Hybridization of atomic orbitals of carbon. Types of hybridization

Examples. Determine the type of chemical bond between atoms in the molecules of substances: sodium hydroxide, sulfuric acid, arsenic hydroxide, sodium sulfate. Show with an arrow to which element the electron pair is shifted. Which bond is more polar? What are the oxidation states of the atoms of the elements?

Execution algorithm 1. Draw a graphical formula. 2. Under each element, put down the electronegativity value from the table. 3. Show the electron density shift with an arrow. 4. Calculate the difference in relative electronegativity and indicate the type of bond (ionic, CP, CNP) 5. Determine the oxidation states of the elements atoms by the direction and number of electron density shifts.

An example of NaOH Na OH 0.93 3.5 2, OEO(O-Na) OEO(O-Na)= 3.5 - 0.93=2.63 OEO(O-H)= 3.5-2, 1=1.4 ionic CP

Continued H 2 SO 4 S O O O O H H OEO(O-H)=3.5-2.1=1.4 KP OEO(O-S)=3.5-2.6=0.9 KP

Determine the type of hybridization of the central atom in molecules 1. CH 4 methane 2. NH 3 ammonia 3. H 2 O Example C HH H H The central atom is carbon. В(С)=4 3. …2s 2 2p s 1 2p 3

5. One s and three p-electronic orbitals are involved in the formation of the structure of the molecule. All bonds in the methane molecule are single bonds. Hybridization type sp 3. All electron clouds involved in hybridization are the same. Therefore, the angles between them are the same and =0. The molecule is non-polar. Geometric shape tetrahedron. Answer sp 3 -hybridization \u003d 0, non-polar molecule

Ammonia molecule Arguing similarly for the ammonia molecule: 1 N H H H 2. B(N)=3, …2s 2 2p 3: bonds + electron pair. 5. SP 3 - hybridization. Electronic clouds of a different nature. The angles between them are not the same. 0. The molecule is polar.

Water molecule 2. Oxygen B=2. :O: H H s 2 2p 4 4. There are 2 bonds and two electron pairs in the molecule. The s- and three p-electron orbitals are involved in the formation of the molecular structure. Hybridization type sp 3. 0 (because the angles between the electron clouds are different). The molecule is polar.

Interactions between molecules. Hydrogen bond Hydrogen bond is a special type of interaction between molecules of substances. A hydrogen bond arises between a hydrogen atom and another more electronegative atom due to the forces of electrostatic attraction according to the donor-acceptor mechanism.

Van der Waals interaction (intermolecular interaction) In 1873, the Dutch scientist I. Van der Waals suggested that there are forces that cause attraction between molecules. Types of interaction: 1) dipole-dipole (orientation) Interaction of polar molecules. 2) Induction. Interaction of polar and nonpolar molecules. The energy of this type of interaction is weaker than the orientational one. 3) Dispersive. In non-polar molecules (inert gases), electron density fluctuations occur, resulting in instantaneous dipoles that can induce neighboring molecules.

STATE AUTONOMOUS EDUCATIONAL INSTITUTION

SECONDARY VOCATIONAL EDUCATION IN THE NOVOSIBIRSK REGION

"KUPINSKY MEDICAL COLLEGE"

TOOLKIT

« »

for independent work of students

in Chemistry

Section: Organic chemistry

Topic: The subject of organic chemistry.

Theory of the structure of organic compounds

Specialty: 34.02.01 "Nursing" 1 course

Kupino

2015 academic year

Considered at the meeting

subject - cyclic methodological commission on

general education disciplines, general humanitarian and

socio-economic, mathematical

and natural science cycle

Protocol from 2015

Chairman ______________ /__________________/

Vede Irina Viktorovna

Explanatory note to the methodological manual

The methodological guide is intended for in-depth study of the topic « Types of carbon atom hybridization ».

Practice shows that many students find it difficult to determine the types of hybridization of carbon atoms and the types of chemical bonds in the study of organic compounds.

