Chemical bond

All interactions leading to the combination of chemical particles (atoms, molecules, ions, etc.) into substances are divided into chemical bonds and intermolecular bonds (intermolecular interactions).

Chemical bonds- bonds directly between atoms. There are ionic, covalent and metallic bonds.

Intermolecular bonds- connections between molecules. These are hydrogen bonds, ion-dipole bonds (due to the formation of this bond, for example, the formation of a hydration shell of ions occurs), dipole-dipole (due to the formation of this bond, molecules of polar substances are combined, for example, in liquid acetone), etc.

Ionic bond- a chemical bond formed due to the electrostatic attraction of oppositely charged ions. In binary compounds (compounds of two elements), it is formed when the sizes of the bonded atoms are very different from each other: some atoms are large, others are small - that is, some atoms easily give up electrons, while others tend to accept them (usually these are atoms of the elements that form typical metals and atoms of elements forming typical nonmetals); the electronegativity of such atoms is also very different.
Ionic bonding is non-directional and non-saturable.

Covalent bond- a chemical bond that occurs due to the formation of a common pair of electrons. A covalent bond is formed between small atoms with the same or similar radii. A necessary condition is the presence of unpaired electrons in both bonded atoms (exchange mechanism) or a lone pair in one atom and a free orbital in the other (donor-acceptor mechanism):

Based on the number of shared electron pairs, covalent bonds are divided into
• simple (single)- one pair of electrons,
• double- two pairs of electrons,
• triples- three pairs of electrons.

Double and triple bonds are called multiple bonds.

According to the distribution of electron density between the bonded atoms, a covalent bond is divided into non-polar And polar. A non-polar bond is formed between identical atoms, a polar one - between different ones.

Electronegativity- a measure of the ability of an atom in a substance to attract common electron pairs.
The electron pairs of polar bonds are shifted towards more electronegative elements. The displacement of electron pairs itself is called bond polarization. The partial (excess) charges formed during polarization are designated + and -, for example: .

Based on the nature of the overlap of electron clouds ("orbitals"), a covalent bond is divided into -bond and -bond.
-A bond is formed due to the direct overlap of electron clouds (along the straight line connecting the atomic nuclei), -a bond is formed due to lateral overlap (on both sides of the plane in which the atomic nuclei lie).

A covalent bond is directional and saturable, as well as polarizable.
The hybridization model is used to explain and predict the mutual direction of covalent bonds.

Hybridization of atomic orbitals and electron clouds- the supposed alignment of atomic orbitals in energy, and electron clouds in shape when an atom forms covalent bonds.
The three most common types of hybridization are: sp-, sp 2 and sp 3 -hybridization. For example:
sp-hybridization - in molecules C 2 H 2, BeH 2, CO 2 (linear structure);
sp 2-hybridization - in molecules C 2 H 4, C 6 H 6, BF 3 (flat triangular shape);
sp 3-hybridization - in molecules CCl 4, SiH 4, CH 4 (tetrahedral form); NH 3 (pyramidal shape); H 2 O (angular shape).

Metal connection- a chemical bond formed by sharing the valence electrons of all bonded atoms of a metal crystal. As a result, a single electron cloud of the crystal is formed, which easily moves under the influence of electrical voltage - hence the high electrical conductivity of metals.
A metallic bond is formed when the atoms being bonded are large and therefore tend to give up electrons. Simple substances with a metallic bond are metals (Na, Ba, Al, Cu, Au, etc.), complex substances are intermetallic compounds (AlCr 2, Ca 2 Cu, Cu 5 Zn 8, etc.).
The metal bond does not have directionality or saturation. It is also preserved in metal melts.

Hydrogen bond- an intermolecular bond formed due to the partial acceptance of a pair of electrons from a highly electronegative atom by a hydrogen atom with a large positive partial charge. It is formed in cases where one molecule contains an atom with a lone pair of electrons and high electronegativity (F, O, N), and the other contains a hydrogen atom bound by a highly polar bond to one of such atoms. Examples of intermolecular hydrogen bonds:

H—O—H OH 2 , H—O—H NH 3 , H—O—H F—H, H—F H—F.

Intramolecular hydrogen bonds exist in the molecules of polypeptides, nucleic acids, proteins, etc.

A measure of the strength of any bond is the bond energy.
Communication energy- the energy required to break a given chemical bond in 1 mole of a substance. The unit of measurement is 1 kJ/mol.

The energies of ionic and covalent bonds are of the same order, the energy of hydrogen bonds is an order of magnitude less.

The energy of a covalent bond depends on the size of the bonded atoms (bond length) and on the multiplicity of the bond. The smaller the atoms and the greater the bond multiplicity, the greater its energy.

The ionic bond energy depends on the size of the ions and their charges. The smaller the ions and the greater their charge, the greater the binding energy.

Structure of matter

According to the type of structure, all substances are divided into molecular And non-molecular. Among organic substances, molecular substances predominate; among inorganic substances, non-molecular substances predominate.

Based on the type of chemical bond, substances are divided into substances with covalent bonds, substances with ionic bonds (ionic substances) and substances with metallic bonds (metals).

