In the definition process geometric shape the chemical particle is important to take into account that the valence electron pairs of the main atom, including those that do not form chemical bonds are on a large distance from each other in space.

Features of the term

Considering the question concerning covalent chemical bond, often apply which concept as hybridization of atomic orbitals. This term is associated with alignment of shape and energy. The hybridization of atomic orbitals is associated with the quantum-chemical process of restructuring. Orbital in comparison with the initial atoms have a different structure. The essence of hybridization is that the electron, which is located next to the core of the associated atom, is not determined by a particular atomic orbital, but their combination with an equal major quantum number. Basically, this process concerns higher, close-in atomic orbitals with electrons.

Process specificity

Types of hybridization of atoms in molecules depends on how the orientation of new orbitals occurs. By type of hybridization, you can determine the geometry of ion or a molecule, assume the features of chemical properties.

Types of hybridization

This type of hybridization, as SP, is a linear structure, the angle between connections is 180 degrees. An example of a molecule with a similar hybridization option is BECL 2.

The following type of hybridization is SP 2. Molecules are characterized by a triangular form, the angle between bonds is 120 degrees. A typical example of such a hybridization variant is BCL 3.

The type of hybridization SP 3 suggests the tetrahedral structure of the molecule, a typical example of a substance with a given hybridization option, the methane CH 4 molecule. The valence angle in this case is 109 degrees of 28 minutes.

In hybridization, not only paired electrons are directly involved, but also unrealized pairs of electrons.

Hybridization in water molecule

For example, two covalent polar bonds exist in the water molecule between the oxygen atom and atoms. In addition, the oxygen atom itself has two vapors of external electrons that do not participate in the creation of a chemical bond. These 4 electronic pairs in space occupy a certain place around the oxygen atom. Since they all possess the same charge, they are repelled in space, the electronic clouds are from each other at a substantial distance. The type of hybridization of atoms in this substance involves changing the shape of atomic orbitals, their pulling and building them to the tetrahedron vertices. As a result, the water molecule purchases the angular shape, between the bonds oxygen-hydrogen, the valented angle is 104.5 o.

To predict the type of hybridization, you can use the donor-acceptor mechanism for the formation of chemical bond. As a result, it is overlapping free orbital element with less electronegativity, as well as element orbitals with greater electrical negativity, on which there is a pair of electrons. In the process of compiling the electronic configuration of the atom, their degree of oxidation is taken into account.

Rules for identifying the type of hybridization

In order to determine the type of carbon hybridization, you can use certain rules:

• the central atom detects, calculate the number of σ-links;
• put in a particle of the degree of oxidation of atoms;
• write down the electronic configuration of the main atom in the desired degree of oxidation;
• make up the distribution scheme for orbitals valence electrons, pairing electrons;
• eliminate orbitals, which are directly involved in the formation of communication, find unpaired electrons (if the number of valence orbitals is insufficient for hybridization, the following energy level orbital is used).

The geometry of the molecule is determined by the type of hybridization. It does not affect the presence of PI-connections. In the case of additional binding it is possible to change the valence angle, the reason consists in a mutual repulsion of electrons forming a multiple communication. Thus, in the molecule of nitrogen oxide (4), with SP 2-hybridization, an increase in the valence angle of 120 degrees to 134 degrees occurs.

Hybridization in ammonia molecule

Untreated electron pair affects the resulting indicator of the dipole moment of the entire molecule. In ammonia, a tetrahedral structure together with an undivided pair of electrons. The ionic communication of nitrogen-hydrogen and nitrogen fluorine has indicators 15 and 19 percent, the lengths are defined in 101 and 137 PM, respectively. Thus, in the molecule of nitrogen fluoride, there must be a larger dipole moment, but the results of the experiment indicate the opposite.

Hybridization in organic compounds

For each class of hydrocarbons, its type of hybridization is characteristic. Thus, in the formation of alkanov class molecules (limiting hydrocarbons), all four electropot of carbon atom form hybrid orbitals. At their overlapping, 4 hybrid clouds are formed, caught up to the tops of the tetrahedron. Next, their peaks overlap with non-librid S-orbital hydrogen, forming a simple connection. For saturated hydrocarbons, SP 3-hybridization is characteristic.

In unsaturated alkenes (their typical representative is ethylene) only three electronic orbitals are involved in hybridization - S and 2 p, three hybrid orbitals form a triangle shape in space. Unhybrid P-orbitals overlap, creating a multiple communication in the molecule. This class of organic hydrocarbons is characterized by SP 2-hybrid state of a carbon atom.

Alkins differ from the previous class of hydrocarbons in that only two types of orbitals are involved in the hybridization process: S and p. The two nonregid p-electrons remaining in each carbon atom overlap in two directions, forming two multiple links. This class of hydrocarbons is characterized by an SP-hybrid state of a carbon atom.

Conclusion

Due to the determination of the type of hybridization in the molecule, the structure of various inorganic and organic substances can be explained, predicted chemical properties Specific substance.

The method of valence relationships allows you to clearly explain the spatial characteristics of many molecules. However, the usual idea of \u200b\u200bthe forms of orbitals is not enough to answer the question why, if there are different atoms at the central atom s., p., d.- valence orbitals formed by him communications in molecules with the same substituents are equivalent in their energy and spatial characteristics. In the twenties XIX century, Linus Pauling was proposed a concept of hybridization of electronic orbitals. Under hybridization, an abstract model of alignment of atomic orbitals in shape and energy is understood.

Examples of the form of hybrid orbitals are presented in Table 5.

Table 5. Hybrid sP, Sp. 2 , sp. 3 orbitals

The concept of hybridization is conveniently used with the explanation of the geometric shape of molecules and the magnitude of valence angles (examples of tasks 2-5).

Algorithm for determining the geometry of molecules by the Sun method:

but. Determine the central atom and the number of σ-bonds with end atoms.

b. Make electronic configurations of all atoms that are part of the molecule and graphic images of external electronic levels.

in. According to the principles of the Sun method on the formation of each connection, a pair of electrons is needed, general, one with each atom. If the unpaired electrons is not enough to the central atom, the atom with the transition of one of the pair of electrons to a higher energy level should be assumed.

g. Assume the need and type of hybridization, taking into account all connections and, for elements of the first period, unpaired electrons.

d. Relying on the above conclusions depict electronic orbitals (hybrid or not) all atoms in the molecule and their overlapping. Make a conclusion about the geometry of the molecule and the approximate value of valence angles.

e. Determine the level of polarity of communication based on the values \u200b\u200bof the electronegateness of atoms (Table 6) to determine the presence of a dipole moment based on the location of the centers of the gravity of positive and negative charges and / or symmetry of the molecule.

Table 6. The values \u200b\u200bof the electronegativity of some elements by Paulong

For examples of tasks

Exercise 1. Describe a chemical connection in the CO molecule.

Solution (Fig.25)

but. Make electronic configurations of all atoms included in the molecule.

b. To form communication, it is necessary to create publicized electronic pairs

Figure 25. Scheme of the formation of communication in the CO molecule (without hybridization of orbital)

Conclusion: in the Molecule CO - Triple Communication S≡o

For the CO molecule, you can assume sp.-Hypebridization of orbitals of both atoms (Fig.26). Paired electrons that do not participate in the formation of communication are on sp.-Hybrid orbitals.

Figure 26. Scheme of the formation of communication in the CO molecule (taking into account the hybridization of orbitals)

Task 2. Based on the Sun method to assume the spatial structure of the Beh 2 molecule and determine whether the dipole molecule is.

The solution to the problem is presented in Table 7.

Table 7. Determination of Beh 2 molecule geometry

	Electronic configuration		Notes
but.			Central atom - beryllium. He needs to form two ϭ-bonds with hydrogen atoms
b.	H: 1. s. 1 BE: 2 s. 2		At the hydrogen atom there is an unpaired electron, at the beryllium atom all electrons are paired, it must be translated into an excited state
in.	H: 1. s. 1 BE *: 2 s. 1 2p. 1		If one hydrogen atom bind to Beryllium due to 2 s.-Electron beryllium, and the other - at the expense of 2 p.-Electron beryllium, the molecule would not possess symmetry, which is not energy not justified, but BE-H communications would not be equal.
G.	H: 1. s. 1 BE *: 2 ( sp.) 2		It should be assumed sp.-Hybridization
d.			Two sp.-Hybrid orbitals are located at an angle of 180 °, BEH 2 molecule - linear
e.		Electricity χ H \u003d 2,1, χ Be \u003d 1.5, therefore, the connection is a covalent polar, the electron density is shifted to the hydrogen atom, a small negative charge Δ- appears on it. On the beryllium atom Δ +. Since the centers of gravity of a positive and negative charge coincide (it is symmetrical), the molecule is not a dipole.

Similar arguments will help to describe the geometry of molecules with sp. 2 - I. sp. 3-hybrid orbital (Table 8).

Table 8. Geometry of BF 3 and CH molecules 4

Task 3. Based on the Sun method, the spatial structure of the H 2 molecule is based on and determine whether the dipole molecule is. Perhaps two solutions, they are presented in Tables 9 and 10.

Table 9. Determination of the geometry of the H 2 O molecule (without hybridization of orbital)

	Electronic configuration	Graphic image Orbitals of external level	Notes
but.
b.	H: 1. s. 1 O: 2 s. 2 2p. 4
in.			Unpaired electrons are sufficient to form two ϭ-bonds with hydrogen atoms.
G.			Hybridization can be neglected
d.
e.

Thus, the water molecule must have a valence angle of about 90 °. However, the angle between connections is about 104 °.

This can be explained

1) repulsion, closely located to each other hydrogen atoms.

2) hybridization of orbital (Table 10).

Table 10. Determination of the geometry of the H 2 O molecule (taking into account the hybridization of orbitals)

	Electronic configuration	Graphic image of an external orbitals	Notes
but.			Central atom - oxygen. He needs to form two ϭ-bonds with hydrogen atoms.
b.	H: 1. s. 1 O: 2 s. 2 2p. 4		At the hydrogen atom, there is an unpaired electron, at an oxygen atom two unpaired electrons.
in.			At the hydrogen atom, there is an unpaired electron, at an oxygen atom two unpaired electrons.
G.			104 ° angle suggests sp. 3-hybridization.
d.			Two sp. 3-hybrid orbitals are located at an angle of about 109 °, the H 2 O molecule is close to the tetrahedron, the decrease in the valence angle is explained by the effect of the electronic non-binding pair.
e.		Electricity χ H \u003d 2,1, χ O \u003d 3.5, therefore, a covalent polar connection, the electron density is shifted to the oxygen atom, it appears a small negative charge 2Δ- on the hydrogen atom Δ +. Since the centers of gravity of a positive and negative charge do not coincide (it is not symmetrical), the molecule is a dipole.

Similar arguments make it possible to explain the valence angles in the NH 3 ammonia molecule. Hybridization involving vapor electronic pairs is usually assumed only for orbital atoms of elements II periods. Valence angles in H 2 S \u003d 92 °, H 2 S \u003d 91 °, H 2 SE \u003d 91 °, H 2 TE \u003d 89 °. The same thing is observed in the NH 3, PH 3, ASH 3. When describing the geometry of these molecules, traditionally, or do not resort to the representations of hybridization, or explain the decrease in the tetrahedral angle with the increasing influence of the meaningless pair.

Concept of hybridization

Concept of hybridization of valence atomic orbitals It was proposed by the American chemist Linus Pauling for an answer to the question why, in the presence of a central atom of different (S, P, D) valence orbital, the bonds formed in polyhydric molecules with the same ligands are equivalent to their energy and spatial characteristics.

Presentations on hybridization occupy a central place in the method of valence relations. Hybridization itself is not a real physical process, but only a convenient model that allows you to explain electronic structure Molecules, in particular, hypothetical modifications of atomic orbitals in the formation of a covalent chemical bond, in particular, leveling the lengths of chemical bonds and valence angles in the molecule.

The concept of hybridization was successfully applied to a qualitative description of simple molecules, but later was expanded for more complex. Unlike the theory of molecular orbitals, it is not strictly quantified, for example, it is not able to predict photoelectron spectra of even such simple molecules like water. Currently used mainly for methodical purposes and in synthetic organic chemistry.

This principle was reflected in the theory of repulsion of electronic pairs of Gillespi - Nijaholm. First and most an important rule which was formulated as follows:

"The electronic pairs take this arrangement on the valence shell of an atom, in which they are as much as possible from each other, i.e. electronic pairs behave as if they were mutually repelled."

The second rule is that "All electronic pairs included in the valence electronic shell are considered located at the same distance from the nucleus".

Types of hybridization

sP-hybridization

It 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 into different directions on the kernel of the carbon atom. The two remaining non-mentioned P-orbitals are located in mutually perpendicular planes and are involved in the formation of π-bonds, or are engaged in the vulnerable pairs of electrons.

sP 2 -Hypebridization

It occurs when mixing one S- and two P-orbitals. Three hybrid orbitals are formed with axes located in one plane and directed to the vertices of the triangle at an angle of 120 degrees. Nonhybrid p-atomic orbital perpendicular to the plane and, as a rule, participates in the formation of π-links

sP 3-hybridization

It occurs when mixing one S and three p-orbitals, forming four equivalent on-form and energy SP3-hybrid orbital. Four σ-bonds with other atoms can be formed or filled with empty pairs of electrons.

SP3-hybrid orbitals are directed to the tops of the correct tetrahedron. The tetrahedral corner between them is 109 ° 28, "which corresponds to the lowest energy of the repulsion of electrons. Also, SP3 orbitals may form four σ-bonds with other atoms or filled with mooring electron pairs.

Hybridization and geometry of molecules

The representations of the hybridization of atomic orbitals underlie the theory of repulsion of electronic pairs of Hillespi-Nijaholm. 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 representations in inorganic chemistry.

The table shows examples of the correspondence of the most common types of hybridization and the geometric structure of molecules under the assumption that all hybrid orbitals are involved in the formation of chemical bonds (there are no vulnerable electronic 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	Tetrahedrical		CH 4, CLO 4 -, SO 4 2-, NH 4 +
dSP 2.	4	Flat-shed		Ni (CO) 4, XeF 4
sP 3 D.	5	Hexahedrical		PCL 5, ASF 5
sP 3 D 2	6	Octahedrical		SF 6, FE (CN) 6 3-, COF 6 3-

Links

Literature

• Pauling L. Nature of chemical communication / trans. from English M. E. Dyatkina. Ed. prof. Ya. K. Syrkina. - m.; L.: Goshimzdat, 1947. - 440 p.
• Paulong L. general chemistry. Per. from English - m .: Mir, 1974. - 846 p.
• Minkin V. I., Simkin B. Ya., Minyaev R. M. The theory of the structure of molecules. - Rostov-on-Don: Phoenix, 1997. - P. 397-406. - ISBN 5-222-00106-7
• Gillespi R. Geometry molecules / trans. from English E. Z. Vodorin and V. S. Mastryukova, ed. Yu. A. Prentin. - m .: Mir, 1975. - 278 p.

see also

Notes

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Let's talk about how to determine the type of hybridization, as well as consider the geometric structure of the molecule.

The history of the emergence of the term

At the beginning of the twentieth century, L. Pingingl was proposed the theory of geometry of molecules with a covalent bond. Overlapping of electronic clouds was taken as the basis for the formation of communication. The method began to be called valence bonds. How to determine the type of hybridization of atoms in connections? The author of the theory offered to take into account the mixing of hybrid orbitals.

Definition

In order to understand how to determine the type of hybridization in the connections, we will analyze what indicates this term.

Hybridization is mixing electronic orbitals. This process accompanied by the distribution of energy in them, changes in their shape. Depending on which S- and P-orbitals are mixed, the type of hybridization may be different. In organic compounds, carbon atom can exist in the state SP2, SP3. There are more complex formsIn addition to SP, D-orbitals are involved.

Rules for identification of inorganic substances in molecules

It is possible to identify the hybridization option for compounds with a covalent chemical bond having a type of WUA. A is the main atom, in the ligand, P is the number from two and higher. In such a situation, only valence orbitals of the main atom will enter into hybridization.

Methods for determining

Talk to detail how to determine the type of hybridization. In a chemical understanding this term Ensures the change in the energy and form of orbitals. There is a similar process in cases where electrons are used to form communication, which belong to different types.

To understand how to determine the type of hybridization, consider the methane molecule. This substance is the first representative of the homologous series of saturated (limit) hydrocarbons. In the space of the CH4 molecule is a tetrahedron. The only carbon atom forms a bond with hydrogen, similar in energy and length. In order to formed such hybrid clouds, three r- and one ES electron are used.