The purpose of the manual is to help students learn to identify the types of hybridization of carbon atoms and the types of chemical bonds in organic compounds.This manual is recommended for 1st year students of the specialty 34.02.01 Nursing. The manual contains theoretical material on the topic, tables for systematizing knowledge, exercises for independent work and detailed answers for each of the tasks.

The manual is aimed at developing the skills of independent work with educational material, the search for and use of information, the formation and development of creative potential, increasing interest in the discipline.

I'm always ready to learn

but I don't always like it

when they teach me

W. Churchill

Types of carbon atom hybridization

The electronic structure of the carbon atom in the ground state is 1s 2 2s 2 2p 2 , there are two unpaired electrons on the p-orbitals of the 2nd level. This allows the carbon atom to form only two covalent bonds by the exchange mechanism. However, in all organic compounds, carbon forms four covalent bonds, which becomes possible as a result of hybridization of atomic orbitals.

Hybridization is the interaction of atomic orbitals with close energy values, accompanied by the formation of new "hybrid" orbitals.

Hybridization is an energy-intensive process, but these costs are more than offset by the energy released when more covalent bonds are formed. the resulting "hybrid" orbitals are shaped like an asymmetric dumbbell and differ sharply from the initial orbitals of the carbon atom.

Three types of hybridization are possible for a carbon atom: sp 3 -hybridization- interacting orbitals are shown by blue arrows:

sp 2 -hybridization:

sp hybridization:

Hybrid orbitals of the carbon atom are able to participate in the formation of only -bonds, p-orbitals unaffected by hybridization form only -bonds. It is this feature that determines the spatial structure of the molecules of organic substances.

Hybridization
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. Everything 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 R X , 2R y and 2 R z according to the axes along which these orbitals are located.

Shape and Orientation
p-electron orbitals

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 - sp 3 - hybridization.
Hybridization– alignment (mixing) of atomic orbitals ( s and R) with the formation of new atomic orbitals, called hybrid orbitals.

Four sp 3 hybrid orbitals
carbon atom

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.

Scheme of overlapping electron clouds
in the ethane molecule

In total, three valence states with different types of hybridization are possible for a carbon atom. Besides 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.
A 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.

Orbitals (three sp 2 and one p)
carbon atom in sp 2 hybridization

Covalent bond formed by lateral overlap R-orbitals of neighboring carbon atoms is called pi( )-bond.

Education
- communications

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.

Atomic orbitals (two sp and two p)
carbon in the state of sp-hybridization

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.

Covalent bonds of carbon

Number of groups
related
with carbon

A type
hybridization

Types
participating
chemical bonds

Examples of compound formulas

sp 3

Four - communications

sp 2

Three - communications and
one is connection

sp

Two - communications
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, WITH 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, WITH or N )?

5. What is an atomic orbital? How many orbitals are in the second energy level of an atom WITH 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?

Answers to exercises

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 a 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 an atom, in which the order of filling of electronic orbitals is observed: 1s 2, 2s 2, 2p 2, 3s 2, 3p 2, 4s 2, 3d 2, 4p 2, etc., is called the ground state. In an excited state, one of the valence electrons of an 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 - 2s, 2p x, 2p y, 2p z. These orbitals are:
a) the shape of the electron cloud (s is a ball, p is a dumbbell);
b) p-orbitals have different orientations in space - along mutually perpendicular axes x, y and z, they are denoted p x, p y, p z.

6. Hybrid orbitals differ from the original (non-hybrid) orbitals in shape and energy. For example, the s-orbital is the shape of a sphere, p is a symmetrical figure-eight, sp-hybrid orbital is an asymmetric figure-eight.
Energy differences: E(s)< E(sр) < E(р). Таким образом, sp-орбиталь – усредненная по форме и энергии орбиталь, полученная смешиванием исходных s- и p-орбиталей.

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 of p-orbitals on both sides of the line connecting the centers of atoms.
- Bonds are shown by the second and third lines between the connected atoms.

10.

