Continuation. See the beginning in № 15, 16/2004

Lesson 5. Hybridization
carbon atomic orbitals

A covalent chemical bond is formed using shared bonding electron pairs like:

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 at a time in an orbital cell.
Atomic orbital is a function that describes the density electronic cloud at every point in space around the nucleus of an atom.
An electron cloud is a region of space in which an electron can be detected with a high probability. For approval electronic structure the carbon atom and the valence of this element use the concept of excitation of the carbon atom. 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 the carbon atom and the valence of this element use the concept of excitation of the carbon atom. In the normal (unexcited) state, the carbon atom has two unpaired 2 s

2 electrons can go to free 2 electrons. 2 22 electrons. 2 2-orbital. Then four unpaired electrons appear in the carbon atom: 2) Let us recall that in the electronic formula of an atom (for example, for carbon 6 C – 1 p 2 electrons. big numbers the carbon atom and the valence of this element use the concept of excitation of the carbon atom. In the normal (unexcited) state, the carbon atom has two unpaired 2 before the letters – 1, 2 – indicate the number of the energy level. Letters 2 electrons. And

indicate the shape of the electron cloud (orbital), and the numbers to the right above the letters indicate the number of electrons in a given orbital. All 2 electrons.-spherical orbitals: the carbon atom and the valence of this element use the concept of excitation of the carbon atom. In the normal (unexcited) state, the carbon atom has two unpaired 2 At the second energy level except 2 the carbon atom and the valence of this element use the concept of excitation of the carbon atom. In the normal (unexcited) state, the carbon atom has two unpaired 2-there are three orbitals 2 the carbon atom and the valence of this element use the concept of excitation of the carbon atom. In the normal (unexcited) state, the carbon atom has two unpaired 2-orbitals. These 2 -orbitals have an ellipsoidal shape, similar to dumbbells, and are oriented in space at an angle of 90° to each other. 2, 2-Orbitals denote 2 p x p y and 2

p z 2 electrons. in accordance with the axes along which these orbitals are located. the carbon atom and the valence of this element use the concept of excitation of the carbon atom. In the normal (unexcited) state, the carbon atom has two unpaired 2 When chemical bonds are formed, the electron orbitals acquire the same shape. Thus, in saturated hydrocarbons one -orbital and three-orbitals of the carbon atom to form four identical (hybrid)

sp -orbital and three 3-orbitals:
This - 3 -hybridization. 2 electrons. big numbers the carbon atom and the valence of this element use the concept of excitation of the carbon atom. In the normal (unexcited) state, the carbon atom has two unpaired 2) 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. -orbital and three 3-In this case, the axes of four hybrid orbitals
turn out to be directed towards the vertices of the tetrahedron (regular triangular pyramid).
Accordingly, the angles between these orbitals are tetrahedral, equal to 109°28". The vertices 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()-connection -orbital and three. For example, in the ethane molecule C 2 H 6, 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 2 electrons. 3-orbitals overlap with

-orbitals of three hydrogen atoms, forming three -bonds. -orbital and three In total, three valence states with different types of hybridization are possible for a carbon atom. Except -orbital and three 3-hybridization exists -orbital and three 2 - and
-orbital and three 2 -This --hybridization. 2 electrons.- mixing one the carbon atom and the valence of this element use the concept of excitation of the carbon atom. In the normal (unexcited) state, the carbon atom has two unpaired 2- and two -orbital and three-orbitals. As a result, three hybrids are formed -orbital and three 2 -orbitals. These, 2-orbitals are located in the same plane (with axes X
the carbon atom and the valence of this element use the concept of excitation of the carbon atom. In the normal (unexcited) state, the carbon atom has two unpaired 2 at -orbital and three) and are directed to the vertices of the triangle with an angle between the orbitals of 120°. Unhybridized -the orbital is perpendicular to the plane of the three hybrid 2-orbitals (oriented along the axis the carbon atom and the valence of this element use the concept of excitation of the carbon atom. In the normal (unexcited) state, the carbon atom has two unpaired 2 z
). Upper half -orbital and three-orbitals are above the plane, the lower half is below the plane. the carbon atom and the valence of this element use the concept of excitation of the carbon atom. In the normal (unexcited) state, the carbon atom has two unpaired 2 Type

