chemical bond
All interactions leading to the association of chemical particles (atoms, molecules, ions, etc.) into substances are divided into chemical bonds and intermolecular bonds (intermolecular interactions).
chemical bonds - bonds directly between atoms. There are ionic, covalent and metallic bonds.
Intermolecular bonds- bonds between molecules. These are a hydrogen bond, an ion-dipole bond (due to the formation of this bond, for example, the formation of a hydration shell of ions occurs), a dipole-dipole bond (due to the formation of this bond, molecules of polar substances are combined, for example, in liquid acetone), etc.
Ionic bond- a chemical bond formed due to the electrostatic attraction of oppositely charged ions. In binary compounds (compounds of two elements), it is formed when the sizes of the atoms being bonded differ greatly from each other: some atoms are large, others are small - that is, some atoms easily give away electrons, while others tend to accept them (usually these are atoms of elements that form typical metals and atoms of elements that form typical non-metals); the electronegativity of such atoms is also very different.
The ionic bond is non-directional and non-saturable.
covalent bond- a chemical bond that occurs due to the formation of a common pair of electrons. A covalent bond is formed between small atoms with the same or close radii. A necessary condition is the presence of unpaired electrons in both bonded atoms (exchange mechanism) or an unshared pair in one atom and a free orbital in another (donor-acceptor mechanism):
| but) | H + H H:H | H-H | H2 | (one shared pair of electrons; H is univalent); |
| b) | NN | N 2 | (three common pairs of electrons; N is trivalent); | |
| in) | H-F | HF | (one common pair of electrons; H and F are univalent); | |
| G) | NH4+ | (four shared pairs of electrons; N is tetravalent) |
- According to the number of common electron pairs, covalent bonds are divided into
- simple (single)- one pair of electrons
- double- two pairs of electrons
- triple- three pairs of electrons.
Double and triple bonds are called multiple bonds.
According to the distribution of electron density between bonded atoms covalent bond divided by non-polar And polar. A non-polar bond is formed between identical atoms, a polar bond is formed between different ones.
Electronegativity- a measure of the ability of an atom in a substance to attract common electron pairs.
The electron pairs of polar bonds are biased towards more electronegative elements. The very displacement of electron pairs is called bond polarization. The partial (excess) charges formed during polarization are denoted by + and -, for example: .
According to the nature of the overlapping of electron clouds ("orbitals"), the covalent bond is divided into -bond and -bond.
- Bond is formed due to direct overlap of electron clouds (along the straight line connecting the nuclei of atoms), - bond - due to lateral overlap (on both sides of the plane in which the nuclei of atoms lie).
A covalent bond is directional and saturable, as well as polarizable.
To explain and predict the mutual direction of covalent bonds, a hybridization model is used.
Hybridization of atomic orbitals and electron clouds- the proposed alignment of atomic orbitals in energy, and electron clouds in shape during the formation of covalent bonds by an atom.
The three most common types of hybridization are: sp-, sp 2 and sp 3 - hybridization. For example:
sp-hybridization - in C 2 H 2, BeH 2, CO 2 molecules (linear structure);
sp 2-hybridization - in C 2 H 4, C 6 H 6, BF 3 molecules (flat triangular shape);
sp 3-hybridization - in CCl 4, SiH 4, CH 4 molecules (tetrahedral form); NH 3 (pyramidal shape); H 2 O (corner shape).
metal connection- a chemical bond formed due to the socialization of valence electrons of all bonded atoms of a metal crystal. As a result, a single electron cloud of the crystal is formed, which is easily displaced under the action of electrical voltage- hence the high electrical conductivity of metals.
A metallic bond is formed when the bonded atoms are large and therefore tend to donate electrons. Simple substances with a metallic bond - metals (Na, Ba, Al, Cu, Au, etc.), complex substances - intermetallic compounds (AlCr 2, Ca 2 Cu, Cu 5 Zn 8, etc.).
The metallic bond does not have saturation directionality. It is also preserved in metal melts.
hydrogen bond- an intermolecular bond formed due to the partial acceptance of a pair of electrons of a highly electronegative atom by a hydrogen atom with a large positive partial charge. It is formed when in one molecule there is an atom with a lone pair of electrons and high electronegativity (F, O, N), and in the other there is a hydrogen atom bound by a strongly polar bond with one of these atoms. Examples of intermolecular hydrogen bonds:
H—O—H ··· OH 2 , H—O—H ··· NH 3 , H—O—H ··· F—H, H—F ··· H—F.
Intramolecular hydrogen bonds exist in the molecules of polypeptides, nucleic acids, proteins, etc.
A measure of the strength of any bond is the bond energy.
Bond energy is the energy required to break a given chemical bond in 1 mole of a substance. The unit of measurement is 1 kJ/mol.
The energies of the ionic and covalent bonds are of the same order, the energy of the hydrogen bond is an order of magnitude less.
The energy of a covalent bond depends on the size of the bonded atoms (bond length) and on the multiplicity of the bond. The smaller the atoms and the greater the multiplicity of the bond, the greater its energy.
The ionic bond energy depends on the size of the ions and on their charges. The smaller the ions and the greater their charge, the greater the binding energy.
The structure of matter
According to the type of structure, all substances are divided into molecular And non-molecular. Among organic matter molecular substances predominate, among inorganic - non-molecular.
According to the type of chemical bond, substances are divided into substances with covalent bonds, substances with ionic bonds(ionic substances) and substances with metallic bonds (metals).
Substances with covalent bonds can be molecular or non-molecular. This significantly affects their physical properties.
Molecular substances consist of molecules interconnected by weak intermolecular bonds, these include: H 2, O 2, N 2, Cl 2, Br 2, S 8, P 4 and others simple substances; CO 2 , SO 2 , N 2 O 5 , H 2 O, HCl, HF, NH 3 , CH 4 , C 2 H 5 OH, organic polymers and many other substances. These substances do not have high strength, have low temperatures melting and boiling, do not conduct electricity, some of them are soluble in water or other solvents.
Non-molecular substances with covalent bonds or atomic substances (diamond, graphite, Si, SiO 2 , SiC and others) form very strong crystals (layered graphite is an exception), they are insoluble in water and other solvents, have high melting and boiling points, most of they do not conduct electric current (except for graphite, which has electrical conductivity, and semiconductors - silicon, germanium, etc.)
