1. Introductory Chemistry, 3rd Edition Nivaldo Tro
Chapter 12
Liquids, Solids, and Intermolecular Forces
Roy Kennedy
Massachusetts Bay Community College
Wellesley Hills, MA
2009, Prentice Hall

2. Interactions Between Molecules
Many of the phenomena we observe are related to interactions between molecules that do not involve a chemical reaction, such as taste, smell at the receptor sites in our tongue and nose, fleeting in nature.
Tro's Introductory Chemistry, Chapter 12

3. Interactions Between Molecules
Important to scientists are the physical properties of solids, liquids and gas:
How can water exists in three states on this planet
Why are there solids
What holds a liquid together
Why are gasses not liquids
Why does matter have such different melting and boiling points
Tro's Introductory Chemistry, Chapter 12

4. The Physical States of Matter
Matter can be classified as solid, liquid, or gas based on what properties it exhibits.
Fixed = Keeps shape when placed in a container.
Indefinite = Takes the shape of the container.
Tro's Introductory Chemistry, Chapter 12

5. Structure Determines Properties
The atoms or molecules have different structures in solids, liquids, and gases, leading to different properties.
Tro's Introductory Chemistry, Chapter 12

6. Properties of the States of Matter: Gases
Low densities compared to solids and liquids.
Fluid.
The material exhibits a smooth, continuous flow as it moves.
Take the shape of their container(s).
Expand to fill their container(s).
Can be compressed into a smaller volume.
Tro's Introductory Chemistry, Chapter 12

7. Properties of the States of Matter: Liquids
High densities compared to gases.
Fluid.
The material exhibits a smooth, continuous flow as it moves.
Take the shape of their container(s).
Keep their volume, do not expand to fill their container(s).
Cannot be compressed into a smaller volume.
Tro's Introductory Chemistry, Chapter 12

8. Properties of the States of Matter: Solids
High densities compared to gases.
Nonfluid.
They move as an entire “block” rather than a smooth, continuous flow.
Keep their own shape, do not take the shape of their container(s).
Keep their own volume, do not expand to fill their container(s).
Cannot be compressed into a smaller volume.
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9. The Structure of Solids, Liquids, and Gases
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10. Tro's Introductory Chemistry, Chapter 12
Gases
In the gas state, the particles have complete freedom from each other.
The particles are constantly flying around, bumping into each other and their container(s).
In the gas state, there is a lot of empty space between the particles.
On average.
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11. Tro's Introductory Chemistry, Chapter 12
Gases, Continued
Because there is a lot of empty space, the particles can be squeezed closer together. Therefore, gases are compressible.
Because the particles are not held in close contact and are moving freely, gases expand to fill and take the shape of their container(s), and will flow.
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12. Tro's Introductory Chemistry, Chapter 12
Liquids
The particles in a liquid are closely packed, but they have some ability to move around.
The close packing results in liquids being incompressible.
But the ability of the particles to move allows liquids to take the shape of their container and to flow. However, they don’t have enough freedom to escape and expand to fill the container(s).
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13. Tro's Introductory Chemistry, Chapter 12
Solids
The particles in a solid are packed close together and are fixed in position.
Though they are vibrating.
The close packing of the particles results in solids being incompressible.
The inability of the particles to move around results in solids retaining their shape and volume when placed in a new container, and prevents the particles from flowing.
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14. Tro's Introductory Chemistry, Chapter 12
Solids, Continued
Some solids have their particles arranged in an orderly geometric pattern. We call these crystalline solids.
Salt and diamonds.
Other solids have particles that do not show a regular geometric pattern over a long range. We call these amorphous solids.
Plastic and glass.
Tro's Introductory Chemistry, Chapter 12

15. Why Is Sugar a Solid, But Water Is a Liquid?
The state a material exists in depends on the attraction between molecules and their ability to overcome the attraction.
The attractive forces between ions or molecules depends on their structure.
The attractions are electrostatic.
They depend on shape, polarity, etc.
The ability of the molecules to overcome the attraction depends on the amount of kinetic energy they possess.
Tro's Introductory Chemistry, Chapter 12

