1

(1) Hybridization is the process of mixing

the atomic orbitals in an atom (usually

the central atom) to generate a set of

new atomic orbitals.

8-2.4 Hybrid Orbital Theory

Ⅰ. The Central Themes of Hybridization Theory

2

(2) The new atomic orbitals are called hybrid orbitals. Hybrid orbital is atomic orbitals obtained when two or more nonequivalent orbitals of the same atom combine, are then used to form covalent bonds.

(3) The number of hybrid orbitals generated is equal to the number of atomic orbitals.

(4) The spatial orientation of these new orbitals lead to more stable bonds and are consistent with the observed molecular shapes.

3

The following points are useful for an understanding of hybridization

(1) The concept of hybridization does not apply to isolated atoms. It is used only to explain a bonding scheme in a molecule.(2) Hybrid orbital is not a pure atomic orbital. Hybrid orbitals have very different shapes from pure atomic orbitals.

4

(4) Covalent bonds in polyatomic molecules are formed by the overlap of a hybrid orbital and a pure atomic orbital, or of two hybrid orbitals.

(3) All the hybrid orbitals are equivalent in every respect, except in their relative orientations in space.

5

Ⅱ. Types of Hybrid Orbitals

1. sp Hybridization

One s orbital and one p orbital form twosp hybrid orbital

Hybridization of all s orbital and a p orbital (of the same atom) produce two sp hybrid orbitals. The twosp hybrid orbitals have a linear arrangement.

6

two sp hybrid orbitals

7

BeCl2 molecules

4Be: 2s2 2p0

hybridizeexcitated

sp hybrid orbital

↑↓ ↑↓

8

The sp hybrid orbitals in gaseous BeCl2

Be (excitated)

9

10

2. sp2 Hybridization

One s orbital and two porbital form three sp2 hybrid orbital

11

• BF3 molecules

• 5B: 2s2 2p1

excitated

hybridizesp2 hybrid orbital

↑↓ ↑↓ ↑↓

↑↑↓

↑ ↑↑

↑ ↑ ↑

BF3

sp2-p

12Figure: The sp2 hybrid orbitals in BF3

13

14

3. sp3

HybridizationOne s orbital and three p orbitalform four sp3 hybrid orbital

15

• 6C: 2s2 2p2 CH4 (methane)

excitated

hybridize

sp3 hybrid orbital

↑↓ ↑↓ ↑↓↑↓

sp3-s σ

16Figure: The sp3 hybrid orbitals in CH4

17

18

CH4

19

Hybridization

Equivalent hybridization

sp: BeCl2

sp2: BF3 , C2H4

sp3: CH4 , CCl4

sp3: NH3 , H2ONonequivalent hybridization

20

• NH3 moleculeCentral atom N7N: 1s2 2s2 2p3

hybridize

sp3 Hybrid orbital(one lone pair electrons)

Nonequivalent hybridization

21

Predict correctbond angle

22

hybridize

sp3 Hybrid orbital(two lone pair electrons)

• H2O moleculeCentral atom O

8O: 1s2 2s2 2p4

23bonding-pair vs. bonding

pair repulsionlone-pair vs. bonding

pair repulsion < < lone-pair vs. lone pairrepulsion

24

NH3H2O

25

sp2 Hybridization of Ethylene

• 6C: 2s2 2p2 CH2=CH2 (ethylene)

excitated

hybridizesp2 hybrid orbital

2py orbital

26

27

28

sp Hybridization of Acetylene

6C: 2s2 2p2 CH ≡ CH (acetylene)

excitated

hybridize

↑

↑↓ ↑↓

↑

sp hybrid orbital

↑↓ ↑↓

29

30

31

• Geometry of the molecule

sp :180° linear

sp2 :120° trigonal planar

sp3 :109.5°tetrahedral

NH3 :107.3°trigonal pyramidal

H2O :104.5°Bent /Angular