2-carbon hybridization 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 an - bond. (The other bonding orbitals of the atom are directed in opposite directions.) The second bond is formed as a result of overlapping non-hybrid the carbon atom and the valence of this element use the concept of excitation of the carbon atom. In the normal (unexcited) state, the carbon atom has two unpaired 2-orbitals on both sides of the line connecting the atomic nuclei. Covalent bond formed by lateral overlap.

-orbitals of neighboring carbon atoms is called pi()-connection

Education
-orbital and three-This --communications Due to less orbital overlap, the -bond is less strong than the -bond.– this is mixing (alignment in shape and energy) of one
the carbon atom and the valence of this element use the concept of excitation of the carbon atom. In the normal (unexcited) state, the carbon atom has two unpaired 2 s- -orbital and three and one -orbital and three-orbitals to form two hybrid -orbitals.-The orbitals are located on the same line (at an angle of 180°) and directed towards
the carbon atom and the valence of this element use the concept of excitation of the carbon atom. In the normal (unexcited) state, the carbon atom has two unpaired 2 opposite sides
from the nucleus of a carbon atom. Two -orbital and three-orbitals are shown along the axis y, and the unhybridized two
the carbon atom and the valence of this element use the concept of excitation of the carbon atom. In the normal (unexcited) state, the carbon atom has two unpaired 2-orbitals – along the axes These big numbers -the orbital is perpendicular to the plane of the three hybrid.

A carbon-carbon triple bond CC consists of an -bond formed by 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 carbon bonds

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 - connection
2	sp	Two - connections and two - connections	H–CC–H

Exercises.

1. Which 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 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 there in the second energy level of the C atom? and how do they differ?

6. How are hybrid orbitals different from the original orbitals from which they were formed?

7. What types of hybridization are known for the carbon atom and what do they consist of?

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

10. connections in connections:

For the carbon atoms of the compounds below, indicate: a) type of hybridization; b) types of its chemical bonds; c) bond angles.

Answers to exercises for topic 1

1. Lesson 5 Electrons that are located one at a time in an orbital are called unpaired electrons

2. . For example, in the electron diffraction formula of an excited carbon atom there are four unpaired electrons, and the nitrogen atom has three: Two electrons involved in the formation of one chemical bond , called shared electron pair

3. . Typically, before a chemical bond is formed, one of the electrons in this pair belonged to one atom, and the other electron belonged to another atom: 2 electrons. 2 , 22 electrons. 2 , 2-orbital. Then four unpaired electrons appear in the carbon atom: 2 , 32 electrons. 2 , 3-orbital. Then four unpaired electrons appear in the carbon atom: 2 , 42 electrons. 2 , 3Electronic state of an atom in which the order of filling electron orbitals is observed: 1 2 , 4-orbital. Then four unpaired electrons appear in the carbon atom: d 2, etc., are called underlying condition . IN

While in the ground state there were only two unpaired valence electrons, in the excited state there are four such electrons.

5. An atomic orbital is a function that describes the density of the electron cloud at each point in space around the nucleus of a given atom. At the second energy level of the carbon atom there are four orbitals - 2 2 electrons., 2p x, 2-Orbitals denote 2, 2p y. These orbitals differ:
a) the shape of the electron cloud ( 2 electrons.– ball, the carbon atom and the valence of this element use the concept of excitation of the carbon atom. In the normal (unexcited) state, the carbon atom has two unpaired 2– dumbbell);
b) the carbon atom and the valence of this element use the concept of excitation of the carbon atom. In the normal (unexcited) state, the carbon atom has two unpaired 2-orbitals have different orientation in space – along mutually perpendicular axes x, y big numbers -the orbital is perpendicular to the plane of the three hybrid, they are designated p x, -Orbitals denote 2, p y.

