Ionic bond
A purely ionic bond is a chemically bound state of atoms, in which a stable electronic environment is achieved by a complete transition of the total electron density to an atom of a more electronegative element.
In practice, the complete transfer of an electron from one atom to another atom - a bond partner is not realized, since each element has a greater or lesser electronegativity, and any chemical bond will be covalent to some extent. If the degree of covalent bond is sufficiently high, then such a chemical bond is a polar covalent bond with varying degrees of ionicity. If the degree of covalence of the bonds is small compared to the degree of its ionicity, then such a bond is considered ionic.
Ionic bonding is possible only between atoms of electropositive and electronegative elements that are in the state of oppositely charged ions. The process of formation of an ionic bond makes it possible to explain the electrostatic model, i.e. consideration of the chemical interaction between negatively and positively charged ions.
ions - These are electrically charged particles formed from neutral atoms or molecules by giving or receiving electrons.
When electrons are given or received by molecules, molecular or polyatomic ions are formed, for example, a dioxygen ion, a nitrite ion.
Monatomic positive ions, or monatomic negative ions, or monatomic anions, arise during a chemical reaction between neutral atoms by mutual transfer of electrons, while an atom, an electropositive element with a small number of external electrons, passes into a more stable state of a monatomic cation by reducing the number of these electrons. On the contrary, an atom of an electronegative element, which has a large number of external electrons, passes into a state of a monatomic ion that is more stable for it by increasing the number of electrons. Monoatomic cations are formed, as a rule, by metals, and monoatomic anions - by non-metals.
When electrons are transferred, atoms of metallic and non-metallic elements tend to form a stable configuration of the electron shell around their nuclei. An atom of a non-metallic element creates an outer shell of the subsequent noble gas around its core. Whereas the atom of a metallic element, after the return of external electrons, receives a stable octet configuration of the previous noble gas.
Ionic crystals
In the interaction of metallic and non-metallic simple substances, accompanied by the return and acceptance of electrons, salts are formed. Example:
2Na + Cl2 = 2NaCl,
2Al + 3F2 = 2AlF3
The ionic bond is characteristic not only for salts of derivatives of oxygen-free and oxygen-containing acids [such as NaCl, AlF3, NaNO3, Al(SO4)3], but also for other classes of inorganic substances - basic oxides and hydroxides [such as Na2O and NaOH], binary compounds [such as Li3N and CaC2]. Between ions with charges opposite in sign, electrostatic forces of attraction appear. Such attractive forces are isotropic, i.e. act the same way in all directions. As a result, the arrangement of ions in solid salts is ordered in space in a certain way. A system of ordered cations and anions is called an ionic crystal lattice, and the solids themselves (salts, basic oxides and hydroxides) are called ionic crystals.
All ionic crystals are salt-like in nature. A salt-like character is understood as a certain set of properties that distinguishes ionic crystals from crystalline substances with other types of lattices. Of course, not all ionic lattices are characterized by such an arrangement of ions in space, the number of ions - neighbors with the opposite charge may be different, however, the alternation of cations and anions in space is mandatory for crystals.
Due to the fact that the Coulomb forces of attraction propagate equally in all directions, the ions at the nodes of the crystal lattice are relatively firmly bound, although each of the ions is not fixed motionless, but continuously performs thermal vibrations around its position in the lattice. There is no translational movement of ions along the lattice, therefore, all substances with ionic bonds at room temperature are solid (crystalline). The amplitude of thermal vibrations can be increased by heating the ionic crystal, which ultimately leads to the destruction of the lattice and the transition of the solid to the liquid state (at the melting point). The melting point of ionic crystals is relatively high, and the boiling point at which a liquid substance passes into the most disordered, gaseous state is very large. Example:
Many salts, especially multi-element complex salts, as well as salts of organic acids, can decompose at temperatures lower than the boiling point and even the melting point.
A typical property of many ionically bonded compounds (which do not react with water or decompose before melting) is their ability to dissociate into their constituent ions; due to the mobility of ions, aqueous solutions or melts of ionic crystals conduct an electric current.
In ionic crystals, there are no bonds between individual pairs of ions; more precisely, it should be said that all the cations and anions contained in the sample of the ionic compound turn out to be bound.
In ionic crystals built from cations and anions, there are no molecules.