Substances with covalent bonds can be molecular or non-molecular. This significantly affects their physical properties.

Molecular substances consist of molecules connected to each other by weak intermolecular bonds, these include: H 2, O 2, N 2, Cl 2, Br 2, S 8, P 4 and other simple substances; CO 2, SO 2, N 2 O 5, H 2 O, HCl, HF, NH 3, CH 4, C 2 H 5 OH, organic polymers and many other substances. These substances do not have high strength, have low melting and boiling points, do not conduct electricity, and some of them are soluble in water or other solvents.

Non-molecular substances with covalent bonds or atomic substances (diamond, graphite, Si, SiO 2, SiC and others) form very strong crystals (with the exception of layered graphite), they are insoluble in water and other solvents, have high melting and boiling points, most of them they do not conduct electric current (except for graphite, which is electrically conductive, and semiconductors - silicon, germanium, etc.)

All ionic substances are naturally non-molecular. These are solid, refractory substances, solutions and melts of which conduct electric current. Many of them are soluble in water. It should be noted that in ionic substances, the crystals of which consist of complex ions, there are also covalent bonds, for example: (Na +) 2 (SO 4 2-), (K +) 3 (PO 4 3-), (NH 4 + )(NO 3-), etc. The atoms that make up complex ions are connected by covalent bonds.

Metals (substances with metallic bonds) very diverse in their physical properties. Among them there are liquid (Hg), very soft (Na, K) and very hard metals (W, Nb).

The characteristic physical properties of metals are their high electrical conductivity (unlike semiconductors, it decreases with increasing temperature), high heat capacity and ductility (for pure metals).

In the solid state, almost all substances are composed of crystals. Based on the type of structure and type of chemical bond, crystals (“crystal lattices”) are divided into atomic(crystals of non-molecular substances with covalent bonds), ionic(crystals of ionic substances), molecular(crystals of molecular substances with covalent bonds) and metal(crystals of substances with a metallic bond).

Tasks and tests on the topic "Topic 10. "Chemical bonding. Structure of matter."

• Types of chemical bond - Structure of matter grade 8–9

  Lessons: 2 Assignments: 9 Tests: 1

• Assignments: 9 Tests: 1

After working through this topic, you should understand the following concepts: chemical bond, intermolecular bond, ionic bond, covalent bond, metallic bond, hydrogen bond, simple bond, double bond, triple bond, multiple bonds, non-polar bond, polar bond, electronegativity, bond polarization , - and -bond, hybridization of atomic orbitals, binding energy.

You must know the classification of substances by type of structure, by type of chemical bond, the dependence of the properties of simple and complex substances on the type of chemical bond and the type of “crystal lattice”.

You must be able to: determine the type of chemical bond in a substance, the type of hybridization, draw up diagrams of bond formation, use the concept of electronegativity, a number of electronegativity; know how electronegativity changes in chemical elements of the same period and one group to determine the polarity of a covalent bond.

After making sure that everything you need has been learned, proceed to completing the tasks. We wish you success.

• O. S. Gabrielyan, G. G. Lysova. Chemistry 11th grade. M., Bustard, 2002.
• G. E. Rudzitis, F. G. Feldman. Chemistry 11th grade. M., Education, 2001.

Atoms of most elements do not exist separately, as they can interact with each other. This interaction produces more complex particles.

The nature of a 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 on the outer electronic levels (valence electrons), being farthest from the nucleus, interact with it weakest, and therefore are able to break away from the nucleus. They are responsible for bonding atoms to each other.

Types of interactions in chemistry

Types of chemical bonds can be presented in the following table:

Characteristics of ionic bonding

Chemical reaction that occurs due to ion attraction having different charges is called ionic. This happens if the atoms being bonded have a significant difference in electronegativity (that is, the ability to attract electrons) and the electron pair goes to the more electronegative element. The result of this transfer of electrons from one atom to another is the formation of charged particles - ions. An attraction arises between them.

They have the lowest electronegativity indices typical metals, and the largest are typical non-metals. Ions are thus formed by the interaction between typical metals and typical nonmetals.

Metal atoms become positively charged ions (cations), donating electrons to their outer electron levels, and nonmetals 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 non-saturable, since the electrostatic interaction occurs in all directions; accordingly, the ion can attract ions of the opposite sign in all directions.

The arrangement of the ions is such that around each there 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 to form the corresponding ions:

Na 0 - 1 e = Na + (cation)

Cl 0 + 1 e = Cl - (anion)

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

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

Ba 0 - 2 e = Ba 2+

S 0 + 2 e = 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 are easily separated 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 separated from atoms.

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

The following examples can be given:

Mg - 2е<->Mg 2+

Cs-e<->Cs+

Ca - 2e<->Ca2+

Fe-3e<->Fe 3+

Covalent: polar and non-polar

The most common type of chemical interaction is a covalent bond. The electronegativity values ​​of the elements that interact do not differ sharply; therefore, only a shift of the common electron pair to a more electronegative atom occurs.

Covalent interactions can be formed by an exchange mechanism or a donor-acceptor mechanism.

