Free fluorine consists of diatomic molecules. From the chemical point of view, fluorine can be characterized as a monovalent non-metal, and, moreover, the most active of all non-metals. This is due to a number of reasons, including the ease of decomposition of the F 2 molecule into individual atoms - the energy required for this is only 159 kJ / mol (against 493 kJ / mol for O 2 and 242 kJ / mol for C 12). Fluorine atoms have a significant electron affinity and are relatively small in size. Therefore, their valence bonds with atoms of other elements turn out to be stronger than similar bonds of other metalloids (for example, the H-F bond energy is - 564 kJ / mol versus 460 kJ / mol for the H-O bond and 431 kJ / mol for the H-C1 bond).
The F-F bond is characterized by a nuclear distance of 1.42 A. For the thermal dissociation of fluorine, the following data were obtained by calculation:
The fluorine atom in the ground state has the structure of the outer electron layer 2s 2 2p 5 and is monovalent. The excitation of the trivalent state associated with the transfer of one 2p electron to the 3s level requires an expenditure of 1225 kJ/mol and is practically not realized.
The electron affinity of a neutral fluorine atom is estimated at 339 kJ/mol. Ion F - is characterized by an effective radius of 1.33 A and a hydration energy of 485 kJ/mol. For the covalent radius of fluorine, a value of 71 pm is usually taken (i.e., half the internuclear distance in the F 2 molecule).
Chemical bonding is an electronic phenomenon in which at least one electron, which was in the force field of its nucleus, finds itself in the force field of another nucleus or several nuclei at the same time.
Most simple substances and all complex substances (compounds) consist of atoms interacting with each other in a certain way. In other words, a chemical bond is established between the atoms. When a chemical bond is formed, energy is always released, i.e., the energy of the formed particle must be less than the total energy of the initial particles.
The transition of an electron from one atom to another, resulting in the formation of oppositely charged ions with stable electronic configurations, between which an electrostatic attraction is established, is the simplest model of ionic bonding:
X → X + + e - ; Y + e - → Y - ; X+Y-
The hypothesis of the formation of ions and the occurrence of electrostatic attraction between them was first put forward by the German scientist W. Kossel (1916).
Another model of bonding is the sharing of electrons by two atoms, as a result of which stable electronic configurations are also formed. Such a bond is called covalent; in 1916, the American scientist G. Lewis began to develop its theory.
The common point in both theories was the formation of particles with a stable electronic configuration coinciding with the electronic configuration of a noble gas.
For example, in the formation of lithium fluoride, the ionic mechanism of bond formation is realized. The lithium atom (3 Li 1s 2 2s 1) loses an electron and turns into a cation (3 Li + 1s 2) with the electron configuration of helium. Fluorine (9 F 1s 2 2s 2 2p 5) accepts an electron, forming an anion (9 F - 1s 2 2s 2 2p 6) with the electronic configuration of neon. An electrostatic attraction arises between the lithium ion Li + and the fluorine ion F -, due to which a new compound is formed - lithium fluoride.
When hydrogen fluoride is formed, the only electron of the hydrogen atom (1s) and the unpaired electron of the fluorine atom (2p) are in the field of action of both nuclei - the hydrogen atom and the fluorine atom. Thus, a common electron pair arises, which means a redistribution of the electron density and the appearance of a maximum electron density. As a result, two electrons are now associated with the nucleus of the hydrogen atom (the electronic configuration of the helium atom), and eight electrons of the outer energy level are associated with the fluorine nucleus (the electronic configuration of the neon atom):
It is indicated by a single dash between the element symbols: H-F.A bond carried out by one electron pair is called a single bond.
The formation of two-electron shells for a lithium ion and a hydrogen atom is a special case.The tendency to form a stable eight-electron shell by transferring an electron from one atom to another (ionic bond) or by sharing electrons (covalent bond) is called the octet rule.
There are, however, compounds that do not follow this rule. For example, the beryllium atom in beryllium fluoride BeF 2 has only a four-electron shell; six electron shells are characteristic of the boron atom (the dots indicate the electrons of the outer energy level):
At the same time, in compounds such as phosphorus (V) chloride and sulfur (VI) fluoride, iodine (VII) fluoride, the electron shells of the central atoms contain more than eight electrons (phosphorus - 10; sulfur - 12; iodine - 14):
In most d-element conjunctions, the octet rule is also not respected.
In all the examples above, a chemical bond is formed between atoms of different elements; it is called heteroatomic. However, a covalent bond can also form between identical atoms. For example, a hydrogen molecule is formed by sharing 15 electrons of each hydrogen atom, as a result of which each atom acquires a stable electronic configuration of two electrons. An octet is formed during the formation of molecules of other simple substances, such as fluorine:
The formation of a chemical bond can also be carried out by the socialization of four or six electrons. In the first case, a double bond is formed, which is two generalized pairs of electrons, in the second - a triple bond (three generalized electron pairs).
For example, when a nitrogen molecule N 2 is formed, a chemical bond is formed by the socialization of six electrons: three unpaired p electrons from each atom. To achieve an eight-electron configuration, three common electron pairs are formed:
A double bond is indicated by two dashes, a triple bond by three. The nitrogen molecule N 2 can be represented as follows: N≡N.
In diatomic molecules formed by atoms of one element, the maximum electron density is located in the middle of the internuclear line. Since there is no separation of charges between atoms, this type of covalent bond is called non-polar. A heteroatomic bond is always more or less polar, since the maximum electron density is shifted towards one of the atoms, due to which it acquires a partial negative charge (denoted σ-). The atom from which the electron density maximum is shifted acquires a partial positive charge (denoted σ+). Electrically neutral particles in which the centers of the partial negative and partial positive charges do not coincide in space are called dipoles. The polarity of a bond is measured by the dipole moment (μ), which is directly proportional to the magnitude of the charges and the distance between them.
Rice. Schematic representation of a dipole
List of used literature
- Popkov V. A., Puzakov S. A. General chemistry: textbook. - M.: GEOTAR-Media, 2010. - 976 p.: ISBN 978-5-9704-1570-2. [With. 32-35]
In 1916, the first extremely simplified theories of the structure of molecules were proposed, in which electronic representations were used: the theory of the American physical chemist G. Lewis (1875-1946) and the German scientist W. Kossel. According to the Lewis theory, the formation of a chemical bond in a diatomic molecule involves the valence electrons of two atoms at once. Therefore, for example, in a hydrogen molecule, instead of a valence prime, they began to draw an electron pair that forms a chemical bond:
A chemical bond formed by an electron pair is called a covalent bond. The hydrogen fluoride molecule is depicted as follows:
The difference between molecules of simple substances (H2, F2, N2, O2) and molecules of complex substances (HF, NO, H2O, NH3) is that the former do not have a dipole moment, while the latter do. The dipole moment m is defined as the product of the absolute value of the charge q and the distance between two opposite charges r:
The dipole moment m of a diatomic molecule can be determined in two ways. First, since the molecule is electrically neutral, the total positive charge of the molecule Z" is known (it is equal to the sum of the charges of the atomic nuclei: Z" = ZA + ZB). Knowing the internuclear distance re, one can determine the location of the center of gravity of the positive charge of the molecule. The value of m molecules is found from the experiment. Therefore, you can find r" - the distance between the centers of gravity of the positive and total negative charge of the molecule:
Secondly, we can assume that when an electron pair forming a chemical bond is displaced to one of the atoms, some excess negative charge -q "appears on this atom and a charge + q" appears on the second atom. The distance between atoms is re:
The dipole moment of the HF molecule is 6.4×10-30 Cl× m, the internuclear distance H-F is 0.917×10-10 m. The calculation of q" gives: q" = 0.4 elementary charge (ie, electron charge). Since an excess negative charge appeared on the fluorine atom, it means that the electron pair that forms a chemical bond in the HF molecule is shifted to the fluorine atom. Such a chemical bond is called a covalent polar bond. Molecules of type A2 do not have a dipole moment. The chemical bonds that form these molecules are called covalent non-polar bonds.
Kossel's theory was proposed to describe molecules formed by active metals (alkali and alkaline earth) and active non-metals (halogens, oxygen, nitrogen). The outer valence electrons of metal atoms are the farthest removed from the atomic nucleus and therefore are relatively weakly retained by the metal atom. For atoms of chemical elements located in the same row of the Periodic system, when moving from left to right, the charge of the nucleus increases all the time, and additional electrons are located in the same electron layer. This leads to the fact that the outer electron shell shrinks and the electrons are more and more firmly held in the atom. Therefore, in the MeX molecule, it becomes possible to move the weakly retained outer valence electron of the metal with the expenditure of energy equal to the ionization potential into the valence electron shell of the nonmetal atom with the release of energy equal to the electron affinity. As a result, two ions are formed: Me+ and X-. The electrostatic interaction of these ions is a chemical bond. This type of connection is called ionic.
If we determine the dipole moments of MeX molecules in pairs, it turns out that the charge from the metal atom does not completely transfer to the non-metal atom, and the chemical bond in such molecules is better described as a covalent highly polar bond. Positive metal cations Me + and negative anions of non-metal atoms X- usually exist at the sites of the crystal lattice of crystals of these substances. But in this case, each positive metal ion first of all interacts electrostatically with the nearest nonmetal anions, then with metal cations, and so on. That is, in ionic crystals, chemical bonds are delocalized, and each ion eventually interacts with all other ions entering the crystal, which is a giant molecule.
Along with well-defined characteristics of atoms, such as the charges of atomic nuclei, ionization potentials, electron affinity, less defined characteristics are also used in chemistry. One of them is electronegativity. It was introduced into science by the American chemist L. Pauling. Let us first consider for the elements of the first three periods the data on the first ionization potential and on the electron affinity.
Regularities in ionization potentials and electron affinity are fully explained by the structure of the valence electron shells of atoms. The electron affinity of an isolated nitrogen atom is much less than that of alkali metal atoms, although nitrogen is an active non-metal. It is in molecules when interacting with atoms of other chemical elements that nitrogen proves that it is an active non-metal. This is what L. Pauling tried to do, introducing "electronegativity" as the ability of atoms of chemical elements to displace an electron pair towards themselves during the formation covalent polar bonds. The electronegativity scale for chemical elements was proposed by L. Pauling. He attributed the highest electronegativity in arbitrary dimensionless units to fluorine - 4.0, oxygen - 3.5, chlorine and nitrogen - 3.0, bromine - 2.8. The nature of the change in the electronegativity of atoms fully corresponds to the laws that are expressed in the Periodic system. Therefore, the use of the concept electronegativity"simply translates into another language those patterns in the change in the properties of metals and non-metals that are already reflected in the Periodic system.
Many metals in the solid state are almost perfectly formed crystals.. At the nodes of the crystal lattice in the crystal are atoms or positive metal ions. The electrons of those metal atoms from which positive ions were formed are in the form of an electron gas in the space between the nodes of the crystal lattice and belong to all atoms and ions. They determine the characteristic metallic luster, high electrical conductivity and thermal conductivity of metals. Type of chemical bonding, which is carried out by socialized electrons in a metal crystal, is calledmetallic bond.
In 1819, French scientists P. Dulong and A. Petit experimentally established that the molar heat capacity of almost all metals in the crystalline state is 25 J/mol. Now we can easily explain why this is so. The atoms of metals in the nodes of the crystal lattice are always in motion - they make oscillatory movements. This complex movement can be decomposed into three simple oscillatory movements in three mutually perpendicular planes. Each oscillatory movement has its own energy and its own law of its change with increasing temperature - its own heat capacity. The limiting value of heat capacity for any oscillatory motion of atoms is equal to R - the Universal Gas Constant. Three independent vibrational motions of atoms in a crystal will correspond to a heat capacity equal to 3R. When metals are heated, starting from very low temperatures, their heat capacity increases from zero. At room and higher temperatures, the heat capacity of most metals reaches its maximum value - 3R.
When heated, the crystal lattice of metals is destroyed and they pass into a molten state. On further heating, the metals evaporate. In vapors, many metals exist as Me2 molecules. In these molecules, metal atoms are able to form covalent nonpolar bonds.
Fluorine is a chemical element (symbol F, atomic number 9), a non-metal that belongs to the halogen group. It is the most active and electronegative substance. At normal temperature and pressure, the fluorine molecule is pale yellow with the formula F 2 . Like other halides, molecular fluorine is very dangerous and causes severe chemical burns on contact with the skin.
Usage
Fluorine and its compounds are widely used, including for the production of pharmaceuticals, agrochemicals, fuels and lubricants, and textiles. is used to etch glass, while fluorine plasma is used to produce semiconductor and other materials. Low concentrations of F ions in toothpaste and drinking water may help prevent dental caries, while higher concentrations are found in some insecticides. Many general anesthetics are hydrofluorocarbon derivatives. The 18 F isotope is a source of positrons for medical imaging by positron emission tomography, and uranium hexafluoride is used for uranium isotope separation and production for nuclear power plants.
Discovery history
Minerals containing fluorine compounds were known many years before the isolation of this chemical element. For example, the mineral fluorspar (or fluorite), consisting of calcium fluoride, was described in 1530 by George Agricola. He noticed that it could be used as a flux, a substance that helps lower the melting point of a metal or ore and helps purify the desired metal. Therefore, fluorine got its Latin name from the word fluere ("flow").
In 1670, glassblower Heinrich Schwanhard discovered that glass was etched by the action of calcium fluoride (fluorspar) treated with acid. Carl Scheele and many later researchers, including Humphry Davy, Joseph-Louis Gay-Lussac, Antoine Lavoisier, Louis Thénard, experimented with hydrofluoric acid (HF), which was easily obtained by treating CaF with concentrated sulfuric acid.
Eventually, it became clear that HF contained a previously unknown element. However, due to its excessive reactivity, this substance could not be isolated for many years. It is not only difficult to separate from compounds, but it immediately reacts with their other components. The isolation of elemental fluorine from hydrofluoric acid is extremely dangerous, and early attempts blinded and killed several scientists. These people became known as the "fluoride martyrs".
Discovery and production
Finally, in 1886, the French chemist Henri Moissan managed to isolate fluorine by electrolysis of a mixture of molten potassium fluorides and hydrofluoric acid. For this he was awarded the 1906 Nobel Prize in Chemistry. His electrolytic approach continues to be used today for the industrial production of this chemical element.
The first large-scale production of fluorine began during World War II. It was required for one of the stages of creating an atomic bomb as part of the Manhattan Project. Fluorine was used to produce uranium hexafluoride (UF 6 ), which in turn was used to separate the two isotopes 235 U and 238 U from each other. Today, gaseous UF 6 is needed to produce enriched uranium for nuclear power.
The most important properties of fluorine
In the periodic table, the element is located at the top of group 17 (formerly group 7A), which is called halogen. Other halogens include chlorine, bromine, iodine and astatine. In addition, F is in the second period between oxygen and neon.
Pure fluorine is a corrosive gas (chemical formula F 2 ) with a characteristic pungent odor that is found at a concentration of 20 nl per liter of volume. As the most reactive and electronegative of all elements, it easily forms compounds with most of them. Fluorine is too reactive to exist in its elemental form and has such an affinity for most materials, including silicon, that it cannot be prepared or stored in glass containers. In humid air, it reacts with water, forming no less dangerous hydrofluoric acid.
Fluorine, interacting with hydrogen, explodes even at low temperatures and in the dark. It reacts violently with water to form hydrofluoric acid and oxygen gas. Various materials, including finely dispersed metals and glasses, burn with a bright flame in a jet of gaseous fluorine. In addition, this chemical element forms compounds with the noble gases krypton, xenon and radon. However, it does not react directly with nitrogen and oxygen.
Despite the extreme activity of fluorine, methods for its safe handling and transportation have now become available. The element can be stored in steel or monel (nickel-rich alloy) containers, as fluorides form on the surface of these materials, which prevent further reaction.
Fluorides are substances in which fluorine is present as a negatively charged ion (F-) in combination with some positively charged elements. Fluorine compounds with metals are among the most stable salts. When dissolved in water, they are divided into ions. Other forms of fluorine are complexes such as - and H 2 F + .
isotopes
There are many isotopes of this halogen, ranging from 14 F to 31 F. But the isotopic composition of fluorine includes only one of them, 19 F, which contains 10 neutrons, since it is the only one that is stable. The radioactive isotope 18 F is a valuable source of positrons.
Biological impact
Fluorine in the body is mainly found in bones and teeth in the form of ions. Fluoridation of drinking water at a concentration of less than one part per million significantly reduces the incidence of caries - according to the National Research Council of the National Academy of Sciences of the United States. On the other hand, excessive accumulation of fluoride can lead to fluorosis, which manifests itself in mottled teeth. This effect is usually observed in areas where the content of this chemical element in drinking water exceeds a concentration of 10 ppm.
Elemental fluorine and fluoride salts are toxic and must be handled with great care. Contact with skin or eyes should be carefully avoided. The reaction with the skin produces which quickly penetrates the tissues and reacts with the calcium in the bones, damaging them permanently.
Fluorine in the environment
The annual world production of the mineral fluorite is about 4 million tons, and the total capacity of explored deposits is within 120 million tons. The main areas for the extraction of this mineral are Mexico, China and Western Europe.
Fluorine occurs naturally in the earth's crust, where it can be found in rocks, coal, and clay. Fluorides are released into the air by wind erosion of soils. Fluorine is the 13th most abundant chemical element in the earth's crust - its content is 950 ppm. In soils, its average concentration is about 330 ppm. Hydrogen fluoride can be released into the air as a result of industrial combustion processes. Fluorides that are in the air end up falling onto the ground or into the water. When fluorine forms a bond with very small particles, it can remain in the air for long periods of time.
In the atmosphere, 0.6 billionths of this chemical element is present in the form of salt fog and organic chlorine compounds. In urban areas, the concentration reaches 50 parts per billion.
Connections
Fluorine is a chemical element that forms a wide range of organic and inorganic compounds. Chemists can replace hydrogen atoms with it, thereby creating many new substances. Highly reactive halogen forms compounds with noble gases. In 1962, Neil Bartlett synthesized xenon hexafluoroplatinate (XePtF6). Krypton and radon fluorides have also been obtained. Another compound is argon fluorohydride, which is stable only at extremely low temperatures.
Industrial Application
In the atomic and molecular state, fluorine is used for plasma etching in the production of semiconductors, flat panel displays, and microelectromechanical systems. Hydrofluoric acid is used to etch glass in lamps and other products.
Along with some of its compounds, fluorine is an important component in the production of pharmaceuticals, agrochemicals, fuels and lubricants, and textiles. The chemical element is needed to produce halogenated alkanes (halons), which, in turn, were widely used in air conditioning and refrigeration systems. Later, such use of chlorofluorocarbons was banned because they contribute to the destruction of the ozone layer in the upper atmosphere.
Sulfur hexafluoride is an extremely inert, non-toxic gas classified as a greenhouse gas. Without fluorine, the production of low friction plastics such as Teflon is not possible. Many anesthetics (eg sevoflurane, desflurane and isoflurane) are CFC derivatives. Sodium hexafluoroaluminate (cryolite) is used in aluminum electrolysis.
Fluorine compounds, including NaF, are used in toothpastes to prevent tooth decay. These substances are added to municipal water supplies to provide water fluoridation, however the practice is considered controversial due to the impact on human health. At higher concentrations, NaF is used as an insecticide, especially for cockroach control.
In the past, fluorides have been used to reduce ores and increase their fluidity. Fluorine is an important component in the production of uranium hexafluoride, which is used to separate its isotopes. 18 F, a radioactive isotope with 110 minutes, emits positrons and is often used in medical positron emission tomography.
Physical properties of fluorine
The basic characteristics of a chemical element are as follows:
- Atomic mass 18.9984032 g/mol.
- Electronic configuration 1s 2 2s 2 2p 5 .
- The oxidation state is -1.
- Density 1.7 g/l.
- Melting point 53.53 K.
- Boiling point 85.03 K.
- Heat capacity 31.34 J/(K mol).
Chemical particles formed from two or more atoms are called molecules(real or conditional formula units polyatomic substances). Atoms in molecules are chemically bonded.
A chemical bond is an electrical force of attraction that holds particles together. Each chemical bond in structural formulas seems valence line, for example:
H - H (bond between two hydrogen atoms);
H 3 N - H + (bond between the nitrogen atom of the ammonia molecule and the hydrogen cation);
(K +) - (I -) (bond between potassium cation and iodide ion).
A chemical bond is formed by a pair of electrons (), which in the electronic formulas of complex particles (molecules, complex ions) is usually replaced by a valence line, in contrast to their own, unshared electron pairs of atoms, for example:
The chemical bond is called covalent, if it is formed by the socialization of a pair of electrons by both atoms.
In the F 2 molecule, both fluorine atoms have the same electronegativity, therefore, the possession of an electron pair is the same for them. Such a chemical bond is called non-polar, since each fluorine atom has electron density the same in electronic formula molecules can be conditionally divided between them equally:
In the HCl molecule, the chemical bond is already polar, since the electron density on the chlorine atom (an element with greater electronegativity) is much higher than on the hydrogen atom:
A covalent bond, for example H - H, can be formed by sharing the electrons of two neutral atoms:
H + H > H – H
This bonding mechanism is called exchange or equivalent.
According to another mechanism, the same covalent bond H - H arises when the electron pair of the hydride ion H is socialized by the hydrogen cation H +:
H + + (:H) - > H - H
The H + cation in this case is called acceptor and the anion H - donor electron pair. The mechanism of formation of a covalent bond in this case will be donor-acceptor, or coordinating.
Single bonds (H - H, F - F, H - CI, H - N) are called a-links, they determine the geometric shape of the molecules.
Double and triple bonds () contain one?-component and one or two?-components; ?-component, which is the main and conditionally formed first, is always stronger than?-components.
The physical (actually measurable) characteristics of a chemical bond are its energy, length, and polarity.
Chemical bond energy (E cv) is the heat that is released during the formation of this bond and is spent on breaking it. For the same atoms, a single bond is always weaker than a multiple (double, triple).
Chemical bond length (l s) - internuclear distance. For the same atoms, a single bond is always longer than a multiple.
Polarity communication is measured electric dipole moment p- the product of a real electric charge (on the atoms of a given bond) by the length of the dipole (i.e., the length of the bond). The larger the dipole moment, the higher the polarity of the bond. The real electric charges on atoms in a covalent bond are always smaller in value than the oxidation states of the elements, but they coincide in sign; for example, for the H + I -Cl -I bond, the real charges are H +0 "17 -Cl -0" 17 (bipolar particle, or dipole).
Polarity of molecules determined by their composition and geometric shape.
Non-polar (p = O) will be:
a) molecules simple substances, since they contain only non-polar covalent bonds;
b) polyatomic molecules difficult substances, if their geometric shape symmetrical.
For example, CO 2, BF 3 and CH 4 molecules have the following directions of equal (along length) bond vectors:
When bond vectors are added, their sum always vanishes, and the molecules as a whole are non-polar, although they contain polar bonds.
Polar (p> O) will be:
a) diatomic molecules difficult substances, since they contain only polar bonds;
b) polyatomic molecules difficult substances, if their structure asymmetrically, i.e., their geometric shape is either incomplete or distorted, which leads to the appearance of a total electric dipole, for example, for NH 3, H 2 O, HNO 3 and HCN molecules.
Complex ions, such as NH 4 + , SO 4 2- and NO 3 - , cannot be dipoles in principle, they carry only one (positive or negative) charge.
Ionic bond arises during the electrostatic attraction of cations and anions with almost no socialization of a pair of electrons, for example, between K + and I -. The potassium atom has a lack of electron density, the iodine atom has an excess. This connection is considered limiting case of a covalent bond, since a pair of electrons is practically in the possession of the anion. Such a connection is most typical for compounds of typical metals and non-metals (CsF, NaBr, CaO, K 2 S, Li 3 N) and substances of the salt class (NaNO 3, K 2 SO 4, CaCO 3). All these compounds under room conditions are crystalline substances, which are united by the common name ionic crystals(crystals built from cations and anions).
There is another type of connection called metallic bond, in which valence electrons are so loosely held by metal atoms that they do not actually belong to specific atoms.
Atoms of metals, left without external electrons clearly belonging to them, become, as it were, positive ions. They form metal crystal lattice. The set of socialized valence electrons ( electron gas) holds positive metal ions together and at specific lattice sites.
In addition to ionic and metallic crystals, there are also atomic and molecular crystalline substances, in the lattice sites of which there are atoms or molecules, respectively. Examples: diamond and graphite - crystals with an atomic lattice, iodine I 2 and carbon dioxide CO 2 (dry ice) - crystals with a molecular lattice.
Chemical bonds exist not only inside the molecules of substances, but can also form between molecules, for example, for liquid HF, water H 2 O and a mixture of H 2 O + NH 3:
hydrogen bond formed due to the forces of electrostatic attraction of polar molecules containing atoms of the most electronegative elements - F, O, N. For example, hydrogen bonds are present in HF, H 2 O and NH 3, but they are not in HCl, H 2 S and PH 3.
Hydrogen bonds are unstable and break quite easily, for example, when ice melts and water boils. However, some additional energy is expended on breaking these bonds, and therefore the melting points (Table 5) and boiling points of substances with hydrogen bonds
(for example, HF and H 2 O) are significantly higher than for similar substances, but without hydrogen bonds (for example, HCl and H 2 S, respectively).
Many organic compounds also form hydrogen bonds; The hydrogen bond plays an important role in biological processes.
Examples of Part A assignments1. Substances with only covalent bonds are
1) SiH 4, Cl 2 O, CaBr 2
2) NF 3, NH 4 Cl, P 2 O 5
3) CH 4 , HNO 3 , Na(CH 3 O)
4) CCl 2 O, I 2, N 2 O
2–4. covalent bond
2. single
3. double
4. triple
present in matter
5. Multiple bonds are present in molecules
6. The particles called radicals are
7. One of the bonds is formed by the donor-acceptor mechanism in the set of ions
1) SO 4 2-, NH 4 +
2) H 3 O +, NH 4 +
3) PO 4 3-, NO 3 -
4) PH 4 + , SO 3 2-
8. The most durable and short bond - in a molecule
9. Substances with only ionic bonds - in the set
2) NH 4 Cl, SiCl 4
10–13. The crystal lattice of matter
13. Va (OH) 2
1) metal
Atom, molecule, nuclear properties
The structure of the fluorine atom.
At the center of an atom is a positively charged nucleus. 9 negatively charged electrons revolve around.
Electronic formula: 1s2;2s2;2p5
m prot. = 1.00783 (a.m.u.)
m neutral = 1.00866 (a.m.u.)
m proton = m electron
Isotopes of fluorine.
Isotope: 18F
Brief description: Prevalence in nature: 0%
The number of protons in the nucleus is 9. The number of neutrons in the nucleus is 9. The number of nucleons is 18.E bonds \u003d 931.5 (9 * m pr. + 9 * m neutron-M (F18)) \u003d 138.24 (MEV) E specific = E bonds/N nucleons = 7.81 (MEV/nucleon)
Alpha decay is impossibleBeta minus decay is impossiblePositron decay: F(Z=9,M=18)-->O(Z=8,M=18)+e(Z=+1,M=0)+0.28( MeV) Electronic capture: F(Z=9,M=18)+e(Z=-1,M=0)-->O(Z=8,M=18)+1.21(MeV)
Isotope: 19F
Brief description: Prevalence in nature: 100%
fluorine molecule.
Free fluorine consists of diatomic molecules. From the chemical point of view, fluorine can be characterized as a monovalent non-metal, and, moreover, the most active of all non-metals. This is due to a number of reasons, including the ease of decomposition of the F2 molecule into individual atoms - the energy required for this is only 159 kJ / mol (against 493 kJ / mol for O2 and 242 kJ / mol for C12). Fluorine atoms have a significant electron affinity and are relatively small in size. Therefore, their valence bonds with atoms of other elements are stronger than similar bonds of other metalloids (for example, the H-F bond energy is - 564 kJ / mol versus 460 kJ / mol for the H-O bond and 431 kJ / mol for the H-C1 bond).
The F-F bond is characterized by a nuclear distance of 1.42 A. For the thermal dissociation of fluorine, the following data were obtained by calculation:
Temperature, °С 300 500 700 900 1100 1300 1500 1700
Degree of dissociation, % 5 10-3 0.3 4.2 22 60 88 97 99
The fluorine atom in the ground state has the structure of the outer electron layer 2s22p5 and is monovalent. The excitation of the trivalent state associated with the transfer of one 2p electron to the 3s level requires an expenditure of 1225 kJ/mol and is practically not realized. The electron affinity of a neutral fluorine atom is estimated at 339 kJ/mol. The F- ion is characterized by an effective radius of 1.33 A and a hydration energy of 485 kJ/mol. The covalent radius of fluorine is usually taken to be 71 pm (i.e., half the internuclear distance in the F2 molecule).
Chemical properties of fluorine.
Since fluorine derivatives of metalloid elements are usually highly volatile, their formation does not protect the surface of the metalloid from further action of fluorine. Therefore, the interaction often proceeds much more vigorously than with many metals. For example, silicon, phosphorus and sulfur ignite in fluorine gas. Amorphous carbon (charcoal) behaves similarly, while graphite reacts only at a red heat temperature. Fluorine does not combine directly with nitrogen and oxygen.
From the hydrogen compounds of other elements, fluorine takes away hydrogen. Most oxides are decomposed by it with the displacement of oxygen. In particular, water interacts according to the scheme F2 + H2O --> 2 HF + O
moreover, the displaced oxygen atoms combine not only with each other, but also partially with water and fluorine molecules. Therefore, in addition to gaseous oxygen, this reaction always produces hydrogen peroxide and fluorine oxide (F2O). The latter is a pale yellow gas, similar in smell to ozone.
Fluorine oxide (otherwise - oxygen fluoride - OF2) can be obtained by passing fluorine in 0.5 N. NaOH solution. The reaction proceeds according to the equation: 2 F2 + 2 NaOH = 2 NaF + H2O + F2OT The following reactions are also characteristic of fluorine:
H2 + F2 = 2HF (with explosion)
(first electron)
(according to Pauling)
| F | 9 |
| 18,9984 | |
| 2s 2 2p 5 | |
| Fluorine | |
Chemical properties
The most active non-metal, it violently interacts with almost all substances (rare exceptions are fluoroplasts), and with most of them - with combustion and explosion. The contact of fluorine with hydrogen leads to ignition and explosion even at very low temperatures (up to −252°C). Even water and platinum: uranium for the nuclear industry burn in a fluorine atmosphere.
chlorine trifluoride ClF 3 - a fluorinating agent and a powerful rocket fuel oxidizer
sulfur hexafluoride SF 6 - gaseous insulator in the electrical industry
metal fluorides (such as W and V), which have some beneficial properties
freons are good refrigerants
teflon - chemically inert polymers
sodium hexafluoroaluminate - for the subsequent production of aluminum by electrolysis
various fluorine compounds
Missile technology
Fluorine compounds are widely used in rocket technology as a propellant oxidizer.Application in medicine
Fluorine compounds are widely used in medicine as blood substitutes.
Biological and physiological role
Fluorine is a vital element for the body. In the human body, fluorine is mainly found in tooth enamel as part of fluorapatite - Ca 5 F (PO 4) 3 . With insufficient (less than 0.5 mg / liter of drinking water) or excessive (more than 1 mg / liter) fluoride intake by the body, dental diseases can develop: caries and fluorosis (mottled enamel) and osteosarcoma, respectively.
To prevent caries, it is recommended to use toothpastes with fluoride additives or drink fluoridated water (up to a concentration of 1 mg/l), or use local applications with a 1-2% solution of sodium fluoride or stannous fluoride. Such actions can reduce the likelihood of caries by 30-50%.
The maximum allowable concentration of bound fluorine in the air of industrial premises is 0.0005 mg/liter.
Additional Information
Fluorine, Fluorum, F(9)
Fluorine (Fluorine, French and German Fluor) was obtained in a free state in 1886, but its compounds have been known for a long time and were widely used in metallurgy and glass production. The first mention of fluorite (CaP,) under the name fluorspar (Fliisspat) dates back to the 16th century. One of the works attributed to the legendary Vasily Valentin mentions stones painted in various colors - fluxes (Fliisse from Latin fluere - flow, pour), which were used as fluxes in the smelting of metals. Agricola and Libavius write about the same. The latter introduces special names for this flux - fluorspar (Flusspat) and mineral melt. Many authors of chemical and technical writings of the 17th and 18th centuries. describe different types of fluorspar. In Russia, these stones were called plavik, spalt, spat; Lomonosov classified these stones as selenites and called them spar or flux (crystal flux). Russian masters, as well as collectors of mineral collections (for example, in the 18th century, Prince P.F. Golitsyn) knew that some types of spars glow in the dark when heated (for example, in hot water). However, even Leibniz in his history of phosphorus (1710) mentions in this connection thermophosphorus (Thermophosphorus).
Apparently, chemists and artisan chemists became acquainted with hydrofluoric acid no later than the 17th century. In 1670, the Nuremberg craftsman Schwanhard used fluorspar mixed with sulfuric acid to etch designs on glass goblets. However, at that time the nature of fluorspar and hydrofluoric acid was completely unknown. It was believed, for example, that silicic acid has an etching effect in the Schwanhard process. This erroneous opinion was eliminated by Scheele, proving that when fluorspar interacts with sulfuric acid, silicic acid is obtained as a result of the erosion of the glass retort by the resulting hydrofluoric acid. In addition, Scheele established (1771) that fluorspar is a combination of calcareous earth with a special acid, which was called "Swedish acid".
Lavoisier recognized the hydrofluoric acid radical (radical fluorique) as a simple body and included it in his table of simple bodies. More or less pure hydrofluoric acid was obtained in 1809. Gay-Lussac and Tenard by distilling fluorspar with sulfuric acid in a lead or silver retort. During this operation, both researchers were poisoned. The true nature of hydrofluoric acid was established in 1810 by Ampère. He rejected Lavoisier's opinion that hydrofluoric acid must contain oxygen, and proved the analogy of this acid with hydrochloric acid. Ampère reported his findings to Davy, who shortly before that had established the elemental nature of chlorine. Davy fully agreed with Ampere's arguments and spent a lot of effort on obtaining free fluorine by electrolysis of hydrofluoric acid and in other ways. Taking into account the strong corrosive effect of hydrofluoric acid on glass, as well as on plant and animal tissues, Ampere suggested calling the element contained in it fluorine (Greek - destruction, death, pestilence, plague, etc.). However, Davy did not accept this name and proposed another - fluorine (Fluorine), by analogy with the then name of chlorine - chlorine (Chlorine), both names are still used in English. In Russian, the name given by Ampere has been preserved.
Numerous attempts to isolate free fluorine in the 19th century did not lead to successful results. Only in 1886 did Moissan manage to do this and obtain free fluorine in the form of a yellow-green gas. Since fluorine is an unusually aggressive gas, Moissan had to overcome many difficulties before he found a material suitable for the apparatus in experiments with fluorine. The U-tube for electrolysis of hydrofluoric acid at 55°C (cooled with liquid methyl chloride) was made of platinum with fluorspar plugs. After the chemical and physical properties of free fluorine were investigated, it found wide application. Today, fluorine is one of the most important components in the synthesis of a wide range of organofluorine compounds. Russian literature of the early 19th century. fluorine was called differently: the base of hydrofluoric acid, fluorine (Dvigubsky, 1824), fluorine (Iovsky), fluor (Shcheglov, 1830), fluor, fluorine, fluorine. Hess from 1831 introduced the name fluorine.
The work selected tasks on chemical bonds.
Pugacheva Elena Vladimirovna
Development Description
6. A covalent non-polar bond is characteristic of
1) Cl 2 2) SO3 3) CO 4) SiO 2
1) NH 3 2) Cu 3) H 2 S 4) I 2
3) ionic 4) metallic
15. Three common electron pairs form a covalent bond in a molecule
16. Hydrogen bonds are formed between molecules
1) HI 2) HCl 3) HF 4) HBr
1) water and diamond 2) hydrogen and chlorine 3) copper and nitrogen 4) bromine and methane
19. Hydrogen bond not typical for substance
1) fluorine 2) chlorine 3) bromine 4) iodine
1) CF 4 2) CCl 4 3) CBr 4 4) CI 4
1) 1 2) 2 3) 3 4) 4
1) 1 2) 2 3) 3 4) 4
32. Atoms of chemical elements of the second period of the periodic system D.I. Mendeleev form compounds with an ionic chemical bond of composition 1) LiF 2) CO 2 3) Al 2 O 3 4) BaS
1) ionic 2) metallic
43. An ionic bond is formed by 1) H and S 2) P and C1 3) Cs and Br 4) Si and F
when interacting
1) ionic 2) metallic
1) ionic 2) metallic
NAME OF THE SUBSTANCE TYPE OF COMMUNICATION
1) zinc A) ionic
2) nitrogen B) metal
62. Match
TYPE OF COMMUNICATION CONNECTION
1) ionic A) H 2
2) metal B) Va
3) covalent polar B) HF
66. The strongest chemical bond takes place in the molecule 1) F 2 2) Cl 2 3) O 2 4) N 2
67. Bond strength increases in the series 1) Cl 2 -O 2 -N 2 2) O 2 - N 2- Cl 2 3) O 2 -Cl 2 -N 2 4) Cl 2 -N 2 -O 2
68. Indicate a series characterized by an increase in the length of a chemical bond
1) O 2, N 2, F 2, Cl 2 2) N 2, O 2, F 2, Cl 2 3) F 2, N 2, O 2, Cl 2 4) N 2, O 2, Cl 2, F2
Let's analyze tasks No. 3 from the USE options for 2016.
Tasks with solutions.
Task number 1.
Compounds with a covalent non-polar bond are located in the series:
1. O2, Cl2, H2
2. HCl, N2, F2
3. O3, P4, H2O
4.NH3, S8, NaF
Explanation: we need to find such a series in which there will be only simple substances, since a covalent non-polar bond is formed only between atoms of the same element. The correct answer is 1.
Task number 2.
Substances with a covalent polar bond are listed in the series:
1. CaF2, Na2S, N2
2. P4, FeCl2, NH3
3. SiF4, HF, H2S
4. NaCl, Li2O, SO2
Explanation: here you need to find a series in which only complex substances and, moreover, all non-metals. The correct answer is 3.
Task number 3.
The hydrogen bond is characteristic of
1. Alkanes 2. Arenes 3. Alcohols 4. Alkynes
Explanation: A hydrogen bond is formed between a hydrogen ion and an electronegative ion. Such a set, among those listed, is only for alcohols.
The correct answer is 3.
Task number 4.
Chemical bond between water molecules
1. Hydrogen
2. Ionic
3. Covalent polar
4. Covalent non-polar
Explanation: a covalent polar bond is formed between the O and H atoms in water, since these are two non-metals, but a hydrogen bond is formed between water molecules. The correct answer is 1.
Task number 5.
Only covalent bonds have each of the two substances:
1. CaO and C3H6
2. NaNO3 and CO
3. N2 and K2S
4.CH4 and SiO2
Explanation: compounds must consist only of non-metals, i.e. the correct answer is 4.
Task number 6.
A substance with a covalent polar bond is
1. O3 2. NaBr 3. NH3 4. MgCl2
Explanation: A polar covalent bond is formed between atoms of different non-metals. The correct answer is 3.
Task number 7.
A non-polar covalent bond is characteristic of each of the two substances:
1. Water and diamond
2. Hydrogen and chlorine
3. Copper and nitrogen
4. Bromine and methane
Explanation: a non-polar covalent bond is characteristic of the connection of atoms of the same non-metal element. The correct answer is 2.
Task number 8.
What chemical bond is formed between atoms of elements with serial numbers 9 and 19?
1. Ionic
2. Metal
3. Covalent polar
4. Covalent non-polar
Explanation: these are elements - fluorine and potassium, that is, a non-metal and a metal, respectively, only an ionic bond can form between such elements. The correct answer is 1.
Task number 9.
A substance with an ionic bond type corresponds to the formula
1. NH3 2. HBr 3. CCl4 4. KCl
Explanation: an ionic bond is formed between a metal atom and a nonmetal atom, that is the correct answer is 4.
Task number 10.
The same type of chemical bond have hydrogen chloride and
1. Ammonia
2. Bromine
3. Sodium chloride
4. Magnesium oxide
Explanation: Hydrogen chloride has a covalent polar bond, that is, we need to find a substance consisting of two different non-metals - this is ammonia.
The correct answer is 1.
Tasks for independent decision.
1. Hydrogen bonds form between molecules
1. Hydrofluoric acid
2. Chloromethane
3. Dimethyl ether
4. Ethylene
2. A compound with a covalent bond corresponds to the formula
1. Na2O 2. MgCl2 3. CaBr2 4. HF
3. A substance with a covalent non-polar bond has the formula
1. H2O 2. Br2 3. CH4 4. N2O5
4. A substance with an ionic bond is
1. CaF2 2. Cl2 3. NH3 4. SO2
5. Hydrogen bonds form between molecules
1. Methanol
3. Acetylene
4. Methyl formate
6. A covalent non-polar bond is characteristic of each of the two substances:
1. Nitrogen and ozone
2. Water and ammonia
3. Copper and nitrogen
4. Bromine and methane
7. A covalent polar bond is characteristic of a substance
1. KI 2. CaO 3. Na2S 4. CH4
8. A covalent non-polar bond is characteristic of
1. I2 2. NO 3. CO 4. SiO2
9. A substance with a covalent polar bond is
1. Cl2 2. NaBr 3. H2S 4. MgCl2
10. A covalent non-polar bond is characteristic of each of the two substances:
1. Hydrogen and chlorine
2. Water and diamond
3. Copper and nitrogen
4. Bromine and methane
This note used assignments from the USE collection of 2016, edited by A.A. Kaverina.
A4 Chemical bond.
Chemical bond: covalent (polar and non-polar), ionic, metallic, hydrogen. Methods for the formation of a covalent bond. Characteristics of a covalent bond: bond length and energy. Formation of an ionic bond.
Option 1 - 1,5,9,13,17,21,25,29,33,37,41,45,49,53,57,61,65
Option 2 - 2,6,10,14,18,22,26,30,34,38,42,46,50,54,58,62,66
Option 3 - 3,7,11,15,19,23,27,31,35,39,43,47,51,55,59,63,67
Option 4 - 4,8,12,16,20,24,28,32,36,40,44,48,52,56,60,64,68
1. In ammonia and barium chloride, the chemical bond, respectively
1) ionic and covalent polar
2) covalent polar and ionic
3) covalent non-polar and metallic
4) covalent non-polar and ionic
2. Substances with only ionic bonds are listed in the series:
1) F 2, CCl 4, KCl 2) NaBr, Na 2 O, KI 3) SO 2 .P 4 .CaF 2 4) H 2 S, Br 2 , K 2 S
3. A compound with an ionic bond is formed by interaction
1) CH 4 and O 2 2) SO 3 and H 2 O 3) C 2 H 6 and HNO 3 4) NH 3 and HCI
4. In what series do all substances have a covalent polar bond?
1) HCl, NaCl, Cl 2 2) O 2, H 2 O, CO 2 3) H 2 O, NH 3, CH 4 4) NaBr, HBr, CO
5. In which row are the formulas of substances written only with a covalent polar bond?
1) Cl 2, NO 2, HCl 2) HBr, NO, Br 2 3) H 2 S, H 2 O, Se 4) HI, H 2 O, PH 3
6. A covalent non-polar bond is characteristic of
1) Cl 2 2) SO3 3) CO 4) SiO 2
7. A substance with a covalent polar bond is
1) C1 2 2) NaBr 3) H 2 S 4) MgCl 2
8. A substance with a covalent bond is
1) CaCl 2 2) MgS 3) H 2 S 4) NaBr
9. A substance with a covalent non-polar bond has the formula
1) NH 3 2) Cu 3) H 2 S 4) I 2
10. Substances with a non-polar covalent bond are
11. A chemical bond is formed between atoms with the same electronegativity
1) ionic 2) covalent polar 3) covalent non-polar 4) hydrogen
12. A covalent polar bond is characteristic of
1) KCl 2) HBr 3) P 4 4) CaCl 2
13. A chemical element in the atom of which the electrons are distributed over the layers as follows: 2, 8, 8, 2 forms a chemical bond with hydrogen
1) covalent polar 2) covalent non-polar
3) ionic 4) metallic
14. In a molecule of what substance is the bond length between carbon atoms the longest?
1) acetylene 2) ethane 3) ethene 4) benzene
15. Three common electron pairs form a covalent bond in a molecule
1) nitrogen 2) hydrogen sulfide 3) methane 4) chlorine
16. Hydrogen bonds are formed between molecules
1) dimethyl ether 2) methanol 3) ethylene 4) ethyl acetate
17. The polarity of the bond is most pronounced in the molecule
1) HI 2) HCl 3) HF 4) HBr
18. Substances with a non-polar covalent bond are
1) water and diamond 2) hydrogen and chlorine 3) copper and nitrogen 4) bromine and methane
19. Hydrogen bond not typical for substance
1) H 2 O 2) CH 4 3) NH 3 4) CH3OH
20. A covalent polar bond is characteristic of each of the two substances, the formulas of which
1) KI and H 2 O 2) CO 2 and K 2 O 3) H 2 S and Na 2 S 4) CS 2 and PC1 5
21. The least strong chemical bond in a molecule
22. In the molecule of which substance is the length of the chemical bond the longest?
1) fluorine 2) chlorine 3) bromine 4) iodine
23. Each of the substances indicated in the series has covalent bonds:
1) C 4 H 10, NO 2, NaCl 2) CO, CuO, CH 3 Cl 3) BaS, C 6 H 6, H 2 4) C 6 H 5 NO 2, F 2, CCl 4
24. Each of the substances indicated in the series has a covalent bond:
1) CaO, C 3 H 6, S 8 2) Fe, NaNO 3, CO 3) N 2, CuCO 3, K 2 S 4) C 6 H 5 N0 2, SO 2, CHC1 3
25. Each of the substances indicated in the series has a covalent bond:
1) C 3 H 4, NO, Na 2 O 2) CO, CH 3 C1, PBr 3 3) P 2 Oz, NaHSO 4, Cu 4) C 6 H 5 NO 2, NaF, CCl 4
26. Each of the substances indicated in the series has covalent bonds:
1) C 3 H a, NO 2, NaF 2) KCl, CH 3 Cl, C 6 H 12 0 6 3) P 2 O 5, NaHSO 4, Ba 4) C 2 H 5 NH 2, P 4, CH 3 Oh
27. Bond polarity is most pronounced in molecules
1) hydrogen sulfide 2) chlorine 3) phosphine 4) hydrogen chloride
28. In the molecule of what substance are chemical bonds the strongest?
1) CF 4 2) CCl 4 3) CBr 4 4) CI 4
29. Among the substances NH 4 Cl, CsCl, NaNO 3, PH 3, HNO 3 - the number of compounds with an ionic bond is
1) 1 2) 2 3) 3 4) 4
30. Among the substances (NH 4) 2 SO 4, Na 2 SO 4, CaI 2, I 2, CO 2 - the number of compounds with a covalent bond is
1) 1 2) 2 3) 3 4) 4
31. In substances formed by combining identical atoms, a chemical bond
1) ionic 2) covalent polar 3) hydrogen 4) covalent non-polar
32. Atoms of chemical elements of the second period of the periodic system D.I. Mendeleev form compounds with an ionic chemical bond of composition 1) LiF 2) CO 2 3) Al 2 O 3 4) BaS
33. Compounds with covalent polar and covalent non-polar bonds are respectively 1) water and hydrogen sulfide 2) potassium bromide and nitrogen 3) ammonia and hydrogen 4) oxygen and methane
34. A covalent non-polar bond is characteristic of 1) water 2) ammonia 3) nitrogen 4) methane
35. Chemical bond in a hydrogen fluoride molecule
1) covalent polar 3) ionic
2) covalent non-polar 4) hydrogen
36. Choose a pair of substances, all bonds in which are covalent:
1) NaCl, Hcl 2) CO 2, BaO 3) CH 3 Cl, CH 3 Na 4) SO 2, NO 2
37. In potassium iodide, a chemical bond
1) covalent non-polar 3) metallic
2) covalent polar 4) ionic
38. In carbon disulfide CS 2 chemical bond
1) ionic 2) metallic
3) covalent polar 4) covalent non-polar
39. A covalent non-polar bond is realized in a compound
1) CrO 3 2) P 2 O 5 3) SO 2 4) F 2
40. A substance with a covalent polar bond has the formula 1) KCl 2) HBr 3) P 4 4) CaCl 2
41. Connection with the ionic nature of the chemical bond
1) phosphorus chloride 2) potassium bromide 3) nitric oxide (II) 4) barium
42. In ammonia and barium chloride, the chemical bond, respectively
1) ionic and covalent polar 2) covalent polar and ionic
3) covalent non-polar and metallic 4) covalent non-polar and ionic
43. An ionic bond is formed by 1) H and S 2) P and C1 3) Cs and Br 4) Si and F
44. What type of bond is in the H 2 molecule?
1) Ionic 2) Hydrogen 3) Covalent non-polar 4) Donor-acceptor
45. A substance with a covalent polar bond is
1) sulfur oxide (IV) 2) oxygen 3) calcium hydride 4) diamond
46. In a fluorine molecule, a chemical bond
1) covalent polar 2) ionic 3) covalent non-polar 4) hydrogen
47. In which series are substances listed only with a covalent polar bond:
1) CH 4 H 2 Cl 2 2) NH 3 HBr CO 2 3) PCl 3 KCl CCl 4 4) H 2 S SO 2 LiF
48. In what series do all substances have a covalent polar bond?
1) Hcl, NaCl, Cl 2 2) O 2 H 2 O, CO 2 3) H 2 O, NH 3, CH 4 4) KBr, HBr, CO
49. In which row are listed substances only with an ionic type of bond:
1) F 2 O LiF SF 4 2) PCl 3 NaCl CO 2 3) KF Li 2 O BaCl 2 4) CaF 2 CH 4 CCl 4
50. A compound with an ionic bond is formed when interacting
1) CH 4 and O 2 2) NH 3 and HCl 3) C 2 H 6 and HNO 3 4) SO 3 and H 2 O
51. A hydrogen bond is formed between the molecules of 1) ethane 2) benzene 3) hydrogen 4) ethanol
52. What substance has hydrogen bonds? 1) Hydrogen sulfide 2) Ice 3) Hydrogen bromide 4) Benzene
53. Relationship formed between elements with serial numbers 15 and 53
1) ionic 2) metallic
3) covalent non-polar 4) covalent polar
54. Relationship formed between elements with serial numbers 16 and 20
1) ionic 2) metallic
3) covalent polar 4) hydrogen
55. A bond arises between the atoms of elements with serial numbers 11 and 17
1) metallic 2) ionic 3) covalent 4) donor-acceptor
56. Hydrogen bonds are formed between molecules
1) hydrogen 2) formaldehyde 3) acetic acid 4) hydrogen sulfide
57. In which row are the formulas of substances written only with a covalent polar bond?
1) Cl 2, NH 3, HCl 2) HBr, NO, Br 2 3) H 2 S, H 2 O, S 8 4) NI, H 2 O, PH 3
58. In what substance are there both ionic and covalent chemical bonds?
1) Sodium chloride 2) Hydrogen chloride 3) Sodium sulfate 4) Phosphoric acid
59. A chemical bond in a molecule has a more pronounced ionic character.
1) lithium bromide 2) copper chloride 3) calcium carbide 4) potassium fluoride
60. In what substance are all chemical bonds - covalent non-polar?
1) Diamond 2) Carbon monoxide (IV) 3) Gold 4) Methane
61. Establish a correspondence between the substance and the type of bond of atoms in this substance.
NAME OF THE SUBSTANCE TYPE OF COMMUNICATION
1) zinc A) ionic
2) nitrogen B) metal
3) ammonia B) covalent polar
4) calcium chloride D) covalent non-polar
62. Match
TYPE OF COMMUNICATION CONNECTION
1) ionic A) H 2
2) metal B) Va
3) covalent polar B) HF
4) covalent non-polar D) BaF 2
63. In what compound is the covalent bond between atoms formed by the donor-acceptor mechanism? 1) KCl 2) CCl 4 3) NH 4 Cl 4) CaCl 2
64. Indicate the molecule in which the binding energy is the highest: 1) N≡N 2) H-H 3) O=O 4) H-F
65. Indicate the molecule in which the chemical bond is the strongest: 1) HF 2) HCl 3) HBr 4) HI
Topics of the USE codifier: Covalent chemical bond, its varieties and mechanisms of formation. Characteristics of a covalent bond (polarity and bond energy). Ionic bond. Metal connection. hydrogen bond
Intramolecular chemical bonds
Let us first consider the bonds that arise between particles within molecules. Such connections are called intramolecular.
chemical bond between atoms of chemical elements has an electrostatic nature and is formed due to interactions of external (valence) electrons, in more or less degree held by positively charged nuclei bonded atoms.
The key concept here is ELECTRONEGNATIVITY. It is she who determines the type of chemical bond between atoms and the properties of this bond.
is the ability of an atom to attract (hold) external(valence) electrons. Electronegativity is determined by the degree of attraction of external electrons to the nucleus and depends mainly on the radius of the atom and the charge of the nucleus.
Electronegativity is difficult to determine unambiguously. L. Pauling compiled a table of relative electronegativity (based on the bond energies of diatomic molecules). The most electronegative element is fluorine with meaning 4 .
It is important to note that in different sources you can find different scales and tables of electronegativity values. This should not be frightened, since the formation of a chemical bond plays a role atoms, and it is approximately the same in any system.
If one of the atoms in the chemical bond A:B attracts electrons more strongly, then the electron pair is shifted towards it. The more electronegativity difference atoms, the more the electron pair is displaced.
If the electronegativity values of the interacting atoms are equal or approximately equal: EO(A)≈EO(V), then the shared electron pair is not displaced to any of the atoms: A: B. Such a connection is called covalent non-polar.
If the electronegativity of the interacting atoms differ, but not much (the difference in electronegativity is approximately from 0.4 to 2: 0,4<ΔЭО<2 ), then the electron pair is shifted to one of the atoms. Such a connection is called covalent polar .
If the electronegativity of the interacting atoms differ significantly (the difference in electronegativity is greater than 2: ΔEO>2), then one of the electrons almost completely passes to another atom, with the formation ions. Such a connection is called ionic.
The main types of chemical bonds are − covalent, ionic and metallic connections. Let's consider them in more detail.
covalent chemical bond
covalent bond – it's a chemical bond formed by formation of a common electron pair A:B . In this case, two atoms overlap atomic orbitals. A covalent bond is formed by the interaction of atoms with a small difference in electronegativity (as a rule, between two non-metals) or atoms of one element.
Basic properties of covalent bonds
- orientation,
- saturability,
- polarity,
- polarizability.
These bond properties affect the chemical and physical properties of substances.
Direction of communication characterizes the chemical structure and form of substances. The angles between two bonds are called bond angles. For example, in a water molecule, the H-O-H bond angle is 104.45 o, so the water molecule is polar, and in the methane molecule, the H-C-H bond angle is 108 o 28 ′.
Saturability is the ability of atoms to form a limited number of covalent chemical bonds. The number of bonds that an atom can form is called.
Polarity bonds arise due to the uneven distribution of electron density between two atoms with different electronegativity. Covalent bonds are divided into polar and non-polar.
Polarizability connections are the ability of bond electrons to be displaced by an external electric field(in particular, the electric field of another particle). The polarizability depends on the electron mobility. The farther the electron is from the nucleus, the more mobile it is, and, accordingly, the molecule is more polarizable.
Covalent non-polar chemical bond
There are 2 types of covalent bonding - POLAR and NON-POLAR .
Example . Consider the structure of the hydrogen molecule H 2 . Each hydrogen atom carries 1 unpaired electron in its outer energy level. To display an atom, we use the Lewis structure - this is a diagram of the structure of the external energy level of an atom, when electrons are denoted by dots. Lewis point structure models are a good help when working with elements of the second period.
H. + . H=H:H
Thus, the hydrogen molecule has one common electron pair and one H–H chemical bond. This electron pair is not displaced to any of the hydrogen atoms, because the electronegativity of hydrogen atoms is the same. Such a connection is called covalent non-polar .
Covalent non-polar (symmetrical) bond - this is a covalent bond formed by atoms with equal electronegativity (as a rule, the same non-metals) and, therefore, with a uniform distribution of electron density between the nuclei of atoms.
The dipole moment of nonpolar bonds is 0.
Examples: H 2 (H-H), O 2 (O=O), S 8 .
Covalent polar chemical bond
covalent polar bond is a covalent bond that occurs between atoms with different electronegativity (usually, different non-metals) and is characterized displacement common electron pair to a more electronegative atom (polarization).
The electron density is shifted to a more electronegative atom - therefore, a partial negative charge (δ-) arises on it, and a partial positive charge arises on a less electronegative atom (δ+, delta +).
The greater the difference in the electronegativity of atoms, the higher polarity connections and even more dipole moment . Between neighboring molecules and charges opposite in sign, additional attractive forces act, which increases strength connections.
Bond polarity affects the physical and chemical properties of compounds. The reaction mechanisms and even the reactivity of neighboring bonds depend on the polarity of the bond. The polarity of a bond often determines polarity of the molecule and thus directly affects such physical properties as boiling point and melting point, solubility in polar solvents.
Examples: HCl, CO 2 , NH 3 .
Mechanisms for the formation of a covalent bond
A covalent chemical bond can occur by 2 mechanisms:
1. exchange mechanism the formation of a covalent chemical bond is when each particle provides one unpaired electron for the formation of a common electron pair:
BUT . + . B= A:B
2. The formation of a covalent bond is such a mechanism in which one of the particles provides an unshared electron pair, and the other particle provides a vacant orbital for this electron pair:
BUT: + B= A:B
In this case, one of the atoms provides an unshared electron pair ( donor), and the other atom provides a vacant orbital for this pair ( acceptor). As a result of the formation of a bond, both electron energy decreases, i.e. this is beneficial for the atoms.
A covalent bond formed by the donor-acceptor mechanism, is not different by properties from other covalent bonds formed by the exchange mechanism. The formation of a covalent bond by the donor-acceptor mechanism is typical for atoms either with a large number of electrons in the external energy level (electron donors), or vice versa, with a very small number of electrons (electron acceptors). The valence possibilities of atoms are considered in more detail in the corresponding.
A covalent bond is formed by the donor-acceptor mechanism:
- in a molecule carbon monoxide CO(the bond in the molecule is triple, 2 bonds are formed by the exchange mechanism, one by the donor-acceptor mechanism): C≡O;
- in ammonium ion NH 4 +, in ions organic amines, for example, in the methylammonium ion CH 3 -NH 2 + ;
- in complex compounds, a chemical bond between the central atom and groups of ligands, for example, in sodium tetrahydroxoaluminate Na the bond between aluminum and hydroxide ions;
- in nitric acid and its salts- nitrates: HNO 3 , NaNO 3 , in some other nitrogen compounds;
- in a molecule ozone O 3 .
Main characteristics of a covalent bond
A covalent bond, as a rule, is formed between the atoms of non-metals. The main characteristics of a covalent bond are length, energy, multiplicity and directivity.
Chemical bond multiplicity
Chemical bond multiplicity - this is the number of shared electron pairs between two atoms in a compound. The multiplicity of the bond can be quite easily determined from the value of the atoms that form the molecule.
For example , in the hydrogen molecule H 2 the bond multiplicity is 1, because each hydrogen has only 1 unpaired electron in the outer energy level, therefore, one common electron pair is formed.
In the oxygen molecule O 2, the bond multiplicity is 2, because each atom has 2 unpaired electrons in its outer energy level: O=O.
In the nitrogen molecule N 2, the bond multiplicity is 3, because between each atom there are 3 unpaired electrons in the outer energy level, and the atoms form 3 common electron pairs N≡N.
Covalent bond length
Chemical bond length
is the distance between the centers of the nuclei of atoms that form a bond. It is determined by experimental physical methods. The bond length can be estimated approximately, according to the additivity rule, according to which the bond length in the AB molecule is approximately equal to half the sum of the bond lengths in the A 2 and B 2 molecules: 
The length of a chemical bond can be roughly estimated along the radii of atoms, forming a bond, or by the multiplicity of communication if the radii of the atoms are not very different.
With an increase in the radii of the atoms forming a bond, the bond length will increase.
For example
With an increase in the multiplicity of bonds between atoms (whose atomic radii do not differ, or differ slightly), the bond length will decrease.
For example . In the series: C–C, C=C, C≡C, the bond length decreases.
Bond energy
A measure of the strength of a chemical bond is the bond energy. Bond energy is determined by the energy required to break the bond and remove the atoms that form this bond to an infinite distance from each other.
The covalent bond is very durable. Its energy ranges from several tens to several hundreds of kJ/mol. The greater the bond energy, the greater the bond strength, and vice versa.
The strength of a chemical bond depends on the bond length, bond polarity, and bond multiplicity. The longer the chemical bond, the easier it is to break, and the lower the bond energy, the lower its strength. The shorter the chemical bond, the stronger it is, and the greater the bond energy.
For example, in the series of compounds HF, HCl, HBr from left to right the strength of the chemical bond decreases, because the length of the bond increases.
Ionic chemical bond
Ionic bond is a chemical bond based on electrostatic attraction of ions.
ions are formed in the process of accepting or giving away electrons by atoms. For example, the atoms of all metals weakly hold the electrons of the outer energy level. Therefore, metal atoms are characterized restorative properties the ability to donate electrons.
Example. The sodium atom contains 1 electron at the 3rd energy level. Easily giving it away, the sodium atom forms a much more stable Na + ion, with the electron configuration of the noble neon gas Ne. The sodium ion contains 11 protons and only 10 electrons, so the total charge of the ion is -10+11 = +1:
+11Na) 2 ) 8 ) 1 - 1e = +11 Na +) 2 ) 8
Example. The chlorine atom has 7 electrons in its outer energy level. To acquire the configuration of a stable inert argon atom Ar, chlorine needs to attach 1 electron. After the attachment of an electron, a stable chlorine ion is formed, consisting of electrons. The total charge of the ion is -1:
+17Cl) 2 ) 8 ) 7 + 1e = +17 Cl — ) 2 ) 8 ) 8
Note:
- The properties of ions are different from the properties of atoms!
- Stable ions can form not only atoms, but also groups of atoms. For example: ammonium ion NH 4 +, sulfate ion SO 4 2-, etc. Chemical bonds formed by such ions are also considered ionic;
- Ionic bonds are usually formed between metals and nonmetals(groups of non-metals);
The resulting ions are attracted due to electrical attraction: Na + Cl -, Na 2 + SO 4 2-.
Let us visually generalize difference between covalent and ionic bond types:
metal chemical bond
metal connection is the relationship that is formed relatively free electrons between metal ions forming a crystal lattice.
The atoms of metals on the outer energy level usually have one to three electrons. The radii of metal atoms, as a rule, are large - therefore, metal atoms, unlike non-metals, quite easily donate outer electrons, i.e. are strong reducing agents
Intermolecular interactions
Separately, it is worth considering the interactions that occur between individual molecules in a substance - intermolecular interactions . Intermolecular interactions are a type of interaction between neutral atoms in which new covalent bonds do not appear. The forces of interaction between molecules were discovered by van der Waals in 1869 and named after him. Van dar Waals forces. Van der Waals forces are divided into orientation, induction and dispersion . The energy of intermolecular interactions is much less than the energy of a chemical bond.
Orientation forces of attraction arise between polar molecules (dipole-dipole interaction). These forces arise between polar molecules. Inductive interactions is the interaction between a polar molecule and a non-polar one. A non-polar molecule is polarized due to the action of a polar one, which generates an additional electrostatic attraction.
A special type of intermolecular interaction is hydrogen bonds. - these are intermolecular (or intramolecular) chemical bonds that arise between molecules in which there are strongly polar covalent bonds - H-F, H-O or H-N. If there are such bonds in the molecule, then between the molecules there will be additional forces of attraction .
Mechanism of Education The hydrogen bond is partly electrostatic and partly donor-acceptor. In this case, an atom of a strongly electronegative element (F, O, N) acts as an electron pair donor, and hydrogen atoms connected to these atoms act as an acceptor. Hydrogen bonds are characterized orientation in space and saturation .
The hydrogen bond can be denoted by dots: H ··· O. The greater the electronegativity of an atom connected to hydrogen, and the smaller its size, the stronger the hydrogen bond. It is primarily characteristic of compounds fluorine with hydrogen , as well as to oxygen with hydrogen , less nitrogen with hydrogen .
Hydrogen bonds occur between the following substances:
— hydrogen fluoride HF(gas, solution of hydrogen fluoride in water - hydrofluoric acid), water H 2 O (steam, ice, liquid water):
— solution of ammonia and organic amines- between ammonia and water molecules;
— organic compounds in which O-H or N-H bonds: alcohols, carboxylic acids, amines, amino acids, phenols, aniline and its derivatives, proteins, solutions of carbohydrates - monosaccharides and disaccharides.
The hydrogen bond affects the physical and chemical properties of substances. Thus, the additional attraction between molecules makes it difficult for substances to boil. Substances with hydrogen bonds exhibit an abnormal increase in the boiling point.
For example As a rule, with an increase in molecular weight, an increase in the boiling point of substances is observed. However, in a number of substances H 2 O-H 2 S-H 2 Se-H 2 Te we do not observe a linear change in boiling points.
Namely, at boiling point of water is abnormally high - not less than -61 o C, as the straight line shows us, but much more, +100 o C. This anomaly is explained by the presence of hydrogen bonds between water molecules. Therefore, under normal conditions (0-20 o C), water is liquid by phase state.