Dipole moments of molecules
The valence bond method is based on the premise that each pair of atoms in a chemical particle is held together by one or more electron pairs. These pairs of electrons belong to two bonded atoms and are localized in the space between them. Due to the attraction of the nuclei of the bound atoms to these electrons, a chemical bond arises.
Overlapping atomic orbitals
When describing the electronic structure of a chemical particle, electrons, including socialized ones, are referred to as individual atoms and their states are described by atomic orbitals. When solving the Schrödinger equation, the approximate wave function is chosen so that it gives the minimum electronic energy of the system, that is, the largest value of the binding energy. This condition is achieved with the greatest overlap of orbitals belonging to one bond. Thus, a pair of electrons that bind two atoms is in the region of overlap of their atomic orbitals.
The overlapped orbitals must have the same symmetry about the internuclear axis.
The overlap of atomic orbitals along the line connecting the nuclei of atoms leads to the formation of σ-bonds. Only one σ-bond is possible between two atoms in a chemical particle. All σ-bonds have axial symmetry about the internuclear axis. Fragments of chemical particles can rotate around the internuclear axis without violating the degree of overlap of atomic orbitals that form σ-bonds. A set of directed, strictly spatially oriented σ-bonds creates the structure of a chemical particle.
With additional overlapping of atomic orbitals perpendicular to the bond line, π bonds are formed.
As a result, multiple bonds appear between atoms:
| Single (σ) | Double (σ + π) | Triple (σ + π + π) |
| F−F | O=O | N≡N |
With the appearance of a π-bond that does not have axial symmetry, the free rotation of fragments of a chemical particle around the σ-bond becomes impossible, since it should lead to the rupture of the π-bond. In addition to σ- and π-bonds, the formation of another type of bond is possible - δ-bond:
Typically, such a bond is formed after the formation of σ- and π-bonds by atoms in the presence of atoms d- and f-orbitals by overlapping their "petals" in four places at once. As a result, the multiplicity of communication can increase up to 4-5.
For example, in the octachlorodirenate(III)-ion 2-, four bonds are formed between the rhenium atoms.
Mechanisms for the formation of covalent bonds
There are several mechanisms for the formation of a covalent bond: exchange(equivalent), donor-acceptor, dative.
When using the exchange mechanism, the formation of a bond is considered as a result of the pairing of spins of free electrons of atoms. In this case, two atomic orbitals of neighboring atoms overlap, each of which is occupied by one electron. Thus, each of the bonded atoms allocates pairs of electrons for socialization, as if exchanging them. for example, when a boron trifluoride molecule is formed from atoms, three atomic orbitals of boron, each of which has one electron, overlap with three atomic orbitals of three fluorine atoms (each of them also has one unpaired electron). As a result of electron pairing, three pairs of electrons appear in the overlapping regions of the corresponding atomic orbitals, binding atoms into a molecule.
According to the donor-acceptor mechanism, an orbital with a pair of electrons of one atom and a free orbital of another atom overlap. In this case, a pair of electrons also appears in the overlap region. According to the donor-acceptor mechanism, for example, the addition of a fluoride ion to a boron trifluoride molecule occurs. Vacant R-boron orbital (electron pair acceptor) in the BF 3 molecule overlaps with R-orbital of the F − ion, which acts as an electron pair donor. In the resulting ion, all four boron–fluorine covalent bonds are equivalent in length and energy, despite the difference in the mechanism of their formation.
Atoms whose outer electron shell consists only of s- and R-orbitals can be either donors or acceptors of an electron pair. Atoms whose outer electron shell includes d-orbitals can act as both a donor and an acceptor of electron pairs. In this case, the dative mechanism of bond formation is considered. An example of the manifestation of the dative mechanism in the formation of a bond is the interaction of two chlorine atoms. Two chlorine atoms in the Cl 2 molecule form a covalent bond by the exchange mechanism, combining their unpaired 3 R-electrons. In addition, there is overlap 3 R-orbitals atom Cl-1, on which there is a pair of electrons, and vacant 3 d-orbitals of the Cl-2 atom, as well as overlap 3 R-orbitals atom Cl-2, which has a pair of electrons, and vacant 3 d-orbitals of the Cl-1 atom. The action of the dative mechanism leads to an increase in the bond strength. Therefore, the Cl 2 molecule is stronger than the F 2 molecule, in which the covalent bond is formed only by the exchange mechanism:
Hybridization of atomic orbitals
When determining the geometric shape of a chemical particle, it should be taken into account that pairs of external electrons of the central atom, including those that do not form a chemical bond, are located in space as far as possible from each other.
When considering covalent chemical bonds, the concept of hybridization of the orbitals of the central atom is often used - the alignment of their energy and shape. Hybridization is a formal technique used for the quantum-chemical description of the rearrangement of orbitals in chemical particles compared to free atoms. The essence of hybridization of atomic orbitals is that an electron near the nucleus of a bound atom is characterized not by a separate atomic orbital, but by a combination of atomic orbitals with the same principal quantum number. This combination is called a hybrid (hybridized) orbital. As a rule, hybridization affects only higher and close in energy atomic orbitals occupied by electrons.
