12-1

Chapter 12Intermolecular Forces:

Liquids, Solids, and Phase Changes

12-2

Intermolecular Forces: Liquids, Solids, and Phase Changes

12.1 An Overview of Physical States and Phase Changes

12.2 Quantitative Aspects of Phase Changes

12.3 Types of Intermolecular Forces

12.4 Properties of the Liquid State

12.5 The Uniqueness of Water

12.6 The Solid State: Structure, Properties, and Bonding

12.7 Advanced Materials

12-3

Table 12.1

A Macroscopic Comparison of Gases, Liquids, and Solids

State Shape and Volume Compressibility Ability to Flow

Gas

Solid

Liquid

Conforms to shape and volume of container

Conforms to shape of container; volume limited by surface

Maintains its own shape and volume

high high

very low moderate

almost none almost none

12-4

Types of Phases Changes

A liquid changing into a gas - vaporization;the reverse process - condensation

A solid changing into a liquid - fusion (melting);the reverse process - freezing (solidification)

A solid changing directly into a gas - sublimation;the reverse process - deposition

Enthalpy changes accompany phase changes.Vaporization, fusion, and sublimation areEXOTHERMIC; the reverse processes ENDOTHERMIC

12-5

Heats of vaporization and fusion for several common substances.

12-6

Phase changes and their enthalpy changes

12-7

Within a phase, a change in heat is accompanied by a change in temperature which is associated with a change in average Ek as the most probable speed of the molecules changes.

Quantitative Aspects of Phase Changes

During a phase change, a change in heat occurs at a constant temperature, which is associated with a change in Ep, as the average distance between molecules changes.

q = (amount)(molar heat capacity)(T)

q = (amount)(enthalpy of phase change)

Energy changes result in a change in temperature and/or change in phase.

12-8

A cooling curve for the conversion of gaseous water to ice

Heat Removed

12-9

Calculating the Loss of Heat -

Cooling steam at 110o C down to ice at -10o C

q = (amount)(molar heat capacity)(T) - change of temp

q = (amount)(enthalpy of phase change) - change of phase

q = n Cwater(g) (100-110) +

q = n (-HOvap) +

q = n Cwater(l) (0-100) +

q = n (-HOfus) +

q = n Cwater(s) (-10-0) =

12-10

Liquid-gas equilibrium

12-11

The effect of temperature on the distribution of molecular speed in a liquid

12-12

Vapor pressure as a function of temperature and intermolecular forces

A linear plot of vapor pressure- temperature relationship

12-13

The Clausius-Clapeyron Equation

ln P =

-HvapR

1T

C

ln P2P1

= -Hvap

R1T2

1T1

Subtraction two equations for two temperatures.

12-14

SAMPLE PROBLEM 12.1 Using the Clausius-Clapeyron Equation

SOLUTION:

PROBLEM: The vapor pressure of ethanol is 115 torr at 34.90C. If Hvap of ethanol is 40.5 kJ/mol, calculate the temperature (in 0C) when the vapor pressure is 760 torr.

PLAN: We are given 4 of the 5 variables in the Clausius-Clapeyron equation. Substitute and solve for T2.

ln

P2P1

= -Hvap

R1

T2

1T1

34.90C = 308.0K

ln760 torr115 torr

=-40.5 x103 J/mol8.314 J/mol*K

1T2

1308K

-

T2 = 350K = 770C

12-15

Phase diagrams for CO2 and H2O

12-16

Types of Intermolecular Forces - Bonding and Nonbonding

12-17

Types of Intermolecular Forces - Bonding and Nonbonding

12-18

Orientation of polar molecules because of dipole-dipole forces

12-19

Dipole moment and boiling point

12-20

The Hydrogen Bond

A special dipole-dipole interaction occurs when a H atom is covalently bonded to a small electronegative atom, i.e. N, O, or F.

The Hydrogen Bond is a through space bond between a H atom that is covalently bonded to one of the electronegative atoms to another of the electronegative atoms.

