Topics of the Unified State Examination codifier: Covalent chemical bond, its varieties and mechanisms of formation. Characteristics of covalent bonds (polarity and bond energy). Ionic bond. Metal connection. Hydrogen bond
Intramolecular chemical bonds
First, let's look at the bonds that arise between particles within molecules. Such connections are called intramolecular.
Chemical bond between atoms chemical elements has an electrostatic nature and is formed due to interaction of external (valence) electrons, in more or less degree held by positively charged nuclei bonded atoms.
The key concept here is ELECTRONEGATIVITY. It is this that determines the type of chemical bond between atoms and the properties of this bond.
is the ability of an atom to attract (hold) external(valence) electrons. Electronegativity is determined by the degree of attraction of outer electrons to the nucleus and depends primarily on the radius of the atom and the charge of the nucleus.
Electronegativity is difficult to determine unambiguously. L. Pauling compiled a table of relative electronegativities (based on the bond energies of diatomic molecules). The most electronegative element is fluorine with meaning 4 .
It is important to note that in different sources you can find different scales and tables of electronegativity values. This should not be alarmed, since the formation of a chemical bond plays a role atoms, and it is approximately the same in any system.
If one of the atoms in the A:B chemical bond attracts electrons more strongly, then the electron pair moves towards it. The more electronegativity difference atoms, the more the electron pair shifts.
If the electronegativities of interacting atoms are equal or approximately equal: EO(A)≈EO(B), then the common electron pair does not shift to any of the atoms: A: B. This connection is called covalent nonpolar.
If the electronegativities of the interacting atoms differ, but not greatly (the difference in electronegativity is approximately from 0.4 to 2: 0,4<ΔЭО<2 ), then the electron pair is displaced to one of the atoms. This connection is called covalent polar .
If the electronegativities of interacting atoms differ significantly (the difference in electronegativity is greater than 2: ΔEO>2), then one of the electrons is almost completely transferred to another atom, with the formation ions. This connection is called ionic.
Basic types of chemical bonds − covalent, ionic And metal communications. Let's take a closer look at them.
Covalent chemical bond
Covalent bond – it's a chemical bond , formed due to formation of a common electron pair A:B . Moreover, two atoms overlap atomic orbitals. A covalent bond is formed by the interaction of atoms with a small difference in electronegativity (usually between two non-metals) or atoms of one element.
Basic properties of covalent bonds
- focus,
- saturability,
- polarity,
- polarizability.
These bonding properties influence the chemical and physical properties of substances.
Communication direction characterizes the chemical structure and form of substances. The angles between two bonds are called bond angles. For example, in a water molecule the bond angle H-O-H is 104.45 o, therefore the water molecule is polar, and in a methane molecule the bond angle H-C-H is 108 o 28′.
Saturability is the ability of atoms to form a limited number of covalent chemical bonds. The number of bonds that an atom can form is called.
Polarity bonding occurs due to the uneven distribution of electron density between two atoms with different electronegativity. Covalent bonds are divided into polar and nonpolar.
Polarizability connections are the ability of bond electrons to shift under the influence of an external electric field(in particular, the electric field of another particle). Polarizability depends on electron mobility. The further the electron is from the nucleus, the more mobile it is, and accordingly the molecule is more polarizable.
Covalent nonpolar chemical bond
There are 2 types of covalent bonding – POLAR And NON-POLAR .
Example . Let's consider the structure of the hydrogen molecule H2. Each hydrogen atom in its outer energy level carries 1 unpaired electron. To display an atom we use the Lewis structure - this is a diagram of the structure of the external energy level atom, when electrons are indicated by dots. Lewis point structure models are quite helpful when working with elements of the second period.
H. + . H = H:H
Thus, a hydrogen molecule has one shared electron pair and one H–H chemical bond. This electron pair does not shift to any of the hydrogen atoms, because Hydrogen atoms have the same electronegativity. This connection is called covalent nonpolar .
Covalent nonpolar (symmetric) bond is a covalent bond formed by atoms with equal electronegativity (usually the same nonmetals) and, therefore, with a uniform distribution of electron density between the nuclei of atoms.
The dipole moment of non-polar bonds is 0.
Examples: H 2 (H-H), O 2 (O=O), S 8.
Covalent polar chemical bond
Covalent polar bond is a covalent bond that occurs between atoms with different electronegativity (usually, various non-metals) and is characterized displacement shared electron pair to a more electronegative atom (polarization).
The electron density is shifted to the more electronegative atom - therefore, a partial negative charge (δ-) appears on it, and a partial positive charge (δ+, delta +) appears on the less electronegative atom.
The greater the difference in electronegativity of atoms, the higher polarity connections and more dipole moment . Additional attractive forces act between neighboring molecules and charges of opposite sign, which increases strength communications.
Bond polarity affects the physical and chemical properties of compounds. The reaction mechanisms and even the reactivity of neighboring bonds depend on the polarity of the bond. The polarity of the connection often determines molecule polarity and thus directly affects such physical properties as boiling point and melting point, solubility in polar solvents.
Examples: HCl, CO 2, NH 3.