The chemical formulas of ionic substances convey only the ratio of cations and anions in the crystal lattice; in general, a sample of an ionic substance is electrically neutral. For example, in accordance with the formula of the Al2O3 ionic crystal, the ratio of Al3+ cations and O2- anions in the lattice is 2:3; the substance is electrically neutral - six positive charges (2 Al3+) are neutralized by six negative charges (3 O2-).
Although real molecules in ionic crystals do not exist, for uniformity with covalent substances, it is customary to convey the composition of conditional molecules using formulas such as NaCl and Al2O3, therefore, to characterize ionic substances by certain values of relative molecular weight. This is all the more justified, since the transition from a covalent bond to an ionic one occurs gradually and has only a conditional boundary with x = 1.7.
The relative molecular mass of substances with an ionic bond is found by adding the relative atomic masses of the corresponding elements, taking into account the number of atoms of each element.
Example: The relative molecular weight of Al2O3 is:
The structure and shape of crystals are the subject of crystallography, and the relationship between the properties of crystals and their structure is studied by crystal chemistry.
It should be noted that there are practically no compounds in which only ionic bonds exist. Covalent bonds always appear between neighboring atoms in a crystal.
A chemical bond arises due to the interaction of electric fields created by electrons and nuclei of atoms, i.e. the chemical bond is electrical in nature.
Under chemical bond understand the result of the interaction of 2 or more atoms leading to the formation of a stable polyatomic system. The condition for the formation of a chemical bond is a decrease in the energy of the interacting atoms, i.e. the molecular state of matter is energetically more favorable than the atomic state. When a chemical bond is formed, atoms tend to obtain a complete electron shell.
There are: covalent, ionic, metallic, hydrogen and intermolecular.
covalent bond- the most general type of chemical bond that arises due to the socialization of an electron pair through exchange mechanism -, when each of the interacting atoms supplies one electron, or donor-acceptor mechanism, if an electron pair is transferred for common use by one atom (donor - N, O, Cl, F) to another atom (acceptor - atoms of d-elements).
Chemical bond characteristics.
1 - multiplicity of bonds - only 1 sigma bond is possible between 2 atoms, but along with it, there can be pi and delta bonds between the same atoms, which leads to the formation of multiple bonds. The multiplicity is determined by the number of common electron pairs.
2 - bond length - the internuclear distance in the molecule, the greater the multiplicity, the smaller its length.
3 - bond strength - this is the amount of energy required to break it
4 - the saturation of the covalent bond is manifested in the fact that one atomic orbital can take part in the formation of only one c.s. This property determines the stoichiometry of molecular compounds.
5 - directivity of the c.s. depending on what shape and what direction electron clouds have in space, when they overlap, compounds with a linear and angular shape of molecules can be formed.
Ionic bond – formed between atoms that are very different in electronegativity. These are compounds of the main subgroups of groups 1 and 2 with elements of the main subgroups of groups 6 and 7. Ionic is a chemical bond, which is carried out as a result of mutual electrostatic attraction of oppositely charged ions.
The mechanism of formation of an ionic bond: a) the formation of ions of interacting atoms; b) the formation of a molecule due to the attraction of ions.
Non-directionality and unsaturation of the ionic bond
The force fields of the ions are evenly distributed in all directions, so each ion can attract ions of the opposite sign in any direction. This is the non-directionality of the ionic bond. The interaction of 2 ions of the opposite sign does not lead to complete mutual compensation of their force fields. Therefore, they retain the ability to attract ions in other directions as well, i.e. an ionic bond is characterized by unsaturation. Therefore, each ion in an ionic compound attracts such a number of ions of the opposite sign that an ionic-type crystal lattice is formed. There are no molecules in an ionic crystal. Each ion is surrounded by a certain number of ions of a different sign (coordination number of the ion).
metal connection- chem. Communication in metals. Metals have an excess of valence orbitals and a lack of electrons. When atoms approach each other, their valence orbitals overlap, due to which electrons move freely from one orbital to another, and a connection is made between all metal atoms. The bond that is carried out by relatively free electrons between metal ions in a crystal lattice is called a metallic bond. The connection is strongly delocalized and does not have directionality and saturation, because valence electrons are evenly distributed throughout the crystal. The presence of free electrons determines the existence of common properties of metals: opacity, metallic luster, high electrical and thermal conductivity, malleability and plasticity.
hydrogen bond– bond between the H atom and a strongly negative element (F, Cl, N, O, S). Hydrogen bonds can be intra- and intermolecular. BC is weaker than a covalent bond. The emergence of VS is explained by the action of electrostatic forces. The H atom has a small radius and, when a single electron H is displaced or donated, it acquires a strong positive charge, which affects the electronegativity.
