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Chapter 14
Liquids and Solids
Chapter 14
Table of Contents
2
14.1 Water and Its Phase Changes
14.2 Energy Requirements for the Changes of State
14.3 Intermolecular Forces
14.4 Evaporation and Vapor Pressure
14.5 The Solid State: Types of Solids
14.6 Bonding in Solids
Chapter 14
Table of Contents
3
Intermolecular Forces
Oδ-
Hδ+ Hδ+
Oδ-
Hδ+ Hδ+
Oδ-
Hδ+ Hδ+
Dipole-Dipole Forces
Solid
Liquid Gas
+ +
-
Section 14.1
Water and Its Phase Changes
Return to TOC
Copyright © Cengage Learning. All rights reserved 4
Reviewing What We Know
• Gases Low density Highly compressible Fill container
• Solids High density Slightly compressible Rigid (keeps its shape)
Section 14.1
Water and Its Phase Changes
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Copyright © Cengage Learning. All rights reserved 5
Heating/Cooling Curve
Section 14.1
Water and Its Phase Changes
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6
Heating/Cooling Curve
• Normal boiling point: at 1 atm = 100°C • Normal freezing point: at 1 atm = 0°C • Density
Liquid water = 1.00 g/mL Ice = 0.917 g/mL
Section 14.1
Water and Its Phase Changes
Return to TOC
Copyright © Cengage Learning. All rights reserved 7
Concept Check
During the process of melting ice by adding heat, the temperature of the ice/liquid water slurry
a) stays constant.b) increases.c) decreases.d) cannot be predicted.
Energy Requirements for the Changes of State
Section 14.2
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Copyright © Cengage Learning. All rights reserved 8
• Changes of state are physical changes. No chemical bonds
are broken. • When a substance changes
from solid to liquid to gas, the molecules remain intact.
• The changes in state are due to changes in the forces among molecules rather than in those within the molecules.
Energy Requirements for the Changes of State
Section 14.2
Return to TOC
9
• Molar heat of fusion – energy required to melt 1 mol of a substance.
• Molar heat of vaporization – energy required to change 1 mol of a liquid to its vapor.
Energy Requirements for the Changes of State
Section 14.2
Return to TOC
Copyright © Cengage Learning. All rights reserved 10
Concept Check
Which would you predict to be larger for a given substance: Hvap or Hfus?
Explain why.
Energy Requirements for the Changes of State
Section 14.2
Return to TOC
11
Concept Check
The unusually high value of the molar heat of vaporization of water (40.6 kJ/mole) is an important factor in moderating the temperature of the earth’s surface, and results in an enormous transfer of energy to the atmosphere as liquid water evaporates as part of the hydrologic cycle. Calculate the amount of heat in kJ needed to evaporate 10.5 kg of liquid water at 100.oC.
a) 4.27 × 105 kJb) 3.15 × 104 kJc) 2.37 × 104 kJd) 1.18 × 103 kJ
422
2
1 mol H O1000 g 40.6 kJ10.5 kg H O 2.37 10 kJ
1 kg 18.016 g H O mol
Energy Requirements for the Changes of State
Section 14.2
Return to TOC
12
Intramolecular Forces
• “Within” the molecule.• Molecules are formed by sharing electrons
between the atoms.• Hold the atoms of a molecule together.
Energy Requirements for the Changes of State
Section 14.2
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Copyright © Cengage Learning. All rights reserved 13
Intermolecular Forces
• Forces that occur between molecules.
• Intramolecular bonds are stronger than intermolecular forces.
Energy Requirements for the Changes of State
Section 14.2
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Copyright © Cengage Learning. All rights reserved 14
Concept Check
Which are stronger, intramolecular bonds or intermolecular forces?
How do you know?
Intermolecular Forces
Section 14.3
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15
• Forces that occur between molecules. Dipole–dipole forces
Hydrogen bonding London dispersion forces
Intermolecular Forces
Section 14.3
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Copyright © Cengage Learning. All rights reserved 16
Dipole–Dipole Attraction
Intermolecular Forces
Section 14.3
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Copyright © Cengage Learning. All rights reserved 17
Dipole-Dipole Forces
• Dipole moment – molecules with polar bonds often behave in an electric field as if they had a center of positive charge and a center of negative charge.