H-F-----H-O-H H2O------H-O-O

12-21

SAMPLE PROBLEM 12.2 Drawing Hydrogen Bonds Between Molecules of a Substance

SOLUTION:

PROBLEM: Which of the following substances exhibits H bonding? For those that do, draw two molecules of the substance with the H bonds between them.

C2H6(a) CH3OH(b) CH3C NH2

O

(c)

PLAN: Find molecules in which H is bonded to N, O or F. Draw H bonds in the format -B: H-A-.

(a) C2H6 has no H bonding sites.

(c)(b)C O H

H

H

H

COH

H

H

H

CH3C N

O

H

H

CH3CN

O

H

H

CH3CN

O

H

H

CH3CN

O

H

H

12-22

Hydrogen bonding and boiling point

12-23

The H-bonding abilitiy of the water molecule

12-24

DISPERSION(London) FORCES among nonpolar molecules

separated Cl2 molecules

instantaneous dipoles

12-25

Effect of Molar Mass and boiling

point

DISPERSION(London) FORCES

12-26

Molecular shape and boiling pointDISPERSION(London) FORCES

12-27

SAMPLE PROBLEM 12.3 Predicting the Type and Relative Strength of Intermolecular Forces

PROBLEM: For each pair of substances, identify the dominant intermolecular forces in each substance, and select the substance with the higher boiling point.

(a) MgCl2 or PCl3

(b) CH3NH2 or CH3F

(c) CH3OH or CH3CH2OH

(d) Hexane (CH3CH2CH2CH2CH2CH3)

or 2,2-dimethylbutaneCH3CCH2CH3

CH3

CH3PLAN:

•Bonding forces are stronger than nonbonding(intermolecular) forces.

•Hydrogen bonding is a strong type of dipole-dipole force.

•Dispersion forces are decisive when the difference is molar mass or molecular shape.

12-28

SOLUTION:

SAMPLE PROBLEM 12.3 Predicting the Type and Relative Strength of Intermolecular Forces

continued

(a) Mg2+ and Cl- are held together by ionic bonds while PCl3 is covalently bonded and the molecules are held together by dipole-dipole interactions. Ionic bonds are stronger than dipole interactions and so MgCl2 has the higher boiling point.

(b) CH3NH2 and CH3F are both covalent compounds and have bonds which are polar. The dipole in CH3NH2 can H bond while that in CH3F cannot. Therefore CH3NH2 has the stronger interactions and the higher boiling point.

(c) Both CH3OH and CH3CH2OH can H bond but CH3CH2OH has more CH for more dispersion force interaction. Therefore CH3CH2OH has the higher boiling point.(d) Hexane and 2,2-dimethylbutane are both nonpolar with only dispersion forces to hold the molecules together. Hexane has the larger surface area, thereby the greater dispersion forces and the higher boiling point.

12-29

Crystal Structures and the Unit Cell

There are three types of cubic unit cells

1) Simple Cubic Unit Cell - 1 atom per unit cell

2) Body-Centered Cubic Unit Cell - 2 atoms per unit cell

3) Face-Centered Cubic Unit Cell - 4 atoms per unit cell

12-30

The crystal lattice and the unit cell

12-31

Figure 12.27 (1 of 3) The three cubic unit cells

Simple Cubic

coordination number = 6

Atoms/unit cell = 1/8 * 8 = 1

1/8 atom at 8 corners

12-32

Figure 12.27 (2 of 3) The three cubic unit cells

Body-centered Cubic

coordination number = 8

1/8 atom at 8 corners

1 atom at center

Atoms/unit cell = (1/8*8) + 1 = 2

12-33

Figure 12.27 (3 of 3) The three cubic unit cells

Face-centered Cubic

coordination number = 12Atoms/unit cell = (1/8*8)+(1/2*6) = 4

1/8 atom at 8 corners

1/2 atom at 6 faces

12-34

Figure 12.28 Packing of spheres

simple cubic

(52% packing efficiency)

body-centered cubic

(68% packing efficiency)

12-35

hexagonal unit cell

Figure 12.26 (continued)

closest packing of first and second layers

layer a

layer a

layer b

layer c

hexagonal closest packing

cubic closest packing

abab… (74%)abcabc… (74%)

expanded side views

face-centered unit cell

12-36

SAMPLE PROBLEM 12.4 Determining Atomic Radius from Crystal Structure

PROBLEM: Barium is the largest nonradioactive alkaline earth metal. It has a body-centered cubic unit cell and a density of 3.62 g/cm3. What is the atomic radius of barium?