16. Properties and Attractive Forces
Phase
Density
Shape
Volume
Relative strength of attractive forces
Gas
Low
Indefinite
Weakest
Liquid
High
Definite
Moderate
Solid
Strongest
Tro's Introductory Chemistry, Chapter 12

17. Phase Changes: Melting
Generally, we convert a material in the solid state into a liquid by heating it.
Adding heat energy increases the amount of kinetic energy of the molecules in the solid.
Eventually, they acquire enough energy to partially overcome the attractive forces holding them in place.
This allows the molecules enough extra freedom to move around a little and rotate.
Tro's Introductory Chemistry, Chapter 12

18. Phase Changes: Boiling
Generally, we convert a material in the liquid state into a gas by heating it.
Adding heat energy increases the amount of kinetic energy of the molecules in the liquid.
Eventually, they acquire enough energy to completely overcome the attractive forces holding them together.
This allows the molecules complete freedom to move around and rotate.
Tro's Introductory Chemistry, Chapter 12

19. Properties of Liquids: Surface Tension
Liquids tend to minimize their surface—a phenomenon we call surface tension.
This tendency causes liquids to have a surface that resists penetration.
The stronger the attractive force between the molecules, the larger the surface tension.
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20. Tro's Introductory Chemistry, Chapter 12
Surface Tension
Molecules in the interior of a liquid experience attractions to surrounding molecules in all directions.
However, molecules on the surface experience an imbalance in attractions, effectively pulling them in.
To minimize this imbalance and maximize attraction, liquids try to minimize the number of molecules on the exposed surface by minimizing their surface area.
Stronger attractive forces between the molecules = larger surface tension.
Tro's Introductory Chemistry, Chapter 12

21. Properties of Liquids: Viscosity
Some liquids flow more easily than others.
The resistance of a liquid’s flow is called viscosity.
The stronger the attractive forces between the molecules, the more viscous the liquid is.
Also, the less round the molecule’s shape, the larger the liquid’s viscosity.
Some liquids are more viscous because their molecules are long and get tangled in each other, causing them to resist flowing.
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22. Tro's Introductory Chemistry, Chapter 12
Evaporation
The evaporation happens at the surface.
Molecules on the surface experience a smaller net attractive force than molecules in the interior.
All the surface molecules do not escape at once, only the ones with sufficient kinetic energy to overcome the attractions will escape.
Tro's Introductory Chemistry, Chapter 12

23. Escaping the Surface
The average kinetic energy is directly proportional to the Kelvin temperature.
Not all molecules in the sample have the same amount of kinetic energy.
Those molecules on the surface that have enough kinetic energy will escape.
Raising the temperature increases the number of molecules with sufficient energy to escape.

24. Escaping the Surface, Continued
Since the higher energy molecules from the liquid are leaving, the total kinetic energy of the liquid decreases, and the liquid cools.
The remaining molecules redistribute their energies, generating more high energy molecules.
The result is that the liquid continues to evaporate .
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25. Factors Effecting the Rate of Evaporation
Liquids that evaporate quickly are called volatile liquids, while those that do not are called nonvolatile.
Increasing the surface area increases the rate of evaporation.
More surface molecules.
Increasing the temperature increases the rate of evaporation.
Raises the average kinetic energy, resulting in more molecules that can escape.
Weaker attractive forces between the molecules = faster rate of evaporation.
Tro's Introductory Chemistry, Chapter 12

26. Reconnecting with the Surface
When a liquid evaporates in a closed container, the vapor molecules are trapped.
The vapor molecules may eventually bump into and stick to the surface of the container or get recaptured by the liquid. This process is called condensation.
A physical change in which a gaseous form is converted to a liquid form.
Tro's Introductory Chemistry, Chapter 12