General and BIOorganic chemistry

(lecture notes)

Part 2. Organic chemistry

For 1st year students of the Faculty of Medicine of the specialty "Dentistry"

Publishing house of the Peoples' Friendship University of Russia,

Approved

RIS Academic Council

Peoples' Friendship University of Russia

Kovalchukova O.V., Avramenko O.V.

General and bioorganic chemistry (lecture notes). Part 2. Organic chemistry. For 1st year students of the Faculty of Medicine of the specialty "Dentistry". Moscow: RUDN University, 2010. 108 p.

Abstract of lectures read for 1st year students of the Faculty of Medicine, specialty "Dentistry". Compiled in accordance with the program of the course "General and Bioorganic Chemistry".

Prepared at the Department of General Chemistry.

© Kovalchukova O.V., Avramenko O.V.

© Publishing House of the Peoples' Friendship University of Russia, 2010

INTRODUCTION

Bioorganic chemistry is a branch of chemistry that is closely related to such special disciplines of medical faculties of universities as biochemistry, pharmacology, physiology, and molecular biology. It is a field of science that studies the structure and functioning mechanisms of biologically active molecules from the positions and ideas of organic chemistry, which determines the patterns in the relationship between the structure and reactivity of organic compounds.

The main attention in this course of lectures is given to the classification of organic compounds according to the structure of the carbon skeleton and the nature of functional groups, the patterns that connect the chemical structure of organic molecules with the nature of their reaction centers, the relationship of their electronic and spatial structure with the mechanisms of chemical transformations.

THEORY OF THE CHEMICAL STRUCTURE OF ORGANIC COMPOUNDS

organic compounds- these are carbon compounds (except for the simplest ones), in which it exhibits valency IV.

Organic chemistry is the chemistry of hydrocarbons and their derivatives.

The carbon atom in organic compounds is in an excited state and has four unpaired electrons:

6 C 1s 2 2s 2 2p 2 → 6 C* 1s 2 2s 1 2p 3

An excited carbon atom is capable of:

1) form strong bonds with other carbon atoms, which leads to the formation of chains and cycles;

2) due to different types of hybridization of orbitals, form simple, double and triple bonds between carbon atoms and with other atoms (H, O, N, S, P, etc.);

3) combine with four different atoms, which leads to the formation of branched carbon chains.

Types of carbon atom hybridization in organic compounds

sp 3 - hybridization

All four valence orbitals participate in hybridization. Valence angle 109 o 28 '(tetrahedron). Carbon atoms form only simple (σ) bonds - the compound is saturated.

sp 2 - hybridization

Three hybrid and one non-hybrid orbital are formed. Valence angle 120 o (flat structures, regular triangle). Hybrid orbitals form σ-bonds. Non-hybrid orbitals form p-bonds. sp 2– Hybridization is typical for unsaturated compounds with one p-bond.

sp - hybridization

Two hybrid and two non-hybrid orbitals are formed. Valence angle 180 o (linear structures). The carbon atom is in the state sp-hybridization takes part in the formation of two double bonds or one triple bond.

Theory of the structure of organic compounds formulated in 1861 by A.M. Butlerov and includes the following provisions:

1. All atoms that make up the molecule are interconnected in a strictly defined sequence in accordance with their valencies. The order in which atoms are combined into a molecule determines its chemical structure .

2. The properties of organic compounds depend not only on the qualitative and quantitative composition of substances, but also on the order of their combination (the chemical structure of the molecule).

3. Atoms in a molecule have mutual influence on each other, i.e. the properties of groups of atoms in a molecule can change depending on the nature of other atoms that make up the molecule. The group of atoms that determines the chemical properties of organic molecules is called functional group .

4. Each organic compound has only one chemical formula. Knowing the chemical formula, you can predict the properties of the compound, and by studying its properties in practice, you can establish the chemical formula.

organic molecule

Types of carbon skeleton:

Acyclic:

· branched;

normal (linear).

Cyclical:

carbocyclic (a cycle of only carbon atoms);

heterocyclic (in addition to carbon atoms, the cycle includes some other atoms - nitrogen, oxygen, sulfur).

