1

Intermolecular Forces and

Bonding in Solids

2

3 States

Solid state - ice

Liquid state - water

Different States of Matter

Gas state - water vapor

3

“Measure” of intermolecular force

boiling point

melting point

Hvap

Hfus

Hsub

Intermolecular Forces

Intermolecular forces are forces between molecules.

Intramolecular forces hold atoms together in a molecule.

Intermolecular vs Intramolecular

• 41 kJ to vaporize 1 mole of water (inter)

• 930 kJ to break all O-H bonds in 1 mole of water (intra)

Generally, intermolecular forces are much weaker than intramolecular forces.

4

Intermolecular Forces

Dipole-Dipole Forces: Attractive and repulsive forces between polar molecules

solid

liquid

5

Intermolecular ForcesHydrogen Bond: a special dipole-dipole interaction between the hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom.

A H…B A H…Aor

A & B are N, O, or F

6

Dispersion Forces: Attractive forces that arise as a result of temporary dipoles induced in atoms or molecules

Intermolecular Forces

7

Dispersion Forces among Nonpolar Molecules

separated Cl2

molecules

instantaneous dipoles

8

Polarizability is the ease with which the electron distribution in the atom or molecule can be distorted.

Polarizability increases with:

• greater number of electrons

• more diffuse electron cloud

Dispersion forces usually increase with molar mass.

Intermolecular Forces

9

SO

O

What type(s) of intermolecular forces exist between each of the following molecules?

HFHF is a polar molecule: dipole-dipole forces. Hydrogen is bounded to F. Hydrogen bonds exist. There are also dispersion forces between HBr molecules.

CH4

CH4 is nonpolar: dispersion forces.

SO2

SO2 is a polar molecule: dipole-dipole forces. There are also dispersion forces between SO2 molecules.

Intermolecular Forces

10

A crystalline solid possesses rigid and long-range order. In a crystalline solid, atoms, molecules or ions occupy specific (predictable) positions.

An amorphous solid does not possess a well-defined arrangement and long-range molecular order.

A unit cell is the basic repeating structural unit of a crystalline solid.

Unit Cell

latticepoint

Unit cells in 3 dimensions

Structures and Types of Solids

11

Seven Types of Unit Cells

12

1 atom/unit cell

(8 x 1/8 = 1)

2 atoms/unit cell

(8 x 1/8 + 1 = 2)

4 atoms/unit cell

(8 x 1/8 + 6 x 1/2 = 4)

Three Types of Cubic Cells

13

14

The Striking Beauty of Crystalline Solids

15

Three Types of Crystalline Solids

atomic solid ionic solid molecular solid

16

Types and Properties of Solids

17

Metallic Crystals

• Lattice points occupied by metal atoms• Held together by metallic bonds• Soft to hard, low to high melting point• Good conductors of heat and electricity

nucleus &inner shell e-

mobile “sea”of e-

18

MO Energy Levels as a Function of the # of AO

19

The band of MOs in lithium metal

ConductionBand

ValenceBand

20

Covalent Crystals

• Lattice points occupied by atoms• Held together by covalent bonds• Hard, high melting point• Poor conductor of heat and electricity

diamond graphite

carbonatoms

21

Graphite Consists of Layers of Carbon Atoms

22

conductor

Electrical Conductivity in Graphite

sp2 hybridization Delocalized orbitals

23

insulator

Electrical Conductivity in Diamond

sp3 hybridization localized orbitals

24

Conductor, Semiconductor, and Insulator

conductor

semiconductor

insulator

25

n-type p-type

Doped Semiconductors

26

Chemistry In Action: High-Temperature Superconductors

27

Acknowledgment

Some images, animation, and material have been taken from the following sources:

Chemistry, Zumdahl, Steven S.; Zumdahl, Susan A.; Houghton Mifflin Co., 6th Ed., 2003;

supplements for the instructor

General Chemistry: The Essential Concepts, Chang, Raymon; McGraw-Hill Co. Inc., 4th

Ed., 2005; supplements for the instructor

Principles of General Chemistry, Silberberg, Martin; McGraw-Hill Co. Inc., 1st Ed., 2006;

supplements for the instructor