As a result of hybridization, new hybrid orbitals appear (Fig. 24), which are oriented in space in such a way that the electron pairs (or unpaired electrons) located on them are as far away from each other as possible, which corresponds to the minimum energy of interelectron repulsion. Therefore, the type of hybridization determines the geometry of the molecule or ion.
TYPES OF HYBRIDIZATION
| Type of hybridization | geometric shape | Angle between bonds | Examples |
| sp | linear | 180o | BeCl2 |
| sp 2 | triangular | 120o | BCl 3 |
| sp 3 | tetrahedral | 109.5o | CH 4 |
| sp 3 d | trigonal-bipyramidal | 90o; 120o | PCl 5 |
| sp 3 d 2 | octahedral | 90o | SF6 |
Hybridization involves not only bonding electrons, but also unshared electron pairs. For example, a water molecule contains two covalent chemical bonds between an oxygen atom and two hydrogen atoms.
In addition to two pairs of electrons common with hydrogen atoms, the oxygen atom has two pairs of external electrons that do not participate in bond formation (lone electron pairs). All four pairs of electrons occupy certain regions in the space around the oxygen atom.
Since the electrons repel each other, the electron clouds are located as far apart as possible. In this case, as a result of hybridization, the shape of atomic orbitals changes, they are elongated and directed towards the vertices of the tetrahedron. Therefore, the water molecule has an angular shape, and the angle between the oxygen-hydrogen bonds is 104.5 o.
To predict the type of hybridization, it is convenient to use donor-acceptor mechanism bond formation: the empty orbitals of a less electronegative element and the orbitals of a more electronegative element overlap with the pairs of electrons on them. When compiling the electronic configurations of atoms, they are taken into account oxidation states is a conditional number characterizing the charge of an atom in a compound, calculated based on the assumption of the ionic structure of the substance.
To determine the type of hybridization and the shape of a chemical particle, proceed as follows:
The presence of π bonds does not affect the type of hybridization. However, the presence of additional bonding can lead to a change in bond angles, since the electrons of multiple bonds repel each other more strongly. For this reason, for example, the bond angle in the NO 2 molecule ( sp 2-hybridization) increases from 120 o to 134 o .
The multiplicity of the nitrogen-oxygen bond in this molecule is 1.5, where one corresponds to one σ-bond, and 0.5 is equal to the ratio of the number of orbitals of the nitrogen atom not participating in hybridization (1) to the number of remaining active electron pairs at the oxygen atom, forming π bonds (2). Thus, delocalization of π-bonds is observed (delocalized bonds are covalent bonds, the multiplicity of which cannot be expressed as an integer).
When sp, sp 2 , sp 3 , sp 3 d 2 hybridizations of a vertex in a polyhedron describing the geometry of a chemical particle are equivalent, and therefore multiple bonds and lone pairs of electrons can occupy any of them. However sp 3 d-hybridization is responsible trigonal bipyramid, in which the bond angles for atoms located at the base of the pyramid (equatorial plane) are 120 o , and the bond angles involving atoms located at the tops of the bipyramid are 90 o . The experiment shows that unshared electron pairs are always located in the equatorial plane of the trigonal bipyramid. On this basis, it is concluded that they require more free space than the pairs of electrons involved in bond formation. An example of a particle with such an arrangement of a lone electron pair is sulfur tetrafluoride (Fig. 27). If the central atom simultaneously has lone pairs of electrons and forms multiple bonds (for example, in the XeOF 2 molecule), then in the case sp 3 d-hybridization, they are located in the equatorial plane of the trigonal bipyramid (Fig. 28).
Dipole moments of molecules
An ideal covalent bond exists only in particles consisting of identical atoms (H 2 , N 2 , etc.). If a bond is formed between different atoms, then the electron density shifts to one of the nuclei of the atoms, that is, the bond is polarized. The polarity of a bond is characterized by its dipole moment.
The dipole moment of a molecule is equal to the vector sum of the dipole moments of its chemical bonds (taking into account the presence of lone pairs of electrons). If the polar bonds are located symmetrically in the molecule, then the positive and negative charges compensate each other, and the molecule as a whole is nonpolar. This happens, for example, with the carbon dioxide molecule. Polyatomic molecules with an asymmetric arrangement of polar bonds (and hence electron density) are generally polar. This applies in particular to the water molecule.
The resulting value of the dipole moment of the molecule can be affected by the lone pair of electrons. So, the NH 3 and NF 3 molecules have a tetrahedral geometry (taking into account the lone pair of electrons). The degrees of ionicity of the nitrogen–hydrogen and nitrogen–fluorine bonds are 15 and 19%, respectively, and their lengths are 101 and 137 pm, respectively. Based on this, one could conclude that the dipole moment NF 3 is larger. However, experiment shows the opposite. With a more accurate prediction of the dipole moment, the direction of the dipole moment of the lone pair should be taken into account (Fig. 29).
