Concepts and types of hybrid orbital theory

A valence bond theory can explain the formation of C with a CO molecule O, O 2 and form CO ₂ molecule, a C excited electrons is formed after the four CH H _.
4 molecule
.

But the valence bond theory cannot explain the geometric configuration of molecules.

In 1931, Pauling proposed hybrid orbital theory on the basis of valence bond theory, which can explain the spatial structure of polyatomic molecules and the bonding process of covalent molecules
.

1.
The main points of hybrid orbital theory

1) The concept of hybrid and hybrid orbitals

In the process of forming polyatomic molecules, several atomic orbitals with similar energies of the central atom are recombined to form a new set of orbitals
.

The process of orbital recombination is called hybridization of orbitals, and the new orbitals produced are called hybrid orbitals

When C forms a CH ₄ molecule with H , a total of 4 atomic orbitals of 1 2s and 3 2p of the central C atom are hybridized to form a new set of atomic orbitals, that is, 4 sp ³ hybrid orbitals
.

Hybrid orbitals have their own wave function, energy, shape and spatial orientation.

2) Number, composition and energy of hybrid orbitals

The number of hybrid orbitals is equal to the number of orbitals participating in the hybridization process
.

When the CH ₄ molecule is formed , the 4 atomic orbitals 2 _s , 2p _x , 2p _y , and 2p _z of C are hybridized, resulting in 4 hybrid orbitals

When a new wave function is generated in the orbital hybridization process, the hybrid orbital has its own shape and angular distribution.
For example, one s orbital hybridizes with one p orbital to produce two sp hybridized orbitals
.

The shape of the two tracks generated by hybridization is different from the s track and the p track, as shown in Figure 6-13

Figure 6-13 Angle distribution of sp hybrid orbit

The s and p orbital components in each sp hybrid orbital each account for 1/2; the s orbital component in each sp ² hybrid orbital occupies 1/3, and the p orbital component occupies 2/3
.

The s orbital is hybridized with the p orbital.
The more the s orbital component, the lower the energy of the hybrid orbital, and the more p orbital component, the higher the energy of the hybrid orbital.

The energy of the hybrid orbitals is between the energy of the orbitals participating in the hybridization
.

When the s orbital is hybridized with the p orbital, the energy of the hybrid orbital is higher than that of the s orbital and lower than that of the p orbital

s orbit<sp hybrid orbit<sp ² hybrid orbit<sp ³ hybrid orbit<p orbit

The electron cloud distribution of the hybrid orbital is more concentrated, which is conducive to the maximum overlap
.

Therefore, the bonding ability of the hybrid orbital is stronger than that of the unhybridized atomic orbitals, and the energy of the system is lower.

3) Types of hybrid orbitals

According to the types of orbitals involved in hybridization, hybrid orbitals are divided into sp type (sp, sp ² , sp ³ ) and spd type (sp ³ d, sp ³ d ² )
.

According to whether the hybridization orbital energy is consistent, it can be divided into equal hybridization and unequal hybridization
.
The components of hybrid orbitals discussed above are all carried out on the basis of isotropic hybridization
.

The orbital energy of isotropic hybridization is the same, such as 4 sp ³ hybrid orbitals of C in methane [Figure 6-14(a)]; 3 sp ² hybrid orbitals of C in ethylene [Figure 6-14(b) ] .

Figure 6-14 Equal hybridization and unequal hybridization

The orbital energies of unequal hybridization are different, such as the four sp ³ hybrid orbitals of O in water molecules [Figure 6-14(c)]
.
There are often electron pairs in unequal hybrid orbitals
.

Generally speaking, from the hybridization process of the orbital and the presence or absence of lone electron pairs after hybridization, it can be judged whether the hybridization is equivalent.
For example, when forming CH ₄ molecules, C undergoes sp ³ isotropic hybridization, and when forming H ₂ O molecules, O conducts Sp ^{3 is} unequal and hybrid, and inorganic chemistry courses basically require this level
.
Strictly speaking, the difference in ligands causes the difference in bond energy, bond length and bond angle.
The energy of the orbital after the central atom is bonded to the ligand is different.
Although there is no lone electron pair, it should be regarded as an unequal hybridization.
Structural chemistry Courses often require this level
.
For example, CHCl ₃ molecule, according to the level of inorganic chemistry knowledge, C adopts sp ³ equal hybridization; according to the structural chemistry knowledge level, C adopts sp ³ unequal hybridization
.
In this book, when judging whether there is an equal hybridization, the discussion is only based on the principle of whether the central atom has a lone electron pair or not.
Readers are invited to pay attention to the difference in the requirements of different textbooks or courses
.

4) Distribution of various hybrid orbitals in space

Different hybridization methods lead to different spatial distribution of hybrid orbitals.
The geometrical distribution and examples of various hybrid orbitals in space are listed in Table 6-6
.

Table 6-6 Geometrical distribution and examples of hybrid orbitals in space