Ch 12

1
Chapter 12 Intermolecular Forces Liquids, Soli
ds, and Phase Changes

2
Intermolecular Forces Liquids, Solids, and Pha
se 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
3
Table 12.1
A Macroscopic Comparison of Gases, Liquids, and
Solids
State
Shape and Volume
Compressibility
Ability to Flow
Gas
Conforms to shape and volume of container
high
high
Liquid
Conforms to shape of container volume limited by
surface
very low
moderate
Solid
Maintains its own shape and volume
almost none
almost none
4
Types of Phases Changes
A liquid changing into a gas - vaporizationthe
reverse process - condensation
A solid changing into a liquid - fusion (melting
)the reverse process - freezing
(solidification) A solid changing directly into
a gas - sublimationthe reverse process -
deposition Enthalpy changes accompany phase cha
nges. Vaporization, fusion, and sublimation areE
XOTHERMIC the reverse processes ENDOTHERMIC
5
Heats of vaporization and fusion for several
common substances.
6
Phase changes and their enthalpy changes
7
Quantitative Aspects of Phase Changes
Energy changes result in a change in temperature
and/or change in phase.
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.
q (amount)(molar heat capacity)(DT)
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)(enthalpy of phase change)
8
A cooling curve for the conversion of gaseous
water to ice
Heat Removed
9
Calculating the Loss of Heat -
Cooling steam at 110o C down to ice at -10o C
q (amount)(molar heat capacity)(DT) -
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)
10
Liquid-gas equilibrium
11
The effect of temperature on the distribution of
molecular speed in a liquid
12
Vapor pressure as a function of temperature and
intermolecular forces
A linear plot of vapor pressure- temperature
relationship
13
The Clausius-Clapeyron Equation
Subtraction two equations for two temperatures.
14
SAMPLE PROBLEM 12.1
Using the Clausius-Clapeyron Equation
SOLUTION
34.90C 308.0K

T2 350K 770C
15
Phase diagrams for CO2 and H2O
16
Types of Intermolecular Forces - Bonding and
Nonbonding
17
Types of Intermolecular Forces - Bonding and
Nonbonding
18
Orientation of polar molecules because of
dipole-dipole forces
19
Dipole moment and boiling point
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 betwee
n 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
21
SAMPLE PROBLEM 12.2
Drawing Hydrogen Bonds Between Molecules
of a Substance
SOLUTION
(a) C2H6 has no H bonding sites.
(c)
22
Hydrogen bonding and boiling point
23
The H-bonding abilitiy of the water molecule
24
separated Cl2 molecules
DISPERSION(London) FORCES among nonpolar
molecules
instantaneous dipoles
25
DISPERSION(London) FORCES
Effect of Molar Mass and boiling point
26
DISPERSION(London) FORCES
Molecular shape and boiling point
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
PLAN

• 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.