• Molecules with dipole moments can attract each other electrostatically. They line up so that the positive and negative ends are close to each other.
• Only about 1% as strong as covalent or ionic bonds.
Intermolecular Forces
Section 14.3
Return to TOC
18
Hydrogen Bonding
• Strong dipole-dipole forces.• Hydrogen is bound to a highly electronegative
atom – nitrogen, oxygen, or fluorine.
Intermolecular Forces
Section 14.3
Return to TOC
19
Hydrogen Bonding in Water
• Blue dotted lines are the intermolecular forces between the water molecules.
Hydrogen Bonds hold DNA together.
Intermolecular Forces
Section 14.3
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Copyright © Cengage Learning. All rights reserved 20
Hydrogen Bonding
• Affects physical properties Boiling point Melting point
Intermolecular Forces
Section 14.3
Return to TOC
About 70% of our planet is covered by water. Perhaps we should call it not “earth” but “ocean”. Where did the water come from?
Intermolecular Forces
Section 14.3
Return to TOC
Some say the water came from comets (mostly water) colliding with earth…Why did thy not collide with other planets that have no water??? Jupiter is 317 times the mass of the earth! Shoemaker-Levi colliding with Jupiter.
Intermolecular Forces
Section 14.3
Return to TOC
Moon rocks have been found to be as old as 4.527 billion years while the oldest earth rock has been found to be 4.28 billion years old. Moon rocks have been found to be magnetic (when they cooled they were under a magnetic field caused by a rapidly rotating planet). The moon is not rotating rapidly now.
The moon and the earth have not always been together!!!
Johnson Space Center Moon Rock Bldg.
Intermolecular Forces
Section 14.3
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Copyright © Cengage Learning. All rights reserved 24
London Dispersion Forces
• Instantaneous dipole that occurs accidentally when a given atom induces a similar dipole in a neighboring atom.
• Significant in large atoms/molecules.• Occurs in all molecules, including nonpolar
ones.
Intermolecular Forces
Section 14.3
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Copyright © Cengage Learning. All rights reserved 25
London Dispersion Forces – Nonpolar Molecules
Intermolecular Forces
Section 14.3
Return to TOC
26
London Dispersion Forces
• Become stronger as the sizes of atoms or molecules increase.
Intermolecular Forces
Section 14.3
Return to TOC
27
Melting and Boiling Points
• In general, the stronger the intermolecular forces, the higher the melting and boiling points.
Intermolecular Forces
Section 14.3
Return to TOC
Copyright © Cengage Learning. All rights reserved 28
Concept Check
Which molecule is capable of forming stronger intermolecular forces?
N2 H2O
Explain.
Intermolecular Forces
Section 14.3
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Copyright © Cengage Learning. All rights reserved 29
Concept Check
Draw two Lewis structures for the formula C2H6O and compare the boiling points of the two molecules.
C
H
H C
H
H
H
O H C
H
H C
H
H
H
O H
Intermolecular Forces
Section 14.3
Return to TOC
Copyright © Cengage Learning. All rights reserved 30
Concept Check
Which gas would behave more ideally at the same conditions of P and T?
CO or N2
Why?
Intermolecular Forces
Section 14.3
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Copyright © Cengage Learning. All rights reserved 31
Concept Check
Consider the following compounds:
NH3 CH4 H2
How many of the compounds above exhibit London dispersion forces?
a) 0
b) 1
c) 2
d) 3
Section 14.4
Evaporation and Vapor Pressure
Return to TOC
32
Vaporization or Evaporation
• Molecules of a liquid can escape the liquid’s surface and form a gas.
• Endothermic process – requires energy to overcome the relatively strong intermolecular forces in the liquid.
