Ionic bond

Chemical bond theory takes important place in modern chemistry. She is explains why atoms combine to form chemical particles, and makes it possible to compare the stability of these particles. Using chemical bond theory, can predict the composition and structure of various compounds. The concept of the breaking of some chemical bonds and the formation of others underlies modern ideas about the transformations of substances in the course of chemical reactions .

chemical bond- this is interaction of atoms , determining the stability of a chemical particle or crystal as a whole . chemical bond formed through electrostatic interaction between charged particles : cations and anions, nuclei and electrons. When atoms approach each other, attractive forces begin to act between the nucleus of one atom and the electrons of another, as well as repulsive forces between nuclei and between electrons. On the some distance these forces balance each other, and a stable chemical particle is formed .

When a chemical bond is formed, a significant redistribution of the electron density of atoms in the compound can occur compared to free atoms.

In the limiting case, this leads to the formation of charged particles - ions (from the Greek "ion" - going).

1 Interaction of ions

If a atom loses one or few electrons, then he turns into a positive ion - cation(translated from Greek - " going down"). This is how cations hydrogen H +, lithium Li +, barium Ba 2+ . Acquiring electrons, atoms turn into negative ions - anions(from the Greek "anion" - going up). Examples of anions are fluoride ion F − , sulfide ion S 2− .

Cations and anions able attract each other. This gives rise to chemical bond, and chemical compounds are formed. This type of chemical bond is called ionic bond :

2 Ionic bond definition

Ionic bond is a chemical bond educated at the expense electrostatic attraction between cations and anions .

The mechanism of formation of an ionic bond can be considered on the example of the reaction between sodium and chlorine . An alkali metal atom easily loses an electron, a halogen atom - acquires. As a result of this, there sodium cation and chloride ion. They form a connection through electrostatic attraction between them .

Interaction between cations and anions does not depend on direction, that's why about ionic bond they talk about non-directional. Each cation maybe attract any number of anions, and vice versa. That's why ionic bond is unsaturated. Number interactions between ions in the solid state is limited only by the size of the crystal. That's why " molecule " ionic compound should be considered the entire crystal .

For the emergence ionic bond necessary, to sum of ionization energies E i(to form a cation) and electron affinity A e(for anion formation) must be energetically profitable. it limits the formation of ionic bonds by atoms of active metals(elements of IA- and IIA-groups, some elements of the IIIA-group and some transitional elements) and active non-metals(halogens, chalcogens, nitrogen).

Ideal ionic bond practically does not exist. Even in those compounds that are usually referred to as ionic , there is no complete transfer of electrons from one atom to another ; electrons partially remain in common use. Yes, the connection lithium fluoride by 80% ionic, and by 20% - covalent. Therefore, it is more correct to speak of degree of ionicity (polarity) covalent chemical bond. It is believed that with a difference electronegativity elements 2.1 communication is on 50% ionic. At greater difference compound can be considered ionic .

The ionic model of a chemical bond is widely used to describe the properties of many substances., in the first place, connections alkaline and alkaline earth metals with non-metals. This is due ease of description of such compounds: believe they are built from incompressible charged spheres, corresponding cations and anions. In this case, the ions tend to arrange themselves in such a way that the attractive forces between them are maximum, and the repulsive forces are minimal.

Ionic bond- a strong chemical bond formed between atoms with a large difference (>1.7 on the Pauling scale) of electronegativity, with which the shared electron pair goes entirely to the atom with the greater electronegativity. This is the attraction of ions as oppositely charged bodies. An example is the compound CsF, in which the "degree of ionicity" is 97%.

Ionic bond- extreme case polarization of a covalent polar bond. Formed between typical metal and non-metal. In this case, the electrons in the metal completely transferred to non-metal . Ions are formed.

If a chemical bond is formed between atoms that have very large electronegativity difference (EO > 1.7 according to Pauling), then the shared electron pair is completely goes to an atom with a higher EC. This results in the formation of a compound oppositely charged ions :

Between the formed ions there is electrostatic attraction, which is called ionic bond. Rather, this view convenient. In practice ionic bond between the atoms in in its pure form is not realized anywhere or almost nowhere, usually in reality the connection is partially ionic , and partially covalent character. At the same time, communication complex molecular ions can often be considered purely ionic. The most important differences between ionic bonds and other types of chemical bonds are non-directionality and unsaturation. That is why crystals formed due to ionic bonding gravitate towards various close packings of the corresponding ions.

