Page 1 CHAPTER 10: L IQUIDS + S OLIDS INTERMOLECULAR FORCES GENERALITIES DIPOLE-DIPOLE FORCES HYDROGEN BONDS H Cl H Cl H C H O H C H O H O H H O H H N H H H N H H H F H F H O H H O H H O H
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CHAPTER 10: LIQUIDS + SOLIDS
INTERMOLECULAR FORCES
GENERALITIES
DIPOLE-DIPOLE FORCES
HYDROGEN BONDS
H Cl H Cl HC
H
O HC
H
O
HO
H
HO
H HN
H
H
HN
H
H
H F H F
HO
H
HO
HH
OH
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LONDON DISPERSION FORCES (LDF)
Electronic orientations at different times Temporarily induced dipoles
Helium is a liquid at 4 Kelvin Methane (CH4) is a liquid at –160 ˚C
Titan (Saturn’s largest moon) has liquid CH4 rivers, oceans, and rain.
Sample Problems:
Identify the IMF pointed to by an arrow. Use a dashed line to show the strongest IMF possible between these two molecules. Also identify the IMF.
IMF: IMF:
He HeHe
HC
H
H H
HC
H
H H
I Cl I ClC
NH
H
H
HH
OH
H
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BOILING POINT
BOILING PROCESS + DHvap
Liquid H2O (water) Which of these represents gaseous H2O (steam)?
→
Boiling (liquid to gas) involves…
Heat of Vaporization (DH˚vap):
Water DHvap = +40.7 kJ/mol
BOILING POINT TRENDS
Molar Mass (g/mol)
DH˚vap (kJ/mol)
Boiling Point (˚C)
O2 32.00 6.8 –183.0
F2 38.00 6.6 –188.1
Cl2 70.90 20.4 –34.0
Br2 159.80 30.0 58.8
Bromine (liquid/gas); Chlorine (gas only)
liquid
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Molar Mass (g/mol)
DH˚vap (kJ/mol)
Boiling Point (˚C)
Methanol
(CH3OH)
IMF:
32.05 38.3 64.7
Formaldehyde
(CH2O) IMF:
30.03 23.3 –19.2
Ethane
(CH3CH3) IMF:
30.08 14.7 –88.6
Sample Problems:
In each pair, determine which should have the higher boiling point, and explain the trend using intermolecular forces.
HCl vs. HF Propane (C3H8) vs. Pentane (C5H12)
HC
O
H H
H
HO
CH
H H
HC
H
O HC
H
O
HC
C
H H
H
H H
HC
C
H H
H
H H
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LIQUID PROPERTIES
SURFACE TENSION
Water beading on waxy surface Scott Kelly with water droplet in space Water skipper
CAPILLARY ACTION
Concave meniscus with water Convex meniscus with mercury
GlassO
Si
OH
H
H
O HHO
HSurface
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VISCOSITY
Honey is viscous Structure of sugar (sucrose, C12H22O11)
“Pitch drop experiment” with asphalt / tar General structure of tar / crude oil
Sample Problems:
Which liquid is the most viscous?
Glycerin (glycerol) 1-propanol 2,4-pentanedione
O
CC
C
CC
C
CC
C
O
O
C HO
H HH
HO
H
OH O
H
H
H
HC
H
OH H
H
OH
O
H
H
C
OH
HH
H
OC
CC
O
O
H
H
H
H H H H
HH
CC
CO
H
H H H H
H HC
CC
CC
H
O O
H H
H
HH
HH
CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3
60-70 of these!
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EVAPORATION
EVAPORATION
VAPOR PRESSURE
Sample Problem:
Equal volumes of liquids A and B are placed in separate beakers on the countertop.
a. After some time, half of “A” has evaporated. After the same amount of time, should there be more or less of “B” remaining?
b. Which has a higher vapor pressure, A or B?
CC
C
O
H
HH
H
HH C
CC
C
H
HH
H
HH
H H
A B
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TEMPERATURE + VAPOR PRESSURE
Temp H2O (˚C)
Vapor Pressure H2O (torr)
0 4.6 20 17.5 40 55.3 60 149.4 90 525.8 100 760.0
LINEAR RELATIONSHIP
Inverse Temp (K–1)
Natural log (ln) of Vapor Pressure
H2O 0.00366 1.52 0.00341 2.864 0.00319 4.013 0.00300 5.0066 0.00275 6.2649 0.00268 6.6333
Logarithm Review:
log (100) means 10? = 100 log (100) = 2 because 102 = 100
ln (7.39) means e? = 7.39 ln (7.39) = 2 because e2 = 7.39
m = –5204 b = 20.6
Water, bp = 100 ˚C
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Clausius-Claperyon Equation
ln$𝑃&'() = −∆𝐻&'(𝑅 /
1𝑇2 + 𝑐
ln 567689 =
∆:;<=>
5 ?@8− ?
@79
ln = natural log (base “e”, not base 10) Pvap = vapor pressure DHvap = heat of vaporization (J/mol) R = gas constant, 8.3145 J/mol·K T = temperature in Kelvin
P1 = vapor pressure at temperature 1 P2 = vapor pressure at temperature 2 T1 = Kelvin temperature 1 T2 = Kelvin temperature 2
Sample Problems:
Give the graphical data for water, calculate water’s heat of vaporization in kJ/mol. (Note: actual DHvap water = +40.7 kJ/mol.)
