=ZnCl2+H ​​2 ; 2.Si + 2NaOH + H 2 O \u003d Na 2 SiO 3 + 2H 2; 3. Al + NaOH + H 2 O \u003d Na (AlOH) 4 + H 2. 4. In industry: conversion, electrolysis: СH4+H2O=CO+3H2\CO+H2O=CO+ H2/Chemistry. N.O.: H 2 + F 2 \u003d 2HF. When irradiated, illuminated, catalysts: H 2 + O 2, S, N, P \u003d H 2 O, H 2 S, NH 3, Ca + H2 \u003d CaH2 \ F2 + H2 \u003d 2HF \ N2 + 3H2 → 2NH3 \ Cl2 + H2 → 2HCl, 2NO+2H2=N2+2H2O,CuO+H2=Cu+H2O,CO+H2=CH3OH. Hydrogen forms hydrides: ionic, covalent and metallic. To ionic -NaH - &, CaH 2 - & + H 2 O \u003d Ca (OH) 2; NaH + H 2 O \u003d NaOH + H 2. Covalent -B 2 H 6, AlH 3, SiH 4. Metal - with d-elements; variable composition: MeH ≤1 , MeH ≤2 - are introduced into the voids between atoms. Conducts heat, current, solid. WATER.sp3-hybrid highly polar.molecule at an angle of 104.5 , dipoles, the most common solvent. Water reacts at room t: with active halogens (F, Cl) and interhaloid compounds with salts, forming a weak acid and a weak base, causing their complete hydrolysis ; with anhydrides and carboxylic and inorganic acid halides. kis-t; with active metalorgan-mi compounds; with carbides, nitrides, phosphides, silicides, active Me hydrides; with many salts, forming hydrates; with boranes, silanes; with ketenes, carbon suboxide; with noble gas fluorides. Water reacts when heated: with Fe, Mg with coal, methane; with some alkyl halides. Application:hydrogen - synthesis of ammonia, methanol, hydrogen chloride, TV fats, hydrogen flame - for welding, melting, in metallurgy for the reduction of Me from oxide, fuel for rockets, in pharmacy - water, peroxide antiseptic, bactericide, washing, hair bleaching, sterilization.

Biol.role: hydrogen-7kg, The main function of hydrogen is the structuring of biological space (water and hydrogen bonds) and the formation of a variety of org molecules (included in the structure of proteins, carbohydrates, fats, enzymes) Thanks to hydrogen bonds,

copying of the DNA molecule. Water takes part in a huge

the number of biochemical reactions, in all physiological and biological

processes, ensures the exchange of substances between the body and external environment, between

cells and within cells. Water is the structural basis of cells, necessary for

maintaining their optimal volume, it determines the spatial structure and

functions of biomolecules.