The exchange mechanism is realized if each of the atoms has unpaired electrons on 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 on the outer electronic level, and the other has a free orbital, then when the atomic orbitals overlap, the electron pair is shared and interacts according to the donor-acceptor mechanism.

Covalent ones are divided by multiplicity into:

• simple or single;
• double;
• triples.

Double ones ensure the sharing of two pairs of electrons at once, and triple ones - three.

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

• non-polar;
• polar.

A nonpolar bond is formed by identical atoms, and a polar bond is formed by different electronegativity.

The interaction of atoms with similar electronegativity is called a nonpolar bond. The common pair of electrons in such a molecule is not attracted to either atom, but belongs equally to both.

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

Properties and characteristics of covalency

Main characteristics of a covalent bond:

• The length is determined by the distance between the nuclei of interacting atoms.
• Polarity is determined by the displacement of the electron cloud towards one of the atoms.
• Directionality is the property of forming bonds oriented in space and, accordingly, molecules having 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 determines its strength.

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

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

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

Ṅ: + Ṅ: → N≡N the molecule is triple nonpolar.

Examples of covalent bonds of chemical elements include molecules of carbon dioxide (CO2) and carbon monoxide (CO), hydrogen sulfide (H2S), 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. Oxygen has two unpaired electrons in its outer shell, while carbon can provide four valence electrons to form the 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 metal substances form a metallic bond, metals with nonmetals form an ionic bond, simple nonmetal substances form a covalent nonpolar bond, and molecules consisting of different nonmetals form through a polar covalent bond.

Topics of the Unified State Examination codifier: Covalent chemical bond, its varieties and mechanisms of formation. Characteristics of covalent bonds (polarity and bond energy). Ionic bond. Metal connection. Hydrogen bond

Intramolecular chemical bonds

First, let's look at the bonds that arise between particles within molecules. Such connections are called intramolecular.

Chemical bond between atoms of chemical elements has an electrostatic nature and is formed due to interaction of external (valence) electrons, to a greater or lesser extent held by positively charged nuclei bonded atoms.

The key concept here is ELECTRONEGATIVITY. It is this that determines the type of chemical bond between atoms and the properties of this bond.

is the ability of an atom to attract (hold) external(valence) electrons. Electronegativity is determined by the degree of attraction of outer electrons to the nucleus and depends primarily on the radius of the atom and the charge of the nucleus.

Electronegativity is difficult to determine unambiguously. L. Pauling compiled a table of relative electronegativities (based on the bond energies of diatomic molecules). The most electronegative element is fluorine with meaning 4 .

It is important to note that in different sources you can find different scales and tables of electronegativity values. This should not be alarmed, since the formation of a chemical bond plays a role atoms, and it is approximately the same in any system.

If one of the atoms in the A:B chemical bond attracts electrons more strongly, then the electron pair moves towards it. The more electronegativity difference atoms, the more the electron pair shifts.

If the electronegativity values ​​of interacting atoms are equal or approximately equal: EO(A)≈EO(B), then the common electron pair does not shift to any of the atoms: A: B. This connection is called covalent nonpolar.

If the electronegativities of the interacting atoms differ, but not greatly (the difference in electronegativity is approximately from 0.4 to 2: 0,4<ΔЭО<2 ), then the electron pair is displaced to one of the atoms. This connection is called covalent polar .

If the electronegativities of interacting atoms differ significantly (the difference in electronegativity is greater than 2: ΔEO>2), then one of the electrons is almost completely transferred to another atom, with the formation ions. This connection is called ionic.

Basic types of chemical bonds − covalent, ionic And metal communications. Let's take a closer look at them.

Covalent chemical bond

Covalent bond – it's a chemical bond , formed due to formation of a common electron pair A:B . Moreover, two atoms overlap atomic orbitals. A covalent bond is formed by the interaction of atoms with a small difference in electronegativity (usually between two non-metals) or atoms of one element.

Basic properties of covalent bonds

• focus,
• saturability,
• polarity,
• polarizability.

These bonding properties influence the chemical and physical properties of substances.

Communication direction characterizes the chemical structure and form of substances. The angles between two bonds are called bond angles. For example, in a water molecule the bond angle H-O-H is 104.45 o, therefore the water molecule is polar, and in a methane molecule the bond angle H-C-H is 108 o 28′.

Saturability is the ability of atoms to form a limited number of covalent chemical bonds. The number of bonds that an atom can form is called.

Polarity bonding occurs due to the uneven distribution of electron density between two atoms with different electronegativity. Covalent bonds are divided into polar and nonpolar.

Polarizability connections are the ability of bond electrons to shift under the influence of an external electric field(in particular, the electric field of another particle). Polarizability depends on electron mobility. The further the electron is from the nucleus, the more mobile it is, and accordingly the molecule is more polarizable.

Covalent nonpolar chemical bond

There are 2 types of covalent bonding – POLAR And NON-POLAR .

Example . Let's consider the structure of the hydrogen molecule H2. Each hydrogen atom in its outer energy level carries 1 unpaired electron. To display an atom, we use the Lewis structure - this is a diagram of the structure of the outer energy level of an atom, when electrons are indicated by dots. Lewis point structure models are quite helpful when working with elements of the second period.