Types of carbon atoms in a hydrocarbon chain:

H 3 C-CH 2 -CH-C- CH 3

Primary carbon atoms (connected in a chain with only one carbon atom, is terminal);

Secondary carbon atom (connected to two adjacent carbon atoms, located in the middle of the chain);

Tertiary carbon atom (located on the branching of the carbon chain, connected to three carbon atoms);

Quaternary carbon atom (has no other substituents other than carbon atoms).

Functional group- a special group of atoms that determines the chemical properties of compounds.

Examples functional groups:

-HE-hydroxyl group (alcohols, phenols);

C=O– carbonyl group (ketones, aldehydes);

WITH- carboxyl group (carboxylic acids);

-NH 2 - amino group (amines);

-SH- thiol group (thioalcohols)

organic compound

compound

properties

chemical structure

The atoms that make up an organic compound can be combined into molecules in different ways. For example, a compound of composition C 2 H 6 O can correspond to two chemical compounds having different physical and chemical properties:

Compound organic compound - the number of atoms of various elements included in its molecule. Isomers Compounds that have the same composition but different chemical structure. Isomers have different chemical properties.

Types of isomerism

STRUCTURAL ISOMERISM

Isomerism of the carbon chain:

Isomerism of the position of multiple bonds:

Interclass isomerism:

stereoisomerism

Geometric(spatial, cis-trans-isomerism of compounds with double bonds):

cis-butene-2	trance-butene-2

Geometric isomerism is possible if each of the carbon atoms involved in the formation of a double bond has different substituents. So, for butene-1 CH 2 \u003d CH-CH 2 -CH 3, geometric isomerism is impossible, since one of the carbon atoms in the double bond has two identical substituents (hydrogen atoms).

Geometric(spatial, cis-trans-isomerism of cyclic limit compounds):

Geometric isomerism is possible if at least two carbon atoms forming the cycle have different substituents.

Optical:

Optical isomerism is a type of stereoisomerism due to the chirality of molecules. In nature, there are compounds that correlate like two hands of one person. One of the properties of these compounds is their incompatibility with their mirror image. This property is called chirality (from the Greek. « With heir"- hand).

The optical activity of molecules is detected when they are exposed to polarized light. If a polarized beam of light is passed through a solution of an optically active substance, then the plane of its polarization will rotate. Optical isomers are designated using prefixes d-

The method of hybridization of atomic orbitals proceeds from the assumption that during the formation of a molecule, instead of the initial atomic and -electron clouds, such equivalent "mixed" or hybrid electron clouds are formed that are elongated towards neighboring atoms, due to which their more complete overlap with the electron clouds of these atoms is achieved. . Such deformation of electron clouds requires energy. But a more complete overlap of valence electron clouds leads to the formation of a stronger chemical bond and, consequently, to an additional gain in energy. If this gain in energy is sufficient to more than compensate for the energy costs for the deformation of the initial atomic electron clouds, such hybridization ultimately leads to a decrease in the potential energy of the resulting molecule and, consequently, to an increase in its stability.

Consider, as an example of hybridization, the formation of a beryllium fluoride molecule. Each fluorine atom in this molecule has one unpaired electron.

which is involved in the formation of a covalent bond. The beryllium atom in the unexcited state has no unpaired electrons:

Therefore, to participate in the formation of chemical bonds, the beryllium atom must go into an excited state:

The resulting excited atom has two non-paired electrons: the electron cloud of one of them corresponds to the state, the other -. When these electron clouds overlap with p-electron clouds of two fluorine atoms, covalent bonds can form (Fig. 38).

However, as already mentioned, with the expenditure of some energy, instead of the initial s- and p-orbitals of the beryllium atom, two equivalent hybrid orbitals (-orbitals) can be formed. The shape and location of these orbitals are shown in fig. 39, from which it can be seen that the hybrid β-orbitals are elongated in opposite directions.

The overlapping of the hybrid -electron clouds of the beryllium atom with the p-electron clouds of fluorine atoms is shown in fig. 40.