Continuation. For the beginning, see № 15, 16/2004
Lesson 5
atomic orbitals of carbon
A covalent chemical bond is formed using common bonding electron pairs of the type:
Form a chemical bond, i.e. only unpaired electrons can create a common electron pair with a “foreign” electron from another atom. When writing electronic formulas, unpaired electrons are located one by one in the orbital cell.
atomic orbital is a function that describes the density of the electron cloud at each point in space around the nucleus of an atom. An electron cloud is a region of space in which an electron can be found with a high probability.
To harmonize the electronic structure of the carbon atom and the valency of this element, the concepts of excitation of the carbon atom are used. In the normal (unexcited) state, the carbon atom has two unpaired 2 R 2 electrons. In an excited state (when energy is absorbed) one of 2 s 2-electrons can pass to free R-orbital. Then four unpaired electrons appear in the carbon atom:
Recall that in the electronic formula of an atom (for example, for carbon 6 C - 1 s 2 2s 2 2p 2) large numbers in front of the letters - 1, 2 - indicate the number of the energy level. Letters s and R indicate the shape of the electron cloud (orbitals), and the numbers to the right above the letters indicate the number of electrons in a given orbital. All s- spherical orbitals:
At the second energy level except 2 s-there are three orbitals 2 R-orbitals. These 2 R-orbitals have an ellipsoidal shape, similar to dumbbells, and are oriented in space at an angle of 90 ° to each other. 2 R-Orbitals denote 2 p x, 2r y and 2 pz according to the axes along which these orbitals are located.
When chemical bonds are formed, the electron orbitals acquire the same shape. So, in saturated hydrocarbons, one s-orbital and three R-orbitals of a carbon atom to form four identical (hybrid) sp 3-orbitals:
This is - sp 3 - hybridization.
Hybridization– alignment (mixing) of atomic orbitals ( s and R) with the formation of new atomic orbitals, called hybrid orbitals.
Hybrid orbitals have an asymmetric shape, elongated towards the attached atom. Electron clouds repel each other and are located in space as far as possible from each other. At the same time, the axes of four sp 3-hybrid orbitals turn out to be directed to the vertices of the tetrahedron (regular triangular pyramid).
Accordingly, the angles between these orbitals are tetrahedral, equal to 109°28".
The tops of electron orbitals can overlap with the orbitals of other atoms. If electron clouds overlap along a line connecting the centers of atoms, then such a covalent bond is called sigma()-bond. For example, in a C 2 H 6 ethane molecule, a chemical bond is formed between two carbon atoms by overlapping two hybrid orbitals. This is a connection. In addition, each of the carbon atoms with its three sp 3-orbitals overlap with s-orbitals of three hydrogen atoms, forming three -bonds.
In total, three valence states with different types of hybridization are possible for a carbon atom. Except sp 3-hybridization exists sp 2 - and sp-hybridization.
sp 2 -Hybridization- mixing one s- and two R-orbitals. As a result, three hybrid sp 2 -orbitals. These sp 2 -orbitals are located in the same plane (with axes X, at) and are directed to the vertices of the triangle with an angle between the orbitals of 120°. unhybridized
R-orbital is perpendicular to the plane of the three hybrid sp 2 orbitals (oriented along the axis z). Upper half R-orbitals are above the plane, the lower half is below the plane.
Type sp 2-hybridization of carbon occurs in compounds with a double bond: C=C, C=O, C=N. Moreover, only one of the bonds between two atoms (for example, C=C) can be a bond. (The other bonding orbitals of the atom are directed in opposite directions.) The second bond is formed as a result of the overlap of non-hybrid R-orbitals on both sides of the line connecting the nuclei of atoms.
Covalent bond formed by lateral overlap R-orbitals of neighboring carbon atoms is called pi()-bond.
Education
|
Due to less overlap of orbitals, the -bond is less strong than the -bond.
sp-Hybridization is a mixing (alignment in form and energy) of one s- and one
R-orbitals with the formation of two hybrid sp-orbitals. sp- Orbitals are located on the same line (at an angle of 180 °) and directed in opposite directions from the nucleus of the carbon atom. Two
R-orbitals remain unhybridized. They are placed perpendicular to each other.
directions - connections. On the image sp-orbitals are shown along the axis y, and the unhybridized two
R-orbitals - along the axes X and z.
The triple carbon-carbon bond CC consists of a -bond that occurs when overlapping
sp-hybrid orbitals, and two -bonds.
The relationship between such parameters of the carbon atom as the number of attached groups, the type of hybridization and the types of chemical bonds formed is shown in Table 4.
Table 4
Covalent bonds of carbon
| Number of groups related with carbon |
Type hybridization |
Types participating chemical bonds |
Examples of compound formulas |
|---|---|---|---|
| 4 | sp 3 | Four - connections | |
| 3 | sp 2 | Three - connections and one is connection |
|
| 2 | sp | Two - connections and two connections |
H-CC-H |
Exercises.
1. What electrons of atoms (for example, carbon or nitrogen) are called unpaired?
2. What does the concept of "shared electron pairs" mean in compounds with a covalent bond (for example, CH 4 or H 2 S )?