Mechanisms of covalent bond formation
Covalent chemical bonds can occur by 2 mechanisms:
1. Exchange mechanism the formation of a covalent chemical bond is when each particle provides one unpaired electron to form a common electron pair:
A . + . B= A:B
2. Covalent bond formation is a mechanism in which one of the particles provides a lone pair of electrons, and the other particle provides a vacant orbital for this electron pair:
A: + B= A:B
In this case, one of the atoms provides a lone pair of electrons ( donor), and the other atom provides a vacant orbital for that pair ( acceptor). As a result of the formation of both bonds, the energy of the electrons decreases, i.e. this is beneficial for the atoms.
A covalent bond formed by a donor-acceptor mechanism is not different in properties from other covalent bonds formed by the exchange mechanism. The formation of a covalent bond by the donor-acceptor mechanism is typical for atoms either with a large number of electrons at the external energy level (electron donors), or, conversely, with a very small number of electrons (electron acceptors). The valence capabilities of atoms are discussed in more detail in the corresponding section.
A covalent bond is formed by a donor-acceptor mechanism:
- in a molecule carbon monoxide CO(the bond in the molecule is triple, 2 bonds are formed by the exchange mechanism, one by the donor-acceptor mechanism): C≡O;
- V ammonium ion NH 4 +, in ions organic amines, for example, in the methylammonium ion CH 3 -NH 2 + ;
- V complex compounds, a chemical bond between the central atom and ligand groups, for example, in sodium tetrahydroxoaluminate Na bond between aluminum and hydroxide ions;
- V nitric acid and its salts- nitrates: HNO 3, NaNO 3, in some other nitrogen compounds;
- in a molecule ozone O3.
Basic characteristics of covalent bonds
Covalent bonds typically form between nonmetal atoms. The main characteristics of a covalent bond are length, energy, multiplicity and directionality.
Multiplicity of chemical bond
Multiplicity of chemical bond - This number of shared electron pairs between two atoms in a compound. The multiplicity of a bond can be determined quite easily from the values of the atoms that form the molecule.
For example , in the hydrogen molecule H 2 the bond multiplicity is 1, because Each hydrogen has only 1 unpaired electron in its outer energy level, hence one shared electron pair is formed.
In the O 2 oxygen molecule, the bond multiplicity is 2, because Each atom at the outer energy level has 2 unpaired electrons: O=O.
In the nitrogen molecule N2, the bond multiplicity is 3, because between each atom there are 3 unpaired electrons at the outer energy level, and the atoms form 3 common electron pairs N≡N.
Covalent bond length
Chemical bond length
is the distance between the centers of the nuclei of the atoms forming the bond. It is determined by experimental physical methods. The bond length can be estimated approximately using the additivity rule, according to which the bond length in the AB molecule is approximately equal to half the sum of the bond lengths in molecules A 2 and B 2: 
The length of a chemical bond can be roughly estimated by atomic radii forming a bond, or by communication multiplicity, if the radii of the atoms are not very different.
As the radii of the atoms forming a bond increase, the bond length will increase.
For example
As the multiplicity of bonds between atoms increases (the atomic radii of which do not differ or differ only slightly), the bond length will decrease.
For example . In the series: C–C, C=C, C≡C, the bond length decreases.
Communication energy
A measure of the strength of a chemical bond is the bond energy. Communication energy determined by the energy required to break a bond and remove the atoms forming that bond to an infinitely large distance from each other.
A covalent bond is very durable. Its energy ranges from several tens to several hundred kJ/mol. The higher the bond energy, the greater the bond strength, and vice versa.
The strength of a chemical bond depends on the bond length, bond polarity, and bond multiplicity. The longer a chemical bond, the easier it is to break, and the lower the bond energy, the lower its strength. The shorter the chemical bond, the stronger it is, and the greater the bond energy.
For example, in the series of compounds HF, HCl, HBr from left to right, the strength of the chemical bond decreases, because The connection length increases.
Ionic chemical bond
Ionic bond is a chemical bond based on electrostatic attraction of ions.
Ions are formed in the process of accepting or donating electrons by atoms. For example, atoms of all metals weakly hold electrons from the outer energy level. Therefore, metal atoms are characterized by restorative properties- ability to donate electrons.
Example. The sodium atom contains 1 electron at energy level 3. By easily giving it up, the sodium atom forms the much more stable Na + ion, with the electron configuration of the noble gas neon Ne. The sodium ion contains 11 protons and only 10 electrons, so the total charge of the ion is -10+11 = +1:
+11Na) 2 ) 8 ) 1 - 1e = +11 Na +) 2 ) 8
Example. A chlorine atom in its outer energy level contains 7 electrons. To acquire the configuration of a stable inert argon atom Ar, chlorine needs to gain 1 electron. After adding an electron, a stable chlorine ion 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 each other metals And nonmetals(non-metal groups);
The resulting ions are attracted due to electrical attraction: Na + Cl -, Na 2 + SO 4 2-.
Let us visually summarize difference between covalent and ionic bond types:
Metal chemical bond
Metal connection is a connection that is formed relatively free electrons between metal ions, forming a crystal lattice.