H. + . H = H:H

Thus, a hydrogen molecule has one shared electron pair and one H–H chemical bond. This electron pair does not shift to any of the hydrogen atoms, because Hydrogen atoms have the same electronegativity. This connection is called covalent nonpolar .

Covalent nonpolar (symmetric) bond is a covalent bond formed by atoms with equal electronegativity (usually the same nonmetals) and, therefore, with a uniform distribution of electron density between the nuclei of atoms.

The dipole moment of non-polar bonds is 0.

Examples: H 2 (H-H), O 2 (O=O), S 8.

Covalent polar chemical bond

Covalent polar bond is a covalent bond that occurs between atoms with different electronegativity (usually various non-metals) and is characterized displacement shared electron pair to a more electronegative atom (polarization).

The electron density is shifted to the more electronegative atom - therefore, a partial negative charge (δ-) appears on it, and a partial positive charge (δ+, delta +) appears on the less electronegative atom.

The greater the difference in electronegativity of atoms, the higher polarity connections and more dipole moment . Additional attractive forces act between neighboring molecules and charges of opposite sign, which increases strength communications.

Bond polarity affects the physical and chemical properties of compounds. The reaction mechanisms and even the reactivity of neighboring bonds depend on the polarity of the bond. The polarity of the connection often determines molecule polarity and thus directly affects such physical properties as boiling point and melting point, solubility in polar solvents.

Examples: HCl, CO 2, NH 3.

Mechanisms of covalent bond formation

Covalent chemical bonds can occur by 2 mechanisms:

1. Exchange mechanism the formation of a covalent chemical bond is when each particle provides one unpaired electron to form a common electron pair:

A . + . B= A:B

2. Covalent bond formation is a mechanism in which one of the particles provides a lone pair of electrons, and the other particle provides a vacant orbital for this electron pair:

A: + B= A:B

In this case, one of the atoms provides a lone pair of electrons ( donor), and the other atom provides a vacant orbital for that pair ( acceptor). As a result of the formation of both bonds, the energy of the electrons decreases, i.e. this is beneficial for the atoms.

A covalent bond formed by a donor-acceptor mechanism no different in properties from other covalent bonds formed by the exchange mechanism. The formation of a covalent bond by the donor-acceptor mechanism is typical for atoms either with a large number of electrons at the external energy level (electron donors), or, conversely, with a very small number of electrons (electron acceptors). The valence capabilities of atoms are discussed in more detail in the corresponding section.

A covalent bond is formed by a donor-acceptor mechanism:

- in a molecule carbon monoxide CO(the bond in the molecule is triple, 2 bonds are formed by the exchange mechanism, one by the donor-acceptor mechanism): C≡O;

- V ammonium ion NH 4 +, in ions organic amines, for example, in the methylammonium ion CH 3 -NH 2 + ;

- V complex compounds, a chemical bond between the central atom and ligand groups, for example, in sodium tetrahydroxoaluminate Na bond between aluminum and hydroxide ions;

- V nitric acid and its salts- nitrates: HNO 3, NaNO 3, in some other nitrogen compounds;

- in a molecule ozone O3.

Basic characteristics of covalent bonds

Covalent bonds typically form between nonmetal atoms. The main characteristics of a covalent bond are length, energy, multiplicity and directionality.

Multiplicity of chemical bond

Multiplicity of chemical bond - This number of shared electron pairs between two atoms in a compound. The multiplicity of a bond can be determined quite easily from the values ​​of the atoms that form the molecule.

For example , in the hydrogen molecule H 2 the bond multiplicity is 1, because Each hydrogen has only 1 unpaired electron in its outer energy level, hence one shared electron pair is formed.

In the O 2 oxygen molecule, the bond multiplicity is 2, because Each atom at the outer energy level has 2 unpaired electrons: O=O.

In the nitrogen molecule N2, the bond multiplicity is 3, because between each atom there are 3 unpaired electrons at the outer energy level, and the atoms form 3 common electron pairs N≡N.

Covalent bond length

Chemical bond length is the distance between the centers of the nuclei of the atoms forming the bond. It is determined by experimental physical methods. The bond length can be estimated approximately using the additivity rule, according to which the bond length in the AB molecule is approximately equal to half the sum of the bond lengths in molecules A 2 and B 2:

The length of a chemical bond can be roughly estimated by atomic radii forming a bond, or by communication multiplicity, if the radii of the atoms are not very different.

As the radii of the atoms forming a bond increase, the bond length will increase.

For example

As the multiplicity of bonds between atoms increases (the atomic radii of which do not differ or differ only slightly), the bond length will decrease.

For example . In the series: C–C, C=C, C≡C, the bond length decreases.

Communication energy

A measure of the strength of a chemical bond is the bond energy. Communication energy determined by the energy required to break a bond and remove the atoms forming that bond to an infinitely large distance from each other.

A covalent bond is very durable. Its energy ranges from several tens to several hundred kJ/mol. The higher the bond energy, the greater the bond strength, and vice versa.

The strength of a chemical bond depends on the bond length, bond polarity, and bond multiplicity. The longer a chemical bond, the easier it is to break, and the lower the bond energy, the lower its strength. The shorter the chemical bond, the stronger it is, and the greater the bond energy.

For example, in the series of compounds HF, HCl, HBr from left to right, the strength of the chemical bond decreases, because The connection length increases.

Ionic chemical bond

Ionic bond is a chemical bond based on electrostatic attraction of ions.

Ions are formed in the process of accepting or donating electrons by atoms. For example, atoms of all metals weakly hold electrons from the outer energy level. Therefore, metal atoms are characterized by restorative properties- ability to donate electrons.

Example. The sodium atom contains 1 electron at energy level 3. By easily giving it up, the sodium atom forms the much more stable Na + ion, with the electron configuration of the noble gas neon Ne. The sodium ion contains 11 protons and only 10 electrons, so the total charge of the ion is -10+11 = +1:

+11Na) 2 ) 8 ) 1 - 1e = +11 Na +) 2 ) 8

Example. A chlorine atom in its outer energy level contains 7 electrons. To acquire the configuration of a stable inert argon atom Ar, chlorine needs to gain 1 electron. After adding an electron, a stable chlorine ion consisting of electrons is formed. The total charge of the ion is -1:

+17Cl) 2 ) 8 ) 7 + 1e = +17 Cl — ) 2 ) 8 ) 8

Please note:

• The properties of ions are different from the properties of atoms!
• Stable ions can form not only atoms, but also groups of atoms. For example: ammonium ion NH 4 +, sulfate ion SO 4 2-, etc. Chemical bonds formed by such ions are also considered ionic;
• Ionic bonds are usually formed between each other metals And nonmetals(non-metal groups);

The resulting ions are attracted due to electrical attraction: Na + Cl -, Na 2 + SO 4 2-.

Let us visually summarize difference between covalent and ionic bond types:

Metal connection is a connection that is formed relatively free electrons between metal ions, forming a crystal lattice.

Metal atoms are usually located on the outer energy level one to three electrons. The radii of metal atoms, as a rule, are large - therefore, metal atoms, unlike non-metals, give up their outer electrons quite easily, i.e. are strong reducing agents.

By donating electrons, metal atoms turn into positively charged ions . The detached electrons are relatively free are moving between positively charged metal ions. Between these particles a connection arises, because shared electrons hold metal cations arranged in layers together , thus creating a fairly strong metal crystal lattice . In this case, the electrons continuously move chaotically, i.e. New neutral atoms and new cations constantly appear.

Intermolecular interactions

Separately, it is worth considering the interactions that arise between individual molecules in a substance - intermolecular interactions . Intermolecular interactions are a type of interaction between neutral atoms in which no new covalent bonds appear. The forces of interaction between molecules were discovered by Van der Waals in 1869, and named after him Van dar Waals forces. Van der Waals forces are divided into orientation, induction And dispersive . The energy of intermolecular interactions is much less than the energy of chemical bonds.

Orientation forces of attraction occur between polar molecules (dipole-dipole interaction). These forces occur between polar molecules. Inductive interactions is the interaction between a polar molecule and a non-polar one. A nonpolar molecule is polarized due to the action of a polar one, which generates additional electrostatic attraction.

A special type of intermolecular interaction is hydrogen bonds. - these are intermolecular (or intramolecular) chemical bonds that arise between molecules that have highly polar covalent bonds - H-F, H-O or H-N. If there are such bonds in a molecule, then between the molecules there will be additional attractive forces .

Education mechanism hydrogen bonding is partly electrostatic and partly donor-acceptor. In this case, the electron pair donor is an atom of a strongly electronegative element (F, O, N), and the acceptor is the hydrogen atoms connected to these atoms. Hydrogen bonds are characterized by focus in space and saturation

Hydrogen bonds can be indicated by dots: H ··· O. The greater the electronegativity of the atom connected to hydrogen, and the smaller its size, the stronger the hydrogen bond. It is typical primarily for connections fluorine with hydrogen , as well as to oxygen and hydrogen , to a lesser extent nitrogen with hydrogen .

Hydrogen bonds occur between the following substances:

— hydrogen fluoride HF(gas, solution of hydrogen fluoride in water - hydrofluoric acid), water H 2 O (steam, ice, liquid water):

— solution of ammonia and organic amines- between ammonia and water molecules;

— organic compounds in which O-H or N-H bonds: alcohols, carboxylic acids, amines, amino acids, phenols, aniline and its derivatives, proteins, solutions of carbohydrates - monosaccharides and disaccharides.

Hydrogen bonding affects the physical and chemical properties of substances. Thus, additional attraction between molecules makes it difficult for substances to boil. Substances with hydrogen bonds exhibit an abnormal increase in boiling point.

For example As a rule, with increasing molecular weight, an increase in the boiling point of substances is observed. However, in a number of substances H 2 O-H 2 S-H 2 Se-H 2 Te we do not observe a linear change in boiling points.

Namely, at water boiling point is abnormally high - no less than -61 o C, as the straight line shows us, but much more, +100 o C. This anomaly is explained by the presence of hydrogen bonds between water molecules. Therefore, under normal conditions (0-20 o C) water is liquid by phase state.