3. What are the electronic states of atoms (for example, C or N ) are called basic, and which are excited?
4. What do the numbers and letters mean in the electronic formula of an atom (for example, C or N )?
5. What is an atomic orbital? How many orbitals are in the second energy level of a C atom and how do they differ?
6. What is the difference between hybrid orbitals and the original orbitals from which they were formed?
7. What types of hybridization are known for the carbon atom and what are they?
8. Draw a picture of the spatial arrangement of orbitals for one of the electronic states of the carbon atom.
9. What chemical bonds are called and what? Specify-and-connections in connections:
10. For the carbon atoms of the compounds below, indicate: a) the type of hybridization; b) types of its chemical bonds; c) bond angles.
Answers to exercises for topic 1
Lesson 5
1. Electrons that are one per orbital are called unpaired electrons. For example, in the electron diffraction formula of an excited carbon atom, there are four unpaired electrons, and the nitrogen atom has three:
2. Two electrons participating in the formation of one chemical bond are called common electron pair. Usually, before the formation of a chemical bond, one of the electrons of this pair belonged to one atom, and the other electron belonged to another atom:
3. The electronic state of the atom, in which the order of filling of electronic orbitals is observed: 1 s 2 , 2s 2 , 2p 2 , 3s 2 , 3p 2 , 4s 2 , 3d 2 , 4p 2 etc. are called main state. AT excited state one of the valence electrons of the atom occupies a free orbital with a higher energy, such a transition is accompanied by the separation of paired electrons. Schematically it is written like this:
Whereas in the ground state there were only two valence unpaired electrons, in the excited state there are four such electrons.
5.
An atomic orbital is a function that describes the density of an electron cloud at each point in space around the nucleus of a given atom. There are four orbitals on the second energy level of the carbon atom - 2 s, 2p x, 2r y,
2pz. These orbitals are:
a) the shape of the electron cloud ( s- ball, R- dumbbell);
b) R-orbitals have different orientations in space - along mutually perpendicular axes x, y and z, they are denoted p x, r y,
pz.
6.
Hybrid orbitals differ from the original (non-hybrid) orbitals in shape and energy. For example, s-orbital - the shape of a sphere, R- symmetrical figure eight, sp-hybrid orbital - asymmetric figure eight.
Energy Differences: E(s) < E(sp) < E(R). Thus, sp-orbital - an orbital averaged in shape and energy, obtained by mixing the initial s-
and p-orbitals.
7. Three types of hybridization are known for the carbon atom: sp 3 , sp 2 and sp (see the text of lesson 5).
9.
-bond - a covalent bond formed by frontal overlapping of orbitals along a line connecting the centers of atoms.
-bond - a covalent bond formed by lateral overlap R-orbitals on either side of the line connecting the centers of atoms.
- Bonds are shown by the second and third lines between the connected atoms.
Concept of hybridization
The concept of hybridization of valence atomic orbitals was proposed by the American chemist Linus Pauling to answer the question why, if the central atom has different (s, p, d) valence orbitals, the bonds formed by it in polyatomic molecules with the same ligands are equivalent in their energy and spatial characteristics.
Ideas about hybridization are central to the method of valence bonds. Hybridization itself is not a real physical process, but only a convenient model that makes it possible to explain the electronic structure of molecules, in particular, hypothetical modifications of atomic orbitals during the formation of a covalent chemical bond, in particular, the alignment of chemical bond lengths and bond angles in a molecule.
The concept of hybridization was successfully applied to the qualitative description of simple molecules, but was later extended to more complex ones. Unlike the theory of molecular orbitals, it is not strictly quantitative, for example, it is not able to predict the photoelectron spectra of even such simple molecules as water. It is currently used mainly for methodological purposes and in synthetic organic chemistry.
This principle is reflected in the Gillespie-Nyholm theory of repulsion of electron pairs. The first and most important rule which was formulated as follows:
"Electronic pairs take such an arrangement on the valence shell of the atom, in which they are as far away from each other as possible, that is, electron pairs behave as if they repel each other."The second rule is that "all electron pairs included in the valence electron shell are considered to be located at the same distance from the nucleus".
Types of hybridization
sp hybridization
Occurs when mixing one s- and one p-orbitals. Two equivalent sp-atomic orbitals are formed, located linearly at an angle of 180 degrees and directed in different directions from the nucleus of the carbon atom. The two remaining non-hybrid p-orbitals are located in mutually perpendicular planes and participate in the formation of π-bonds, or are occupied by lone pairs of electrons.
sp 2 hybridization
Occurs when mixing one s- and two p-orbitals. Three hybrid orbitals are formed with axes located in the same plane and directed to the vertices of the triangle at an angle of 120 degrees. The non-hybrid p-atomic orbital is perpendicular to the plane and, as a rule, participates in the formation of π-bonds
sp 3 hybridization
Occurs when mixing one s- and three p-orbitals, forming four sp3-hybrid orbitals of equal shape and energy. They can form four σ-bonds with other atoms or be filled with lone pairs of electrons.
The axes of sp3-hybrid orbitals are directed to the vertices of a regular tetrahedron. The tetrahedral angle between them is 109°28", which corresponds to the lowest electron repulsion energy. Sp3 orbitals can also form four σ-bonds with other atoms or be filled with unshared pairs of electrons.
Hybridization and molecular geometry
Ideas about the hybridization of atomic orbitals underlie the Gillespie-Nyholm theory of repulsion of electron pairs. Each type of hybridization corresponds to a strictly defined spatial orientation of the hybrid orbitals of the central atom, which allows it to be used as the basis of stereochemical concepts in inorganic chemistry.
The table shows examples of the correspondence between the most common types of hybridization and the geometric structure of molecules, assuming that all hybrid orbitals participate in the formation of chemical bonds (there are no unshared electron pairs).
| Type of hybridization | Number hybrid orbitals |
Geometry | Structure | Examples |
|---|---|---|---|---|
| sp | 2 | Linear | BeF 2 , CO 2 , NO 2 + | |
| sp 2 | 3 | triangular |  |
BF 3, NO 3 -, CO 3 2- |
| sp 3 | 4 | tetrahedral |  |
CH 4, ClO 4 -, SO 4 2-, NH 4 + |
| dsp2 | 4 | flat square |  |
Ni(CO) 4 , XeF 4 |
| sp 3 d | 5 | Hexahedral |  |
PCl 5 , AsF 5 |
| sp 3 d 2 | 6 | Octahedral |  |
SF 6 , Fe(CN) 6 3- , CoF 6 3- |
Links
Literature
- Pauling L. The nature of the chemical bond / Per. from English. M. E. Dyatkina. Ed. prof. Ya. K. Syrkina. - M.; L.: Goshimizdat, 1947. - 440 p.
- Pauling L. General chemistry. Per. from English. - M .: Mir, 1974. - 846 p.
- Minkin V. I., Simkin B. Ya., Minyaev R. M. Theory of the structure of molecules. - Rostov-on-Don: Phoenix, 1997. - S. 397-406. - ISBN 5-222-00106-7
- Gillespie R. Geometry of molecules / Per. from English. E. Z. Zasorina and V. S. Mastryukov, ed. Yu. A. Pentina. - M .: Mir, 1975. - 278 p.
see also
Notes
Wikimedia Foundation. 2010 .
Instruction
Consider a molecule of the simplest saturated hydrocarbon, methane. Its looks like this: CH4. The spatial model of a molecule is a tetrahedron. A carbon atom forms bonds with four hydrogen atoms that are exactly the same in length and energy. According to the above example, they involve 3 - P electron and 1 S - an electron whose orbital has become exactly the same as the orbitals of the other three electrons as a result of what happened. This type of hybridization is called sp^3 hybridization. It is inherent in all the ultimate.
But the simplest representative of unsaturated - ethylene. Its formula is as follows: C2H4. What type of hybridization is inherent in carbon in the molecule of this substance? As a result, three orbitals are formed in the form of asymmetric "eights" lying in the same plane at an angle of 120 ^ 0 to each other. They were formed by 1 - S and 2 - P electrons. The last 3rd P - the electron did not modify its orbital, that is, it remained in the form of a regular "eight". This type of hybridization is called sp^2 hybridization.
How are bonds formed in a molecule? Two hybridized orbitals of each atom entered into with two hydrogen atoms. The third hybridized orbital formed a bond with the same orbital of another. Are the remaining R orbitals? They are "attracted" to each other on both sides of the plane of the molecule. A bond has formed between the carbon atoms. It is the atoms with a "double" bond that sp^2 is inherent in.
And what happens in the acetylene molecule or? Its formula is as follows: C2H2. In each carbon atom, only two electrons undergo hybridization: 1 - S and 1 - P. The remaining two retained orbitals in the form of "regular eights" overlapping in the plane of the molecule and on both sides of it. That is why this type of hybridization is called sp - hybridization. It is inherent in atoms with a triple bond.
All the words, existing in a particular language, can be divided into several groups. This is important in determining both meaning and grammatical functions. the words. Assigning it to a certain type, you can modify it according to the rules, even if you haven't seen it before. Element types the words lexicology deals with the rnogo composition of the language.
You will need
- - text;
- - vocabulary.
Instruction
Select the word you want to type. Its belonging to one or another part of speech does not yet play a role, as well as its form and function in a sentence. It can be absolutely any word. If it is not indicated in the task, write out the first one that comes across. Determine whether it names an object, quality, action or not. For this setting, all the words are divided into significant, pronominal, numerals, service and interjection. To the first type include nouns, adjectives, verbs and . They denote the names of objects, qualities and actions. The second type of words that have a naming function is pronominal. The ability to name is absent in , interjection and service types. These are relatively small groups of words, but they are in everyone.
Determine if the given word is capable of expressing the concept. This feature has the words significant units of a significant type, because they form the conceptual range of any language. However, any number also belongs to the category of concepts, and, accordingly, also carries this function. Functional words also have it, but pronouns and interjections do not.
Consider what the word would be like if it were in a sentence. Can it be? It can be any word of significant type. But this possibility is also in, as well as in the numeral. And here are the official the words play an auxiliary role, they cannot be the subject, nor the secondary members of the sentence, as well as interjections.
For convenience, you can make a plate of four columns of six rows. In the top line, name the corresponding columns "Types of words", "Name", "Concept" and "Able to be a member of the sentence." In the first left column, write down the names of the types of words, there are five in total. Determine which functions the given word has and which it does not. In the appropriate column, put the pluses and. If there are pluses in all three columns, then this is a significant type. The pronominal pluses will be in the first and third columns, in the second and third. Service the words can only express the concept, that is, they have one plus in the second column. Opposite interjections in all three columns there will be minuses.
Related videos
Hybridization is the process of obtaining hybrids - plants or animals descended from the crossing of different varieties and breeds. The word hybrid (hybrida) is translated from Latin as "mixture".
Hybridization: natural and artificial
The process of hybridization is based on the combination in one cell of the genetic material of different cells from different individuals. There is a difference between intraspecific and remote, in which the connection of different genomes occurs. In nature, natural hybridization has occurred and continues to occur without human intervention all the time. It was by interbreeding within a species that plants changed and improved and new varieties and breeds of animals appeared. From the point of view, there is a hybridization of DNA, nucleic acids, changes at the atomic and intraatomic levels.
In academic chemistry, hybridization is understood as a specific interaction of atomic orbitals in the molecules of a substance. But this is not a real physical process, but only a hypothetical model, concept.
Hybrids in crop production
In 1694, the German scientist R. Camerarius proposed artificially obtaining. And in 1717, the English T. Fairchild first crossed different types of carnations. Today, intraspecific hybridization of plants is carried out in order to obtain high-yielding or adapted, for example, frost-resistant varieties. Hybridization of forms and varieties is one of the methods of plant breeding. Thus, a huge number of modern crop varieties have been created.
With distant hybridization, when representatives of different species are crossed and different genomes are combined, the resulting hybrids in most cases do not give offspring or produce low-quality crossbreeds. That is why it makes no sense to leave the seeds of hybrid cucumbers that have ripened in the garden, and every time to buy their seeds in a specialized store.
Selection in animal husbandry
In the world, natural hybridization, both intraspecific and distant, also takes place. Mules have been known to man for two thousand years before our era. And at present, the mule and hinny are used in the household as a relatively cheap working animal. True, such hybridization is interspecific, therefore hybrid males are necessarily born sterile. Females very rarely give offspring.
A mule is a hybrid of a mare and a donkey. A hybrid obtained from crossing a stallion and a donkey is called a hinny. Mules are specially bred. They are taller and stronger than a hinny.
But crossing a domestic dog with a wolf was a very common activity among hunters. Then, the resulting offspring were subjected to further selection, as a result, new breeds of dogs were created. Today, animal breeding is an important component of the success of the livestock industry. Hybridization is carried out purposefully, with a focus on the specified parameters.
Hybridization– alignment (mixing) of atomic orbitals ( s and R) with the formation of new atomic orbitals, called hybrid orbitals.
atomic orbital is a function that describes the density of the electron cloud at each point in space around the nucleus of an atom. An electron cloud is a region of space in which an electron can be found with a high probability.
Sp hybridization
Occurs when mixing one s- and one p-orbitals. Two equivalent sp-atomic orbitals are formed, located linearly at an angle of 180 degrees and directed in different directions from the nucleus of the central atom. The two remaining non-hybrid p-orbitals are located in mutually perpendicular planes and participate in the formation of π-bonds, or are occupied by lone pairs of electrons.
Sp2 hybridization
Sp2 hybridization
Occurs when mixing one s- and two p-orbitals. Three hybrid orbitals are formed with axes located in the same plane and directed to the vertices of the triangle at an angle of 120 degrees. The non-hybrid p-atomic orbital is perpendicular to the plane and, as a rule, participates in the formation of π-bonds
The table shows examples of the correspondence between the most common types of hybridization and the geometric structure of molecules, assuming that all hybrid orbitals are involved in the formation of chemical bonds (there are no unshared electron pairs)
|
Type of hybridization |
Number of hybrid orbitals |
Geometry |
Structure |
Examples |
|
Linear |
|
BeF 2 , CO 2 , NO 2 + |
||
|
sp 2 |
triangular |
|
BF 3, NO 3 -, CO 3 2- |
|
|
sp 3 |
tetrahedral |
|
CH 4, ClO 4 -, SO 4 2-, NH 4 + |
|
|
dsp 2 |
flat square |
|
Ni(CO) 4 , 2- |
|
|
sp 3 d |
Hexahedral |
| ||
|
sp 3 d 2 , d 2 sp 3 |
Octahedral |
|
SF 6 , Fe(CN) 6 3- , CoF 6 3- |
4. Electrovalent, covalent, donor-acceptor, hydrogen bonds. Electronic structure of σ and π bonds. The main characteristics of a covalent bond: bond energy, length, bond angle, polarity, polarizability.