Four clouds are mixed, and four identical (hybrid) species that have the form of incorrect eights occurs. Call such a type of hybridization SP3. All hydrocarbons in which only simple (single) communications are characterized by such a type of hydridization of the carbon atom. The valence angle is 109 degrees of 28 minutes.

Let us continue the conversation on how to determine the type of hybridization. Examples of the ethylene row give an idea of \u200b\u200bSP2 hybridization. For example, in ethylene molecule of four in the formation of a chemical bond, only three are used. The remaining nonhybrid P-electron goes to the formation of a double bond.

Acetylene is the simplest representative of the SPN2P-2 class. A feature of this class of hydrocarbons is the presence of triple bond. Of the four valence electrons of the carbon atom, only two change their shape and energy, becoming hybrid. The two remaining electrons take part in the formation of two double bonds, determining the unsaturated character of this class of organic compounds.

Conclusion

Considering the question concerning organic and for the hybridization, the equalization of their energy and the form takes place. The electron, located near the core of the bound atom, is characterized by a set of orbital, which possess the same information on the type of hybridization makes it possible to evaluate the chemical properties of the substance.

SP- hybridization

sP-hybridization occurs, for example, in the formation of halides BE, Zn, CO and HG (II). In the valence, all metals halides contain at the corresponding energy level S and p-unpaired electrons. When the molecule is formed, one S- and one p-orbital form two hybrid SP-orbitals at an angle of 180 o.

Fig. 3. SP-hybrid orbitals

Experimental data show that all BE, ZN, CD and HG (II) halides are linear and both bonds have the same length.

sP 2 -Hypebridization

As a result of the hybridization of one S-orbital and two p-orbitals, three hybrid SP 2 are formed, located in the same plane at an angle of 120 per friend. Such, for example, the configuration of the BF 3 molecule:

Fig.4sP 2 -Hypebridization

sP 3-hybridization

sP 3-hybridization is characteristic of carbon compounds. As a result of the hybridization of one S-orbital and three

p-orbitals are formed by four hybrid SP 3 -Orbital, aimed at the tops of the tetrahedron with an angle between the orbitals of 109.5 oh. Hybridization is manifested in the complete equivalence of bonds of carbon atom with other atoms in compounds, for example, in CH 4, CCl 4, C (CH 3) 4, etc.

Fig.5 SP 3-hybridization

If all hybrid orbitals are associated with the same atoms, then the relationships do not differ from each other. In other cases there are small deviations from standard valence angles. For example, in the water molecule H 2 O oxygen - SP 3-Gybrid, is located in the center of the wrong tetrahedron, the tops of which "look" two hydrogen atoms and two vapor pairs of electrons (Fig. 2). The shape of the angular molecule, if you look through atom centers. The horn valence corner is 105 o, which is quite close to the theoretical value of 109 o.

Fig.6. SP 3-hybridization of oxygen and nitrogen atoms in molecules A) H 2 O and B) NCl 3.

If it had not been hybridization ("alignment" o-H connections), HOH valence angle would be 90 °, because hydrogen atoms would be attached to two mutually perpendicular p-orbitals. In this case, our world would probably look completely different.

The theory of hybridization explains the geometry of the ammonia molecule. As a result of the hybridization of 2s and three 2P nitrogen orbital, Four hybrid orbitals SP 3 are formed. The configuration of the molecule is a distorted tetrahedron, in which three hybrid orbitals participate in the formation of a chemical bond, and the fourth with a pair of electrons - no. Corners of each n-H connections Not equal to 90 o as in the pyramid, but are not equal to 109.5 o, corresponding to the tetrahedra.

Fig.7. SP 3 - hybridization in ammonia molecule

In the interaction of ammonia with a hydrogen ion as a result of donor-acceptor interaction, ammonium ion is formed, the configuration of which is a tetrahedron.

Hybridization also explains the difference between the angle between connections oh-n In the angular molecule of water. As a result of the hybridization of 2S and three 2P oxygen orbital, SP 3 hybrid orbitals are formed, of which only two are involved in the formation of a chemical bond, which leads to distortion of an angle corresponding to the tetrahedra.

Fig.8. SP 3-hybridization in water molecule

In hybridization, not only S and R-, but also D- and F-orbitals may be included.

With SP 3 D 2-hybridization, 6 equal clouds are formed. It is observed in such compounds as 4-, 4-. At the same time, the molecule has an octahedron configuration.