Metal atoms are usually located on the outer energy level one to three electrons. The radii of metal atoms, as a rule, are large - therefore, metal atoms, unlike non-metals, give up their outer electrons quite easily, i.e. are strong reducing agents
Intermolecular interactions
Separately, it is worth considering the interactions that arise between individual molecules in a substance - intermolecular interactions . Intermolecular interactions are a type of interaction between neutral atoms in which no new covalent bonds appear. The forces of interaction between molecules were discovered by Van der Waals in 1869, and named after him Van dar Waals forces. Van der Waals forces are divided into orientation, induction And dispersive . The energy of intermolecular interactions is much less than the energy of chemical bonds.
Orientation forces of attraction occur between polar molecules (dipole-dipole interaction). These forces occur between polar molecules. Inductive interactions is the interaction between a polar molecule and a non-polar one. A nonpolar molecule is polarized due to the action of a polar one, which generates additional electrostatic attraction.
A special type of intermolecular interaction is hydrogen bonds. - these are intermolecular (or intramolecular) chemical bonds that arise between molecules that have highly polar covalent bonds - H-F, H-O or H-N. If there are such bonds in a molecule, then between the molecules there will be additional attractive forces .
Education mechanism hydrogen bonding is partly electrostatic and partly donor-acceptor. In this case, the electron pair donor is an atom of a strongly electronegative element (F, O, N), and the acceptor is the hydrogen atoms connected to these atoms. Hydrogen bonds are characterized by focus in space and saturation
Hydrogen bonds can be indicated by dots: H ··· O. The greater the electronegativity of the atom connected to hydrogen, and the smaller its size, the stronger the hydrogen bond. It is typical primarily for connections fluorine with hydrogen , as well as to oxygen and hydrogen , 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 the bonds are O-H or N-H: alcohols, carboxylic acids, amines, amino acids, phenols, aniline and its derivatives, proteins, solutions of carbohydrates - monosaccharides and disaccharides.
Hydrogen bonding affects the physical and chemical properties of substances. Thus, additional attraction between molecules makes it difficult for substances to boil. Substances with hydrogen bonds exhibit an abnormal increase in boiling point.
For example As a rule, with increasing molecular weight, an increase in the boiling point of substances is observed. However, in a number of substances H 2 O-H 2 S-H 2 Se-H 2 Te we do not observe a linear change in boiling points.
Namely, at water boiling point is abnormally high - no less than -61 o C, as the straight line shows us, but much more, +100 o C. This anomaly is explained by the presence of hydrogen bonds between water molecules. Therefore, under normal conditions (0-20 o C) water is liquid by phase state.
Atom, molecule, nuclear properties
Structure of the fluorine atom.
At the center of the atom is a positively charged nucleus. There are 9 negatively charged electrons spinning around.
Electronic formula: 1s2;2s2;2p5
m prot. = 1.00783 (amu)
m neutr.= 1.00866 (a.m.u.)
m proton = m electron
Fluorine isotopes.
Isotope: 18F
a brief description of: 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 = 931.5(9*m pr.+9*m neutron-M(F18)) = 138.24 (MEV)E specific = E bonds/N nucleons = 7.81 (MEV/nucleon)
Alpha decay is impossible Beta minus decay is impossible Positron decay: F(Z=9,M=18)-->O(Z=8,M=18)+e(Z=+1,M=0)+0.28( MeV)Electron capture: F(Z=9,M=18)+e(Z=-1,M=0)-->O(Z=8,M=18)+1.21(MeV)
Isotope: 19F
Brief characteristics: 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 (versus 493 kJ/mol for O2 and 242 kJ/mol for C12). Fluorine atoms have significant electron affinity and relatively small sizes. Therefore, their valence bonds with atoms of other elements turn out to be stronger than similar bonds of other metalloids (for example, energy H-F connections is - 564 kJ/mol versus 460 kJ/mol for N-O connections and 431 kJ/mol for the H-C1 bond).
F-F communication characterized by a nuclear distance of 1.42 A. For the thermal dissociation of fluorine, the following data were obtained by calculation:
Temperature, °C 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 its 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 a cost 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 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 is often much more energetic than with many metals. For example, silicon, phosphorus and sulfur ignite in fluorine gas. Amorphous carbon (charcoal) behaves similarly, while graphite reacts only at red heat. Fluorine does not combine directly with nitrogen and oxygen.
Fluorine removes hydrogen from hydrogen compounds of other elements. Most oxides are decomposed by it, displacing 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 oxygen gas, 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 known as oxygen fluoride - ОF2) 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 + F2О. The following reactions are also characteristic of fluorine:
H2 + F2 = 2HF (with explosion)
Chemistry preparation for cancer and DPA
Comprehensive edition
PART AND
GENERAL CHEMISTRY
CHEMISTRY OF ELEMENTS
HALOGENS
Simple substances
Chemical properties of fluorine
Fluorine is the strongest oxidizing agent in nature. It does not react directly only with helium, neon and argon.