Rice. 38. Scheme of overlapping -electron clouds of fluorine atoms with and -electron clouds of a beryllium atom (for each bond separately). The areas of overlapping electron clouds are shaded.

Rice. 39. Shape (schematic representation) and mutual arrangement of hybrid -electron clouds of a beryllium atom (for each hybrid orbital separately).

Rice. 40. Scheme of the formation of chemical bonds in a molecule. In order to simplify the figure, the hybrid -electron clouds of the beryllium atom are shown incompletely.

Due to the elongated shape of the hybrid orbitals, a more complete overlap of the interacting electron clouds is achieved, which means that stronger chemical bonds are formed. The energy released during the formation of these bonds is greater than the total energy consumption for the excitation of the beryllium atom and the hybridization of its atomic orbitals. Therefore, the process of formation of a molecule is energetically favorable.

The considered case of hybridization of one s- and one p-orbital, leading to the formation of two -orbitals, is called -hybridization. As shown in fig. 39, -orbitals are oriented in opposite directions, which leads to a linear structure of the molecule. Indeed, the molecule is linear, and both bonds in this molecule are equivalent in all respects.

Other cases of hybridization of atomic orbitals are also possible, but the number of hybrid orbitals formed is always equal to the total number of initial atomic orbitals involved in hybridization. So, during the hybridization of one s- and two p-orbitals (-hybridization - it reads "es-pe-two"), three equivalent -orbitals are formed. In this case, the hybrid electron clouds are arranged in directions lying in the same plane and oriented at angles of 120° to each other (Fig. 41). Obviously, this type of hybridization corresponds to the formation of a flat triangular molecule.

An example of a molecule in which -hybridization occurs is the boron fluoride molecule. Here, instead of the original one s- and two p-orbitals of the excited boron atom

three equivalent -orbitals are formed. Therefore, the molecule is built in the form of a regular triangle, in the center of which there is a boron atom, and at the vertices there are fluorine atoms. All three bonds in a molecule are equal.

If one s- and three p-orbitals (-hybridization) participate in hybridization, then four hybrid-orbitals are formed as a result, elongated in directions to the vertices of the tetrahedron, i.e., oriented at angles to each other (Fig. 42). Such hybridization is carried out, for example, in an excited carbon atom during the formation of a methane molecule.

Rice. 41. Mutual arrangement of hybrid -electron clouds.

Rice. 42. Mutual arrangement of hybrid -electron clouds.

Therefore, the methane molecule has the shape of a tetrahedron, and all four bonds in this molecule are equivalent.

Let us return to the consideration of the structure of the water molecule. When it is formed, -hybridization of oxygen atomic orbitals occurs. That is why the HOH bond angle in the molecule is close not to, but to the tetrahedral angle. The slight difference between this angle and 109.5° can be understood if we take into account the unequal state of the electron clouds surrounding the oxygen atom in the water molecule. Indeed, in a methane (I) molecule

all eight electrons occupying hybrid -orbitals in the carbon atom participate in the formation of covalent bonds. This causes a symmetrical distribution of electron clouds with respect to the nucleus of the carbon atom. Meanwhile, in the molecule, only four of the eight electrons occupying the hybrid -orbitals of the oxygen atom form bonds, and two electron pairs remain unshared, that is, they belong only to the oxygen atom. This leads to some asymmetry in the distribution of electron clouds surrounding the oxygen atom, and, as a result, to the deviation of the angle between bonds from .

When the ammonia molecule is formed, atomic orbitals of the central atom (nitrogen) also occur. That is why the bond angle is close to tetrahedral. The slight difference between this angle and 109.5° is explained, as in the water molecule, by the asymmetry in the distribution of electron clouds around the nucleus of the nitrogen atom: out of four electron pairs, three participate in the formation of N-H bonds, and one remains unshared.

As shown in Fig. 39, 41 and 42, the hybrid electron clouds are displaced relative to the nucleus of the atom.