3 Ionic radii

In idle electrostatic model of ionic bond concept is used ionic radii . The sum of the radii of the neighboring cation and anion must be equal to the corresponding internuclear distance :

r 0 = r + + r −

At the same time, it remains obscure where to take boundary between cation and anion . Known today , that a purely ionic bond does not exist, as always there is some electron cloud overlap. For ion radii calculations use research methods, which allow you to determine the electron density between two atoms . The internuclear distance is divided at a point, where electron density is minimal .

Ion size depends on many factors. At constant charge of the ion with increasing serial number(and consequently, nuclear charge) ionic radius decreases. This is especially noticeable in the lanthanide series, where ionic radii change monotonically from 117 pm for (La 3+) to 100 pm (Lu 3+) at a coordination number of 6. This effect is called lanthanide compression .

AT element groups ionic radii generally increase with increasing atomic number. However for d-elements of the fourth and fifth periods due to lanthanide compression even a decrease in the ionic radius can occur(for example, from 73 pm for Zr 4+ to 72 pm for Hf 4+ with a coordination number of 4).

In the period, there is a noticeable decrease in the ionic radius associated with an increase in the attraction of electrons to the nucleus with a simultaneous increase in the charge of the nucleus and the charge of the ion itself: 116 pm for Na +, 86 pm for Mg 2+ , 68 pm for Al 3+ (coordination number 6). For the same reason an increase in the charge of an ion leads to a decrease in the ionic radius for one element: Fe 2+ 77 pm, Fe 3+ 63 pm, Fe 6+ 39 pm (coordination number 4).

Comparison ionic radii can carried out only with the same coordination number, because the it affects the size of the ion due to the repulsive forces between the counterions. This is clearly seen in the example Ag+ ion; its ionic radius is 81, 114 and 129 pm for coordination numbers 2, 4 and 6 , respectively .

Structure perfect ionic compound, due to maximum attraction between dissimilar ions and minimum repulsion between like ions, in many ways determined by the ratio of the ionic radii of cations and anions. It can be shown simple geometric constructions.

4 Ionic bond energy

Bond energy and for ionic compound- this is energy, which in is released during its formation from gaseous counterions infinitely distant from each other . Considering only electrostatic forces corresponds to about 90% of the total interaction energy, which includes also the contribution of non-electrostatic forces(for example, repulsion of electron shells).

When ionic bond between two free ion energy them attraction is determined by Coulomb's law :

E(adj.) = q+ q− / (4π r ε),

where q+ and q−- charges interacting ions , r - the distance between them , ε - medium permittivity .

Since one of the charges negative, then energy value also will be negative .

According to Coulomb's law, on the At infinitesimal distances, the energy of attraction must become infinitely large. However, this not happening, because ions are not point charges. At approach of ions there is a repulsive force between them, due to interaction of electron clouds . Ion repulsion energy described Born equation :

E (ott.) \u003d B / rn,

where AT - some constant , n maybe take values ​​from 5 to 12(depends on ion size). The total energy is determined by the sum of the energies of attraction and repulsion :

E \u003d E (adv.) + E (ott.)

Its meaning goes through minimum . The coordinates of the minimum point correspond to the equilibrium distance r 0 and equilibrium energy of interaction between ions E 0 :

E0 = q+ q− (1 - 1 / n) / (4π r0 ε)

AT crystal lattice always there are more interactions, how between a pair of ions. This number determined primarily by the type of crystal lattice. For accounting for all interactions(weakening with increasing distance) into the expression for ionic energy crystal lattice introduce the so-called constant Madelunga A :

E(adj.) = A q+ q− / (4π r ε)

Constant value Madelunga determined only lattice geometry and not depends on the radius and charge of the ions. For example, for sodium chloride it is equal to 1,74756 .

5 polarization of ions

Apart from charge magnitude and radius important characteristic and she are his polarization properties. Let's consider this question in more detail. At non-polar particles (atoms, ions, molecules) the centers of gravity of positive and negative charges coincide. In an electric field, the electron shells are displaced in the direction of a positively charged plate, and nuclei - in the direction of a negatively charged plate. Due to particle deformation arises in it dipole, she becomes polar .

source electric field in compounds with an ionic type of bond are the ions themselves. Therefore, speaking of polarization properties of the ion , necessary making a difference the polarizing effect of a given ion and the ability of itself to polarize in an electric field .