All currently known chemical elements located on the periodic table are divided into two large groups: metals and non-metals. In order for them to become not just elements, but compounds, chemical substances, and be able to interact with each other, they must exist in the form of simple and complex substances.

This is why some electrons try to accept, while others try to give away. By replenishing each other in this way, the elements form various chemical molecules. But what keeps them together? Why do there exist substances of such strength that even the most serious instruments cannot be destroyed? Others, on the contrary, are destroyed by the slightest impact. All this is explained by the formation of various types of chemical bonds between atoms in molecules, the formation of a crystal lattice of a certain structure.

Types of chemical bonds in compounds

In total, there are 4 main types of chemical bonds.

1. Covalent non-polar. It is formed between two identical non-metals due to the sharing of electrons, the formation of common electron pairs. Valence unpaired particles take part in its formation. Examples: halogens, oxygen, hydrogen, nitrogen, sulfur, phosphorus.
2. Covalent polar. Formed between two different non-metals or between a metal with very weak properties and a non-metal with weak electronegativity. It is also based on common electron pairs and the pulling of them towards itself by the atom whose electron affinity is higher. Examples: NH 3, SiC, P 2 O 5 and others.
3. Hydrogen bond. The most unstable and weakest, it is formed between a highly electronegative atom of one molecule and a positive atom of another. Most often this happens when substances are dissolved in water (alcohol, ammonia, etc.). Thanks to this connection, macromolecules of proteins, nucleic acids, complex carbohydrates, and so on can exist.
4. Ionic bond. It is formed due to the forces of electrostatic attraction of differently charged metal and non-metal ions. The stronger the difference in this indicator, the more clearly the ionic nature of the interaction is expressed. Examples of compounds: binary salts, complex compounds - bases, salts.
5. A metal bond, the formation mechanism of which, as well as its properties, will be discussed further. It is formed in metals and their alloys of various kinds.

There is such a thing as the unity of a chemical bond. It just says that it is impossible to consider every chemical bond as a standard. They are all just conventionally designated units. After all, all interactions are based on a single principle - electron-static interaction. Therefore, ionic, metallic, covalent and hydrogen bonds have the same chemical nature and are only marginal cases of each other.

Metals and their physical properties

Metals are found in the overwhelming majority of all chemical elements. This is due to their special properties. A significant part of them was obtained by humans through nuclear reactions in laboratory conditions; they are radioactive with a short half-life.

However, the majority are natural elements that form entire rocks and ores and are part of most important compounds. It was from them that people learned to cast alloys and make a lot of beautiful and important products. These are copper, iron, aluminum, silver, gold, chromium, manganese, nickel, zinc, lead and many others.

For all metals, common physical properties can be identified, which are explained by the formation of a metallic bond. What are these properties?

1. Malleability and ductility. It is known that many metals can be rolled even to the state of foil (gold, aluminum). Others produce wire, flexible metal sheets, and products that can be deformed during physical impact, but immediately restore their shape after it stops. It is these qualities of metals that are called malleability and ductility. The reason for this feature is the metal type of connection. The ions and electrons in the crystal slide relative to each other without breaking, which allows maintaining the integrity of the entire structure.
2. Metallic shine. It also explains the metallic bond, the formation mechanism, its characteristics and features. Thus, not all particles are able to absorb or reflect light waves of the same wavelength. The atoms of most metals reflect short-wave rays and acquire almost the same color of silver, white, and pale bluish tint. The exceptions are copper and gold, their colors are red-red and yellow, respectively. They are able to reflect longer wavelength radiation.
3. Thermal and electrical conductivity. These properties are also explained by the structure of the crystal lattice and the fact that the metallic type of bond is realized in its formation. Due to the “electron gas” moving inside the crystal, electric current and heat are instantly and evenly distributed between all atoms and ions and are conducted through the metal.
4. Solid state of aggregation under normal conditions. The only exception here is mercury. All other metals are necessarily strong, solid compounds, as well as their alloys. This is also a result of metallic bonding being present in metals. The mechanism of formation of this type of particle binding fully confirms the properties.

These are the main physical characteristics of metals, which are explained and determined precisely by the scheme of formation of a metallic bond. This method of connecting atoms is relevant specifically for metal elements and their alloys. That is, for them in a solid and liquid state.

Metal type chemical bond

What is its peculiarity? The thing is that such a bond is formed not due to differently charged ions and their electrostatic attraction and not due to the difference in electronegativity and the presence of free electron pairs. That is, ionic, metallic, covalent bonds have slightly different natures and distinctive features of the particles being bonded.

All metals have the following characteristics:

• a small number of electrons per (except for some exceptions, which may have 6,7 and 8);
• large atomic radius;
• low ionization energy.

All this contributes to the easy separation of outer unpaired electrons from the nucleus. At the same time, the atom has a lot of free orbitals. The diagram of the formation of a metallic bond will precisely show the overlap of numerous orbital cells of different atoms with each other, which as a result form a common intracrystalline space. Electrons are fed into it from each atom, which begin to wander freely through different parts of the lattice. Periodically, each of them attaches to an ion at a site in the crystal and turns it into an atom, then detaches again to form an ion.