If an electrostatic interaction takes place between two atoms or two groups of atoms, leading to strong attraction and the formation of a chemical bond, then such a bond is called electrovalent or heteropolar.
covalent bond- a chemical bond formed by the overlap of a pair of valence electron clouds. The electron clouds that provide communication are called a common electron pair.
Donor-acceptor bond - this is a chemical bond between two atoms or a group of atoms, carried out due to the lone pair of electrons of one atom (donor) and the free level of another atom (acceptor). This bond differs from the covalent bond in the origin of the electron bond.
hydrogen bond - this is a type of chemical interaction of atoms in a molecule, characterized in that a hydrogen atom, already bound by a covalent bond with other atoms, takes a significant part in it
The σ bond is the first and stronger bond that is formed when electron clouds overlap in the direction of the straight line connecting the centers of atoms.
σ bond is the usual covalent bonds of carbon atoms with hydrogen atoms. Molecules of saturated carbons contain only σ bonds.
π bond is a weaker bond that is formed when the electron plane of the atoms of the nuclei overlaps
The electrons of the π and σ bonds lose their belonging to a particular atom.
Features of σ and π bonds: 1) the rotation of carbon atoms in a molecule is possible if they are connected by a σ bond; 2) the appearance of a π bond deprives the carbon atom in the molecule of free rotation.
Communication length- is the distance between the centers of the bonded atoms.
Valence angle- is the angle between two bonds that has a common atom.
Communication energy- the energy released during the formation of a chemical. bonds and characterized by its strength
Polarity connection is due to the uneven distribution of electron density due to differences in the electronegativity of atoms. On this basis, covalent bonds are divided into non-polar and polar. Polarizability the bond is expressed in the displacement of bond electrons under the influence of an external electric field, including another reacting particle. Polarizability is determined by the electron mobility. The polarity and polarizability of covalent bonds determine the reactivity of molecules with respect to polar reagents.
5. Ionic bond (electrovalent) - a very strong chemical bond formed between atoms with a large difference in electronegativity, in which the common electron pair passes predominantly to an atom with a greater electronegativity. Covalent bond - occurs due to the socialization of an electron pair through an exchange mechanism, when each of the interacting atoms supplies one electron. Donor-acceptor bond (coordination bond) is a chemical bond between two atoms or a group of atoms, carried out due to the lone pair of electrons of one atom (donor) and the free orbital of another atom (acceptor). Example NH4 For the occurrence of hydrogen bonds, it is important that there are atoms in the molecules of a substance hydrogen bonds to small but electronegative atoms, for example: O, N, F. This creates a noticeable partial positive charge on the hydrogen atoms. On the other hand, it is important that electronegative atoms have lone electron pairs. When an electron-depleted hydrogen atom of one molecule (acceptor) interacts with an unshared electron pair on the N, O, or F atom of another molecule (donor), a bond similar to a polar covalent bond arises. When a covalent bond is formed in the molecules of organic compounds, a common electron pair populates the bonding molecular orbitals, which have a lower energy. Depending on the form of the MO - σ-MO or π-MO - the resulting bonds are classified as σ- or p-type. σ-bond - a covalent bond formed by overlapping s-, p- and hybrid AO along the axis connecting the nuclei of the bonded atoms (i.e., with axial overlap of AO) . π-bond - a covalent bond that occurs during the lateral overlap of non-hybrid p-AO. Such overlap occurs outside the straight line connecting the nuclei of atoms. 
π-bonds arise between atoms already connected by a σ-bond (in this case, double and triple covalent bonds are formed). The π-bond is weaker than the σ-bond due to the less complete overlap of the p-AO. 
The different structure of σ- and π-molecular orbitals determines the characteristic features of σ- and π-bonds. 1.σ-bond is stronger than π-bond. This is due to the more efficient axial overlap of AOs during the formation of σ-MOs and the presence of σ-electrons between the nuclei. 2. By σ-bonds, intramolecular rotation of atoms is possible, since the form of σ-MO allows such rotation without breaking the bond (see anim. Picture below)). Rotation along a double (σ + π) bond is impossible without breaking the π bond! 3. Electrons on the π-MO, being outside the internuclear space, have greater mobility than σ-electrons. Therefore, the polarizability of the π bond is much higher than that of the σ bond.
The characteristic properties of a covalent bond - directionality, saturation, polarity, polarizability - determine the chemical and physical properties of compounds.
The direction of the bond is due to the molecular structure of the substance and the geometric shape of their molecule. The angles between two bonds are called bond angles.
Saturation - the ability of atoms to form a limited number of covalent bonds. The number of bonds formed by an atom is limited by the number of its outer atomic orbitals.
The polarity of the bond is due to the uneven distribution of the electron density due to differences in the electronegativity of the atoms. On this basis, covalent bonds are divided into non-polar and polar (non-polar - a diatomic molecule consists of identical atoms (H 2, Cl 2, N 2) and the electron clouds of each atom are distributed symmetrically with respect to these atoms; polar - a diatomic molecule consists of atoms of different chemical elements , and the general electron cloud shifts towards one of the atoms, thereby forming an asymmetry in the distribution of electric charge in the molecule, generating the dipole moment of the molecule).
The polarizability of a bond is expressed in the displacement of bond electrons under the influence of an external electric field, including that of another reacting particle. Polarizability is determined by the electron mobility. The polarity and polarizability of covalent bonds determine the reactivity of molecules with respect to polar reagents.
6.Nomenclature is a system of rules that allows you to give a unique name to each individual connection. For medicine, knowledge of the general rules of nomenclature is of particular importance, since the names of numerous medicines are built in accordance with them. Currently generally accepted IUPAC systematic nomenclature(IUPAC - International Union of Pure and Applied Chemistry)*.
However, they are still preserved and widely used (especially in medicine) trivial(ordinary) and semi-trivial names used even before the structure of matter became known. These names may reflect natural sources and methods of preparation, especially noticeable properties and applications. For example, lactose (milk sugar) is isolated from milk (from lat. lactum- milk), palmitic acid - from palm oil, pyruvic acid obtained by pyrolysis of tartaric acid, the name of glycerin reflects its sweet taste (from the Greek. glykys- sweet).
Trivial names especially often have natural compounds - amino acids, carbohydrates, alkaloids, steroids. The use of some established trivial and semi-trivial names is permitted by IUPAC rules. Such names include, for example, "glycerol" and the names of many well-known aromatic hydrocarbons and their derivatives.
Rational nomenclature of saturated hydrocarbons
Unlike the trivial names, they are based on the structure of molecules. The names of complex structures are made up of the names of the blocks of those radicals associated with the main most important site of the molecule; according to this nomenclature, alkanes are considered as derivatives of methane in which hydrogen atoms are replaced by the corresponding radicals. The choice of methane carbon is arbitrary, therefore 1 compound can have several names. According to this nomenclature, alkenes are considered as derivatives of ethylene and alkynes-acetylene.
7. Homology of organic compoundsor the law of homologues- consists in the fact that substances of the same chemical function and the same structure, which differ from each other on their atomic composition is only nCH 2, they turn out to be consolidated and in all their rest chem. character, and the difference in their physical properties increases or generally changes correctly as the difference in composition, determined by the number n of CH 2 groups, increases. Such chem. similar compounds form the so-called. a homological series, the atomic composition of all members of which can be expressed by a general formula depending on the composition of the first member of the series and the number of carbon atoms; organic substances of one name such as alkanes only.
Isomers are compounds that have the same composition but different structure and properties.
8.Nucleofandelectric and electrophoricandle reactantsents. Reagents involved in substitution reactions are divided into nucleophilic and electrophilic. Nucleophilic reagents, or nucleophiles, provide their pair of electrons to form a new bond and displace the leaving group (X) from the RX molecule with the pair of electrons that formed the old bond, for example:
(where R is an organic radical).
Nucleophiles include negatively charged ions (Hal - , OH - , CN - , NO 2 - , OR - , RS - , NH 2 - , RCOO - and others), neutral molecules with a free pair of electrons (for example, H 2 O , NH3, R 3 N, R 2 S, R 3 P, ROH, RCOOH), and organometallic. R-Me compounds with a sufficiently polarized C-Me + bond, i.e., capable of being R- carbanion donors. Reactions involving nucleophiles (nucleophilic substitution) are mainly characteristic of aliphatic compounds, for example, hydrolysis (OH - , H 2 O), alcoholysis (RO - , ROH), acidolysis (RCOO - , RCOOH), amination (NH - 2, NH 3 , RNH 2, etc.), cyanidation (CN -), etc.
Electrophilic reagents, or electrophiles, when a new bond is formed, serve as electron pair acceptors and displace the leaving group in the form of a positively charged particle. Electrophiles include positively charged ions (for example, H +, NO 2 +), neutral molecules with an electron deficit, for example SO 3, and highly polarized molecules (CH 3 COO - Br +, etc.), and polarization is especially effectively achieved by complex formation with coefficients Lewis (Hal + - Hal - A, R + - Cl - A, RCO + - Cl - A, where A \u003d A1C1 3, SbCl 5, BF 3, etc.). Reactions involving electrophiles (electrophilic substitution) include the most important reactions of aromatic hydrocarbons (for example, nitration, halogenation, sulfonation, the Friedel-Crafts reaction):
(E + \u003d Hal +, NO + 2, RCO +, R +, etc.)
In certain systems, reactions involving nucleophiles are carried out in the aromatic series, and reactions involving electrophiles are carried out in the aliphatic series (most often in the series of organometallic compounds).
53. interaction of oxo compounds with organometallics (ketone or aldehyde plus organometallics)
Reactions are widely used to obtain alcohols. When a Grignard reagent (R-MgX) is added to formaldehyde, a primary alcohol is formed, another aldehyde is secondary, and ketones are tritiary alcohols