Ionic bond
(materials of the website 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 that have large differences in electronegativity (usually greater than 1.7 on the Pauling scale), for example, between alkali metals and halogens.
Let us consider the appearance of an ionic bond using 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 give up one electron than to add seven, and it is easier for a chlorine atom to add one than to give up seven. In chemical reactions, the sodium atom donates one electron, and the chlorine atom accepts it. As a result, the electron shells of sodium and chlorine atoms are converted into stable electron 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 ions leads to the formation of the NaCl molecule.
The nature of the chemical bond is often reflected in the state of aggregation and the physical properties of the 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 "+" and "-" ions.
A negatively charged chloride ion attracts not only "its own" 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.
The structure of the sodium chloride NaCl crystal.
In fact, there are 6 sodium ions around each chloride ion, and 6 chloride ions around each sodium ion. Such an ordered packing of ions is called an ionic crystal. If a separate 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 an increase in temperature. But if sodium chloride is melted and continued to be heated in a vacuum, then it evaporates, forming diatomic NaCl molecules. This suggests that covalent bonding forces are never completely turned off.
Main characteristics of ionic bond and properties of ionic compounds
1. An ionic bond is a strong chemical bond. The energy of this bond is about 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 the opposite sign does not lead to complete mutual compensation of their force fields.
4. In the process of formation of molecules with an ionic bond, there is no complete transfer of electrons, therefore, a 100% ionic bond does not exist in nature. In the NaCl molecule, the chemical bond is only 80% ionic.
5. Ionic compounds are crystalline solids with high melting and boiling points.
6. Most ionic compounds dissolve in water. Solutions and melts of ionic compounds conduct electric current.
metal connection
Metal crystals are arranged differently. If you consider 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 a spirit lamp (melting point 97.8 o C). In a sodium crystal, each atom is surrounded by eight other similar atoms.
The structure of the crystal of metallic Na.
It can be seen from the figure 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 a crystal, since they are all the same. The crystal consists of "infinitely" repeating fragments shown in this picture.
Metal atoms at the outer 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, the metal cations are located in the nodes of the crystal lattice, and the electrons move freely in the field of positive centers, forming the so-called "electron gas".
The presence of a negatively charged electron between two cations leads to the fact that each cation interacts with this electron.
Thus, a metallic bond is a bond between positive ions in metal crystals, which is carried out by the attraction of electrons freely moving throughout the crystal.
Since the valence electrons in the metal are evenly distributed throughout the crystal, the metallic bond, like the ionic one, is an undirected bond. Unlike a covalent bond, a metallic bond is an unsaturated bond. A metallic bond differs from a covalent bond in strength as well. The energy of a metallic bond is about 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 its electronic structure is actually 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., individual, unrelated atoms). A typical example is mercury vapor. Thus, a metallic bond between metal atoms occurs only in the liquid and solid state of aggregation.
A metallic 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 (in 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, a part of the electrons always ends up in the space between the atoms in the form of an "electron gas".
These free electrons, firstly, hold the metal atoms at a certain equilibrium distance from each other.
Secondly, they give metals a characteristic "metallic sheen" (free electrons can interact with light quanta).
Thirdly, 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.
A simplified model of the electronic structure of a metal crystal.
******** On the example of sodium metal, let us consider the nature of the metallic bond from the point of view of ideas about atomic orbitals. The sodium atom, like many other metals, has a lack of valence electrons, but there are free valence orbitals. The only 3s electron of sodium is able to move to any of the free and close in energy neighboring orbitals. When atoms in a crystal approach each other, 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 disordered, as it might seem. Free electrons in a metal crystal are in overlapping orbitals and are socialized to some extent, forming a kind of covalent bonds. Sodium, potassium, rubidium, and other metallic s-elements simply have few shared electrons, so their crystals are fragile and fusible. With an increase in the number of valence electrons, 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 the metallic bond, are so socialized that they can move throughout the entire metal crystal and provide a high electrical conductivity of the metal.
The NaCl crystal does not conduct electricity because there are no free electrons in the space between the ions. All electrons donated by sodium atoms firmly hold chloride ions around them. This is one of the essential differences between ionic crystals and metallic ones.
What you now know about the metallic bond also explains the high malleability (ductility) of most metals. Metal can be flattened into a thin sheet, pulled into a wire. The fact is that separate layers of atoms in a metal crystal can relatively easily slide one over another: the mobile "electron gas" constantly softens the movement of individual positive ions, shielding them from each other.
Of course, nothing of the kind can be done with table salt, although salt is also a crystalline substance. In ionic crystals, valence electrons are firmly bound to the nucleus of an atom. The shift of one layer of ions relative to another leads to the convergence of ions of the same charge and causes a strong repulsion between them, resulting in the destruction of the crystal (NaCl is a brittle substance).
The shift of the layers of the ionic crystal causes the appearance of large repulsive forces between like ions and the destruction of the crystal.
Navigation
- Solving combined problems based on the quantitative characteristics of a substance
- Problem solving. The law of the constancy of the composition of substances. Calculations using the concepts of "molar mass" and "chemical amount" of a substance
The nature of the metallic bond. The structure of metal crystals.
1. With. 71–73; 2. With. 143–147; 4. With. 90–93; 8. With. 138–144; 3. With. 130–132.
Ionic chemical bond called the bond that is formed between cations and anions as a result of their electrostatic interaction. An ionic bond can be viewed as the limiting case of a covalent polar bond formed by atoms with very different electronegativity values.
When an ionic bond is formed, a significant shift of the common pair of electrons to a more electronegative atom occurs, which thus acquires a negative charge and turns into an anion. Another atom, having lost its electron, forms a cation. An ionic bond is formed only between atomic particles of such elements that differ greatly in their electronegativity (Δχ ≥ 1.9).
Ionic bond is characterized non-directionality in space and insatiability. The electric charges of the ions determine their attraction and repulsion and determine the stoichiometric composition of the compound.
In general, an ionic compound is a giant association of ions with opposite charges. Therefore, the chemical formulas of ionic compounds reflect only the simplest ratio between the numbers of atomic particles forming such associations.
Metal connection -Vinteraction that holds atomic particles of metals in crystals.
The nature of a metallic bond is similar to a covalent bond: both types of bonds are based on the socialization of valence electrons. However, in the case of a covalent bond, the valence electrons of only two neighboring atoms are shared, while in the formation of a metallic bond, all atoms take part in the sharing of these electrons at once. The low ionization energies of metals make it easy for valence electrons to detach from atoms and move throughout the entire volume of the crystal. Due to the free movement of electrons, metals have high electrical and thermal conductivity.
Thus, a relatively small number of electrons ensures the binding of all atoms in a metal crystal. A bond of this type, in contrast to a covalent bond, is non-localized And non-directional.
7. Intermolecular interaction . Orientation, induction and dispersion interaction of molecules. Dependence of the energy of intermolecular interaction on the value of the dipole moment, polarizability and size of molecules. Energy of intermolecular interaction and aggregate state of substances. The nature of the change in the boiling and melting points of simple substances and molecular compounds of p-elements of groups IV-VII.
1. With. 73–75; 2. With. 149–151; 4. With. 93–95; 8. With. 144–146; 11. With. 139–140.
Although the molecules as a whole are electrically neutral, intermolecular interactions take place between them.
The cohesive forces acting between single molecules and leading first to the formation of a molecular liquid, and then molecular crystals, are calledintermolecular forces , or van der Waals forces .
Intermolecular interaction, like a chemical bond, has electrostatic nature, but, unlike the latter, is very weak; manifests itself at much greater distances and is characterized by the absence of satiety.
There are three types of intermolecular interaction. The first type is orientationalinteraction polar molecules. When approaching, the polar molecules orient themselves relative to each other in accordance with the signs of the charges at the ends of the dipoles. The more polar the molecules, the stronger the orientation interaction. Its energy is determined primarily by the magnitude of the electric moments of the dipoles of molecules (ie, their polarity).
Inductive interaction – it is an electrostatic interaction between polar and non-polar molecules.
In a non-polar molecule, under the influence of the electric field of a polar molecule, an "induced" (induced) dipole arises, which is attracted to the constant dipole of the polar molecule. The energy of the inductive interaction is determined by the electric moment of the dipole of the polar molecule and the polarizability of the nonpolar molecule.
Dispersion interaction arises as a result of mutual attraction of the so-called instantaneous dipoles. Dipoles of this type arise in non-polar molecules at any time due to the mismatch between the electrical centers of gravity of the electron cloud and nuclei, caused by their independent vibrations.
The relative value of the contribution of individual components to the total energy of intermolecular interaction depends on two main electrostatic characteristics of the molecule - its polarity and polarizability, which, in turn, are determined by the size and structure of the molecule.
8. hydrogen bond . Mechanism of formation and nature of the hydrogen bond. Comparison of hydrogen bond energy with chemical bond energy and intermolecular interaction energy. Intermolecular and intramolecular hydrogen bonds. The nature of the change in the melting and boiling points of hydrides of p-elements of IV-VII groups. Importance of hydrogen bonds for natural objects. Anomalous properties of water.
1. With. 75–77; 2. With. 147–149; 4. With. 95–96; 11. With. 140–143.
One of the varieties of intermolecular interaction is hydrogen bond . It is carried out between the positively polarized hydrogen atom of one molecule and the negatively polarized X atom of another molecule:
Х δ- ─Н δ+ Х δ- ─Н δ+ ,
where X is an atom of one of the most electronegative elements - F, O or N, and the symbol is a symbol for a hydrogen bond.
The formation of a hydrogen bond is primarily due to the fact that the hydrogen atom has only one electron, which, when a polar covalent bond is formed with the X atom, is shifted towards it. A high positive charge arises on the hydrogen atom, which, combined with the absence of internal electron layers in the hydrogen atom, allows another atom to approach it up to distances close to the lengths of covalent bonds.
Thus, a hydrogen bond is formed as a result of the interaction of dipoles. However, unlike the usual dipole-dipole interaction, the mechanism of hydrogen bonding is also due to the donor-acceptor interaction, where the donor of an electron pair is the X atom of one molecule, and the acceptor is the hydrogen atom of another.
The hydrogen bond has the properties of directionality and saturation. The presence of a hydrogen bond significantly affects the physical properties of substances. For example, the melting and boiling points of HF, H 2 O and NH 3 are higher than those of hydrides of other elements of the same groups. The reason for the anomalous behavior is the presence of hydrogen bonds, the breaking of which requires additional energy.
The first of these is the formation of an ionic bond. (The second is education, which will be discussed below). When an ionic bond is formed, a metal atom loses electrons, and a nonmetal atom gains. For example, consider the electronic structure of sodium and chlorine atoms:
Na 1s 2 2s 2 2 p6 3 s 1 - one electron in the outer level
Cl 1s 2 2s 2 2 p6 3 s2 3 p 5 — seven electrons in the outer level
If the sodium atom donates its single 3s electron to the chlorine atom, the octet rule will hold for both atoms. The chlorine atom will have eight electrons in the outer third layer, and the sodium atom will also have eight electrons in the second layer, which has now become outer:
Na + 1s 2 2s 2 2 p 6
Cl - 1s 2 2s 2 2 p6 3 s2 3 p6 - eight electrons in the outer level
At the same time, the nucleus of the sodium atom still contains 11 protons, but the total number of electrons has decreased to 10. This means that the number of positively charged particles is one more than the number of negatively charged ones, so the total charge of the "atom" of sodium is +1.
An "atom" of chlorine now contains 17 protons and 18 electrons and has a charge of -1.
Charged atoms formed as a result of the loss or gain of one or more electrons are called ions. Positively charged ions are called cations, and the negatively charged ones are called anions.
Cations and anions, having opposite charges, are attracted to each other by electrostatic forces. This attraction of oppositely charged ions is called ionic bonding.
. It occurs in compounds formed by a metal and one or more non-metals.
The following compounds meet this criterion and are ionic in nature: MgCl 2, Fel 2, CuF, Na 2 0, Na 2 S0 4, Zn(C 2 H 3 0 2) 2.
There is another way to represent ionic compounds:
In these formulas, dots show only the electrons located on the outer shells ( valence electrons ). Such formulas are called Lewis formulas in honor of the American chemist G. N. Lewis, one of the founders (along with L. Pauling) of the theory of chemical bonding.
The transfer of electrons from a metal atom to a non-metal atom and the formation of ions are possible due to the fact that non-metals have a high electronegativity, and metals have a low one.
Due to the strong attraction of ions to each other, ionic compounds are mostly solid and have a rather high melting point.
An ionic bond is formed by the transfer of electrons from a metal atom to a nonmetal atom. The resulting ions are attracted to each other by electrostatic forces.