All ionic substances are naturally non-molecular. These are solid refractory substances whose solutions and melts conduct electric current. Many of them are soluble in water. It should be noted that in ionic substances, the crystals of which consist of complex ions, there are also covalent bonds, for example: (Na +) 2 (SO 4 2-), (K +) 3 (PO 4 3-), (NH 4 + )(NO 3-), etc. The atoms that make up complex ions are bound by covalent bonds.
Metals (substances with a metallic bond) very diverse in their physical properties. Among them are liquid (Hg), very soft (Na, K) and very hard metals (W, Nb).
characteristic physical properties metals is their high electrical conductivity (unlike semiconductors, decreases with increasing temperature), high heat capacity and ductility (pure metals).
In the solid state, almost all substances are composed of crystals. According to the type of structure and type of chemical bond, crystals ("crystal lattices") are divided into atomic(crystals are not molecular substances with a covalent bond) ionic(crystals of ionic substances), molecular(crystals of molecular substances with a covalent bond) and metal(crystals of substances with a metallic bond).
Tasks and tests on the topic "Topic 10. "Chemical bond. The structure of matter."
- Types of chemical bond - The structure of matter 8–9 class
Lessons: 2 Assignments: 9 Tests: 1
- Tasks: 9 Tests: 1
After working through this topic, you should learn the following concepts: chemical bond, intermolecular bond, ionic bond, covalent bond, metallic bond, hydrogen bond, simple connection, double bond, triple bond, multiple bonds, nonpolar bond, polar bond, electronegativity, bond polarization, - and -bond, hybridization of atomic orbitals, bond energy.
You must know the classification of substances according to the type of structure, according to the type of chemical bond, the dependence of the properties of simple and complex substances on the type of chemical bond and the type of "crystal lattice".
You should be able to: determine the type of chemical bond in a substance, the type of hybridization, draw up bonding patterns, use the concept of electronegativity, a number of electronegativity; know how electronegativity changes chemical elements one period, and one group to determine the polarity of the covalent bond.
After making sure that everything you need is learned, proceed to the tasks. We wish you success.
Recommended literature:
- O. S. Gabrielyan, G. G. Lysova. Chemistry 11 cells. M., Bustard, 2002.
- G. E. Rudzitis, F. G. Feldman. Chemistry 11 cells. M., Education, 2001.
4. Nature and types of chemical bonds. covalent bond
Appendix. Spatial structure of molecules
Each molecule (for example, CO 2, H 2 O, NH 3) or molecular ion (for example, CO 3 2 -, H 3 O +, NH 4 +) has a certain qualitative and quantitative composition, as well as a structure (geometry). Molecule geometry formed by a fixed relative position atoms and values of bond angles.
The bond angle is the angle between imaginary straight lines passing through the nuclei of chemically bonded atoms. You can also say that this is the angle between two bond lines that have a common atom.
A bond line is a line connecting the nuclei of two chemically bonded atoms.
Only in the case of diatomic molecules (H 2 , Cl 2 , etc.) the question of their geometry does not arise - they are always linear, i.e. the nuclei of atoms are located on one straight line. The structure of more complex molecules may resemble different geometric figures, for example:
- triatomic molecules and ions of the type AX 2 (H 2 O, CO 2, BeCl 2)
- four-atomic molecules and ions such as AX 3 (NH 3, BF 3, PCl 3, H 3 O +, SO 3) or A 4 (P 4, As 4)
- pentaatomic molecules and ions of the type AX 4 (CH 4, XeF 4, GeCl 4)
There are particles and more complex structure(octahedron, trigonal bipyramid, flat regular hexagon). In addition, molecules and ions may have the shape of a distorted tetrahedron, an irregular triangle; in angular structure molecules, the values of α can be different (90°, 109°, 120°).
The structure of molecules is reliably established experimentally using various physical methods. To explain the reasons for the formation of a particular structure, the prediction of the geometry of molecules, various theoretical models have been developed. The easiest to understand are the model of repulsion of valence electron pairs (the OVEP model) and the model of hybridization of valence atomic orbitals (the GVAO model).
The basis of all (including the two mentioned) theoretical models, explaining the structure of molecules, is the following statement: the stable state of a molecule (ion) corresponds to such spatial arrangement nuclei of atoms, at which the mutual repulsion of the electrons of the valence layer will be minimal.
This takes into account the repulsion of electrons both participating in the formation of a chemical bond (bond electrons) and not participating (lone pairs of electrons). It is taken into account that the orbital of the bonding electron pair is compactly concentrated between two atoms and therefore occupies less space than the orbital of the lone pair of electrons. For this reason, the repulsive effect of a nonbonding (lone) pair of electrons and its effect on bond angles are more pronounced than those of a bonding pair.
OVEP model. This theory proceeds from the following main provisions (set out in a simplified way):
- the geometry of the molecule is determined only by σ-bonds (but not π-);
- the angles between the bonds depend on the number of lone pairs of electrons in the central atom.
These provisions should be considered jointly, since both chemical bond electrons and lone pairs of electrons repel each other, which ultimately leads to the formation of such a molecular structure in which this repulsion will be minimal.
Let us consider the geometry of some molecules and ions from the standpoint of the ECEP method; σ-bond electrons will be denoted by two dots (:), lone pairs of electrons - by a conventional symbol ( or ) or a dash.
Let's start with the five-atom methane CH 4 molecule. In this case, the central atom (this carbon) has completely exhausted its valence possibilities and does not contain unshared pairs of valence electrons, i.e. all four valence electrons form four σ bonds. How should the σ-bond electrons be located relative to each other so that the repulsion between them is minimal? Obviously, at an angle of 109 °, i.e. along lines directed to the vertices of an imaginary tetrahedron, in the center of which is a carbon atom. In this case, the electrons involved in bond formation are as far apart as possible (for a square configuration, the distance between these bond electrons is greater and the interelectron repulsion is smaller). For this reason, the methane molecule, as well as the CCl 4, CBr 4, CF 4 molecules, have the shape of a regular tetrahedron (they are said to have a tetrahedral structure):
The ammonium cation NH + 4 and the anion BF 4 − have the same structure, since the nitrogen and boron atoms form four σ-bonds each, and they do not have lone pairs of electrons.
Consider the structure of the four-atomic ammonia NH 3 molecule. In the ammonia molecule, there are three pairs of bonding electrons and one lone pair of electrons at the nitrogen atom, i.e. also four pairs of electrons. However, will bond angle stay at 109°? No, since the lone pair of electrons, which occupy a larger volume in space, has a strong repulsive effect on the σ-bond electrons, which leads to some decrease in the bond angle, in this case this angle is approximately 107 °. The ammonia molecule has the shape of a trigonal pyramid (pyramidal structure):
The tetraatomic hydroxonium ion H 3 O + also has a pyramidal structure: the oxygen atom forms three σ-bonds and contains one lone pair of electrons.
In the four-atom BF 3 molecule, the number of σ-bonds is also three, but the boron atom has no lone pairs of electrons. Obviously, the interelectronic repulsion will be minimal if the BF 3 molecule has the shape of a regular flat triangle with a bond angle of 120°:
The molecules BCl 3 , BH 3 , AlH 3 , AlF 3 , AlCl 3 , SO 3 have the same structure and for the same reasons.
What is the structure of a water molecule?
There are four pairs of electrons in a triatomic water molecule, but only two of them are σ-bond electrons, the remaining two are lone pairs of electrons of the oxygen atom. The repulsive effect of two lone pairs of electrons in an H 2 O molecule is stronger than in an ammonia molecule with one lone pair, so the bond angle H–O–H less than an angle H–N–H in an ammonia molecule: in a water molecule, the bond angle is approximately 105°:
The CO2 molecule (O=C=O) also has two pairs of bonding electrons (we consider only σ-bonds), however, unlike the water molecule, the carbon atom has no lone pairs of electrons. Obviously, the repulsion between pairs of electrons in this case will be minimal if they are located at an angle of 180°, i.e. with a linear form of a CO 2 molecule:
Molecules BeH 2 , BeF 2 , BeCl 2 have a similar structure and for the same reasons. In the triatomic SO 2 molecule, the central atom (sulfur atom) also forms two σ-bonds, but has an unshared pair of electrons, therefore, the sulfur (IV) oxide molecule has an angular structure, but the bond angle in it is larger than in the water molecule (the oxygen atom two lone pairs of electrons, while the sulfur atom has only one):
Some triatomic molecules of ABC composition also have a linear structure (for example, H–C≡N, Br–C≡N, S=C=Te, S=C=O), in which the central atom does not have unshared pairs of electrons. But the HClO molecule has an angular structure (α ≈ 103°), since the central atom, the oxygen atom, contains two lone pairs of electrons.
Using the OVEP model, one can also predict the structure of molecules of organic substances. For example, in a C 2 H 2 acetylene molecule, each carbon atom forms two σ-bonds, and carbon atoms do not have lone pairs of electrons; therefore, the molecule has a linear structure H–C≡C–H.
In the C 2 H 4 ethene molecule, each carbon atom forms three σ-bonds, which, in the absence of lone pairs of electrons at carbon atoms, leads to a triangular arrangement of atoms around each carbon atom:
In table. 4.2 summarizes some data on the structure of molecules and ions.
Table 4.2
Relationship between the structure of molecules (ions) and the number σ -bonds and lone pairs of electrons of the central atom
| Type of molecule (ion) | Number of σ-bonds formed by the central atom | Number of lone pairs of electrons | Structure, bond angle | Particle examples (central atom highlighted) |
|---|---|---|---|---|
| AB 2 | 2 | 0 | Linear, α = 180° | C O 2, Be H 2, HC N, Be Cl 2, C 2 H 2, N 2 O, C S 2 |
| 1 | Angle, 90°< α < 120° | SnCl 2, S O 2, N O 2 - | ||
| 2 | Angular, α< 109° | H 2 O , O F 2 , H 2 S , H 2 Se , S F 2 , Xe O 2 , − | ||
| AB 3 | 3 | 0 | Triangular, α ≈ 120° | B F 3 , B H 3 , B Cl 3 , Al F 3 , S O 3 , C O 3 2 − , N O 3 − |
| 1 | Trigonal pyramid, α< 109° | N H 3 , H 3 O + , N F 3 , S O 3 2 − , P F 3 , P Cl 3 , As H 3 | ||
| AB 4 | 4 | 0 | Tetrahedron, α = 109° | N H 4 + , C H 4 , Si H 4 , B F 4 , B H 4 − , S O 4 2 − , A l H 4 − |
GUAO model. The main position of this model is that not "pure" valence s -, p - and d - orbitals participate in the formation of covalent bonds, but the so-called hybrid orbitals. Further, hybridization is considered only with the participation of 2p - and 2s -AO.
Hybridization is the phenomenon of mixing valence orbitals, as a result of which they are aligned in shape and energy.
The concept of hybridization is always used when electrons of different energy sublevels are involved in the formation of chemical bonds, not very different in energy: 2s and 2p, 4s, 4p and 3d, etc.
The hybrid orbital is not similar in shape to the original 2p- and 2s-AO. It has the shape of an irregular volume eight:
As can be seen, hybrid AOs are more elongated, so they can overlap better and form stronger covalent bonds. When hybrid orbitals overlap, only σ bonds are formed; hybrid AOs do not participate in the formation of π-bonds due to their specific form (π-bonds form only non-hybrid AOs). The number of hybrid orbitals is always equal to the number of initial AO participating in hybridization. Hybrid orbitals should be oriented in space so that their maximum distance from each other is ensured. In this case, the repulsion of the electrons located on them (bonding and non-bonding) will be minimal; the energy of the entire molecule will also be minimal.
The HLAO model assumes that orbitals with close energy values (i.e., valence orbitals) and sufficiently high electron density participate in hybridization. The electron density of an orbital decreases with an increase in its size; therefore, the role in hybridization is especially significant for molecules of elements of small periods.
It should be remembered that the GVAO is not real physical phenomenon, and the convenient concept ( mathematical model), which allows describing the structure of some molecules. None physical methods the formation of hybrid AO is not fixed. Nevertheless, the theory of hybridization has some physical justification.
Consider the structure of the methane molecule. It is known that the СН4 molecule has the shape of a regular tetrahedron with a carbon atom in the center; all four С–Н bonds are formed by the exchange mechanism and have the same energy and length, i.e. are equivalent. It is quite simple to explain the presence of four unpaired electrons in a carbon atom, assuming its transition to an excited state:
However, this process does not explain in any way the equivalence of all four C–H bonds, since, according to the above scheme, three of them are formed with the participation of the 2p-AO of the carbon atom, one is formed with the participation of the 2s-AO, and the shape and energy of 2p- and 2s-AO are different.
To explain this and other similar facts, L. Pauling developed the concept of GVAO. It is assumed that the mixing of orbitals occurs at the moment of formation of chemical bonds. This process requires the expenditure of energy for electron pairing, which, however, is compensated by the release of energy during the formation of stronger (compared to non-hybrid) bonds by hybrid AOs.
Several types of hybridization are distinguished based on the nature and number of AOs involved in hybridization.
In the case of sp 3 hybridization, one s and three p orbitals are mixed (hence the name of the type of hybridization). For a carbon atom, the process can be represented as follows:
1 s 2 2 s 2 2 p x 1 2 p y 1 → electron transition 1 s 2 2 s 1 2 p x 1 2 p y 1 2 p z 1 → hybridization 1 s 2 2 (s p 3) 4
or via electronic configurations:
Four sp 3 -hybrid AOs are intermediate in energy between 2p - and 2s -AO.
The scheme of sp 3 hybridization can be represented using images of the shape of the AO of the carbon atom:
Thus, as a result of sp 3 hybridization, four hybrid orbitals are formed, each of which contains an unpaired electron. These orbitals in space are located at an angle of 109°28', which ensures minimal repulsion of the electrons located on them. If you connect the vertices of hybrid orbitals, you get volumetric figure- tetrahedron. For this reason, molecules of the composition АХ 4 (CH 4 , SiH 4 , CCl 4 , etc.), in which this type of hybridization occurs, have the form of a tetrahedron.
The concept of sp 3 hybridization of AO also explains well the structure of H 2 O and NH 3 molecules. It is assumed that 2s and 2p AOs of nitrogen and oxygen atoms are involved in hybridization. In these atoms, the number of valence electrons (5 and 6, respectively) exceeds the number of sp 3 -hybrid AOs (4), therefore, some of the hybrid AOs contain unpaired electrons, and some contain lone pairs of electrons:
We see that in the nitrogen atom, the lone pair of electrons is located on one hybrid AO, and in the oxygen atom, on two. Only AOs with unpaired electrons are involved in the formation of bonds with hydrogen atoms, and lone pairs of electrons will have a repulsive effect (Fig. 4.5) on each other (in the case of oxygen) and on bonding electrons (for oxygen and nitrogen).
Rice. 4.5. Scheme of the repulsive action of bonding and non-bonding orbitals in the molecule of ammonia (a) and water (b)
Stronger repulsion is expressed in the case of a water molecule. Since the oxygen atom has two lone pairs of electrons, the deviation from the ideal value of the bond angle for this type of hybridization (109°28′) in the water molecule is greater than in the ammonia molecule (in H 2 O and NH 3 molecules, the bond angle is 104, respectively ,5° and 107°).
The sp 3 hybridization model is used to explain the structure of diamond, silicon, NH 4 + and H 3 O + ions, alkanes, cycloalkanes, etc. In the case of carbon, this type of hybridization is always used when an atom of this element forms only σ-bonds.
In the case of sp 2 hybridization, one s and two p orbitals are mixed. Let us consider this type of hybridization using the example of a boron atom. The process is represented by energy diagrams
Thus, as a result of the sp 2 hybridization of the valence orbitals of the boron atom, three hybrid AOs are formed, directed at an angle of 120°, and one of the 2p orbitals does not take part in hybridization. Hybrid orbitals contain one unpaired electron each, are located in the same plane, and if you connect their vertices, you get a regular triangle. For this reason, molecules of the composition АХ 3 with sp 2 hybridization of the orbitals of the A atom have a triangular structure, as shown for the BF 3 molecule:
The nonhybrid 2p AO of the boron atom is free (not occupied) and is oriented perpendicular to the B–F bond plane; therefore, the BF3 molecule is an electron acceptor in the formation of a covalent bond by the donor–acceptor mechanism upon interaction with an ammonia molecule.
The concept of sp 2 hybridization is used to explain the nature of the carbon-carbon double bond in alkenes, the structure of benzene and graphite, i.e. in cases where the carbon atom forms three σ- and one π-bond.
The spatial arrangement of the orbitals of the carbon atom for sp 2 hybridization looks like this: the non-hybrid 2p-AO is oriented perpendicular to the plane in which the hybrid orbitals are located (both hybrid and non-hybrid AO contain an unpaired electron).
Consider the formation of chemical bonds in the ethylene molecule H 2 C=CH 2 . In it, hybrid AOs overlap with each other and with the 1s-AO of the hydrogen atom, forming five σ-bonds: one C–C and four C–H. Non-hybrid 2p-AOs overlap sideways and form a π-bond between carbon atoms (Fig. 4.6).
Rice. 4.6. Scheme of the formation of σ-bonds (a) and π-bonds (b) in an ethylene molecule
In the case of sp hybridization, one s and one p orbital are mixed. Let us consider this type of hybridization using the example of a beryllium atom. Let's imagine the hybridization process using the energy scheme:
and with the image of the shape of the orbitals
Thus, as a result of sp hybridization, two hybrid AOs containing one unpaired electron each are formed. Two 2p-AOs do not take part in hybridization and remain vacant in the case of beryllium. Hybrid orbitals are oriented at an angle of 180 °, therefore, molecules of the type AX 2 with sp hybridization of the orbitals of the atom A have a linear structure (Fig. 4.7).
Rice. 4.7. Spatial structure of the BeCl 2 molecule
Using the sp hybridization model of the carbon atom orbitals, the nature of the triple bond in alkyne molecules is explained. In this case, two hybrid and two non-hybrid 2p-AOs (shown by horizontal arrows →, ←) contain an unpaired electron each:
In the acetylene molecule HC≡CH, σ-bonds C–H and C–C are formed due to hybrid AOs:
Hybrid 2p-AO overlap in two perpendicular planes and form two π-bonds between carbon atoms (Fig. 4.8).
Rice. 4.8. Schematic representation of π-bonds (a) and planes of π-bonds (b) in an acetylene molecule (the wavy line shows the lateral overlap of the 2p-AO of the carbon atom)
The concept of sp hybridization of carbon atom orbitals makes it possible to explain the formation of chemical bonds in carbyne, CO and CO 2 molecules, propadiene (CH 2 =C=CH 2), i.e. in all cases where the carbon atom forms two σ- and two π-bonds.
The main characteristics of the types of hybridization considered and the geometric configurations of molecules corresponding to certain types of hybridization of the orbitals of the central atom A (taking into account the influence of nonbonding electron pairs) are presented in Table 1. 4.3 and 4.4.
Table 4.3
Main characteristics different types hybridization
Comparing the data in Table. 4.2 and 4.4, we can conclude that both models - OVEP and HLAO - lead to the same results regarding the structure of molecules.
Table 4.4
Types of spatial configuration of molecules corresponding to certain types of hybridization
The chemical structure is the sequence of connection of atoms in a molecule and their arrangement in space. The chemical structure is depicted using structural formulas. The dash represents a covalent chemical bond. If the connection is multiple: double, triple, then they put two (not to be confused with the “equal” sign) or three dashes. The angles between the bonds are depicted whenever possible.
To correctly compose the structural formulas of organic substances, you need to remember that carbon atoms form 4 bonds each.
(i.e., the valency of carbon in terms of the number of bonds is four. In organic chemistry Predominantly, it is the valence according to the number of bonds that is used).
Methane(it is also called marsh, mine gas) consists of one carbon atom bound by covalent bonds with four hydrogen atoms. Molecular formula CH 4 . Structural formula:
H
l
H-C-H
l
H
The angle between the bonds in the methane molecule is about 109 ° - electron pairs that form covalent bonds of the carbon atom (in the center) with hydrogen atoms are located in space at the maximum distance from each other.
In grades 10-11, it is studied that the methane molecule has the shape of a triangular pyramid - a tetrahedron, like the famous Egyptian pyramids.
Ethylene C 2 H 4 contains two carbon atoms connected by a double bond:
The angle between the bonds is 120° (electron pairs repel each other and are located at the maximum distance from each other). The atoms are in the same plane.
If we do not depict each hydrogen atom separately, then we obtain an abbreviated structural formula:
Acetylene C 2 H 2 contains a triple bond:
H–C ≡ C–H
The angle between the bonds is 180°, the molecule has a linear shape.
When burning hydrocarbons, oxides of carbon (IV) and hydrogen are formed, i.e. carbon dioxide and water, while a lot of heat is released:
CH 4 + 2O 2 → CO 2 + 2H 2 O
C 2 H 4 + 3O 2 → 2CO 2 + 2H 2 O
2C 2 H 2 + 5O 2 → 4CO 2 + 2H 2 O
Of great practical importance polymerization reaction ethylene - compound a large number molecules to form polymer macromolecules - polyethylene. Bonds between molecules are formed by breaking one of the bonds of a double bond. IN general view it can be written like this:
nCH 2 \u003d CH 2 → (- CH 2 - CH 2 -) n
where n is the number of connected molecules, called the degree of polymerization. The reaction takes place at elevated pressure and temperature, in the presence of a catalyst.
Polyethylene is used to make a film for greenhouses, tires for cans, etc.
The formation of benzene from acetylene is also referred to as a polymerization reaction.
The molecular structure has
1) silicon(IV) oxide
2) barium nitrate
3) sodium chloride
4) carbon monoxide (II)
Solution.
The structure of a substance is understood from which particles of molecules, ions, atoms its crystal lattice is built. Substances with ionic and metallic bonds have a non-molecular structure. Substances in whose molecules atoms are connected by covalent bonds can have molecular and atomic crystal lattices. Atomic crystal lattices: C (diamond, graphite), Si, Ge, B, SiO 2 , SiC (carborundum), BN, Fe 3 C, TaC, red and black phosphorus. This group includes substances, as a rule, solid and refractory substances.
Silicon oxide (IV) - covalent bonds, solid, refractory substance, atomic crystal lattice. Barium nitrate and sodium chloride substances with ionic bonds - the crystal lattice is ionic. Carbon monoxide (II) is a gas in a molecule of covalent bonds, which means that this is the correct answer, the crystal lattice is molecular.
Answer: 4
Source: Demo version of the USE-2012 in chemistry.
In solid form, the molecular structure is
1) silicon(IV) oxide
2) calcium chloride
3) copper (II) sulfate
Solution.
The structure of a substance is understood from which particles of molecules, ions, atoms its crystal lattice is built. Substances with ionic and metallic bonds have a non-molecular structure. Substances in the molecules of which atoms are connected by covalent bonds can have molecular and atomic crystal lattices. Atomic crystal lattices: C (diamond, graphite), Si, Ge, B, SiO 2 , SiC (carborundum), BN, Fe 3 C, TaC, red and black phosphorus. This group includes substances, as a rule, solid and refractory substances.
Substances with a molecular crystal lattice have lower boiling points than all other substances. According to the formula, it is necessary to determine the type of bond in the substance, and then determine the type of crystal lattice. Silicon oxide (IV) - covalent bonds, solid, refractory substance, atomic crystal lattice. Calcium chloride and copper sulfate are substances with ionic bonds - the crystal lattice is ionic. There are covalent bonds in the iodine molecule, and it easily sublimes, which means that this is the correct answer, the crystal lattice is molecular.
Answer: 4
Source: Demo version of the USE-2013 in chemistry.
1) carbon monoxide (II)
3) magnesium bromide
Solution.
Substances with ionic and metallic bonds have a non-molecular structure. Substances in whose molecules atoms are connected by covalent bonds can have molecular and atomic crystal lattices. Atomic crystal lattices: C (diamond, graphite), Si, Ge, B, SiO2, SiC (carborundum), BN, Fe3 C, TaC, red and black phosphorus. This group includes substances, as a rule, solid and refractory substances.
Answer: 3
Source: USE in Chemistry 06/10/2013. main wave. Far East. Option 1.
The ionic crystal lattice has
2) carbon monoxide (II)
4) magnesium bromide
Solution.
Substances with ionic and metallic bonds have a non-molecular structure. Substances in whose molecules atoms are connected by covalent bonds can have molecular and atomic crystal lattices. Atomic crystal lattices: C (diamond, graphite), Si, Ge, B, SiO2, CaC2, SiC (carborundum), BN, Fe3 C, TaC, red and black phosphorus. This group includes substances, as a rule, solid and refractory substances.
Substances with a molecular crystal lattice have lower boiling points than all other substances. According to the formula, it is necessary to determine the type of bond in the substance, and then determine the type of crystal lattice.
Magnesium bromide has an ionic crystal lattice.
Answer: 4
Source: USE in Chemistry 06/10/2013. main wave. Far East. Option 2.
Sodium sulfate has a crystal lattice
1) metal
3) molecular
4) nuclear
Solution.
Substances with a molecular crystal lattice have lower boiling points than all other substances. According to the formula, it is necessary to determine the type of bond in the substance, and then determine the type of crystal lattice.
Sodium sulfate is a salt having an ionic crystal lattice.
Answer: 2
Source: USE in Chemistry 06/10/2013. main wave. Far East. Option 3.
Each of the two substances has a non-molecular structure:
1) nitrogen and diamond
2) potassium and copper
3) water and sodium hydroxide
4) chlorine and bromine
Solution.
Substances with ionic and metallic bonds have a non-molecular structure. Substances in whose molecules atoms are connected by covalent bonds can have molecular and atomic crystal lattices. Atomic crystal lattices: C (diamond, graphite), Si, Ge, B, SiO2, SiC (carborundum), BN, red and black phosphorus. This group includes substances, as a rule, solid and refractory substances.
Substances with a molecular crystal lattice have lower boiling points than all other substances. According to the formula, it is necessary to determine the type of bond in the substance, and then determine the type of crystal lattice.
Of these substances, only diamond, potassium, copper and sodium hydroxide have a non-molecular structure.
Answer: 2
Source: USE in Chemistry 06/10/2013. main wave. Far East. Option 4.
A substance with an ionic type of crystal lattice is
3) acetic acid
4) sodium sulfate
Solution.
Substances with ionic and metallic bonds have a non-molecular structure. Substances in whose molecules atoms are connected by covalent bonds can have molecular and atomic crystal lattices. Atomic crystal lattices: C (diamond, graphite), Si, Ge, B, SiO2, CaC2, SiC (carborundum), BN, Fe3 C, TaC, red and black phosphorus. This group includes substances, as a rule, solid and refractory substances.
Substances with a molecular crystal lattice have lower boiling points than all other substances. According to the formula, it is necessary to determine the type of bond in the substance, and then determine the type of crystal lattice.
Sodium sulfate has an ionic crystal lattice.
Answer: 4
Source: USE in Chemistry 06/10/2013. main wave. Siberia. Option 1.
The metallic crystal lattice is characteristic of
2) white phosphorus
3) aluminum oxide
4) calcium
Solution.
The metallic crystal lattice is characteristic of metals, such as calcium.
Answer: 4
Source: USE in Chemistry 06/10/2013. main wave. Ural. Option 1.
Maxim Avramchuk 22.04.2015 16:53
All metals except mercury have a metallic crystal lattice. Can you tell me what is the crystal lattice of mercury and amalgam?
Alexander Ivanov
Mercury in the solid state also has a metallic crystal lattice
2) calcium oxide
4) aluminum
Solution.
Substances with ionic and metallic bonds have a non-molecular structure. Substances in whose molecules atoms are connected by covalent bonds can have molecular and atomic crystal lattices. Atomic crystal lattices: C (diamond, graphite), Si, Ge, B, SiO2, CaC2, SiC (carborundum), BN, Fe3 C, TaC, red and black phosphorus. This group includes substances, as a rule, solid and refractory substances.
Substances with a molecular crystal lattice have lower boiling points than all other substances. According to the formula, it is necessary to determine the type of bond in the substance, and then determine the type of crystal lattice.
Calcium oxide has an ionic crystal lattice.
Answer: 2
Source: USE in Chemistry 06/10/2013. main wave. Siberia. Option 2.
The molecular crystal lattice in the solid state has
1) sodium iodide
2) sulfur oxide (IV)
3) sodium oxide
4) iron(III) chloride
Solution.
Substances with ionic and metallic bonds have a non-molecular structure. Substances in whose molecules atoms are connected by covalent bonds can have molecular and atomic crystal lattices. Atomic crystal lattices: C (diamond, graphite), Si, Ge, B, SiO2, CaC2, SiC (carborundum), BN, Fe3 C, TaC, red and black phosphorus. This group includes substances, as a rule, solid and refractory substances.
Substances with a molecular crystal lattice have lower boiling points than all other substances. According to the formula, it is necessary to determine the type of bond in the substance, and then determine the type of crystal lattice.
Among the above substances, all except sulfur oxide (IV) have an ionic crystal lattice, and it has a molecular one.
Answer: 2
Source: USE in Chemistry 06/10/2013. main wave. Siberia. Option 4.
The ionic crystal lattice has
3) sodium hydride
4) nitric oxide (II)
Solution.
Substances with ionic and metallic bonds have a non-molecular structure. Substances in whose molecules atoms are connected by covalent bonds can have molecular and atomic crystal lattices. Atomic crystal lattices: C (diamond, graphite), Si, Ge, B, SiO2, CaC2, SiC (carborundum), BN, Fe3 C, TaC, red and black phosphorus. This group includes substances, as a rule, solid and refractory substances.
Substances with a molecular crystal lattice have lower boiling points than all other substances. According to the formula, it is necessary to determine the type of bond in the substance, and then determine the type of crystal lattice.
Sodium hydride has an ionic crystal lattice.
Answer: 3
Source: USE in Chemistry 06/10/2013. main wave. Ural. Option 5.
For substances with a molecular crystal lattice, a characteristic property is
1) refractoriness
2) low boiling point
3) high melting point
4) electrical conductivity
Solution.
Substances with a molecular crystal lattice have lower boiling points than all other substances. Answer: 2
Answer: 2
Source: USE in Chemistry 06/10/2013. main wave. Centre. Option 1.
For substances with a molecular crystal lattice characteristic property is an
1) refractoriness
2) high boiling point
3) low melting point
4) electrical conductivity
Solution.
Substances with a molecular crystal lattice have lower melting and boiling points than all other substances.
Answer: 3
Source: USE in Chemistry 06/10/2013. main wave. Centre. Option 2.
The molecular structure has
1) hydrogen chloride
2) potassium sulfide
3) barium oxide
4) calcium oxide
Solution.
Substances with ionic and metallic bonds have a non-molecular structure. Substances in whose molecules atoms are connected by covalent bonds can have molecular and atomic crystal lattices. Atomic crystal lattices: C (diamond, graphite), Si, Ge, B, SiO2, CaC2, SiC (carborundum), BN, Fe3 C, TaC, red and black phosphorus. This group includes substances, as a rule, solid and refractory substances.
Substances with a molecular crystal lattice have lower boiling points than all other substances. According to the formula, it is necessary to determine the type of bond in the substance, and then determine the type of crystal lattice.
Of these substances, all have an ionic crystal lattice, except for hydrogen chloride.
Answer: 1
Source: USE in Chemistry 06/10/2013. main wave. Centre. Option 5.
The molecular structure has
1) silicon(IV) oxide
2) barium nitrate
3) sodium chloride
4) carbon monoxide (II)
Solution.
Substances with ionic and metallic bonds have a non-molecular structure. Substances in whose molecules atoms are connected by covalent bonds can have molecular and atomic crystal lattices. Atomic crystal lattices: C (diamond, graphite), Si, Ge, B, SiO2, CaC2, SiC (carborundum), BN, Fe3 C, TaC, red and black phosphorus. This group includes substances, as a rule, solid and refractory substances.
Substances with a molecular crystal lattice have lower boiling points than all other substances. According to the formula, it is necessary to determine the type of bond in the substance, and then determine the type of crystal lattice.
Among these substances, carbon monoxide has a molecular structure.
Answer: 4
Source: Demo version of the USE-2014 in chemistry.
The molecular structure is
1) ammonium chloride
2) cesium chloride
3) iron(III) chloride
4) hydrogen chloride
Solution.
The structure of a substance is understood from which particles of molecules, ions, atoms its crystal lattice is built. Substances with ionic and metallic bonds have a non-molecular structure. Substances in whose molecules atoms are connected by covalent bonds can have molecular and atomic crystal lattices. Atomic crystal lattices: C (diamond, graphite), Si, Ge, B, SiO2, SiC (carborundum), BN, Fe3C, TaC, red and black phosphorus. This group includes substances, as a rule, solid and refractory substances.
Substances with a molecular crystal lattice have lower boiling points than all other substances. According to the formula, it is necessary to determine the type of bond in the substance, and then determine the type of crystal lattice.
1) ammonium chloride - ionic structure
2) cesium chloride - ionic structure
3) iron(III) chloride - ionic structure
4) hydrogen chloride - molecular structure
Answer: 4
Which of the chlorine compounds has the highest melting point?
| 1) | 2) | 3) | 4) |
Answer: 3
Which of the oxygen compounds has the highest melting point?
Answer: 3
Alexander Ivanov
No. This is an atomic crystal lattice
Igor Srago 22.05.2016 14:37
Since the USE teaches that the bond between the atoms of metals and non-metals is ionic, aluminum oxide must form an ionic crystal. And substances of an ionic structure, too (as well as atomic) have a melting point higher than molecular substances.
Anton Golyshev
Substances with an atomic crystal lattice are better to just learn.
For substances with a metallic crystal lattice is uncharacteristic
1) fragility
2) plasticity
3) high electrical conductivity
4) high thermal conductivity
Solution.
Metals are characterized by plasticity, high electrical and thermal conductivity, but fragility is not typical for them.
Answer: 1
Source: USE 05/05/2015. Early wave.
Solution.
Substances in whose molecules atoms are connected by covalent bonds can have molecular and atomic crystal lattices. Atomic crystal lattices: C (diamond, graphite), Si, Ge, B, SiO2, SiC (carborundum), BN, Fe3C, TaC, red and black phosphorus. This group includes substances, as a rule, solid and refractory substances.
Answer: 1
The molecular crystal lattice has
Solution.
Substances with ionic (BaSO 4) and metallic bonds have a non-molecular structure.
Substances whose atoms are connected by covalent bonds can have molecular and atomic crystal lattices.
Atomic crystal lattices: C (diamond, graphite), Si, Ge, B, SiO 2, SiC (carborundum), B 2 O 3, Al 2 O 3.
Substances that are gaseous under normal conditions (O 2, H 2, NH 3, H 2 S, CO 2), as well as liquid (H 2 O, H 2 SO 4) and solid, but fusible (S, glucose), have a molecular structure
Therefore, the molecular crystal lattice has - carbon dioxide.
Answer: 2
The atomic crystal lattice has
1) ammonium chloride
2) cesium oxide
3) silicon(IV) oxide
4) crystalline sulfur
Solution.
Substances with ionic and metallic bonds have a non-molecular structure.
Substances in whose molecules atoms are connected by covalent bonds can have molecular and atomic crystal lattices. Atomic crystal lattices: C (diamond, graphite), Si, Ge, B, SiO2, SiC (carborundum), BN, Fe3C, TaC, red and black phosphorus. The rest refer to substances with a molecular crystal lattice.
Therefore, silicon (IV) oxide has an atomic crystal lattice.
Answer: 3
A solid brittle substance with a high melting point, the solution of which conducts an electric current, has a crystal lattice
2) metal
3) nuclear
4) molecular
Solution.
Such properties are characteristic of substances with an ionic crystal lattice.
Answer: 1
Which silicon compound has a molecular crystal lattice in the solid state?
| 1) | 2) | 3) | 4) |
Option 2
Part A:
A 1. A pair of elements between which an ionic chemical bond is formed:
a) carbon and sulfur, b) hydrogen and nitrogen, c) potassium and oxygen, d) silicon and hydrogen.
A 2.The formula of a substance with a covalent bond:
a) NaCl, b) HCl, c) BaO, d) Ca 3 N 2.
A 3.The least polar bond is:
a) C - H, b) C - Cl, c) C - F, d) C - Br.
A 4. The correct statement is that δ is a bond, in contrast to π is a bond:
a) less strong, b) formed by lateral overlap of atomic orbitals,
c) is not covalent, d) is formed by axial overlapping of atomic orbitals.
A 5.A substance in the molecule of which there is no π-bond:
a) ethylene, b) benzene, c) ammonia, d) nitrogen.
A 6. The strongest molecule is:
a) H 2 , b) N 2 , c) F 2 , d) O 2 .
A 7. In the CO 3 2- ion, the carbon atom is in the sp 2 - hybrid state, so the ion has the form:
a) linear, b) tetrahedron, c) triangle, d) octahedron.
A 8. The carbon atom has an oxidation state of -3 and a valence of 4 in conjunction with the formula:
a) CO 2, b) C 2 H 6, c) CH 3 Cl, d) CaC 2.
A 9. The atomic crystal lattice has:
a) soda, b) water, c) diamond, d) paraffin.
A 10. A substance between the molecules of which there is a hydrogen bond:
a) ethane, b) sodium fluoride, c) carbon monoxide (4), d) ethanol.
A 11. Select a group of elements arranged in ascending order of electronegativity:
a) Cl, Si, N, O, b) Si, P, N, F, c) F, Cl, O, Si, d) O, N, F, Cl.
A 12. There is a covalent bond between atoms, formed by the donor-acceptor mechanism in a substance, the formula of which is:
13.
A 14.The formation of hydrogen bonds can be explained by:
a) the solubility of acetic acid in water, b) acid properties ethanol,
c) high melting point of many metals, d) insolubility of methane in water.
A 15.The formula of a substance with a covalent polar bond:
a) Cl 2, b) KCl, c) NH 3, d) O 2.
Part B:
B 1. From among those proposed, select a substance in the molecule of which there are π - bonds: H 2, CH 4, Br 2, N 2, H 2 S, CH 3 OH, NH 3. Write the name of this substance.
B 2. The process of interaction of electron orbitals, leading to their alignment in shape and energy, is called ......
B 3. What is the name of the phenomenon of enlargement of colloidal particles and their precipitation from a colloidal solution?
B 4. Give an example of a substance in the molecule of which there are three δ - and one π - bonds. Name the substance in the nominative case.
B 5. In which of the following substances, the bonds are most polar: hydrogen chloride, fluorine, water, ammonia, hydrogen sulfide. Write down the chosen substance by the formula.
Part C:
From 1. Write the structural formulas of all isomeric substances of the composition C 4 H 8. Name each substance.
From 2 . Compose the structural formulas of substances: CHF 3, C 2 H 2 Br 2, O 2.
Make graphic formulas: Mg 3 N 2, Na 2 SO 4, KHCO 3.
From 3.
Mg 3 N 2, Cl 2, ZnSO 4, KHS, CH 3 Cl, FeOHCl 2, BrO 2, AsO 4 3-, NH 4 +
Test№2 "STRUCTURE OF THE SUBSTANCE".
Option 3
Part A:
A 1. Chemical bonds in substances whose formulas are CH 4 and CaCl 2, respectively:
a) ionic and covalent polar, b) covalent polar and ionic,
c) covalent non-polar and ionic, d) covalent polar and metallic.
A 2.The polarity of the bond is greater in a substance with the formula:
a) Br 2 , b) LiBr, c) HBr, d) KBr
A 3.The ionic nature of the bond in the series of compounds Li 2 O - Na 2 O - K 2 O - Rb 2 O:
a) increases, b) decreases, c) does not change, d) first decreases, then increases.
A 4. There is a covalent bond between atoms, formed by the donor-acceptor mechanism in a substance, the formula of which is:
a) Al(OH) 3, b) [CH 3 NH 3 ]Cl, c) C 2 H 5 OH, d) C 6 H 12 O 6.
A 5.A pair of formulas of substances in the molecules of which there are only δ - bonds:
a) CH 4 and O 2, b) C 2 H 5 OH and H 2 O, c) N 2 and CO 2, d) HBr and C 2 H 4.
A 6. The strongest connection of the following:
a) C - Cl, b) C - F, c) C - Br, d) C - I.
A 7. A group of formulas of compounds in which there is a similar orientation of bonds due to sp 3 - hybridization of electronic orbitals:
a) CH 4, C 2 H 4, C 2 H 2, b) NH 3, CH 4, H 2 O, c) H 2 O, C 2 H 6, C 6 H 6, d) C 3 H 8, BCl 3 , BeCl 2 .
A 8. The valency and oxidation state of the carbon atom in the methanol molecule, respectively, are:
a) 4 and +4, b) 4 and -2, c) 3 and +2, d) 4 and -3.
A 9. Substances with an ionic crystal lattice are characterized by:
a) poor solubility in water, b) high boiling point, c) fusibility, d) volatility.
A 10. The formation of a hydrogen bond between molecules leads to:
a) to a decrease in the boiling points of substances, b) to a decrease in the solubility of substances in water,
c) to an increase in the boiling points of substances, d) to an increase in the volatility of substances.
A 11. The formula of a substance with an ionic bond:
a) NH 3, b) C 2 H 4, c) KH, d) CCl 4.
A 12. Only δ - the bond is in the molecule:
a) nitrogen, b) ethanol, c) ethylene, d) carbon monoxide (4).
13. The molecular structure has a substance with the formula:
a) CH 4, b) NaOH, c) SiO 2, d) Al.
A 14.A hydrogen bond is formed between:
a) water molecules, b) hydrogen molecules,
c) hydrocarbon molecules, d) metal atoms and hydrogen atoms.
A 15.If you vigorously shake the mixture of vegetable oil and water, you get:
a) suspension, b) emulsion, c) foam, d) aerosol.
Part B:
B 1. The number of common electron pairs between bromine atoms in a Br 2 molecule is ......
B 2. From which bonds a triple bond is formed in the N 2 molecule (imagine the answer in the nominative case).
B 3. At the nodes of the metal crystal lattice are ...... .. .
B 4. Give an example of a substance in the molecule of which there are five δ - and two π - bonds. Name the substance in the nominative case.
B 5. What is the maximum number of π bonds that can form between two atoms in a molecule? (Give your answer as a number)
Part C:
From 1. Write the structural formulas of all isomeric substances of the composition C 5 H 10 O. Name each substance.
From 2 . Compose the structural formulas of substances: CHCl 3, C 2 H 2 Cl 2, F 2.
Make graphic formulas: AlN, CaSO 4 , LiHCO 3 .
From 3. Determine the degree of oxidation in chemical compounds and ions:
HNO 3 , HClO 4 , K 2 SO 3 , KMnO 4 , CH 3 F, MgOHCl 2 , ClO 3 - , CrO 4 2- , NH 4 +
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