(Volume of a sphere: V = 4/3r3)

PLAN: We can use the density and molar mass to find the volume of 1 mol of Ba. Since 68%(for a body-centered cubic) of the unit cell contains atomic material, dividing by Avogadro’s number will give us the volume of one atom of Ba. Using the volume of a sphere, the radius can be calculated.

density of Ba (g/cm3)

volume of 1 mol Ba metal volume of 1 Ba atom

radius of a Ba atom

multiply by packing efficiency

reciprocal divided by M V = 4/3r3

volume of 1 mol Ba atoms

divide by Avogadro’s number

12-37

SAMPLE PROBLEM 12.4 Determining Atomic Radius from Crystal Structure

SOLUTION:

continued

Volume of Ba metal =137.3 g Ba

mol Ba= 37.9 cm3/mol Ba

37.9 cm3/mol Ba x 0.68 = 26 cm3/mol Ba atoms

mol Ba atoms

6.022x1023 atoms= 4.3x10-23 cm3/atom

r3 = 3V/4 r=

3V4

3 3(4.3x10-23cm3)

4 x 3.143 = 2.2 x 10-8cm

1 cm3

3.62 gx

26 cm3

mol Ba atomsx

12-38

End of Chapter 12

12-39

Figure 12.29 Figure 12.30

Cubic closest packing for frozen argon

Cubic closest packing of frozen methane

12-40

Table 12.5 Characteristics of the Major Types of Crystalline Solids

ParticlesInterparticle Forces

Physical Behavior Examples (mp,0C)

Atomic

Molecular

Ionic

Metallic

Network

Group 8A(18)[Ne-249 to Rn-71]

Molecules

Positive & negative ions

Atoms

Atoms

Soft, very low mp, poor thermal & electrical conductors

DispersionAtoms

Dispersion, dipole-dipole, H bonds

Fairly soft, low to moderate mp, poor thermal & electrical conductors

Nonpolar - O2[-219], C4H10[-138], Cl2

[-101], C6H14[-95]

Polar - SO2[-73], CHCl3[-64], HNO3[-42], H2O[0.0]

Covalent bond

Metallic bond

Ion-ion attraction

Very hard, very high mp, usually poor thermal and electrical conductors

Soft to hard, low to very high mp, excellent thermal and electrical conductors, malleable and ductile

SiO2 (quartz)[1610]

C(diamond)[4000]

Hard & brittle, high mp, good thermal & electrical conductors when molten

NaCl [801]CaF2 [1423]

MgO [2852]

Na [97.8]Zn [420]Fe [1535]

12-41

Figure 12.31 The sodium chloride structure

12-42

Figure 12.32 The zinc blende structure

12-43

Figure 12.33 The fluorite (CaF2) structure

12-44

Figure 12.34 Crystal structures of metals

cubic closest packing hexagonal closest packing

12-45

Figure 12.35 Crystalline and amorphous silicon dioxide

12-46

Figure 12.36

The band of molecular orbitals in lithium metal

12-47

Figure 12.37

Electrical conductivity in a conductor, semiconductor, and insulator

conductor

semiconductor

insulator

12-48

Figure 12.19

The molecular basis of surface tension

12-49

Figure 12.22 The hexagonal structure of ice

12-50

Figure 12.24The macroscopic properties of water and their atomic

and molecular “roots”.