6. Hybrid orbitals differ from the original (non-hybrid) orbitals in shape and energy. For example, 2 electrons.-orbital – the shape of a sphere, the carbon atom and the valence of this element use the concept of excitation of the carbon atom. In the normal (unexcited) state, the carbon atom has two unpaired 2– symmetrical figure eight, sp-hybrid orbital – asymmetric figure eight.
Energy differences: E(2 electrons.) < E(-orbital and three) < E(the carbon atom and the valence of this element use the concept of excitation of the carbon atom. In the normal (unexcited) state, the carbon atom has two unpaired 2). sp Thus, 2 electrons.- -orbital – an orbital averaged in shape and energy, obtained by mixing the original -orbital. Then four unpaired electrons appear in the carbon atom: And

7. -orbitals. sp 3 , sp For a carbon atom, three types of hybridization are known: sp (2 and).

9. see text of lesson 5
-bond - a covalent bond formed by head-on overlapping of orbitals along a line connecting the centers of atoms. the carbon atom and the valence of this element use the concept of excitation of the carbon atom. In the normal (unexcited) state, the carbon atom has two unpaired 2-bond – a covalent bond formed by lateral overlap
-orbitals on both sides of the line connecting the centers of the atoms.

-Bonds are shown by the second and third lines between connected atoms. To explain the facts when an atom forms larger number

bonds than the number of unpaired electrons in its ground state (for example, a carbon atom), the postulate of hybridization of atomic orbitals of similar energy is used. AO hybridization occurs during the formation of a covalent bond if more efficient overlapping of orbitals is achieved. Hybridization of a carbon atom is accompanied by its excitation and electron transfer from 2s- to 2 p-AO:

AOs with a large difference in energy (for example, 1s and 2p) do not enter into hybridization. Depending on the number of p-AOs participating in hybridization, the following types of hybridization are possible: for carbon and nitrogen atoms - sp3, sp2 and sp; for the oxygen atom - sp3, sp2; for halogens - sp3.

Sp2-Hybridization (planar-trigonal) One s- and two p-orbitals are mixed, and three equivalent sp2-hybrid orbitals are formed, located in the same plane at an angle of 120°. They can form three s-bonds. The third p-orbital remains unhybridized and is oriented perpendicular to the plane of location of the hybrid orbitals. This p-AO is involved in the formation of a p-bond.

This lesson will help you get an idea of ​​the topic “Geometry of Molecules. The concept of the theory of hybridization." The universal nature of the hybridization process for organic, complex inorganic substances and allotropic modifications of carbon. You will learn about the dependence of the geometry of molecules on the type of hybridization of electronic orbitals and the properties of substances on the geometry of molecules.

Topic: Introduction to organic chemistry

Lesson: Geometry of molecules. The concept of hybridization theory

using the example of molecules with single bonds

External level carbon atom in the ground (unexcited) state described by the formula 2s 2 2p 2 or the diagram:

2 2 electrons.

This building contains the prerequisites for a unique symmetry- for four electrons there are just 4 orbitals. Back in the middle of the 19th century, the German scientist Friedrich Kekule rightly suggested that in organic compounds The valency of carbon is four.

From the point of view of the electronic structure of the atom, this can be explained as follows:

One electron from the 2s orbital “jumps” to the 2p orbital, and the carbon atom goes into the so-called excited state:

Excited state of an atom carbon 2s 1 2p 3:

2 2 electrons.

allows a carbon atom to form 4 covalent bonds through an exchange mechanism.

The three p-orbitals are traditionally depicted in the form of “dumbbells” mutually perpendicular to each other, and the s-orbital is in the shape of a ball. The three bonds formed by the p electrons must be at 90 degrees to each other and are significantly longer than the bond formed by the s electron. But methane CH 4 is a symmetric tetrahedron.

Back in 1874, many years before it became possible direct definition molecular structure, Jacob Henrik van't Hoff (1852-1911), while a student at Utrecht University, suggested that the carbon atom in compounds has a tetrahedral structure. The structure of the CH 4 methane molecule is a regular tetrahedron with a carbon atom in the center. Bond angles N-C-N bonds equal 109 o 28’.