Thus, a metallic bond is the bond between atoms, ions and free electrons in a common metal crystal. An electron cloud moving freely within a structure is called an “electron gas.” This is what explains most metals and their alloys.

How exactly does a metal chemical bond realize itself? Various examples can be given. Let's try to look at it on a piece of lithium. Even if you take it the size of a pea, there will be thousands of atoms. So let’s imagine that each of these thousands of atoms gives up its single valence electron to the common crystalline space. At the same time, knowing the electronic structure of a given element, you can see the number of empty orbitals. Lithium will have 3 of them (p-orbitals of the second energy level). Three for each atom out of tens of thousands - this is the common space inside the crystal in which the “electron gas” moves freely.

A substance with a metal bond is always strong. After all, electron gas does not allow the crystal to collapse, but only displaces the layers and immediately restores them. It shines, has a certain density (usually high), fusibility, malleability and plasticity.

Where else is metal bonding sold? Examples of substances:

• metals in the form of simple structures;
• all metal alloys with each other;
• all metals and their alloys in liquid and solid states.

There are simply an incredible number of specific examples, since there are more than 80 metals in the periodic table!

Metal bond: mechanism of formation

If we consider it in general terms, we have already outlined the main points above. The presence of free electrons and electrons that are easily detached from the nucleus due to low ionization energy are the main conditions for the formation of this type of bond. Thus, it turns out that it is realized between the following particles:

• atoms at the sites of the crystal lattice;
• free electrons that were valence electrons in the metal;
• ions at the sites of the crystal lattice.

The result is a metal bond. The mechanism of formation is generally expressed by the following notation: Me 0 - e - ↔ Me n+. From the diagram it is obvious what particles are present in the metal crystal.

The crystals themselves can have different shapes. It depends on the specific substance we are dealing with.

Types of metal crystals

This structure of a metal or its alloy is characterized by a very dense packing of particles. It is provided by ions in the crystal nodes. The lattices themselves can have different geometric shapes in space.

1. Body-centric cubic lattice - alkali metals.
2. Hexagonal compact structure - all alkaline earths except barium.
3. Face-centric cubic - aluminum, copper, zinc, many transition metals.
4. Mercury has a rhombohedral structure.
5. Tetragonal - indium.

The lower and lower it is located in the periodic system, the more complex its packaging and spatial organization of the crystal. In this case, the metallic chemical bond, examples of which can be given for each existing metal, is decisive in the construction of the crystal. Alloys have very diverse organizations in space, some of which have not yet been fully studied.

Communication characteristics: non-directional

Covalent and metallic bonds have one very pronounced distinctive feature. Unlike the first, the metallic bond is not directional. What does it mean? That is, the electron cloud inside the crystal moves completely freely within its boundaries in different directions, each electron is capable of attaching to absolutely any ion at the nodes of the structure. That is, interaction is carried out in different directions. Hence they say that the metallic bond is non-directional.

The mechanism of covalent bonding involves the formation of shared electron pairs, that is, clouds of overlapping atoms. Moreover, it occurs strictly along a certain line connecting their centers. Therefore, they talk about the direction of such a connection.

Saturability

This characteristic reflects the ability of atoms to have limited or unlimited interaction with others. Thus, covalent and metallic bonds according to this indicator are again opposites.

The first is saturable. The atoms taking part in its formation have a strictly defined number of valence external electrons, which are directly involved in the formation of the compound. It will not have more electrons than it has. Therefore, the number of bonds formed is limited by valency. Hence the saturation of the connection. Due to this characteristic, most compounds have a constant chemical composition.

Metallic and hydrogen bonds, on the contrary, are unsaturated. This is explained by the presence of numerous free electrons and orbitals inside the crystal. Ions also play a role at the nodes of the crystal lattice, each of which can become an atom and again an ion at any time.

Another characteristic of metallic bonding is the delocalization of the internal electron cloud. It manifests itself in the ability of a small number of shared electrons to bind together many atomic nuclei of metals. That is, the density is, as it were, delocalized, distributed evenly between all parts of the crystal.

Examples of bond formation in metals

Let's look at a few specific options that illustrate how a metallic bond is formed. Examples of substances are:

• zinc;
• aluminum;
• potassium;
• chromium.

Formation of a metallic bond between zinc atoms: Zn 0 - 2e - ↔ Zn 2+. The zinc atom has four energy levels. Based on the electronic structure, it has 15 free orbitals - 3 in p-orbitals, 5 in 4 d and 7 in 4f. The electronic structure is as follows: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 0 4d 0 4f 0, a total of 30 electrons in the atom. That is, two free valence negative particles are able to move within 15 spacious and unoccupied orbitals. And so it is for every atom. The result is a huge common space consisting of empty orbitals and a small number of electrons that bind the entire structure together.

Metallic bond between aluminum atoms: AL 0 - e - ↔ AL 3+. The thirteen electrons of an aluminum atom are located at three energy levels, which they clearly have in abundance. Electronic structure: 1s 2 2s 2 2p 6 3s 2 3p 1 3d 0 . Free orbitals - 7 pieces. Obviously, the electron cloud will be small compared to the total internal free space in the crystal.

Chrome metal bond. This element is special in its electronic structure. Indeed, to stabilize the system, the electron falls from the 4s to the 3d orbital: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 5 4p 0 4d 0 4f 0 . There are 24 electrons in total, of which six are valence electrons. They are the ones who go into the common electronic space to form a chemical bond. There are 15 free orbitals, which is still much more than required to fill. Therefore, chromium is also a typical example of a metal with a corresponding bond in the molecule.

One of the most active metals that reacts even with ordinary water with fire is potassium. What explains these properties? Again, in many ways - by a metal type of connection. This element has only 19 electrons, but they are located at 4 energy levels. That is, in 30 orbitals of different sublevels. Electronic structure: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 0 4p 0 4d 0 4f 0 . Only two with very low ionization energy. They break away freely and go into the common electronic space. There are 22 orbitals for movement per atom, that is, a very large free space for “electron gas”.

Similarities and differences with other types of connections

In general, this issue has already been discussed above. One can only generalize and draw a conclusion. The main features of metal crystals that distinguish them from all other types of connections are:

• several types of particles participating in the binding process (atoms, ions or atom-ions, electrons);
• different spatial geometric structures of crystals.

Metallic bonds have in common with hydrogen and ionic bonds unsaturation and non-directionality. With covalent polar - strong electrostatic attraction between particles. Separately from ionic - a type of particles at the nodes of a crystal lattice (ions). With covalent nonpolar - atoms in the nodes of the crystal.

Types of bonds in metals of different states of aggregation

As we noted above, a metallic chemical bond, examples of which are given in the article, is formed in two states of aggregation of metals and their alloys: solid and liquid.

The question arises: what type of bond is in metal vapors? Answer: covalent polar and non-polar. As with all compounds that are in the form of a gas. That is, when the metal is heated for a long time and transferred from a solid to a liquid state, the bonds do not break and the crystalline structure is preserved. However, when it comes to transferring the liquid into a vapor state, the crystal is destroyed and the metallic bond is converted into a covalent one.

CHEMICAL BOND

Chemical bond is the interaction of two atoms carried out by exchanging electrons. When a chemical bond is formed, atoms tend to acquire a stable eight-electron (or two-electron) outer shell, corresponding to the structure of the atom of the nearest inert gas. The following types of chemical bonds are distinguished: covalent(polar and nonpolar; exchange and donor-acceptor), ionic, hydrogen And metal.

COVALENT BOND

It is carried out due to the electron pair belonging to both atoms. There are exchange and donor-acceptor mechanisms for the formation of covalent bonds.

1) Exchange mechanism . Each atom contributes one unpaired electron to a common electron pair:

2) Donor-acceptor mechanism . One atom (donor) provides an electron pair, and the other atom (acceptor) provides an empty orbital for that pair;

Two atoms can not socialize c how many pairs of electrons? In this case they talk about multiples connections:

If the electron density is located symmetrically between atoms, the covalent bond is called non-polar.

If the electron density is shifted towards one of the atoms, then the covalent bond is called polar.

The greater the difference in the electronegativity of the atoms, the greater the polarity of the bond.

Electronegativity is the ability of an atom to attract electron density from other atoms. The most electronegative element is fluorine, the most electropositive is francium.

IONIC BOND

Ions- these are charged particles into which atoms turn as a result of the loss or addition of electrons.

(sodium fluoride is made up of sodium ions Na+ and fluoride ions F - )

If the difference in the electronegativity of the atoms is large, then the electron pair performing the bond goes to one of the atoms, and both atoms turn into ions.

The chemical bond between ions due to electrostatic attraction is calledionic bond.

HYDROGEN BONDING

Hydrogen bond - This is a bond between a positively charged hydrogen atom of one molecule and a negatively charged atom of another molecule. The hydrogen bond is partly electrostatic and partly donor-acceptor in nature.

The presence of hydrogen bonds explains the high boiling temperatures of water, alcohols, and carboxylic acids.

METAL LINK

The valence electrons of metals are rather weakly bound to their nuclei and can easily be detached from them. Therefore, the metal contains a number of positive ions located at certain positions in the crystal lattice, and a large number of electrons moving freely throughout the crystal. Electrons in a metal provide bonds between all metal atoms.

ORBITAL HYBRIDISATION

Orbital hybridization is a change in the shape of some orbitals during the formation of a covalent bond to achieve more efficient orbital overlap.

A

sp 3 - Hybridization. One s orbital and three p - the orbitals turn into four identical “hybrid” orbitals, the angle between the axes of which is 109° 28".

sp 3 - hybridization, have tetrahedral geometry ( CH 4, NH 3).

B

sp 2 - Hybridization. One s-orbital and two p-orbitals turn into three identical “hybrid” orbitals, the angle between their axes is 120°.

Molecules in which it takes place sp

Two sp - orbitals can form two s - bonds (BeH 2, ZnCl 2). Two more p - connections can be formed if two p - orbitals not involved in hybridization contain electrons (acetylene C 2 H 2 ).

Molecules in which it takes place sp - hybridization, have linear geometry.

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