Section 14.4
Evaporation and Vapor Pressure
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Copyright © Cengage Learning. All rights reserved 33
Vapor Pressure
• Amount of liquid first decreases then becomes constant. • Condensation - process by which vapor molecules
convert to a liquid. • When no further change is visible the opposing
processes balance each other – equilibrium
Section 14.4
Evaporation and Vapor Pressure
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34
Vapor Pressure
• Pressure of the vapor present at equilibrium.• The system is at equilibrium when no net
change occurs in the amount of liquid or vapor because the two opposite processes exactly balance each other.
Section 14.4
Evaporation and Vapor Pressure
Return to TOC
35
Ilustration of Vapor Pressure
Budda
Water
Budda (air pressure) will keep the liquid water down while the heat vaporizes the surface water.
Who’s this?
Section 14.4
Evaporation and Vapor Pressure
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36
Ilustration of Vapor Pressure
WaterWhen the vapor pressure exceeds the air pressure, Budda cannot keep the liquid water down.
Then Budda rises and vapor bubbles form throughout the liquid. And it boils!
Section 14.4
Evaporation and Vapor Pressure
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Copyright © Cengage Learning. All rights reserved 37
Concept Check
What is the vapor pressure of water at 100°C? How do you know?
1 atm
Section 14.4
Evaporation and Vapor Pressure
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Copyright © Cengage Learning. All rights reserved 38
Vapor Pressure
• Liquids in which the intermolecular forces are strong have relatively low vapor pressures.
Section 14.4
Evaporation and Vapor Pressure
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Copyright © Cengage Learning. All rights reserved 39
Concept Check
Which of the following would be expected to have the highest vapor pressure at room temperature?
a) CH3CH2CH2OHb) CH3CH2CH2NH2
c) CH3CH2CH2CH3
d) CH3CH2CH3
Section 14.5
The Solid State: Types of Solids
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Copyright © Cengage Learning. All rights reserved 40
Crystalline Solids
• Regular arrangement of their components.
Section 14.5
The Solid State: Types of Solids
Return to TOC
41
Types of Crystalline Solids
Diamonds
Section 14.5
The Solid State: Types of Solids
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42
Types of Crystalline Solids
• Ionic Solids – ions at the points of the lattice that describes the structure of the solid.
• Molecular Solids – discrete covalently bonded molecules at each of its lattice points.
• Atomic Solids – atoms at the lattice points that describe the structure of the solid.
Section 14.5
The Solid State: Types of Solids
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Copyright © Cengage Learning. All rights reserved 43
Examples of Three Types of Crystalline Solids
Section 14.6
Bonding in Solids
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Copyright © Cengage Learning. All rights reserved 44
Examples of the Various Types of Solids
Section 14.6
Bonding in Solids
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Copyright © Cengage Learning. All rights reserved 45
Ionic Solids
• Stable substances with high melting points. • Held together by strong forces between ions.
Section 14.6
Bonding in Solids
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Copyright © Cengage Learning. All rights reserved 46
Molecular Solids
• Fundamental particle is a molecule. • Melt at relatively low temperatures. • Held together by weak intermolecular forces.
Section 14.6
Bonding in Solids
Return to TOC
47
Atomic Solids
• Fundamental particle is the atom. • Properties vary greatly.
Group 8 – low melting points Diamond – very high melting point
Section 14.6
Bonding in Solids
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48
Dr. Tacy Hall’s Artificial Diamond Presses
Pictures to the left and below are of diamonds made from graphite. Dr. Hall made diamonds from
peanut butter as well.
Section 14.6
Bonding in Solids
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49
Bonding in Metals
• Metals are held together by nondirectional covalent bonds (called the electron sea model) among the closely packed atoms.
The word ICE made from Nitinol wire, stretched, reforms in warm water.
Section 14.6
Bonding in Solids
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Copyright © Cengage Learning. All rights reserved 50
Bonding in Metals
• Metals form alloys of two types. Substitutional – different atoms are substituted for
the host metal atoms.
Section 14.6
Bonding in Solids
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Copyright © Cengage Learning. All rights reserved 51
Bonding in Metals
• Metals form alloys of two types. Interstitial – small atoms are introduced into the
“holes” in the metallic structure.