A simplified explanation: all orbitals of the outer level of carbon are aligned in energy and shape, mixing, i.e. “hybridize”, forming identical hybrid orbitals. See fig. 1.

Rice. 1. Hybridization is the mixing of electron clouds during the formation of chemical bonds

Mixing one s-orbitals and three p-orbitals gives four sp 3-hybrid orbitals, elongated at the corners of the tetrahedron with the C atom in the center. Carbon in methane is in a state of sp 3 hybridization. Rice. 2.

Rice. 2. Structure of methane

The structure of ammonia

In the same way, the four orbitals of the nitrogen atom are hybridized in ammonia molecule NH 3: The nitrogen atom has 5 electrons in its outer shell. Therefore, one sp 3 orbital contains a lone pair of electrons, and the other three contain electron pairs N-H bonds. All four electron pairs are located at the corners of the distorted tetrahedron (the electron cloud of the lone pair is larger than that of the bonding pair). Rice. 3

Rice. 3. Structure of ammonia

Structure of water

The oxygen atom has 6 electrons in its outer shell. Therefore, two sp 3 orbitals contain lone pairs of electrons, and the remaining two contain electron pairs O-H bonds. The molecule has an angular structure. Rice. 4.

Rice. 4. Structure of water

When analyzing the structure of molecules in this way, it is important not to confuse the geometry of the arrangement of electron pairs in space and the geometry of chemical bonds. We see that in ammonia and water not all electron pairs participate in the formation of chemical bonds.

The geometry of molecules or chemical bonds considers the arrangement of atoms in space, without describing the arrangement of lone electron pairs. The electron clouds of hybrid orbitals try to push themselves as far away from each other as possible. If there are four clouds, then they will disperse to the corners of the tetrahedron, three - they will be located in the plane at an angle of 120°.

Molecule structureBF 3

There are 3 electrons in the outer level of a boron atom. When bonds are formed, boron, like carbon, goes into an excited state. One s and two p orbitals, which contain electrons, hybridize to form three identical sp 2 hybrid orbitals located at the corners of an equilateral triangle with a boron atom in the center. Rice. 5

Rice. 5. Structure of boron fluoride

Conclusion: Molecular geometry considers the arrangement of atoms in space without describing the arrangement of lone electron pairs. Thus, the structure of a water molecule, consisting of three atoms, is not tetrahedral, but angular.

Summing up the lesson

You have gained an idea of ​​the topic “Geometry of Molecules. The concept of the theory of hybridization." The universal nature of the hybridization process for organic, complex inorganic substances and allotropic modifications of carbon was revealed. You learned about the dependence of the geometry of molecules on the type of hybridization of electronic orbitals and the properties of substances on the geometry of molecules.

Bibliography

1. Rudzitis G.E. Chemistry. Fundamentals of general chemistry. 10th grade: textbook for educational institutions: a basic level of/ G. E. Rudzitis, F. G. Feldman. - 14th edition. - M.: Education, 2012.

2. Chemistry. Grade 10. Profile level: textbook for general education institutions/ V.V. Eremin, N.E. Kuzmenko, V.V. Lunin et al. - M.: Bustard, 2008. - 463 p.

3. Chemistry. Grade 11. Profile level: academic. for general education institutions/ V.V. Eremin, N.E. Kuzmenko, V.V. Lunin et al. - M.: Bustard, 2010. - 462 p.

4. Khomchenko G.P., Khomchenko I.G. Collection of problems in chemistry for those entering universities. - 4th ed. - M.: RIA "New Wave": Publisher Umerenkov, 2012. - 278 p.

Homework

1. Nos. 1-3 (p. 22) Rudzitis G.E. , Feldman F.G. Chemistry: Organic chemistry. 10th grade: textbook for general education institutions: basic level / G. E. Rudzitis, F.G. Feldman. - 14th edition. - M.: Education, 2012.

2. Why, having the same type of hybridization (which one?), do methane and ammonia molecules have different spatial structures?