The vapor pressure of alcohol (ethanol) at 34.7 ˚C is 100.0 mmHg, and the heat of vaporization of alcohol is 38.6 kJ/mol. Calculate the vapor pressure of alcohol at 65.0 ˚C.
m = –5204 b = 20.6
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The normal boiling point of acetone is 56.5 ˚C. At the Donner Summit (~7200 ft) on Highway 80 on the road to Reno and South Lake Tahoe, the atmospheric pressure is 585 mmHg.
a. At the normal boiling point, what is the vapor pressure of acetone?
b. When acetone is boiling at Donner Summit, what is its vapor pressure?
c. What is the boiling point (in K and ̊ C) of acetone (DHvap = 32.0 kJ/mol) at Donner Summit?
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MULTIPLE PHASE TRANSITIONS
HEATING CURVE
Phases Water Water / steam Water / steam Steam Steam
Temp (˚C)
Sample Problem:
Calculate the amount of energy (as heat) needed to boil 50.0 g of water at 100.0 ˚C.
What is the q of the opposite process (100.0˚C steam to 100.0 ˚C water)?
For H2O: sice = 2.03 J/g˚C swater = 4.184 J/g˚C ssteam = 2.06 J/g˚C DHvap = 40.7 kJ/mol DHfus = 6.02 kJ/mol
q = swater·m·DT
q = sice·m·DT
q = ssteam·m·DT
solid
liquid
gas q =
q =
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Sample Problem:
Calculate the heat energy (q) associated with bringing 50.0 g of ice at –10.0 ˚C to its boiling point.
PHASE DIAGRAMS
Melting: Boiling: Sublimation:
Freezing: Condensing: Deposition:
Triple Point:
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Critical Point:
Supercritical Fluid:
Phase Diagram for Propane (C3H8) Phase Diagram for Carbon
gas
100500–50–100–150–2000
10
20
30
50
40
liquid
solid
Pres
sure
(bar
)
Temperature (˚C)
supercritical fluid
Piece of “dry ice” (solid CO2)
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Sample Problems:
1. At which point(s) on the phase diagram do the following exist? Liquid only __________
Both solid and liquid __________
A supercritical fluid __________
2. If the substance is at point “b” and the
pressure is lowered without changing the temperature, what will eventually happen? a. It will melt b. It will freeze c. It will boil d. It will condense
SOLIDS
BROAD CATEGORIZATION
Obsidian (glassy SiO2) Quartz (crystalline SiO2)
Amorphous solid:
Crystalline solid:
Crystalline “lattice”
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2-D PACKING IN CRYSTALLINE SOLIDS
Packing Efficiency = A('BCD'ECFGH('IDJBKCAA('BC'&'JK'GKCJFLFJDBCKK
× 100
Coordination Number =
3-D PACKING IN CRYSTALLINE SOLIDS
Simple Cubic Body-Centered Cubic Face-Centered Cubic
Unit Cell
Examples Polonium (very few examples)
Iron, Chromium, Tungsten, Niobium, Uranium
(very common)
Lead, Aluminum, Copper, Gold, Silver
(very common)
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Sample Problems:
Calculate the packing efficiency for crystalline lead, which adopts a face-centered cubic (fcc) unit cell.
Packing Efficiency = ('IDJBKC&MKLNCLFJDBCKK&MKLNC
× 100
Calculate the length of one side of the unit cell of crystalline gold, which adopts a face-centered cubic (fcc) arrangement. The radius of a gold atom is 135 pm, where 1 × 1012 pm = 1 m.
Pythagorean theorem
a2 + b2 = c2
c
b
a
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UNIT CELL SUMMARY – AFTER ACTIVITY
Simple Cubic (sc)
Body-Centered Cubic (bcc)
Face-Centered Cubic (fcc)
Coordination Number
Packing Efficiency
Length of unit cell
METAL ALLOYS
Substitutional alloy: different elements replace (substitute) each other in the crystal lattice.
Brass: alloy of copper and zinc (often 2:1); exist as mixtures of face-centered / body-centered cubic.
Bronze: alloy of copper and tin (often 88% Cu, 12% Sn).
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Interstitial alloy: other elements fit in the cracks (“interstices”) of the crystal lattice.
Steel: Iron in a face-centered cubic lattice, with carbon (up to 2%) in the cracks.
IONIC SOLIDS
Sodium chloride (NaCl) Ammonium chloride
METALLIC BONDING
Metal Properties:
• Conductors of electricity:
• Conductors of heat:
• Malleable:
Electron “Sea” Model:
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OTHER SOLIDS
Ionic Solids Molecular Solids Network Solids Metallic Solids
NaCl
I2
diamond
Zn
NaCl, MgO, CaCl2 etc.
Ice (H2O), Dry Ice (CO2), Sugar
(C12H22O11), S8, P4
Glass, rock (SiO2), Diamond (C) Fe, Mg, Zn, etc.
m.p. NaCl: 801 ˚C
m.p. Al2O3: 2072 ˚C
m.p. sugar: ~140 ˚C m.p. sand: 1600 ˚C
m.p. diamond: 3800 ˚C
m.p. Cu: 1085 ˚C
m.p. W: 3422 ˚C
Sample Problem:
Which should have the lowest melting point?
a. Aspirin (C9H8O4) b. Sodium acetate (NaC2H3O2) c. Titanium (Ti) d. Quartz (SiO2)