12-1 Chapter 12 Intermolecular Forces: Liquids, Solids, and Phase Changes.
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Transcript of 12-1 Chapter 12 Intermolecular Forces: Liquids, Solids, and Phase Changes.
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