27. Evaporation and Condensation
Shortly, the water
starts to evaporate.
Initially the rate
of evaporation is much faster than rate of condensation
When water is just
added to the flask and it is capped, all the water molecules are in the liquid.
Opposite processes that occur at the same rate in the same system are said to be in dynamic equilibrium.
Eventually, the condensation and evaporation reach the same speed. The air in the flask is now saturated with water vapor.
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28. Tro's Introductory Chemistry, Chapter 12
Vapor Pressure
Once equilibrium is reached, from that time forward, the amount of vapor in the container will remain the same.
As long as you don’t change the conditions.
The partial pressure exerted by the vapor is called the vapor pressure.
The vapor pressure of a liquid depends on the temperature and strength of intermolecular attractions.
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29. Tro's Introductory Chemistry, Chapter 12
Boiling
In an open container, as you heat a liquid the average kinetic energy of the molecules increases, giving more molecules enough energy to escape the surface.
So the rate of evaporation increases.
Eventually, the temperature is high enough for molecules in the interior of the liquid to escape. A phenomenon we call boiling.
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30. Tro's Introductory Chemistry, Chapter 12
Boiling Point
The temperature at which the vapor pressure of the liquid is the same as the atmospheric pressure is called the boiling point.
The normal boiling point is the temperature required for the vapor pressure of the liquid to be equal to 1 atm.
The boiling point depends on what the atmospheric pressure is.
The temperature of boiling water on the top of a mountain will be cooler than boiling water at sea level.
Tro's Introductory Chemistry, Chapter 12

31. Temperature and Boiling
As you heat a liquid, its temperature increases until it reaches its boiling point.
All the energy from the heat source is being used to overcome all of the attractive forces in the liquid.
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32. Energetics of Evaporation
As it loses its high energy molecules through evaporation, the liquid cools.
Then the liquid absorbs heat from its surroundings to raise its temperature back to the same as the surroundings.
Processes in which heat flows into a system from the surroundings are said to be endothermic.
As heat flows out of the surroundings, it causes the surroundings to cool.
As alcohol evaporates off your skin, it causes your skin to cool.
Tro's Introductory Chemistry, Chapter 12

33. Energetics of Condensation
As it gains the high energy molecules through condensation, the liquid warms.
Then the liquid releases heat to its surroundings to reduce its temperature back to the same as the surroundings.
Processes in which heat flows out of a system into the surroundings are said to be exothermic.
As heat flows into the surroundings, it causes the surroundings to warm.
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34. Tro's Introductory Chemistry, Chapter 12
Heat of Vaporization
The amount of heat needed to vaporize one mole of a liquid is called the heat of vaporization.
DHvap
It requires 40.7 kJ of heat to vaporize one mole of water at
100 °C.
Always endothermic.
Number is +.
DHvap depends on the initial temperature.
Since condensation is the opposite process to evaporation, the same amount of energy is transferred but in the opposite direction.
DHcondensation = −DHvaporization
Tro's Introductory Chemistry, Chapter 12

35. Heats of Vaporization of Liquids at Their Boiling Points and at 25 °C
Chemical
formula
Normal boiling point, °C
DHvap at boiling point, (kJ/mol)
DHvap at 25 °C, (kJ/mol)
Water
H2O
100
+40.7
+44.0
Isopropyl alcohol
C3H7OH
82.3
+39.9
+45.4
Acetone
C3H6O
56.1
+29.1
+31.0
Diethyl ether
C4H10O
34.5
+26.5
+27.1
Tro's Introductory Chemistry, Chapter 12

36. Example 12.1—Calculate the Mass of Water that Can Be Vaporized with 155 KJ of Heat at 100 °C.
Given:
Find:
155 kJ
g H2O
Solution Map:
Relationships:
1 mol H2O = 40.7 kJ, 1 mol = g kJ
mol H2O
g H2O
Solution:
Check:
Since the given amount of heat is almost 4x the DHvap, the amount of water makes sense.

37. Tro's Introductory Chemistry, Chapter 12
Practice—How Much Heat Energy, in kJ, is Required to Vaporize 87 g of Acetone, C3H6O, (MM 58.08) at 25 C? (DHvap = 31.0 kJ/mol)
Tro's Introductory Chemistry, Chapter 12

38. Practice—How Much Heat Energy, in kJ, Is Required to Vaporize 87 g of Acetone, C3H6O, (MM 58.08) at 25 C? (DHvap = 31.0 kJ/mol), Continued
Given:
Find:
87 g C3H6O kJ
Solution Map:
Relationships:
1 mol C3H6O = 31.0 kJ at 25 C, 1 mol = g
g C3H6O
mol C3H6O kJ
Solution:
Check:
Since the given mass is than one mole, the answer being greater than DHvap makes sense.