28
SAMPLE PROBLEM 12.3
Predicting the Type and Relative Strength of
Intermolecular Forces
continued
SOLUTION
(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.
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 u
nit cell 3) Face-Centered Cubic Unit Cell - 4 a
toms per unit cell
30
The crystal lattice and the unit cell
31
Figure 12.27 (1 of 3)
The three cubic unit cells
Simple Cubic
Atoms/unit cell 1/8 8 1
coordination number 6
32
Figure 12.27 (2 of 3)
The three cubic unit cells
Body-centered Cubic
Atoms/unit cell (1/88) 1 2
33
Figure 12.27 (3 of 3)
The three cubic unit cells
Face-centered Cubic
Atoms/unit cell (1/88)(1/26) 4
34
Packing of spheres
Figure 12.28
simple cubic (52 packing efficiency)
body-centered cubic (68 packing efficiency)
35
Figure 12.26 (continued)
closest packing of first and second layers
abab (74)
abcabc (74)
36
SAMPLE PROBLEM 12.4
Determining Atomic Radius from Crystal Structure
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 Avogadros 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)
radius of a Ba atom
volume of 1 mol Ba metal
volume of 1 Ba atom
37
SAMPLE PROBLEM 12.4
Determining Atomic Radius from Crystal Structure
continued
SOLUTION
Volume of Ba metal
37.9 cm3/mol Ba
37.9 cm3/mol Ba
x 0.68
26 cm3/mol Ba atoms
4.3x10-23 cm3/atom
r3 3V/4p
2.2 x 10-8cm
38
End of Chapter 12
39
Figure 12.29
Figure 12.30
Cubic closest packing for frozen argon
40
Table 12.5 Characteristics of the Major Types
of Crystalline Solids
Interparticle Forces
Physical Behavior
Particles
Examples (mp,0C)
Atomic
Group 8A(18) Ne-249 to Rn-71
Soft, very low mp, poor thermal electrical
conductors
Dispersion
Atoms
Molecular
Molecules
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, H2O0.0
Ionic
Positive negative ions
Ion-ion attraction
Hard brittle, high mp, good thermal
electrical conductors when molten
NaCl 801 CaF2 1423 MgO 2852
Metallic
Atoms
Metallic bond
Soft to hard, low to very high mp, excellent
thermal and electrical conductors, malleable and
ductile
Na 97.8 Zn 420 Fe 1535
Network
Atoms
Covalent bond
Very hard, very high mp, usually poor thermal and
electrical conductors
SiO2 (quartz)1610 C(diamond)4000
41
Figure 12.31
The sodium chloride structure
42
The zinc blende structure
Figure 12.32
43
The fluorite (CaF2) structure
Figure 12.33
44
Crystal structures of metals
Figure 12.34
cubic closest packing
45
Figure 12.35
Crystalline and amorphous silicon dioxide
46
Figure 12.36
The band of molecular orbitals in lithium metal
47
Figure 12.37
Electrical conductivity in a conductor,
semiconductor, and insulator
conductor
insulator
semiconductor
48
Figure 12.19
The molecular basis of surface tension
49
The hexagonal structure of ice
Figure 12.22
50
The macroscopic properties of water and their
atomic and molecular roots.
Figure 12.24
51
Table 12.3
Surface Tension and Forces Between Particles
Surface Tension (J/m2) at 200C
Substance
Formula
Major Force(s)
diethyl ether
dipole-dipole dispersion
CH3CH2OCH2CH3
1.7x10-2
ethanol
H bonding
2.3x10-2
CH3CH2OH
butanol
H bonding dispersion
2.5x10-2
CH3CH2CH2CH2OH
water
H bonding
7.3x10-2
H2O
mercury
metallic bonding
48x10-2
Hg
52
Shape of water or mercury meniscus in glass
Figure 12.20
53
Table 12.4 Viscosity of Water at Several
Temperatures
Viscosity (Ns/m2)
Temperature(0C)
20
1.00x10-3
40
0.65x10-3
0.47x10-3
60
80
0.35x10-3
The units of viscosity are newton-seconds per
square meter.
54
Periodic trends in covalent and van der Waals
radii (in pm)
Figure 12.11
55
Covalent and van der Waals radii
Figure 12.10
56
(No Transcript)
57
Figure 12.39
Crystal structures and band representations of
doped semiconductors
58
Figure 12.40
Forward bias
The p-n junction
Reverse bias
59
Steps in manufacturing a p-n junction
Figure 12.41
60
Structures of two typical liquid crystal molecules
Figure 12.42
61
Figure 12.43
The three common types of liquid crystal phases
62
Figure 12.45
Schematic of a liquid crystal display (LCD)
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
Cutting tools, edge sharpeners(as coatings and
whole devices), scissors, surgical tools,
industrial diamond
BN, SiC
Armor-plating reinforcement fibers(as in Kevlar
composites)
ZrO2, Al2O3
Surgical implants(hip and knee joints)
64
Unit cells of some modern ceramic materials
Figure 12.46
SiC
BN cubic boron nitride (borazon)
65
Table 12.8 Molar Masses of Some Common Polymers
Name
Mpolymer (g/mol)
n
Uses
66
The random coil shape of a polymer chain
Figure 12.47
67
Figure 12.48
The semicrystallinity of a polymer chain
68
The viscosity of a polymer in solution
Figure 12.49
69
Table 12.9 Some Common Elastomers
Name
Tg (0C)
Uses
Poly(dimethyl siloxane)
-123
Breast implants
-106
Polybutadiene
Rubber bands
-65
Polyisoprene
Surgical gloves
-43
Polychloroprene (neoprene)
Footwear medical tubing
Glass transition temperature
70
Figure 12.50
Manipulating atoms
tip of an atomic force microscope (AFM)
71
Figure 12.50
Manipulating atoms
nanotube gear
72
Tools of the Laboratory
Figure B12.1
Diffraction of x-rays by crystal planes
73
Tools of the Laboratory
Figure B12.2
Formation of an x-ray diffraction pattern of the

protein hemoglobin
74
Tools of the Laboratory
Figure B12.3
Scanning tunneling micrographs
gallium arsenide semiconductor
metallic gold