Announcement

March 19, Thursday

◦ LT#3: 120 points: 40 items MC x 2.5 pts

each + 2 PS items x 10 pts each

◦ 6-7:30 PM

◦ Schmitt Hall C-114

◦ Coverage: Chapters 7-11

March 20, Friday

◦ Quiz # 10, 11, 12

1

Electron and Molecular Geometry

Electron geometry: geometry of all electron groups

Molecular geometry: geometry of only the atoms bonded to the central atom

2

Bond Polarity, Bond Angle, and

Dipole Moment

Overall molecular polarity depends on both

shape and bond polarity.

A molecule is polar if

- it contains one or more polar bonds and

- the individual bond dipoles do not cancel.

3

C (EN = 2.5) and

O (EN = 3.5) H (EN = 2.1) and

O (EN = 3.5)

4

Molecules with the same shape may have

different polarities.

CCl4

Bonds are polar, but

individual bond

polarities cancel.

CHCl3

Bond polarities do

not cancel. This

molecule is polar.

Bond Polarity, Bond Angle, and Dipole Moment

Chapter 11 Theories of Covalent Bonding

Chapter Outline

Valence Bond (VB) Theory and Orbital

Hybridization

Modes of Orbital Overlap and the

Types of Covalent Bonds

Excluded Topic:

11.3 Molecular Orbital (MO) Theory

and Electron Delocalization

6

Valence Bond Theory

A covalent bond forms when the

orbitals of two atoms overlap and a

pair of electrons occupy the overlap

region.

7

Shared space is occupied

by 2 e-, which have

opposite spins.

8

Bonding in HF

Bonding in F2

The greater the extent of orbital overlap, the

stronger the bond.

Bonding in carbon presents a problem as

combining atomic orbitals fails. Valence

Bond Theory solves this by allowing the

blending or mixing of pure atomic orbitals in

a process called hybridization.

9

Pure atomic

orbitals

sp3

hybridized

orbitals

hybridization

sp3 sp3 sp3 sp3

Hybridization combines or mixes different

numbers of pure atomic orbitals that match

one of the VSEPRT geometries.

10

s-orbital + p-orbital 2 sp hybrid

orbitals

2 superimposed sp

hybrid orbitals

s-orbital + 2 p-orbitals 3 sp2 hybrid

orbitals

trigonal

planar

Hybridization combines or mixes different

numbers of pure atomic orbitals that match

one of the VSEPRT geometries.

11

s-orbital + 3 p-orbital 4 sp3 hybrid

orbitals tetrahedral

Characteristics of Hybrid

Orbitals

1. The number of hybrid orbitals obtained equals

the number of atomic orbitals mixed.

2. The name and shape of a “hybrid orbital”

varies with the types of atomic orbitals mixed.

3. Each hybrid orbital has a specific geometry

that matches one of five VSEPRT shapes.

12

sp Hybridization

Show the bonding scheme and hybridized

orbitals used in BeCl2.

13

After hybridization,

central atom now has

2 pure p-orbitals and

2 sp hybrids.

s + p hybridization 2 sp

sp Hybridization

Show the bonding scheme and hybridized

orbitals used in BeCl2.

14

After hybridization,

central atom now has

2 pure p-orbitals and

2 sp hybrids.

s + p hybridization 2 sp

sp Hybridization

Show the bonding scheme and hybridized

orbitals used in BeCl2.

15

2 sp orbitals

2 pure p-orbitals

Linear

sp2 Hybridization (ie BF3)

16

Trigonal

Planar

sp3 Hybridization (ie CH4)

17 Tetrahedral

sp3 Hybridization (ie NH3)

18

Trigonal

pyramidal

sp3 Hybridization (ie H2O)

19 Bent

sp3d Hybridization (ie PCl5)

20

Trigonal

bipyramidal

sp3d2 Hybridization (ie SF6)

21 Octahedral

24

Learning Check

Determine the VSEPRT geometry,

bond angle, and hybridization of each

indicated atom in the following

molecule.

25

Types of Covalent Bonds

1. A sigma (σ) bond is formed by end-to-end overlap of orbitals.

◦ All single bonds are σ bonds.

2. A pi (p) bond is formed by sideways overlap of orbitals.

◦ A p bond is weaker than a σ bond because sideways overlap is less effective than end-to-end overlap.

◦ A double bond consists of one σ bond and one p bond.

26

Double Bond (ie ethylene)

27

unhybridized 2p orbitals

Triple Bond (ie acetylene)

28

Each C is sp hybridized and has

two unhybridized p orbitals.

Announcement

March 19, Thursday

◦ LT#3: 120 points: 40 items MC x 2.5 pts

each + 2 PS items x 10 pts each

◦ 6:00-7:30 PM

◦ Schmitt Hall C-114

◦ Coverage: Chapters 7-11

March 20, Friday

◦ Quiz # 10, 11, 12

29