Therefore, the center of the electric charge of the unshared electron pair located in the hybrid orbital does not coincide with the position of the atomic nucleus, i.e., with the center of the positive charge present in the atom. Such a shift in the charge of the unshared electron pair leads to the appearance of a dipole moment, which makes a significant contribution to the total dipole moment of the molecule. It follows from this that the polarity of a molecule depends not only on the polarity of the individual bonds and their mutual arrangement (see Sec. 40), but also on the presence of unshared electron pairs in the hybrid orbitals and on the spatial arrangement of these orbitals.

For elements of the third and subsequent periods, the -orbitals can also participate in the formation of hybrid electron clouds. The case of -hybridization is especially important, when one, three and two -orbitals participate in the formation of hybrid orbitals. In this case, six equivalent hybrid orbitals are formed, elongated in directions towards the vertices of the octahedron. The octahedral structure of the molecule, ions, and many others is explained by the hybridization of the atomic orbitals of the central atom.

Problem 261.
What types of carbon AO hybridization correspond to the formation of CH molecules 4, C 2 H 6, C 2 H 4, C 2 H 2?
Solution:
a) In CH molecules 4 and C 2 H 6 The valence electron layer of a carbon atom contains four electron pairs:

Therefore, the electron clouds of the carbon atom in CH 4 , C 2 H 6 molecules will be maximally removed from each other during sp3 hybridization, when their axes are directed to the vertices of the tetrahedron. In this case, in the CH 4 molecule, all the vertices of the tetrahedron will be occupied by hydrogen atoms, so that the CH4 molecule has a tetrahedral configuration with a carbon atom in the center of the tetrahedron. In the C 2 H 6 molecule, hydrogen atoms occupy three vertices of the tetrahedron, and the common electron cloud of another carbon atom is directed to the fourth vertex, i.e. two carbon atoms are connected to each other. This can be represented by diagrams:

b) In the C 2 H 4 molecule, the valence electron layer of the carbon atom, as in the CH 4, C 2 H 6 molecules. contains four electron pairs:

During the formation of C 2 H 4, three covalent bonds are formed according to the usual mechanism, i.e. are - links, and one - - link. When a C 2 H 4 molecule is formed, each carbon atom with two hydrogen atoms - bonds and with each other two bonds, one - and one - bonds. Hybrid clouds corresponding to this type of hybridization are located in the carbon atom so that the interaction between electrons is minimal, i.e. as far apart as possible. This arrangement of carbon atoms (two double bonds between carbon atoms) is typical for sp 2 hybridization of carbon AOs. During sp 2 hybridization, electron clouds in carbon atoms are oriented in directions lying in the same plane and making angles of 120 0 with each other, i.e. in directions to the vertices of an equilateral triangle. In the ethylene molecule, three sp 2 hybrid orbitals of each carbon atom participate in the formation of bonds, two between two hydrogen atoms and one with the second carbon atom, and the bond is formed due to the p-electron clouds of each carbon atom. The structural formula of the C 2 H 4 molecule will look like:

c) In the C 2 H 2 molecule, the valence electron layer of the carbon atom contains four pairs of electrons:

The structural formula C 2 N 2 has the form:

Each carbon atom has one electron pair with a hydrogen atom and three electron pairs with another carbon atom. Thus, in an acetylene molecule, carbon atoms are connected to each other by one -bond and two -bonds. Each carbon atom is bonded to hydrogen. Two sp-hybrid AOs are involved in the formation of -bonds, which are located relative to each other so that the interaction between them is minimal, i.e. as far apart as possible. Therefore, during sp hybridization, electron clouds between carbon atoms are oriented in opposite directions relative to each other, i.e. the angle between the C-C bonds is 180 0 . Therefore, the C 2 H 2 molecule has a linear structure:

Problem 262.
Indicate the type of silicon AO hybridization in SiH 4 and SiF 4 molecules. Are these molecules polar?
Solution:
In SiH 4 and SiF 4 molecules, the valence electron layer contains four pairs of electrons:

Therefore, in both cases, the electron clouds of the silicon atom will be maximally removed from each other during sp 3 hybridization, when their axes are directed towards the vertices of the tetrahedron. Moreover, in the SiH 4 molecule, all the vertices of the tetrahedron are occupied by hydrogen atoms, and in the SiF 4 molecule, by fluorine atoms, so that these molecules have a tetrahedral configuration with a silicon atom in the center of the tetrahedron:

In tetrahedral SiH 4 and SiF 4 molecules, the dipole moments of the Si-H and Si-F bonds mutually compensate each other, so that the total dipole moments of both molecules will be equal to zero. These molecules are non-polar, despite the polarity of the Si-H and Si-F bonds.

Problem 263.
In SO 2 and SO 3 molecules, the sulfur atom is in the state of sp 2 hybridization. Are these molecules polar? What is their spatial structure?
Solution:
During sp 2 hybridization, hybrid clouds are located in the sulfur atom in directions that lie in the same plane and make angles of 120 0 with each other, i.e. directed towards the vertices of an equilateral triangle.

a) In the SO 2 molecule, two sp 2 hybrid AOs form a bond with two oxygen atoms, the third sp 2 hybrid orbital will be occupied by a free electron pair. This electron pair will shift the electron plane and the SO 2 molecule will take the form of an irregular triangle, i.e. the OSO angle will not be equal to 120 0 . Therefore, the SO 2 molecule will have an angular shape with sp 2 hybridization of the orbitals of the atom, the structure:

In the SO 2 molecule, the mutual compensation of the dipole moments of the S-O bonds does not occur; the dipole moment of such a molecule will have a value greater than zero, i.e. the molecule is polar.

b) In the corner SO3 molecule, all three sp2-hybrid AO form bonds with three oxygen atoms. The SO 3 molecule will have the shape of a flat triangle with sp 2 hybridization of the sulfur atom:

In a triangular SO 3 molecule, the dipole moments of the S-O bonds mutually compensate each other, so that the total dipole moment will be zero, the molecule is polar.

Task 264.
When SiF4 interacts with HF, a strong acid H 2 SiF 6 is formed, which dissociates into H + and SiF 6 2- ions. Can the reaction between CF 4 and HF proceed in a similar way? Indicate the type of silicon AO hybridization in the SiF 6 2- ion.
Solution:
a) When excited, the silicon atom passes from the state 1s 2 2s 2 2p 6 3s 2 3p 3 to the state 1s 2 2s 2 2p 6 3s 1 3p 4 3d 0, and the electronic structure of the valence orbitals corresponds to the scheme:

Four unpaired electrons of an excited silicon atom can participate in the formation of four covalent bonds according to the usual mechanism with fluorine atoms (1s 2 2s 2 2p 5) having one unpaired electron each with the formation of a SiF 4 molecule.

When SiF 4 interacts with HF, acid H 2 SiF 6 is formed. This is possible because the SiF 4 molecule has free 3d orbitals, while the F ion has (1s 2 2s 2 2p 6) free pairs of electrons. Communication is carried out according to the donor-acceptor mechanism due to a pair of electrons of each of the two ions F - (HF ↔ H + + F -) and free 3d-orbitals of the SiF 4 molecule. In this case, an ion SiF 6 2- is formed, which with ions H + forms an acid molecule H 2 SiF 6 .

b) Carbon (1s 2 2s 2 2p 2) can form, like silicon, a CF 4 compound, while the valence possibilities of the carbon atom will be exhausted (there are no unpaired electrons, free pairs of electrons and free valence orbitals at the valence level). The scheme of the structure of the valence orbitals of an excited carbon atom has the form:

When CF 4 is formed, all valence orbitals of carbon are occupied, so an ion cannot be formed.

In the SiF 4 molecule, the valence electron layer of the silicon atom contains four pairs of electrons:

The same is observed for the CF 4 molecule. therefore, in both cases, the electron clouds of silicon and carbon atoms will be maximally removed from each other during sp3 hybridization. When their axes are directed towards the vertices of the tetrahedron: