Ionic bond formation examples. Chemical bond

It goes mainly to the atom with higher electronegativity. This is the attraction of ions as oppositely charged bodies. An example is the CsF compound, in which the "degree of ionicity" is 97%. Ionic bond is an extreme case of polarization of a covalent polar bond. Formed between typical metal and non-metal. In this case, the electrons of the metal are completely transferred to the non-metal, and ions are formed.

A ⋅ + ⋅ B → A + [: B -] (\ displaystyle (\ mathsf (A)) \ cdot + \ cdot (\ mathsf (B)) \ to (\ mathsf (A)) ^ (+) [: (\ mathsf (B)) ^ (-)])

An electrostatic attraction arises between the formed ions, which is called ionic bond. Rather, this look is convenient. In fact, the pure ionic bond between atoms is not realized anywhere or almost nowhere; usually, in fact, the bond is partially ionic and partially covalent. At the same time, the bond of 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 tend to different densest packings of the corresponding ions.

Characteristic such compounds are good solubility in polar solvents (water, acids, etc.). This is due to the charge on the parts of the molecule. In this case, the solvent dipoles are attracted to the charged ends of the molecule, and, as a result of Brownian motion, "pull" the substance molecule to pieces and surround them, preventing them from reuniting. The result is ions surrounded by solvent dipoles.

When dissolving such compounds, as a rule, energy is released, since the total energy of the formed solvent-ion bonds is greater than the energy of the anion-cation bond. 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 laws that are considered in physical chemistry. Interaction of ions

If an atom loses one or more electrons, then it turns into a positive ion - a cation (translated from Greek - "going down.) This is how hydrogen cations H +, lithium Li +, barium Ba2 + are formed. By acquiring electrons, atoms turn into negative ions - anions (from the Greek for "anion" - going up.) Examples of anions are fluoride ion F−, sulfide ion S2−.

Cations and anions are able to attract each other. In this case, a chemical bond arises, and chemical compounds are formed. This type of chemical bond is called ionic bond:

An ionic bond is a chemical bond formed by electrostatic attraction between cations and anions.

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An example of ionic bond formation

Let's consider the method of formation using the example of "sodium chloride" NaCl... The electronic configuration of sodium and chlorine atoms can be represented: N a 11 1 s 2 2 s 2 2 p 6 3 s 1 (\ displaystyle (\ mathsf (Na ^ (11) 1s ^ (2) 2s ^ (2) 2p ^ (6) 3s ^ (1)))) and C l 17 1 s 2 2 s 2 2 p 6 3 s 2 3 p 5 (\ displaystyle (\ mathsf (Cl ^ (17) 1s ^ (2) 2s ^ (2) 2p ^ (6) 3s ^ (2) 3p ^ (5))))... These are atoms with incomplete energy levels. Obviously, to complete them, it is easier for the sodium atom to donate one electron than to attach seven, and it is easier for the chlorine atom to attach one electron than to donate seven. In chemical interaction, the sodium atom completely donates one electron, and the chlorine atom accepts it.

Schematically it can be written as follows:

N a - e → N a + (\ displaystyle (\ mathsf (Na-e \ rightarrow Na ^ (+))))- sodium ion, stable eight-electron shell ( N a + 1 s 2 2 s 2 2 p 6 (\ displaystyle (\ mathsf (Na ^ (+) 1s ^ (2) 2s ^ (2) 2p ^ (6))))) due to the second energy level. C l + e → C l - (\ displaystyle (\ mathsf (Cl + e \ rightarrow Cl ^ (-))))- chlorine ion, stable eight-electron shell.

Between the ions N a + (\ displaystyle (\ mathsf (Na ^ (+)))) and C l - (\ displaystyle (\ mathsf (Cl ^ (-)))) forces of electrostatic attraction arise, as a result of which a connection is formed.

The atoms of most elements do not exist separately, as they can interact with each other. This interaction creates 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.

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

Types of interactions in chemistry

The types of chemical bonds can be represented in the form of the following table:

Ionic bond characteristic

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

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

Metal atoms become positively charged ions (cations), donating electrons to external electronic levels, and non-metals take 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, respectively, 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 with the formation of 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 around each chlorine ion there are six sodium ions.

During the formation of interaction between atoms in barium sulfide, the following processes occur:

Ba 0 - 2 e = Ba 2+

S 0 + 2 e = S 2-

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

Metallic chemical bond

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

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

Examples include:

Mg - 2e<->Mg 2+

Cs - e<->Cs +

Ca - 2e<->Ca 2+

Fe - 3e<->Fe 3+

Covalent: polar and non-polar

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

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

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

Covalent ones are divided by multiplicity into:

simple or single;
double;
triple.

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

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

non-polar;
polar.

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

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

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

Properties and characteristics of covalence

Main characteristics of a covalent bond:

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

An example of a covalent non-polar interaction can be 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 the molecule has a double non-polar,

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

Molecules of carbon dioxide (CO2) and carbon monoxide (CO) gas, hydrogen sulfide (H2S), hydrochloric acid (HCL), water (H2O), methane (CH4), sulfur oxide (SO2) and many others can be cited as examples of the covalent bond of chemical elements. ...

In a CO2 molecule, the relationship between carbon and oxygen atoms is covalent polar, since the more electronegative hydrogen attracts the electron density to itself. Oxygen has two unpaired electrons at the outer level, and carbon can provide four valence electrons to form interactions. 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 the atoms that make it up. Simple substances metals form metallic, metals with non-metals - ionic, simple substances non-metals - covalent non-polar, and molecules consisting of different non-metals are formed through a covalent polar bond.

Ionic bond

(materials from the site http://www.hemi.nsu.ru/ucheb138.htm were used)

Ionic bonding is carried out by electrostatic attraction between oppositely charged ions. These ions are formed as a result of the transfer of electrons from one atom to another. An ionic bond is formed between atoms with large electronegativity differences (usually greater than 1.7 on the Pauling scale), for example, between alkali metal and halogen atoms.

Let us consider the formation of an ionic bond by the example of the formation of NaCl.

From the electronic formulas of atoms

Na 1s 2 2s 2 2p 6 3s 1 and

Cl 1s 2 2s 2 2p 6 3s 2 3p 5

it can be seen that to complete the external level, it is easier for a sodium atom to donate one electron than to attach seven, and it is easier for a chlorine atom to attach one than to donate seven. In chemical reactions, the sodium atom donates one electron, and the chlorine atom accepts it. As a result, the electronic shells of sodium and chlorine atoms are converted into stable electronic shells of noble gases (the electronic configuration of the sodium cation

Na + 1s 2 2s 2 2p 6,

and the electronic configuration of the chlorine anion

Cl - - 1s 2 2s 2 2p 6 3s 2 3p 6).

The electrostatic interaction of the ions leads to the formation of the NaCl molecule.

The nature of the chemical bond is often reflected in the state of aggregation and physical properties of a substance. Ionic compounds such as sodium chloride NaCl are solid and refractory because there are powerful forces of electrostatic attraction between the charges of their ions "+" and "-".

A negatively charged chlorine ion attracts not only "its" Na + ion, but also other sodium ions around it. This leads to the fact that near any of the ions there is not one ion with the opposite sign, but several.

Crystal structure of sodium chloride NaCl.

In fact, around each chlorine ion there are 6 sodium ions, and around each sodium ion there are 6 chlorine ions. This ordered packing of ions is called an ionic crystal. If a single chlorine atom is isolated in a crystal, then among the surrounding sodium atoms it is no longer possible to find the one with which chlorine reacted.

Attracted to each other by electrostatic forces, the ions are extremely reluctant to change their location under the influence of an external force or a rise in temperature. But if sodium chloride is melted and heated in a vacuum, then it evaporates, forming diatomic NaCl molecules. This suggests that the forces of covalent bonding are never completely turned off.

Main characteristics of ionic bonding and properties of ionic compounds

1. Ionic bond is a strong chemical bond. The energy of this bond is of the order of 300 - 700 kJ / mol.

2. Unlike a covalent bond, an ionic bond is non-directional, since an ion can attract ions of the opposite sign to itself in any direction.

3. Unlike a covalent bond, an ionic bond is unsaturated, since the interaction of ions of opposite sign does not lead to a complete mutual compensation of their force fields.

4. In the process of formation of molecules with ionic bond, there is no complete transfer of electrons, therefore, one hundred percent ionic bond does not exist in nature. In the NaCl molecule, the chemical bond is only 80% ionic.

5. Compounds with ionic bonds are solid crystalline substances with high melting and boiling points.

6. Most ionic compounds dissolve in water. Solutions and melts of ionic compounds conduct electric current.

Metal bond

Metal crystals are arranged differently. If you examine a piece of metallic sodium, you will find that outwardly it is very different from table salt. Sodium is a soft metal, easily cut with a knife, flattened with a hammer, it can be easily melted in a cup on an alcohol lamp (melting point 97.8 ° C). In a sodium crystal, each atom is surrounded by eight other similar atoms.

Crystal structure of metallic Na.

The figure shows that the Na atom in the center of the cube has 8 nearest neighbors. But the same can be said about any other atom in the crystal, since they are all the same. The crystal is made up of "infinitely" repeating fragments depicted in this figure.

Metal atoms at the external energy level contain a small number of valence electrons. Since the ionization energy of metal atoms is low, valence electrons are weakly retained in these atoms. As a result, positively charged ions and free electrons appear in the crystal lattice of metals. In this case, metal cations are located in the nodes of the crystal lattice, and electrons freely move in the field of positive centers, forming the so-called "electron gas".

The presence of a negatively charged electron between two cations causes each cation to interact with this electron.

Thus, a metal bond is a bond between positive ions in metal crystals, which is carried out by the attraction of electrons that move freely throughout the crystal.

Since the valence electrons in a metal are evenly distributed throughout the crystal, the metal bond, like the ionic bond, is an undirectional bond. Unlike a covalent bond, a metal bond is an unsaturated bond. A metallic bond also differs from a covalent bond in strength. The energy of a metal bond is approximately three to four times less than the energy of a covalent bond.

Due to the high mobility of the electron gas, metals are characterized by high electrical and thermal conductivity.

A metal crystal looks simple enough, but in fact its electronic structure is more complex than that of ionic salt crystals. There are not enough electrons on the outer electron shell of metal elements to form a full-fledged "octet" covalent or ionic bond. Therefore, in the gaseous state, most metals consist of monatomic molecules, (i.e., separate, not connected atoms). A typical example is mercury vapor. Thus, a metallic bond between metal atoms occurs only in a liquid and solid state of aggregation.

The metal bond can be described as follows: some of the metal atoms in the resulting crystal give up their valence electrons to the space between the atoms (for sodium it is ... 3s1), turning into ions. Since all metal atoms in a crystal are the same, each of them has an equal chance of losing a valence electron.

In other words, the transition of electrons between neutral and ionized metal atoms occurs without energy consumption. In this case, some of the electrons always appear in the space between the atoms in the form of an "electron gas".

These free electrons, firstly, keep the metal atoms at a certain equilibrium distance from each other.

Secondly, they give metals a characteristic "metallic luster" (free electrons can interact with light quanta).

Third, free electrons provide metals with good electrical conductivity. The high thermal conductivity of metals is also explained by the presence of free electrons in the interatomic space - they easily "respond" to changes in energy and contribute to its rapid transfer in the crystal.

Simplified model of the electronic structure of a metal crystal.

******** Using sodium metal as an example, let us consider the nature of the metal bond from the point of view of the concept of atomic orbitals. The sodium atom, like many other metals, has a lack of valence electrons, but it has free valence orbitals. The only 3s electron of sodium is capable of moving to any of the free and close in energy neighboring orbitals. When atoms come closer together in a crystal, the outer orbitals of neighboring atoms overlap, due to which the donated electrons move freely throughout the crystal.

However, the "electron gas" is not at all as messy as it might seem. Free electrons in a metal crystal are located in overlapping orbitals and to some extent socialize, forming a semblance of covalent bonds. Sodium, potassium, rubidium and other metallic s-elements have just a few socialized electrons, so their crystals are fragile and fusible. As the number of valence electrons increases, the strength of metals, as a rule, increases.

Thus, elements tend to form a metallic bond, the atoms of which on the outer shells have few valence electrons. These valence electrons, which carry out a metal bond, are socialized so much that they can move throughout the metal crystal and provide a high electrical conductivity of the metal.

The NaCl crystal does not conduct electric current, because there are no free electrons in the space between the ions. All electrons donated by sodium atoms firmly hold chlorine ions around them. This is one of the essential differences between ionic and metallic crystals.

What you now know about the metallic bond also explains the high ductility (ductility) of most metals. Metal can be flattened into a thin sheet, pulled into a wire. The fact is that individual layers of atoms in a metal crystal can relatively easily slide over one another: the mobile "electron gas" constantly softens the movement of individual positive ions, shielding them from each other.

Of course, nothing like this can be done with table salt, although salt is also a crystalline substance. In ionic crystals, valence electrons are firmly bound to the atomic nucleus. The shift of one layer of ions relative to the other leads to the approach of ions of the same charge and causes a strong repulsion between them, as a result of which the destruction of the crystal occurs (NaCl is a fragile substance).

The shift of the layers of an ionic crystal causes the appearance of large repulsive forces between the ions of the same name and the destruction of the crystal.

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

Ionization energy

For the detachment of the external electrons weakly bound to the nucleus, the ionization energy (EI) is required. The unit of change for this physical quantity is 1 electron-volt. There are patterns of change in the EI in the rows and columns of the periodic system, depending on the increase in the nuclear charge. In periods from left to right, the ionization energy increases and acquires the greatest 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. By the magnitude of the EI, one can judge whether an ionic bond arises. Properties also depend on the ionization energy. For example, alkali and alkaline earth metals have low EI values. They have pronounced restorative (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 the electron affinity. The unit of measurement is the same as 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 atoms of elements - 7 electrons, only one is missing to an octet. The electron affinity of halogens is high; they have strong oxidizing (non-metallic) properties.

Interactions of atoms during the formation of an ionic bond

Atoms with an incomplete outer level are in an unstable energetic 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 among themselves in a number of indicators (EO, EI and electron affinity). For them, this type of interaction is more suitable, such as ionic chemical bond, in which the unifying molecular orbital (common electron pair) moves. It is believed that when ions are formed, 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 test substance. This physical quantity is known as bond energy. For ionic compounds, its values range from several tens to hundreds of kJ / mol.

Ion formation

An atom that donates its electrons during chemical interactions turns into a cation (+). The receiving particle is the anion (-). To find out how atoms will behave, whether ions will arise, it is necessary to establish the difference between their EO. The easiest way to do 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 to donate 1 electron to the atom than to attach 7. The structure of the chlorine valence layer is described by the formula 3s 2 3p 5. In total, the atom has 17 electrons, 7 - external. One is missing to achieve an octet and a stable structure. Chemical properties support the assumption that the sodium atom gives up and chlorine accepts electrons. Ions are formed: 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 an inert gas of 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 electrical charge is called the charge of the ion. For example, Na +, Ca 2+, Cl -, F -. The ions can contain atoms of several elements: NH 4 +, SO 4 2-. Within such complex ions, particles are bound by a donor-acceptor or covalent mechanism. Electrostatic attraction arises between oppositely charged particles. Its value in the case of an ionic bond is proportional to the charges, and with an increase in the distance between atoms, it weakens. Characteristic signs of 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 the outer shells;
an electrostatic attraction arises 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. Non-metals of the 6th and 7th groups usually attach electrons (with the exception of reactions with fluorine). One- and two-charged negative ions appear. Energy costs for these processes, as a rule, are compensated when creating a crystal of a substance. Ionic compounds are usually in a solid state, form 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 Ionic Bond Substances

Ionic crystalline substances are characterized by high boiling and melting points. Usually these compounds are heat resistant. The following feature can be found when dissolving such substances 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 an electric current. Substances with ionic bonds 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.