During the reaction with metals, fluorides, ionic compounds, are formed:
Fluorine reacts vigorously with many nonmetals, even with some inert gases:
Chemical properties of Chlorine. Interaction with complex substances
Chlorine is a stronger oxidizer than bromine or iodine, so chlorine displaces heavy halogens from their salts:
Dissolving in water, chlorine partially reacts with it, resulting in the formation of two acids: chloride and hypochlorite. In this case, one Chlorine atom increases the oxidation state, and the other atom decreases it. Such reactions are called disproportionation reactions. Disproportionation reactions are self-healing-self-oxidation reactions, i.e. reactions in which one element exhibits the properties of both an oxidizer and a reducing agent. During disproportionation, compounds are simultaneously formed in which the element is in a more oxidized and reduced state compared to the original one. The oxidation state of the Chlorine atom in the hypochlorite acid molecule is +1:
The interaction of chlorine with alkali solutions proceeds similarly. In this case, two salts are formed: chloride and hypochlorite.
Chlorine interacts with various oxides:
Chlorine oxidizes some salts in which the metal is not in its maximum oxidation state:
Molecular chlorine reacts with many organic compounds. In the presence of ferrum(III) chloride as a catalyst, chlorine reacts with benzene to form chlorobenzene, and when irradiated with light, the same reaction results in the formation of hexachlorocyclohexane:
Chemical properties of bromine and iodine
Both substances react with hydrogen, fluorine and alkalis:
Iodine is oxidized by various strong oxidizing agents:
Methods for extracting simple substances
Fluoride extraction
Since fluorine is the strongest chemical oxidizer, it is impossible to isolate it using chemical reactions from compounds in free form, and therefore fluorine is extracted by the physicochemical method - electrolysis.
To extract fluorine, potassium fluoride melt and nickel electrodes are used. Nickel is used due to the fact that the metal surface is passivated by fluorine due to the formation of insoluble
NiF2, therefore, the electrodes themselves are not destroyed by the substance that is released on them:Chlorine extraction
Chlorine is produced on an industrial scale by electrolysis of a sodium chloride solution. As a result of this process, sodium hydroxide is also produced:
In no large quantities Chlorine is produced from the oxidation of hydrogen chloride solution using various methods:
Chlorine is a very important product of the chemical industry.
Its global production amounts to millions of tons.
Extracts of bromine and iodine
For industrial use, bromine and iodine are obtained from the oxidation of bromides and iodides, respectively. For oxidation, molecular chlorine, concentrated sulfate acid or manganese dioxide are most often used:
Fluorine and some of its compounds are used as an oxidizer for rocket fuel. Large quantities of fluorine are used to extract various refrigerants (freons) and some polymers that are characterized by chemical and thermal resistance (Teflon and some others). Fluorine is used in nuclear technology to separate uranium isotopes.
Most chlorine is used to produce hydrochloric acid, and also as an oxidizing agent for the production of other halogens. In industry it is used to bleach fabrics and paper. In larger quantities than fluorine, it is used for the production of polymers (PVC and others) and refrigerants. Chlorine is used to disinfect drinking water. It is also needed for the extraction of certain solvents, such as chloroform, methylene chloride, and carbon tetrachloride. It is also used for the production of many substances, such as potassium chlorate (Berthollet salt), bleach and many other compounds containing Chlorine atoms.
Bromine and iodine are not used in industry on the same scale as chlorine or fluorine, but the use of these substances is increasing every year. Bromine is used in the production of various sedative medications. Iodine is used in the manufacture of antiseptic drugs. Bromine and Iodine compounds are widely used in the quantitative analysis of substances. Some metals are purified with the help of iodine (this process is called iodine refining), such as titanium, vanadium and others.
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 (versus 493 kJ/mol for O 2 and 242 kJ/mol for C 12). Fluorine atoms have significant electron affinity and relatively small sizes. 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 its 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 a cost 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. The covalent radius of fluorine is usually taken to be 71 pm (i.e., half the internuclear distance in the F 2 molecule).
A chemical bond 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 that interact with each other in a certain way. In other words, a chemical bond is established between atoms. When a chemical bond is formed, energy is always released, i.e., the energy of the resulting particle must be less than the total energy of the original 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 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 expressed by the German scientist W. Kossel (1916).
Another model of communication is the sharing of electrons by two atoms, which also results in the formation of stable electronic configurations. Such a bond is called covalent; its theory began to be developed in 1916 by the American scientist G. Lewis.
The common point in both theories was the formation of particles with a stable electronic configuration coinciding with the electronic configuration of the noble gas.
For example, during the formation of lithium fluoride, ion mechanism communication education. The lithium atom (3 Li 1s 2 2s 1) loses an electron and becomes 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 electron configuration of neon. Electrostatic attraction occurs 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) find themselves in the field of action of both nuclei - the hydrogen atom and the fluorine atom. In this way, a common electron pair appears, 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 (electronic configuration of the helium atom), and eight electrons of the outer energy level are now associated with the fluorine nucleus (electronic configuration of the neon atom):
It is indicated by one line between the symbols of the elements: H-F.A bond made through one pair of electrons is called a single bond.
The formation of two-electron shells between 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 sharing electrons (covalent bond) is called the octet rule.
There are, however, compounds that do not meet 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):
Most d-element compounds do not follow the octet rule either.
In all the examples presented 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 from each hydrogen atom, resulting in each atom acquiring a stable electronic configuration of two electrons. An octet is formed when molecules of other simple substances, for example fluorine, are formed:
The formation of a chemical bond can also be carried out by sharing 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 is formed (three generalized pairs of electrons).