12-51

Table 12.3

Surface Tension and Forces Between Particles

Substance FormulaSurface Tension

(J/m2) at 200C Major Force(s)

diethyl ether

ethanol

butanol

water

mercury

dipole-dipole; dispersion

H bonding

H bonding; dispersion

H bonding

metallic bonding

1.7x10-2

2.3x10-2

2.5x10-2

7.3x10-2

48x10-2

CH3CH2OCH2CH3

CH3CH2OH

CH3CH2CH2CH2OH

H2O

Hg

12-52

Figure 12.20 Shape of water or mercury meniscus in glass

adhesive forces

stronger cohesive forces

12-53

Table 12.4 Viscosity of Water at Several Temperatures

Temperature(0C)Viscosity (N*s/m2)*

20

40

60

80

1.00x10-3

0.65x10-3

0.47x10-3

0.35x10-3

*The units of viscosity are newton-seconds per square meter.

12-54

Figure 12.11Periodic trends in covalent and

van der Waals radii (in pm)

12-55

Figure 12.10 Covalent and van der Waals radii

12-56

12-57

Figure 12.39 Crystal structures and band representations of doped

semiconductors

12-58

Forward bias

Reverse bias

p-n junctionFigure 12.40

The p-n junction

12-59

heat in furnace with O2

treat with photoresist apply templateexpose to light and solvent remove template

etch SiO2 with HF remove photoresist

treat with Ga vapor remove SiO2

Figure 12.41 Steps in manufacturing a p-n junction

12-60

Figure 12.42Structures of two typical liquid crystal molecules

12-61

Figure 12.43 The three common types of liquid crystal phases

12-62

Figure 12.45

Schematic of a liquid crystal display (LCD)

12-63

Table 12.7 Some Uses of New Ceramics and Ceramic Materials

Ceramic Applications

SiC, Si3N4, TiB2, Al2O3 Whiskers(fibers) to strength Al and other ceramics

Si3N4 Car engine parts; turbine rotors for “turbo” cars; electronic sensor units

Si3N4, BN, Al2O3 Supports or layering materials(as insulators) in electronic microchips

SiC, Si3N4, TiB2, ZrO2, Al2O3, BN

ZrO2, Al2O3

Cutting tools, edge sharpeners(as coatings and whole devices), scissors, surgical tools, industrial “diamond”

BN, SiC Armor-plating reinforcement fibers(as in Kevlar composites)

Surgical implants(hip and knee joints)

12-64

Figure 12.46 Unit cells of some modern ceramic materials

SiC BN

cubic boron nitride (borazon)

12-65

Table 12.8 Molar Masses of Some Common Polymers

Name Mpolymer (g/mol) n Uses

Acrylates 2 x105 2 x103 Rugs, carpets

Polyamide(nylons) 1.5 x104 1.2 x102 Tires, fishing line

Polycarbonate 1 x105 4 x102 Compact disks

Polyethylene 3 x105 1 x104 Grocery bags

Polyethylene (ultra- high molecular weight)

5 x106 2 x105 Hip joints

Poly(ethylene terephthalate)

2 x104 1 x102 Soda bottles

Polystyrene 3 x105 3 x103 Packing; coffee cups

Poly(vinyl chloride) 1 x105 1.5 x103 Plumbing

12-66

Figure 12.47 The random coil shape of a polymer chain

12-67

Figure 12.48 The semicrystallinity of a polymer chain

12-68

Figure 12.49 The viscosity of a polymer in solution

12-69

Table 12.9 Some Common Elastomers

Name Tg (0C)*

*Glass transition temperature

Uses

Poly(dimethyl siloxane) -123

-106

-65

-43

Polybutadiene

Polyisoprene

Polychloroprene (neoprene)

Breast implants

Rubber bands

Surgical gloves

Footwear; medical tubing

12-70

Figure 12.50Manipulating atoms

tip of an atomic force microscope (AFM)

12-71

Figure 12.50Manipulating atoms

nanotube gear

12-72

Figure B12.1

Diffraction of x-rays by crystal planes

Tools of the Laboratory

12-73

Figure B12.2

Formation of an x-ray diffraction pattern of the protein hemoglobin

Tools of the Laboratory

12-74

Tools of the Laboratory

Figure B12.3 Scanning tunneling micrographs

gallium arsenide semiconductor metallic gold