The polarizing effect of the ion will be the one big, how more of his force field, i.e. than more charge and less ion radius. Therefore, in within subgroups in the Periodic Table of the Elements the polarizing effect of ions decreases from top to bottom, because in subgroups with a constant value of the charge of the ion from top to bottom, its radius increases .

That's why the polarizing effect of alkali metal ions, for example, increases from cesium to lithium, and in a row halide ions - from I to F. In periods the polarizing effect of the ions increases from left to right together with an increase in the charge of the ion and decreasing its radius .

Ion polarizability, its ability to deformations increase with decreasing force field, i.e. with a decrease in the amount of charge and increase in radius . Anion polarizability usually above, how cations and in a row halides grows from F to I .

On the polarization properties of cations renders influence the nature of their outer electron shell . Polarization properties of cations how in active, as well as in passive sense at the same charge and a close radius increase on passing from cations with a filled shell to cations with an incomplete outer shell and further to cations with an 18-electron shell.

For example, in the series of cations Mg 2+ , Ni 2+ , Zn 2+ polarization properties intensify. This pattern is consistent with the change in the ion radius and the structure of its electron shell given in the series:

for anions polarization properties deteriorate in this order:

I - , Br - , Cl - , CN - , OH - , NO 3 - , F - , ClO 4 - .

result polarization interaction of ions is deformation of their electron shells and, as a consequence of this, shortening of interionic distances and incomplete separation of the negative and positive charges between ions.

For example, in a crystal sodium chloride the amount of charge on sodium ion is +0,9 , and on chlorine ion - 0.9 instead of expected unit. In a molecule KCl located in vapor state, value charges on potassium ions and chlorine is 0.83 charge units, and in the molecule hydrogen chloride- only 0,17 units of charge.

Ion polarization renders noticeable effect on the properties of compounds with ionic bond , lowering their melting and boiling points , reducing electrolytic dissociation in solutions and melts, etc. .

Ionic compounds formed when interaction of elements , significantly different in chemical properties. The more the distance between elements in the periodic table, topics in ionic bond is more pronounced in their compounds . Against, in molecules, formed by the same atoms or atoms of elements that are similar in chemical properties, arise other types of communication. That's why ionic bond theory It has limited use .

6 Effect of ion polarization on the properties of substances and properties of ionic bonds and ionic compounds

Ideas about ion polarizations help explain differences in the properties of many similar substances. For example, comparison sodium chloride and potassium with silver chloride shows that when close ionic radii

polarizability of the Ag+ cation having 18-electron outer shell , above, what leads to an increase in the metal-chlorine bond strength and lower solubility of silver chloride in water .

Mutual polarization of ions facilitates the destruction of crystals, that leads to lowering the melting points of substances. For this reason melting temperature TlF (327 oС) significantly lower than RbF (798 oC). The decomposition temperature of substances will also decrease with an increase in the mutual polarization of ions. That's why iodides generally decompose at lower temperatures, how other halides, a lithium compounds - thermally less stable , than compounds of other alkaline elements .

Deformability of electron shells affects the optical properties of substances. How more polarized particle , the lower the energy of electronic transitions. If a polarization is low , excitation of electrons requires higher energy, which answers ultraviolet part of the spectrum. Such substances are usually colorless. In the case of strong polarization of ions, the excitation of electrons occurs upon absorption of electromagnetic radiation in the visible region of the spectrum. That's why some substances, formed colorless ions, colored .

characteristic ionic compounds serves good solubility in polar solvents (water, acids, etc.). This is due to the charge of the parts of the molecule. Wherein solvent dipoles are attracted to the charged ends of the molecule, and as a result brownian motion , « take away» molecule substances into parts and surround them , preventing reconnection. The result is ions surrounded by solvent dipoles .

When such compounds are dissolved, as a rule, energy is released, since the total energy of the formed bonds solvent-ion has more anion-cation bond energy. Exceptions are many salts of nitric acid (nitrates), which absorb heat when dissolved (solutions are cooled). The latter fact is explained on the basis of the laws that considered in physical chemistry .

7 Crystal lattice

Ionic compounds(e.g. sodium chloride NaCl) - solid and refractory because of between the charges of their ions("+" and "-") exist powerful forces of electrostatic attraction .

The negatively charged chloride ion attracts Not only " mine " Na+ ion, but also other sodium ions around. it leads to, what near any of the ions there is more than one ion with the opposite sign , but a few(Fig. 1).

Rice. one. Crystal structure common salt NaCl .

In fact, about every chloride ion is located 6 sodium ions, and about each sodium ion - 6 chloride ions .

This ordered packing of ions is called ionic crystal. If we single out a separate chlorine atom, then among surrounding sodium atoms already impossible to find one, which chlorine reacted.. Drawn to each other electrostatic forces , ions are extremely reluctant to change their location under the influence of an external force or temperature increase. But if the temperature is very high (approx. 1500°C), then NaCl evaporates, forming diatomic molecules. This suggests that covalent bonding forces never turn off completely .

Ionic crystals different high melting points, usually significant band gap, possess ionic conductivity at high temperatures and a number of specific optical properties(for example, transparency in the near IR spectrum). They can be built from monatomic, and from polyatomic ions. Example ionic crystals of the first type - alkali halide crystals and alkaline earth metals ; anions are arranged according to the law of closest spherical packing or dense ball masonry , cations occupy the corresponding voids. Most characteristic structures of this type are NaCl, CsCl, CaF2. Ionic crystals of the second type built from monatomic cations of the same metals and finite or infinite anionic fragments . Terminal anions(acid residues) - NO3-, SO42-, CO32- and others . Acidic residues can form endless chains , layers or form a three-dimensional frame, in the cavities of which cations are located, as, for example, in crystal structures of silicates. For ionic crystals it is possible to calculate the energy of the crystal structure U(see table), approximately equal to enthalpy of sublimation; results are in good agreement with the experimental data. According to the equation Born-Meyer, for crystal, consisting of formally singly charged ions :

U \u003d -A / R + Be-R / r - C / R6 - D / R8 + E0

(R - shortest inter-ion distance , BUT - Madelung constant , dependent from structure geometry , AT and r - options , describing repulsion between particles , C/R6 and D/R8 characterize the respective dipole-dipole and dipole-quadrupole interaction of ions , E 0 - zero point energy , e - electron charge). FROM as the cation grows larger, the contribution of dipole-dipole interactions increases .

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Lesson Objectives:

• To form the concept of chemical bonds using the example of an ionic bond. To achieve an understanding of the formation of an ionic bond as an extreme case of a polar one.
• During the lesson, ensure the assimilation of the following basic concepts: ions (cation, anion), ionic bond.
• To develop the mental activity of students through the creation of a problem situation when studying new material.

Tasks:

• learn to recognize the types of chemical bonds;
• repeat the structure of the atom;
• to investigate the mechanism of formation of ionic chemical bond;
• teach how to draw up formation schemes and electronic formulas of ionic compounds, reaction equations with the designation of the transition of electrons.

Equipment Keywords: computer, projector, multimedia resource, periodic system of chemical elements D.I. Mendeleev, table "Ionic bond".

Lesson type: Formation of new knowledge.

Type of lesson: multimedia lesson.

X one lesson

I.Organizing time.

II . Checking homework.

Teacher: How can atoms take on stable electronic configurations? What are the ways of forming a covalent bond?

Student: Polar and non-polar covalent bonds are formed by the exchange mechanism. The exchange mechanism includes cases when one electron is involved in the formation of an electron pair from each atom. For example, hydrogen: (slide 2)

The bond arises due to the formation of a common electron pair due to the union of unpaired electrons. Each atom has one s-electron. The H atoms are equivalent and the pairs equally belong to both atoms. Therefore, the formation of common electron pairs (overlapping p-electron clouds) occurs during the formation of the F 2 molecule. (slide 3)

H entry · means that the hydrogen atom has 1 electron on the outer electron layer. The record shows that there are 7 electrons on the outer electron layer of the fluorine atom.

During the formation of the N 2 molecule. 3 common electron pairs are formed. The p-orbitals overlap. (slide 4)

The bond is called non-polar.

Teacher: We have now considered cases when molecules of a simple substance are formed. But there are many substances around us, a complex structure. Let's take a hydrogen fluoride molecule. How does the formation of a connection take place in this case?

Student: When a hydrogen fluoride molecule is formed, the orbital of the s-electron of hydrogen and the orbital of the p-electron of fluorine H-F overlap. (slide 5)

The bonding electron pair is shifted to the fluorine atom, resulting in the formation dipole. Connection called polar.

III. Knowledge update.

Teacher: A chemical bond arises as a result of changes that occur with the outer electron shells of the connecting atoms. This is possible because the outer electron layers are not complete in elements other than inert gases. The chemical bond is explained by the desire of atoms to acquire a stable electronic configuration, similar to the configuration of the "nearest" inert gas to them.

Teacher: Write down a diagram of the electronic structure of the sodium atom (at the blackboard). (slide 6)

Student: To achieve the stability of the electron shell, the sodium atom must either give up one electron or accept seven. Sodium will easily give up its electron far from the nucleus and weakly bound to it.

Teacher: Make a diagram of the recoil of an electron.

Na° - 1ē → Na+ = Ne

Teacher: Write down a diagram of the electronic structure of the fluorine atom (at the blackboard).

Teacher: How to achieve the completion of the filling of the electronic layer?

Student: To achieve the stability of the electron shell, the fluorine atom must either give up seven electrons or accept one. It is energetically more favorable for fluorine to accept an electron.

Teacher: Make a scheme for receiving an electron.

F° + 1ē → F- = Ne

IV. Learning new material.

The teacher addresses a question to the class in which the task of the lesson is set:

Are there other options in which atoms can take on stable electronic configurations? What are the ways of formation of such bonds?

Today we will consider one of the types of bonds - ionic bonds. Let us compare the structure of the electron shells of the already named atoms and inert gases.

Conversation with the class.

Teacher: What charge did the sodium and fluorine atoms have before the reaction?

Student: The atoms of sodium and fluorine are electrically neutral, because. the charges of their nuclei are balanced by electrons revolving around the nucleus.

Teacher: What happens between atoms when giving and receiving electrons?

Student: Atoms acquire charges.

The teacher gives explanations: In the formula of an ion, its charge is additionally recorded. To do this, use the superscript. In it, a number indicates the amount of charge (they do not write a unit), and then a sign (plus or minus). For example, a Sodium ion with a charge of +1 has the formula Na + (read "sodium plus"), a Fluorine ion with a charge of -1 - F - ("fluorine minus"), a hydroxide ion with a charge of -1 - OH - (" o-ash-minus"), a carbonate ion with a charge of -2 - CO 3 2- ("tse-o-three-two-minus").

In the formulas of ionic compounds, first write down, without indicating the charges, positively charged ions, and then - negatively charged. If the formula is correct, then the sum of the charges of all ions in it is equal to zero.

positively charged ion called a cation, and a negatively charged ion-anion.

Teacher: We write the definition in workbooks:

And he is a charged particle into which an atom turns into as a result of receiving or giving off electrons.

Teacher: How to determine the charge of the calcium ion Ca 2+?

Student: An ion is an electrically charged particle formed as a result of the loss or gain of one or more electrons by an atom. Calcium has two electrons in the last electronic level, the ionization of a calcium atom occurs when two electrons are given away. Ca 2+ is a doubly charged cation.

Teacher: What happens to the radii of these ions?

During the transition electrically neutral atom into an ionic state, the particle size changes greatly. An atom, giving up its valence electrons, turns into a more compact particle - a cation. For example, during the transition of a sodium atom to the Na+ cation, which, as indicated above, has a neon structure, the radius of the particle is greatly reduced. The radius of an anion is always greater than the radius of the corresponding electrically neutral atom.

Teacher: What happens to oppositely charged particles?

Student: Oppositely charged sodium and fluorine ions, resulting from the transition of an electron from a sodium atom to a fluorine atom, are mutually attracted and form sodium fluoride. (slide 7)

Na + + F - = NaF

The scheme of formation of ions that we have considered shows how a chemical bond is formed between the sodium atom and the fluorine atom, which is called ionic.

Ionic bond- a chemical bond formed by the electrostatic attraction of oppositely charged ions to each other.

The compounds that form in this case are called ionic compounds.

V. Consolidation of new material.

Tasks to consolidate knowledge and skills

1. Compare the structure of the electron shells of the calcium atom and the calcium cation, the chlorine atom and the chloride anion:

Comment on the formation of an ionic bond in calcium chloride:

2. To complete this task, you need to divide into groups of 3-4 people. Each member of the group considers one example and presents the results to the whole group.

Students response:

1. Calcium is an element of the main subgroup of group II, a metal. It is easier for its atom to donate two outer electrons than to accept the missing six:

2. Chlorine is an element of the main subgroup of group VII, a non-metal. It is easier for its atom to accept one electron, which it lacks before the completion of the outer level, than to give up seven electrons from the outer level:

3. First, find the least common multiple between the charges of the formed ions, it is equal to 2 (2x1). Then we determine how many calcium atoms need to be taken so that they donate two electrons, that is, one Ca atom and two CI atoms must be taken.

4. Schematically, the formation of an ionic bond between calcium and chlorine atoms can be written: (slide 8)

Ca 2+ + 2CI - → CaCI 2

Tasks for self-control

1. Based on the scheme for the formation of a chemical compound, make up an equation for a chemical reaction: (slide 9)

2. Based on the scheme for the formation of a chemical compound, make up an equation for a chemical reaction: (slide 10)

3. A scheme for the formation of a chemical compound is given: (slide 11)

Choose a pair of chemical elements whose atoms can interact in accordance with this scheme:

a) Na and O;
b) Li and F;
in) K and O;
G) Na and F

Electrons from one atom can completely transfer to another. This redistribution of charges leads to the formation of positively and negatively charged ions (cations and anions). A special type of interaction arises between them - an ionic bond. Let us consider in more detail the method of its formation, the structure and properties of substances.

Electronegativity

Atoms differ in electronegativity (EO) - the ability to attract electrons to themselves from the valence shells of other particles. For quantitative determination, the scale of relative electronegativity proposed by L. Polling (dimensionless value) is used. The ability to attract electrons from fluorine atoms is more pronounced than other elements, its EO is 4. In the Polling scale, oxygen, nitrogen, and chlorine immediately follow fluorine. The EO values ​​of hydrogen and other typical non-metals are equal to or close to 2. Of the metals, most have electronegativity between 0.7 (Fr) and 1.7. There is a dependence of the bond ionicity on the difference between the EO of chemical elements. The larger it is, the higher the probability that an ionic bond will occur. This type of interaction is more common when the difference EO=1.7 and higher. If the value is less, then the compounds are polar covalent.

Ionization energy

Ionization energy (EI) is required for detachment of external electrons weakly bound to the nucleus. The unit of change of this physical quantity is 1 electron volt. There are patterns of change in EI in the rows and columns of the periodic system, depending on the increase in the charge of the nucleus. In periods from left to right, the ionization energy increases and acquires the highest values ​​for non-metals. In groups, it decreases from top to bottom. The main reason is the increase in the radius of the atom and the distance from the nucleus to the outer electrons, which are easily detached. A positively charged particle appears - the corresponding cation. The value of EI can be used to judge whether an ionic bond occurs. The properties also depend on the ionization energy. For example, alkali and alkaline earth metals have low EI values. They have pronounced reducing (metallic) properties. Inert gases are chemically inactive due to their high ionization energy.

electron affinity

In chemical interactions, atoms can attach electrons to form a negative particle - an anion, the process is accompanied by the release of energy. The corresponding physical quantity is electron affinity. The unit of measurement is the same as the ionization energy (1 electron volt). But its exact values ​​are not known for all elements. Halogens have the highest electron affinity. At the outer level of the atoms of the elements - 7 electrons, only one is missing up to an octet. The electron affinity of halogens is high, they have strong oxidizing (non-metallic) properties.

Interactions of atoms in the formation of an ionic bond

Atoms that have an incomplete external level are in an unstable energy state. The desire to achieve a stable electronic configuration is the main reason that leads to the formation of chemical compounds. The process is usually accompanied by the release of energy and can lead to molecules and crystals that differ in structure and properties. Strong metals and non-metals differ significantly from each other in a number of indicators (EO, EI, and electron affinity). For them, this type of interaction is more suitable as an ionic chemical bond, in which the unifying molecular orbital (common electron pair) moves. It is believed that during the formation of ions, metals completely transfer electrons to non-metals. The strength of the resulting bond depends on the work required to destroy the molecules that make up 1 mol of the substance under study. This physical quantity is known as the binding energy. For ionic compounds, its values ​​range from several tens to hundreds of kJ/mol.