For example, when a nitrogen molecule N2 is formed, a chemical bond is formed by sharing six electrons: three unpaired p electrons from each atom. To achieve the 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 N2 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 charge separation does not occur between atoms, this type of covalent bond is called nonpolar. A heteroatomic bond is always polar to one degree or another, 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 maximum electron density is displaced acquires a partial positive charge (denoted σ+). Electrically neutral particles in which the centers of partial negative and partial positive charges do not coincide in space are called dipoles. Bond polarity 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 pp.: ISBN 978-5-9704-1570-2. [With. 32-35]
In 1916, the first extremely simplified theories of the structure of molecules were proposed, which used electronic concepts: the theory of the American physical chemist G. Lewis (1875-1946) and the German scientist W. Kossel. According to Lewis's 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 line, they began to draw an electron pair forming 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 absolute value charge q by the distance between two opposite charges r:
The dipole moment m of a diatomic molecule can be determined in two ways. Firstly, since the molecule is electrically neutral, the total positive charge of the molecule Z" is known (it equal to the sum charges of atomic nuclei: Z" = ZA + ZB). Knowing the internuclear distance re, you can determine the location of the center of gravity of the positive charge of the molecule. The value m of the molecule is found from 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 6.4H 10-30 ClH m, internuclear H-F distance equals 0.917H 10-10 m. Calculation of q" gives: q" = 0.4 elementary charge (i.e. electron charge). Once an excess negative charge appears on the fluorine atom, it means that the electron pair forming a chemical bond in the HF molecule is shifted towards the fluorine atom. This chemical bond is called a polar covalent bond. Molecules of type A2 do not have a dipole moment. The chemical bonds that these molecules form are called covalent nonpolar bonds.
Kossel theory was proposed to describe molecules formed by active metals (alkali and alkaline earth) and active nonmetals (halogens, oxygen, nitrogen). The outer valence electrons of metal atoms are furthest away from the nucleus of the atom and are therefore relatively weakly held by the metal atom. For atoms of chemical elements located in the same row of the Periodic Table, when moving from left to right, the charge of the nucleus increases all the time, and additional electrons are located in the same electronic layer. This leads to the fact that the outer electron shell is compressed and the electrons are held more and more firmly in the atom. Therefore, in the MeX molecule it becomes possible to move the weakly retained outer valence electron of the metal with an energy expenditure equal to the ionization potential into the valence electron shell of a 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 was 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 nonmetal 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 electrostatically interacts with the non-metal anions closest to it, then with metal cations, etc. That is, in ionic crystals, chemical bonds are delocalized and each ion ultimately interacts with all other ions included in the crystal, which is a giant molecule.
Along with clearly defined characteristics of atoms, such as 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. First, let us consider data on the first ionization potential and electron affinity for elements of the first three periods.
Regularities in ionization potentials and electron affinities are fully explained by the structure of the valence electron shells of atoms. The electron affinity of an isolated nitrogen atom is much lower 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 by introducing “electronegativity” as the ability of atoms of chemical elements to displace an electron pair towards themselves when forming covalent polar bonds. The electronegativity scale for chemical elements was proposed by L. Pauling. He attributed the highest electronegativity in conventional dimensionless units to fluorine - 4.0, oxygen - 3.5, chlorine and nitrogen - 3.0, bromine - 2.8. The nature of the change in electronegativity of atoms fully corresponds to the laws expressed in the Periodic Table. Therefore, the application of the concept " electronegativity“simply translates into another language those patterns in changes in the properties of metals and non-metals that are already reflected in the Periodic Table.
Many metals in the solid state are almost perfectly formed crystals. At the lattice sites in a crystal there are atoms or positive ions of metals. The electrons of those metal atoms from which positive ions were formed, in the form of an electron gas, are located 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 chemical bond, which is carried out by shared electrons in a metal crystal, is calledmetal 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. Metal atoms in the nodes of the crystal lattice are always in motion - they perform oscillatory movements. This complex movement can be decomposed into three simple oscillatory movements in three mutually perpendicular planes. Each oscillatory motion 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 vibrational motion of atoms is equal to R - the Universal Gas Constant. Three independent vibrational movements 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 turn into a molten state. With further heating, the metals evaporate. In vapor, many metals exist in the form of Me2 molecules. In these molecules, metal atoms are capable of forming covalent nonpolar bonds.
Fluorine is a chemical element (symbol F, atomic number 9), a non-metal that belongs to the group of halogens. It is the most active and electronegative substance. At normal temperature and pressure, the fluorine molecule is pale yellow in color with the formula F 2 . Like other halides, molecular fluorine is very dangerous and causes severe chemical burns upon contact with skin.
Usage
Fluorine and its compounds are widely used, including for the production of pharmaceuticals, agrochemicals, fuels and lubricants and textiles. is used for glass etching, and fluorine plasma is used for the production of 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 18F isotope is a source of positrons for medical imaging using positron emission tomography, and uranium hexafluoride is used to separate uranium isotopes and produce them for nuclear power plants.