3. How does the ground state of a carbon atom differ from the excited state?

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Slide captions:

Hybridization of atomic orbitals

Linus Carl Pauling

Atomic orbital hybridization is a change in the shape and energy of the orbitals of an atom during the formation of a covalent bond to achieve more efficient orbital overlap.

Different orbitals with slightly different energies form a corresponding number of hybrid orbitals. The number of hybrid orbitals is equal to the number of atomic orbitals involved in hybridization. Hybrid orbitals are identical in electron cloud shape and energy.

Hybridization involves not only bonding electrons, but also lone electron pairs.

Compared to atomic orbitals, hybrid orbitals are more elongated in the direction of formation of chemical bonds and therefore provide better overlap of electron clouds.

The hybrid orbital is more elongated on one side of the nucleus than on the other.

Coord. number Type of hybridization Spatial configuration of the molecule, the central atom of which is subject to hybridization Arrangement of atoms in the molecule Examples of compounds 2 sp Linear BeCl 2, CO 2, HCN 3 sp 2 Trigonal BF 3, BCl 3, NO 3 -, HgI 3 -, CdCl 3 - 4 sp 3 Tetrahedral CH 4 , CCl 4 , XeO 4 , HgI 4 - ,

sp hybridization is a hybridization that involves the atomic orbitals of one s and one p electron

During the hybridization process, 2 hybrid orbitals are formed, which are oriented to each other at an angle of 180 °

The concept of sp-hybridization of orbitals can be used to explain linear shape BeH 2 molecule, in which the beryllium atom is formed by hybrid sp orbitals.

Formation of a beryllium fluoride molecule. Each fluorine atom that is part of this molecule has one unpaired electron, which participates in the formation of a covalent bond.

A beryllium atom in an unexcited state does not have unpaired electrons: Therefore, in order to participate in the formation of chemical bonds, the beryllium atom must go into an excited state:

with the expenditure of some energy, instead of the original s and p orbitals of the beryllium atom, two equivalent hybrid orbitals (sp orbitals) can be formed.

Examples chemical compounds, which are characterized by sp-hybridization: BeCl 2, BeH 2, CO, CO 2, HCN, carbine, acetylene hydrocarbons (alkynes).

sp 2 hybridization - hybridization in which the atomic orbitals of one s and two p electrons participate

As a result of hybridization, three hybrid sp 2 orbitals are formed, located in the same plane at an angle of 120° to each other

This type of hybridization is observed in the BCl 3 molecule.

sp 2 - hybridization of a boron atom in a boron fluoride molecule. Here, instead of the original one s- and two p-orbitals of the excited boron atom

three equivalent sp 2 orbitals are formed. Therefore, the molecule is built in the shape of a regular triangle, with a boron atom in the center and fluorine atoms at the vertices.

Examples of compounds in which sp 2 hybridization is observed: SO 3, BCl 3, BF 3, AlCl 3, CO 3 2-, NO 3 -, graphite, ethylene hydrocarbons (alkenes), carboxylic acids and aromatic hydrocarbons(arenas).

sp 3 - hybridization - hybridization in which the atomic orbitals of one s and three p electrons participate

Four sp 3 hybrid orbitals are symmetrically oriented in space at an angle of 109°28"

The spatial configuration of a molecule does not always correspond to a tetrahedron; it depends on the number of atoms in the molecule. An example of this is the molecules of water and ammonia NH 3.

The valency of the nitrogen atom is III, its five electrons of the outer level occupy four orbitals, which means the type of hybridization is sp 3, but only three orbitals take part in the formation of a chemical bond. A tetrahedron without one vertex turns into a pyramid. Therefore, the ammonia molecule has a pyramidal shape and the bond angle is distorted to 107°30′.

oxygen in a water molecule is in an sp 3 hybrid state, and the shape of the molecule is angular, the bond angle is 104°27′.

Examples of compounds characterized by sp 3 hybridization: H 2 O, NH 3, POCl 3, SO 2 F 2, SOBr 2, NH 4+, H 3 O +, diamond, saturated hydrocarbons (alkanes, cycloalkanes).