39. Temperature and Melting
As you heat a solid, its temperature increases until it reaches its melting point.
Once the solid starts to melt, the temperature remains the same until it all turns to a liquid.
All the energy from the heat source is being used to overcome some of the attractive forces in the solid that hold them in place.
Tro's Introductory Chemistry, Chapter 12

40. Energetics of Melting and Freezing
When a solid melts, it absorbs heat from its surroundings, it is endothermic.
As heat flows out of the surroundings, it causes the surroundings to cool.
As heat flows out of your drink into the ice cubes (causing them to melt), the liquid gets cooler.
When a liquid freezes, it releases heat into its surroundings, it is exothermic.
As heat flows into the surroundings, it causes the surroundings to warm.
Orange growers often spray their oranges with water when a freeze is expected. Why?
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41. Tro's Introductory Chemistry, Chapter 12
Heat of Fusion
The amount of heat needed to melt one mole of a solid is called the heat of fusion.
DHfus
Fusion is an old term for heating a substance until it melts, it is not the same as nuclear fusion.
Since freezing (crystallization) is the opposite process of melting, the amount of energy transferred is the same, but in the opposite direction.
DHcrystal = -DHfus
In general, DHvap > DHfus because vaporization requires breaking all attractive forces.
Tro's Introductory Chemistry, Chapter 12

42. Heats of Fusion of Several Substances
Liquid
Chemical
formula
Melting point, °C
DHfusion, (kJ/mol)
Water
H2O
0.00
6.02
Isopropyl alcohol
C3H7OH
-89.5
5.37
Acetone
C3H6O
-94.8
5.69
Diethyl ether
C4H10O
-116.3
7.27
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43. Tro's Introductory Chemistry, Chapter 12
Practice—How Much Heat Energy, in kJ, is Required to Melt 87 g of Acetone, C3H6O, (MM 58.08)? (DHfus = 5.69 kJ/mol)
Tro's Introductory Chemistry, Chapter 12

44. Practice—How Much Heat Energy, in kJ, Is Required to Melt 87 g of Acetone, C3H6O, (MM 58.08)?, Continued
Given:
Find:
87 g C3H6O kJ
Solution Map:
Relationships:
1 mol C3H6O = 5.69 kJ at C, 1 mol = g
g C3H6O
mol C3H6O kJ
Solution:
Check:
Since the given mass is more than one mole, the answer being greater than DHvap makes sense.

45. Tro's Introductory Chemistry, Chapter 12
Sublimation
Sublimation is a physical change in which the solid form changes directly to the gaseous form.
Without going through the liquid form.
Like melting, sublimation is endothermic.
Tro's Introductory Chemistry, Chapter 12

46. Intermolecular Attractive Forces
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47. Effect of the Strength of Intermolecular Attractions on Properties
The stronger the intermolecular attractions are, the more energy it takes to separate the molecules.
Substances with strong intermolecular attractions have higher boiling points, melting points, and heat of vaporization; they also have lower vapor pressures.
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48. Tro's Introductory Chemistry, Chapter 12
Practice—Pick the Substance in Each Pair with the Stronger Intermolecular Attractions.
sugar or water.
water or acetone.
ice or dry ice.
sugar or water
water or acetone
ice or dry ice
Tro's Introductory Chemistry, Chapter 12

49. Attractive Forces and Properties
Like dissolves like.
Miscible = Liquids that do not separate, no matter what the proportions.
Ionic
Polar molecules dissolve in polar solvents.
Water, alcohol, CH2Cl2.
A special case of polarity: Molecules with O or N higher solubility in H2O due to H-bonding with H2O.
Nonpolar molecules dissolve in nonpolar solvents or Dispersion forces
Ligroin (hexane), toluene, CCl4.
If molecule has both polar and nonpolar parts, then hydrophilic-hydrophobic competition.

50. Tro's Introductory Chemistry, Chapter 12
Dispersion Forces
Also known as London forces or instantaneous dipoles.
Caused by distortions in the electron cloud of one molecule inducing distortion in the electron cloud on another.
Distortions in the electron cloud lead to a temporary dipole.
The temporary dipoles lead to attractions between molecules—dispersion forces.
All molecules have attractions caused by dispersion forces.
Tro's Introductory Chemistry, Chapter 12

51. Instantaneous Dipoles
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52. Strength of the Dispersion Force
Depends on how easily the electrons can move, or be polarized.
The more electrons and the farther they are from the nuclei, the larger the dipole that can be induced.
Strength of the dispersion force gets larger with larger molecules.
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53. Dispersion Force and Molar Mass
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54. Tro's Introductory Chemistry, Chapter 12
Practice—The Following Are All Made of Non–Polar Molecules. Pick the Substance in Each Pair with the Highest Boiling Point.
CH4 or C3H8.
BF3 or BCl3.
CO2 or CS2.
CH4 or C3H8
BF3 or BCl3
CO2 or CS2
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55. Tro's Introductory Chemistry, Chapter 12
Permanent Dipoles
Because of the kinds of atoms that are bonded together and their relative positions in the molecule, some molecules have a permanent dipole.
Polar molecules.
The size of the molecule’s dipole is measured in debyes, D.
Tro's Introductory Chemistry, Chapter 12

56. Dipole-to-Dipole Attraction
Polar molecules have a permanent dipole.
A + end and a – end.
The + end of one molecule will be attracted to the – end of another.
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57. Polarity and Dipole-to-Dipole Attraction
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58. Tro's Introductory Chemistry, Chapter 12
Attractive Forces
Dispersion forces—All molecules. _ +
Dipole-to-dipole forces—Polar molecules.
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59. Intermolecular Attraction and Properties
All molecules are attracted by dispersion forces.
Polar molecules are also attracted by dipole-dipole attractions.
Therefore, the strength of attraction is stronger between polar molecules than between nonpolar molecules of the same size.
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60. Tro's Introductory Chemistry, Chapter 12
Practice—Determine Which of the Following Has Dipole–Dipole Attractive Forces. (EN C= 2.5, F = 4, H = 2.1, S = 2.5)
CS2
CH2F2
CF4
CS2 Nonpolar bonds = nonpolar molecule.
CH2F2 Polar bonds and asymmetrical = polar molecule.
CF4 Polar bonds and symmetrical shape = nonpolar molecule. 
Tro's Introductory Chemistry, Chapter 12

61. Attractive Forces and Properties
Like dissolves like.
Miscible = Liquids that do not separate, no matter what the proportions.
Ionic
Polar molecules dissolve in polar solvents.
Water, alcohol, CH2Cl2.
Molecules with O or N higher solubility in H2O due to H-bonding with H2O.
Nonpolar molecules dissolve in nonpolar solvents.
Ligroin (hexane), toluene, CCl4.
If molecule has both polar and nonpolar parts, then hydrophilic-hydrophobic competition.

62. Tro's Introductory Chemistry, Chapter 12
Immiscible Liquids
When liquid pentane, a nonpolar substance, is mixed with water, a polar substance, the two liquids separate because they are more attracted to their own kind of molecule than to the other.
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63. Tro's Introductory Chemistry, Chapter 12
Hydrogen Bonding
HF, or molecules that have OH or NH groups have particularly strong intermolecular attractions.
Unusually high melting and boiling points.
Unusually high solubility in water.
This kind of attraction is called a hydrogen bond.
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64. Tro's Introductory Chemistry, Chapter 12

65. Properties and H-Bonding
Name
Formula
Molar mass
(g/mol)
Structure
Boiling point, °C
Melting point,
Solubility in water
Ethane
C2H6
30.0
-88
-172
Immiscible
Ethanol
CH4O
32.0
64.7
-97.8
Miscible
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66. Intermolecular H-Bonding
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67. Tro's Introductory Chemistry, Chapter 12
Hydrogen Bonding
When a very electronegative atom is bonded to hydrogen, it strongly pulls the bonding electrons toward it.
Since hydrogen has no other electrons, when it loses the electrons, the nucleus becomes deshielded.
Exposing the proton.
The exposed proton acts as a very strong center of positive charge, attracting all the electron clouds from neighboring molecules.
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68. H-Bonds vs. Chemical Bonds
Hydrogen bonds are not chemical bonds.
Hydrogen bonds are attractive forces between molecules.
Chemical bonds are attractive forces that make molecules.
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69. Attractive Forces and Properties
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70. Tro's Introductory Chemistry, Chapter 12
Example 12.5—Which of the Following Is a Liquid at Room Temperature? (The Other Two Are Gases.)
formaldehyde, CH2O.
30.03 g/mol.
polar molecule  dipole–dipole attractions present.
Polar C=O bond and asymmetric.
fluoromethane, CH3F.
34.03 g/mol.
Polar C−F bond and asymmetric.
hydrogen peroxide, H2O2
34.02 g/mol.
Polar H−O bonds and asymmetric.
H−O bonds  hydrogen-bonding present.
formaldehyde, CH2O
30.03 g/mol
polar molecule  dipole–dipole attractions present
polar C=O bond & asymmetric
fluoromethane, CH3F
34.03 g/mol
polar C−F bond & asymmetric
hydrogen peroxide, H2O2
34.02 g/mol
polar H−O bonds & asymmetric
H−O bonds  Hydrogen bonding present
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71. Tro's Introductory Chemistry, Chapter 12
Practice–Pick the Compound in Each Pair Expected to Have the Higher Solubility in H2O.
CH3CH2OCH2CH3 or CH3CH2CH2CH2CH3.
CH3CH2NHCH3 or CH3CH2CH2CH3.
CH3CH2OH or CH3CH2CH2CH2CH2OH.
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72. Tro's Introductory Chemistry, Chapter 12
Practice–Pick the Compound in Each Pair Expected to Have the Higher Solubility in H2O, Continued.
CH3CH2OCH2CH3 or CH3CH2CH2CH2CH3 contains polar O.
CH3CH2NHCH3 or CH3CH2CH2CH3 contains polar N.
CH3CH2OH or CH3CH2CH2CH2CH2OH contains less nonpolar parts.
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73. Types of Intermolecular Forces
Type of force
Relative strength
Present in
Example
Dispersionforce
Weak, but increases with molar mass
All atoms and molecules H2
Dipole– Dipole force
Moderate
Only polar molecules
HCl
Hydrogen Bond
Strong
Molecules having H bonded to F, O, or N HF

74. Tro's Introductory Chemistry, Chapter 12
Crystalline Solids
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75. Types of Crystalline Solids
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76. Molecular Crystalline Solids
Molecular solids are solids whose composite units are molecules.
Solid held together by intermolecular attractive forces.
Dispersion, dipole-dipole, or H-bonding.
Generally low melting points and DHfusion.
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77. Ionic Crystalline Solids
Ionic solids are solids whose composite units are formula units.
Solid held together by electrostatic attractive forces between cations and anions.
Cations and anions arranged in a geometric pattern called a crystal lattice to maximize attractions.
Generally higher melting points and DHfusion than molecular solids.
Because ionic bonds are stronger than intermolecular forces.
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78. Atomic Crystalline Solids
Atomic solids are solids whose composite units are individual atoms.
Solids held together by either covalent bonds, dispersion forces, or metallic bonds.
Melting points and DHfusion vary depending on the attractive forces between the atoms.
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79. Tro's Introductory Chemistry, Chapter 12
Practice—Classify Each of the Following Crystalline Solids as Molecular, Ionic, or Atomic.
H2O(s)—molecular.
Si(s)—atomic.
C12H22O11(s)—molecular.
CaF2(s)—ionic.
Sc(NO3)3(s)—ionic.
H2O(s)
Si(s)
C12H22O11(s)
CaF2(s)
Sc(NO3)3(s)
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80. Metallic Bonding
The model of metallic bonding can be used to explain the properties of metals.
The luster, malleability, ductility, and electrical and thermal conductivity are all related to the mobility of the electrons in the solid.
The strength of the metallic bond varies, depending on the charge and size of the cations, so the melting points and DHfusion of metals vary as well.