History of discovery
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 clean required metal. Therefore, fluorine got its Latin name from the word fluere (“to flow”).
In 1670, glassblower Heinrich Schwanhard discovered that glass was etched by calcium fluoride (fluorspar) treated with acid. Karl Scheele and many later researchers, including Humphry Davy, Joseph-Louis Gay-Lussac, Antoine Lavoisier, Louis Thénard, experimented with hydrofluoric acid (HF), which was easily prepared by treating CaF with concentrated sulfuric acid.
Eventually, it became clear that HF contained a previously unknown element. This substance, however, due to its excessive reactivity, could not be isolated for many years. Not only is it difficult to separate from compounds, but it immediately reacts with their other components. Isolating 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 succeeded in isolating fluorine by electrolysis of a mixture of molten potassium fluorides and hydrofluoric acid. For this he was awarded Nobel Prize 1906 in the field of 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 creation stages atomic bomb as part of the Manhattan Project. Fluorine was used to produce uranium hexafluoride (UF 6), which in turn was used to separate two isotopes, 235 U and 238 U. Today, UF 6 gas is needed to produce enriched uranium for nuclear power.
The most important properties of fluorine
On the periodic table, the element is at the top of group 17 (formerly group 7A), which is called the halogen element. 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, which is detected in a concentration of 20 nl per liter of volume. As the most reactive and electronegative of all the elements, it easily forms compounds with most of them. Fluorine is too reactive to exist in 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 equally 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 fine metals and glass, burn with a bright flame in a stream of fluorine gas. 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 processing and transportation are now available. The element can be stored in containers made of steel or monel (a nickel-rich alloy), since fluorides form on the surface of these materials, which prevent further reaction.
Fluorides are substances in which fluoride 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 separate into ions. Other forms of fluorine are complexes, for example, -, 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 effects
Fluoride 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 dental caries, according to the National Research Council of the US National Academy of Sciences. On the other hand, excess fluoride accumulation can lead to fluorosis, which manifests itself as mottled teeth. This effect is usually observed in areas where the content of this chemical element in drinking water exceeds the concentration of 10 ppm.
Elemental fluorine and fluoride salts are toxic and should be handled with great care. Contact with skin or eyes should be carefully avoided. It produces a reaction with the skin that quickly penetrates tissue and reacts with calcium in the bones, damaging them permanently.
Fluorine in the environment
The annual world production of the fluorite mineral is about 4 million tons, and the total capacity of explored deposits is within 120 million tons. The main mining areas for 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 enter the air through 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 approximately 330 ppm. Hydrogen fluoride can be released into the air as a result of combustion processes in industry. Fluorides that are in the air eventually fall out onto the ground or into the water. When fluoride bonds with very small particles, it can remain in the air for a long period of time.
In the atmosphere, 0.6 ppb of this chemical element is present in the form of salt fog and organic chlorine compounds. In urban environments, concentrations reach 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). Fluorides of krypton and radon have also been obtained. Another compound is argon fluorohydride, which is stable only at extremely low temperatures.
Industrial Application
In 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 for etching 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 necessary for the production of halogenated alkanes (halons), which in turn were widely used in air conditioning and refrigeration systems. This use of chlorofluorocarbons was later 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 substance that causes Greenhouse effect. Without fluorine, low-friction plastics such as Teflon cannot be produced. Many anesthetics (eg, sevoflurane, desflurane, and isoflurane) are hydrofluorocarbon derivatives. Sodium hexafluoroaluminate (cryolite) is used in the electrolysis of aluminum.
Fluoride compounds, including NaF, are used in toothpastes to prevent tooth decay. These substances are added to municipal water supplies to fluoridate the water, but the practice is considered controversial due to its effects on human health. At higher concentrations, NaF is used as an insecticide, especially to control cockroaches.
In the past, fluorides were 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 the chemical element are as follows:
- Atomic mass 18.9984032 g/mol.
- The electronic configuration is 1s 2 2s 2 2p 5.
- Oxidation state -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.
Chemical bonding refers to the electrical forces of attraction that hold particles together. Every 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 feature, in contrast to the own, lone electron pairs of atoms, for example:
The chemical bond is called covalent, if it is formed by sharing a pair of electrons with 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 nonpolar, since each fluorine atom electron density is the same in electronic formula molecules can be conditionally divided equally between them:
In the hydrogen chloride molecule HCl, the chemical bond is already polar, since the electron density on the chlorine atom (an element with higher electronegativity) is significantly 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 mechanism of bond formation is called exchange or equivalent.
According to another mechanism, the same covalent H – H bond occurs when the electron pair of the hydride ion H is shared by the hydrogen cation H +:
H + + (:H) - > H – H
The H+ cation in this case is called acceptor a anion H – donor electron pair. The mechanism of covalent bond formation will be donor-acceptor, or coordination.
Single bonds (H – H, F – F, H – CI, H – N) are called a-bonds, they determine the geometric shape of molecules.
Double and triple bonds () contain one?-component and one or two?-components; The ?-component, which is the main one and conditionally formed first, is always stronger than the ?-components.
The physical (actually measurable) characteristics of a chemical bond are its energy, length and polarity.