Ion formation

An atom that gives up its electrons during chemical interactions turns into a cation (+). The receiving particle is an anion (-). To find out how atoms will behave, whether ions will appear, it is necessary to establish the difference between their EC. The easiest way to carry out such calculations is for a compound of two elements, for example, sodium chloride.

Sodium has only 11 electrons, the configuration of the outer layer is 3s 1 . To complete it, it is easier for an atom to give up 1 electron than to attach 7. The structure of the valence layer of chlorine is described by the formula 3s 2 3p 5. In total, an atom has 17 electrons, 7 are external. One is missing to achieve an octet and a stable structure. The chemical properties support the assumption that the sodium atom donates and chlorine accepts electrons. There are ions: positive (sodium cation) and negative (chlorine anion).

Ionic bond

Losing an electron, sodium acquires a positive charge and a stable shell of an atom of the inert gas neon (1s 2 2s 2 2p 6). Chlorine, as a result of interaction with sodium, receives an additional negative charge, and the ion repeats the structure of the atomic shell of the noble gas argon (1s 2 2s 2 2p 6 3s 2 3p 6). The acquired electric charge is called the charge of the ion. For example, Na + , Ca 2+ , Cl - , F - . Ions can contain atoms of several elements: NH 4 + , SO 4 2- . Inside such complex ions, the particles are linked by a donor-acceptor or covalent mechanism. Electrostatic attraction occurs between oppositely charged particles. Its value in the case of an ionic bond is proportional to the charges, and with increasing distance between atoms, it weakens. Characteristic features of an ionic bond:

• strong metals react with active non-metallic elements;
• electrons move from one atom to another;
• the resulting ions have a stable configuration of outer shells;
• There is an electrostatic attraction between oppositely charged particles.

Crystal lattices of ionic compounds

In chemical reactions, metals of the 1st, 2nd and 3rd groups of the periodic system usually lose electrons. One-, two- and three-charged positive ions are formed. Nonmetals of the 6th and 7th groups usually add electrons (with the exception of reactions with fluorine). There are singly and doubly charged negative ions. The energy costs for these processes, as a rule, are compensated when a substance crystal is created. Ionic compounds are usually in a solid state, forming structures consisting of oppositely charged cations and anions. These particles are attracted and form giant crystal lattices in which positive ions are surrounded by negative particles (and vice versa). The total charge of a substance is zero, because the total number of protons is balanced by the number of electrons of all atoms.

Properties of substances with an ionic bond

Ionic crystalline substances are characterized by high boiling and melting points. Typically, these compounds are heat resistant. The following feature can be found when such substances are dissolved in a polar solvent (water). Crystals are easily destroyed, and ions pass into a solution that has electrical conductivity. Ionic compounds are also destroyed when melted. Free charged particles appear, which means that the melt conducts electric current. Substances with an ionic bond are electrolytes - conductors of the second kind.

Oxides and halides of alkali and alkaline earth metals belong to the group of ionic compounds. Almost all of them are widely used in science, technology, chemical production, metallurgy.

Structural chemistry
Chemical bond:	Aromaticity | Covalent bond | Ionic bond| Metal connection | Hydrogen bond | Donor-acceptor bond | Tautomerism
Structure display:	Functional group | Structural formula | Chemical formula | ligand
Electronic properties:	Electronegativity | Electron affinity | Ionization energy | Dipole | Octet Rule
Stereochemistry:	Asymmetric atom | Isomerism | Configuration | Chirality | Conformation

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See what "Ionic chemical bond" is in other dictionaries:

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chemical bond- mutual attraction of atoms, leading to the formation of molecules and crystals. The valence of an atom shows the number of bonds formed by a given atom with neighboring ones. The term "chemical structure" was introduced by Academician A. M. Butlerov in ... ... Encyclopedic Dictionary of Metallurgy

The interaction of atoms, which determines their connection into molecules and crystals. This interaction leads to a decrease in the total energy of the resulting molecule or crystal compared to the energy of non-interacting atoms and is based on ... ... Big encyclopedic polytechnic dictionary

Covalent bond on the example of a methane molecule: a complete external energy level for hydrogen (H) 2 electrons, and for carbon (C) 8 electrons. Covalent bond bond formed by directed valence electron clouds. Neutral ... ... Wikipedia

Chemical bonding is the phenomenon of the interaction of atoms, due to the overlap of electron clouds, binding particles, which is accompanied by a decrease in the total energy of the system. The term "chemical structure" was first introduced by A. M. Butlerov in 1861 ... ... Wikipedia

Ionic bond- a chemical bond formed as a result of mutual electrostatic attraction of oppositely charged ions, in which a stable state is achieved by a complete transition of the total electron density to an atom of a more electronegative element.

A purely ionic bond is the limiting case of a covalent bond.

In practice, a complete transition of electrons from one atom to another atom through a bond is not realized, since each element has a greater or lesser (but not zero) EO, and any chemical bond will be covalent to some extent.

Such a bond arises in the case of a large difference in the ER of atoms, for example, between cations s-metals of the first and second groups of the periodic system and anions of non-metals of groups VIA and VIIA (LiF, NaCl, CsF, etc.).

Unlike a covalent bond, ionic bond has no direction . This is explained by the fact that the electric field of the ion has spherical symmetry, i.e. decreases with distance according to the same law in any direction. Therefore, the interaction between ions is independent of direction.

The interaction of two ions of opposite sign cannot lead to complete mutual compensation of their force fields. Because of this, they retain the ability to attract ions of the opposite sign in other directions. Therefore, unlike a covalent bond, ionic bond is also characterized by unsaturability .

The lack of orientation and saturation of the ionic bond causes the tendency of ionic molecules to associate. All ionic compounds in the solid state have an ionic crystal lattice in which each ion is surrounded by several ions of the opposite sign. In this case, all bonds of a given ion with neighboring ions are equivalent.

metal connection

Metals are characterized by a number of special properties: electrical and thermal conductivity, characteristic metallic luster, malleability, high ductility, and high strength. These specific properties of metals can be explained by a special type of chemical bond called metallic .

A metallic bond is the result of overlapping delocalized orbitals of atoms approaching each other in the crystal lattice of a metal.

Most metals have a significant number of vacant orbitals and a small number of electrons at the outer electronic level.

Therefore, it is energetically more favorable that the electrons are not localized, but belong to the entire metal atom. At the lattice sites of a metal, there are positively charged ions that are immersed in an electron "gas" distributed throughout the metal:

Me ↔ Me n + + n .

Between positively charged metal ions (Me n +) and non-localized electrons (n) there is an electrostatic interaction that ensures the stability of the substance. The energy of this interaction is intermediate between the energies of covalent and molecular crystals. Therefore, elements with a purely metallic bond ( s-, and p-elements) are characterized by relatively high melting points and hardness.

The presence of electrons, which can freely move around the volume of the crystal, and provide specific properties of the metal

hydrogen bond

hydrogen bond – a special type of intermolecular interaction. Hydrogen atoms that are covalently bonded to an atom of an element that has a high electronegativity value (most commonly F, O, N, but also Cl, S, and C) carry a relatively high effective charge. As a result, such hydrogen atoms can electrostatically interact with the atoms of these elements.

So, the H d + atom of one water molecule is oriented and accordingly interacts (as shown by three points) with the O d atom - another water molecule:

The bonds formed by an H atom located between two atoms of electronegative elements are called hydrogen bonds:

d- d+ d-

A − H × × × B

The energy of a hydrogen bond is much less than the energy of an ordinary covalent bond (150–400 kJ / mol), but this energy is sufficient to cause the aggregation of molecules of the corresponding compounds in a liquid state, for example, in liquid hydrogen fluoride HF (Fig. 2.14). For fluorine compounds, it reaches about 40 kJ/mol.

Rice. 2.14. Aggregation of HF molecules due to hydrogen bonds

The length of the hydrogen bond is also less than the length of the covalent bond. So, in the polymer (HF) n, the F−H bond length is 0.092 nm, and the F∙∙∙H bond is 0.14 nm. For water, the O−H bond length is 0.096 nm, and the O∙∙∙H bond length is 0.177 nm.

The formation of intermolecular hydrogen bonds leads to a significant change in the properties of substances: an increase in viscosity, dielectric constant, boiling and melting points.