Chemical bond energy (E sv) is the heat that is released during the formation of a given 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 (lсв) – 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 the 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. Real electric charges on atoms in a covalent bond is always less in value than the oxidation states of the elements, but 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).
Molecular polarity 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 complex substances, if their geometric shape symmetrical.
For example, CO 2, BF 3 and CH 4 molecules have the following directions of equal (in length) bond vectors:
When adding bond vectors, their sum always goes to zero, and the molecules as a whole are nonpolar, although they contain polar bonds.
Polar (p> O) will be:
A) diatomic molecules complex substances, since they contain only polar bonds;
b) polyatomic molecules complex 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, in the molecules NH 3, H 2 O, HNO 3 and HCN.
Complex ions, for example NH 4 +, SO 4 2- and NO 3 -, cannot be dipoles in principle; they carry only one (positive or negative) charge.
Ionic bond occurs during the electrostatic attraction of cations and anions with almost no sharing of a pair of electrons, for example between K + and I -. The potassium atom has a lack of electron density, while the iodine atom has an excess. This connection is considered extreme a case of a covalent bond, since the pair of electrons is practically in the possession of the anion. This 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 at room conditions are crystalline substances that combine common nameionic crystals(crystals built from cations and anions).
Another type of connection is known, called metal bond, in which valence electrons are so loosely held by metal atoms that they actually do not belong to specific atoms.
Metal atoms, 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 whose lattice sites there are atoms or molecules, respectively. Examples: diamond and graphite are crystals with an atomic lattice, iodine I 2 and carbon dioxide CO 2 (dry ice) are 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 is 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 spent on breaking these bonds, and therefore the melting temperatures (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; important role Hydrogen bonding plays a role in biological processes.
Examples of Part A tasks1. 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 the substance
5. Multiple bonds exist in molecules
6. Particles called radicals are
7. One of the bonds is formed by a donor-acceptor mechanism in a 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. 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. Crystal lattice of matter
13. Ba(OH) 2
1) metal
The work contains tasks on chemical bonds.
Pugacheva Elena Vladimirovna
Description of the development
6. Covalent nonpolar 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) metal
15. Three common electron pairs form a covalent bond in a molecule
16. Hydrogen bonds form 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)СF 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 table D.I. Mendeleev form compounds with ionic chemical bonds of the composition 1) LiF 2) CO 2 3) Al 2 O 3 4) BaS
1) ionic 2) metal
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) metal
1) ionic 2) metal
NAME OF SUBSTANCE TYPE OF COMMUNICATION
1) zinc A) ionic
2) nitrogen B) metal
62. Match
COMMUNICATION TYPE CONNECTION
1) ionic A) H 2
2) metal B) Va
3) covalent polar B) HF
66. The strongest chemical bond occurs 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 , F 2
Let's look at tasks No. 3 from Unified State Exam options for 2016.
Tasks with solutions.
Task No. 1.
Compounds with a covalent nonpolar 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 a series in which there will only be simple substances, since a covalent nonpolar bond is formed only between atoms of the same element. The correct answer is 1.
Task No. 2.
Substances with covalent polar bonds are listed in the following 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 No. 3.
Hydrogen bonding is characteristic of
1. Alkanov 2. Arenov 3. Alcohols 4. Alkinov
Explanation: A hydrogen bond is formed between a hydrogen ion and an electronegative ion. Among those listed, only alcohols have such a set.
The correct answer is 3.
Task No. 4.
Chemical bond between water molecules
1. Hydrogen
2. Ionic
3. Covalent polar
4. Covalent nonpolar
Explanation: A polar covalent bond is formed between the O and H atoms in water, since these are two non-metals, but there is a hydrogen bond between water molecules. The correct answer is 1.
Task No. 5.
Each of the two substances has only covalent bonds:
1. CaO and C3H6
2. NaNO3 and CO
3. N2 and K2S
4. CH4 and SiO2
Explanation: connections must consist only of non-metals, that is the correct answer is 4.
Task No. 6.
A substance with a polar covalent bond is
1. O3 2. NaBr 3. NH3 4. MgCl2
Explanation: A polar covalent bond is formed between atoms of different nonmetals. The correct answer is 3.
Task No. 7.
A nonpolar covalent bond is characteristic of each of 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 No. 8.
What chemical bond is formed between atoms of elements with atomic numbers 9 and 19?
1. Ionic
2. Metal
3. Covalent polar
4. Covalent nonpolar
Explanation: these are the 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 No. 9.
A substance with an ionic type of bond corresponds to the formula
1. NH3 2. HBr 3. CCl4 4. KCl
Explanation: an ionic bond is formed between a metal atom and a non-metal atom, that is the correct answer is 4.
Task No. 10.
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 solution.
1. Hydrogen bonds form between molecules
1. Hydrofluoric acid
2. Methane chloride
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 nonpolar 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 nonpolar bond is characteristic of each of 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. Covalent nonpolar bond is characteristic of
1. I2 2. NO 3. CO 4. SiO2
9. A substance with a polar covalent bond is
1. Cl2 2. NaBr 3. H2S 4. MgCl2
10. A covalent nonpolar bond is characteristic of each of two substances:
1. Hydrogen and chlorine
2. Water and diamond
3. Copper and nitrogen
4. Bromine and methane
This note uses tasks from the 2016 Unified State Exam collection edited by A.A. Kaverina.
A4 Chemical bond.
Chemical bond: covalent (polar and non-polar), ionic, metallic, hydrogen. Methods for forming covalent bonds. Characteristics of a covalent bond: length and bond energy. Formation of 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 is respectively
1) ionic and covalent polar
2) covalent polar and ionic
3) covalent nonpolar and metallic
4) covalent nonpolar and ionic
2. Substances with only ionic bonds are listed in the following 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 which series do all substances have a polar covalent 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 series are the formulas of substances with only a polar covalent bond written?
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. Covalent nonpolar bond is characteristic of
1) Cl 2 2) SO3 3) CO 4) SiO 2
7. A substance with a polar covalent 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 nonpolar bond has the formula
1) NH 3 2) Cu 3) H 2 S 4) I 2
10. Substances with non-polar covalent bonds are
11. A chemical bond is formed between atoms with the same electronegativity
1) ionic 2) covalent polar 3) covalent nonpolar 4) hydrogen
12. Covalent polar bonds are 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 among the layers as follows: 2, 8, 8, 2 forms a chemical bond with hydrogen
1) covalent polar 2) covalent nonpolar
3) ionic 4) metal
14. In the molecule of which substance does the bond between carbon atoms have the longest length?
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 form between molecules
1) dimethyl ether 2) methanol 3) ethylene 4) ethyl acetate
17. Bond polarity is most pronounced in the molecule
1) HI 2) HCl 3) HF 4) HBr
18. Substances with non-polar covalent bonds 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 whose formulas are
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 weakest chemical bond in a molecule
22. Which substance has the longest chemical bond in its molecule?
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 which substance are the chemical bonds the strongest?
1)СF 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 ionic bonds is equal
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 equal
1) 1 2) 2 3) 3 4) 4
31. In substances formed by joining identical atoms, a chemical bond
1) ionic 2) covalent polar 3) hydrogen 4) covalent nonpolar
32. Atoms of chemical elements of the second period periodic table DI. Mendeleev form compounds with ionic chemical bonds of the composition 1) LiF 2) CO 2 3) Al 2 O 3 4) BaS
33. Compounds with covalent polar and covalent nonpolar bonds are, respectively, 1) water and hydrogen sulfide 2) potassium bromide and nitrogen 3) ammonia and hydrogen 4) oxygen and methane
34. Covalent nonpolar bonds are 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 nonpolar 4) hydrogen
36. Select a pair of substances in which all bonds 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 the chemical bond
1) covalent nonpolar 3) metallic
2) covalent polar 4) ionic
38. In carbon disulfide CS 2 chemical bond
1) ionic 2) metal
3) covalent polar 4) covalent nonpolar
39. A covalent nonpolar 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. Compound with an ionic chemical bond
1) phosphorus chloride 2) potassium bromide 3) nitrogen oxide (II) 4) barium
42. In ammonia and barium chloride, the chemical bond is 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 H2 molecule?
1) Ionic 2) Hydrogen 3) Covalent nonpolar 4) Donor-acceptor
45. Substances with a covalent polar bond are
1) sulfur oxide (IV) 2) oxygen 3) calcium hydride 4) diamond
46. There is a chemical bond in the fluorine molecule
1) covalent polar 2) ionic 3) covalent nonpolar 4) hydrogen
47. Which series lists substances with only covalent polar bonds:
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 which series do all substances have a polar covalent 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. Which series lists substances with only ionic bonds:
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. Which substance has hydrogen bonds? 1) Hydrogen sulfide 2) Ice 3) Hydrogen bromide 4) Benzene
53. The connection formed between elements with serial numbers 15 and 53
1) ionic 2) metal
3) covalent non-polar 4) covalent polar
54. The connection formed between elements with serial numbers 16 and 20
1) ionic 2) metal
3) covalent polar 4) hydrogen
55. A bond arises between atoms of elements with serial numbers 11 and 17
1) metallic 2) ionic 3) covalent 4) donor-acceptor
56. Hydrogen bonds form between molecules
1) hydrogen 2) formaldehyde 3) acetic acid 4) hydrogen sulfide
57. In which series are the formulas of substances with only a polar covalent bond written?
1) Cl 2, NH 3, HCl 2) HBr, NO, Br 2 3) H 2 S, H 2 O, S 8 4) HI, H 2 O, PH 3
58.Which substance contains 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 which substance are all chemical bonds covalent nonpolar?
1) Diamond 2) Carbon monoxide (IV) 3) Gold 4) Methane
61. Establish a correspondence between a substance and the type of connection of atoms in this substance.
NAME OF SUBSTANCE TYPE OF COMMUNICATION
1) zinc A) ionic
2) nitrogen B) metal
3) ammonia B) covalent polar
4) calcium chloride D) covalent nonpolar
62. Match
COMMUNICATION TYPE CONNECTION
1) ionic A) H 2
2) metal B) Va
3) covalent polar B) HF
4) covalent nonpolar D) BaF 2
63. In which compound is a covalent bond between atoms formed by a 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
