1. Intermolecular Forces and
Liquids and Solids
Chapter 12
Copyright © The McGraw-Hill Companies, Inc.  Permission required for reproduction or display.

2. Homework pages
1-7, 9-16, 18, 21, 29, 30, 35-39,
41, 42, 51, 53-56, 59-62, 65-67,
72, 82, 86-88, 92, 94, 95, 98, 100

3. A phase is a homogeneous part of the system in contact with other parts of the system but separated from them by a well-defined boundary.
2 Phases
Solid phase - ice
Liquid phase - water

4. Intermolecular Forces
Intermolecular forces are attractive forces between molecules.
Intramolecular forces hold atoms together in a molecule.
Intermolecular vs Intramolecular
41 kJ to vaporize 1 mole of water (inter)
930 kJ to break all O-H bonds in 1 mole of water (intra)
“Measure” of intermolecular force
boiling point
melting point
DHvap
DHfus
DHsub
Generally, intermolecular forces are much weaker than intramolecular forces.

5. Intermolecular Forces
Dipole-Dipole Forces
Attractive forces between polar molecules
Orientation of Polar Molecules in a Solid
11.2

6. Intermolecular Forces
Ion-Dipole Forces
Attractive forces between an ion and a polar molecule
Ion-Dipole Interaction
11.2

7. Dispersion (London) force - arise as a
result of temporary dipoles induced in
the molecules or atoms.
- act between all molecules
- only force between nonpolar molecules
and noble gas atoms
- strength depends primarily on size of
molecule, very weak for small molec.
but fairly strong for large ones.
(Shape plays a role too.)

8. Intermolecular Forces
Dispersion Forces Continued
Polarizability is the ease with which the electron distribution in the atom or molecule can be distorted.
Polarizability increases with:
greater number of electrons
more diffuse electron cloud
Dispersion forces usually increase with molar mass.
11.2

9. What type(s) of intermolecular forces exist between each of the following molecules?
HBr
HBr is a polar molecule: dipole-dipole forces. There are also dispersion forces between HBr molecules.
CH4
CH4 is nonpolar: dispersion forces. S O
CO2
SO2
11.2

10. Intermolecular Forces
Hydrogen Bond
The hydrogen bond is a special dipole-dipole interaction between the hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom. A H … B or
A & B are N, O, or F
11.2

11. Why is the hydrogen bond considered a “special” dipole-dipole interaction?
Decreasing molar mass
Decreasing boiling point
11.2

12. thymine-adenine
cytosine-guanine

13. Dispersion forces affect all molecules.
H bonds are found between two molecules of the same kind only if they contain an O-H, N-H, or F-H bond. (water and acetone)
These forces only affect molecular substances.

14. Test on chapters 12 & 13 – EH Assignment Due
Unit 14 Liquids and Solids
Mininum score
Sec 1 Changes of Physical State 90
Sec 2 Types of Bonding in Solids
Sec 3 Crystalline Solids
Optional
Sec 4 Intermolecular Forces
Sec 5 Vapor Pressure
Sec 6 Phase Diagrams
Test on chapters 12 & 13 –

15. Strong intermolecular forces
Properties of Liquids
Surface tension is the amount of energy required to stretch or increase the surface of a liquid by a unit area.
Strong intermolecular forces
High surface tension
11.3

16. Properties of Liquids
Cohesion is the intermolecular attraction between like molecules
Adhesion is an attraction between unlike molecules
Adhesion
Cohesion
11.3

17. Strong intermolecular forces
Properties of Liquids
Viscosity is a measure of a fluid’s resistance to flow.
Strong intermolecular forces
High viscosity
Note glycerol
11.3

18. Predicting the Type and Relative Strength of Intermolecular Forces
Problem: Identify the dominant intermolecular
force that is present in each of the following
substances, and select the substance with the
higher boiling point in each pair:
NCl3 or BeF2 b) CH3Cl or CH3OH
c) CH3CH2OH or C2H4(OH)2
d) Butane, C4H10 or Pentane, C5H12

19. The Uniqueness of Water
Water is an excellent solvent for many ionic compounds and for many molecules capable of forming hydrogen bonds with water.
Water has a very high boiling point for such a small molecule. It also has a high specific heat, surface tension, heat of vaporization, etc.
The solid form of water is less dense than the liquid form. Ice floats.
All due to strong H bonds.

20. Ice is less dense than water
Water is a Unique Substance
Maximum Density
40C
Density of Water
Ice is less dense than water
11.3

21. The Solid State
1. Crystalline solids have well defined
shapes because their particles
(atoms, molecules, ions) occur in an
orderly arrangement. They have sharp
melting points.

22. TA p387

23. The Solid State
2. Amorphous solids such as glass have poorly defined shapes because their particles do not occur in an orderly arrangement. They don’t melt sharply, but gradually soften over a range of temperature.

24. Skip section 12.4
11.4

25. 11.4

26. 11.4

27. 11.4

28. Shared by 8 unit cells
Shared by 2 unit cells
11.4

29. 1 atom/unit cell
2 atoms/unit cell
4 atoms/unit cell
(8 x 1/8 = 1)
(8 x 1/8 + 1 = 2)
(8 x 1/8 + 6 x 1/2 = 4)
11.4

30. 11.4

31. 11.5

32. Types of Solids Ionic Crystals
Lattice points occupied by cations and anions
Held together by electrostatic attraction
Hard, brittle, high melting point
Poor conductor of heat and electricity
CsCl
ZnS
CaF2
11.6

33. Types of Solids Covalent Crystals (Network Covalent or Macromolecular)
Lattice points occupied by atoms
Held together by covalent bonds
Hard, high melting point
Poor conductor of heat and electricity
carbon
atoms
diamond
graphite
11.6

34. Types of Solids Molecular Crystals
Lattice points occupied by molecules
Held together by intermolecular forces
Soft, low melting point
Poor conductor of heat and electricity
11.6

35. Cross Section of a Metallic Crystal
Types of Solids
Metallic Crystals
Lattice points occupied by metal atoms
Held together by metallic bonds
Soft to hard, low to high melting point
Good conductors of heat and electricity
Cross Section of a Metallic Crystal
nucleus &
inner shell e-
mobile “sea”
of e-
11.6

36. Other examples of covalent are BN, Si, and SiC
Types of Crystals
Other examples of covalent are BN, Si, and SiC
11.6

37. An amorphous solid does not possess a well-defined arrangement and long-range molecular order.
A glass is an optically transparent fusion product of inorganic materials that has cooled to a rigid state without crystallizing
Crystalline
quartz (SiO2)
Non-crystalline
quartz glass
11.7

38. Not all solids fall into one of the four classes just discussed
Not all solids fall into one of the four classes just discussed. Many minerals have a structure
consisting of a network covalent structure that has a negative charge. Metal cations form
ionic bonds to this network covalent anion.
The silicates are the largest, the most interesting and the most complicated class of minerals by
far. Approximately 30% of all minerals are silicates and some geologists estimate that 90% of
the Earth's crust is made up of silicates. With oxygen and silicon the two most abundant
elements in the earth's crust silicates abundance is no real surprise.
The basic chemical unit of silicates is the (SiO4) tetrahedron shaped anionic group with a
negative four charge (-4). The oxygens can bond to another silicon atom and therefore
linking one (SiO4) tetrahedron to another and another, etc..
The complicated structures that these silicate tetrahedrons form is truly amazing. They can
form as single units, double units, chains, sheets, rings and framework structures. The
different ways that the silicate tetrahedrons combine is what makes the Silicate Class the
largest, the most interesting and the most complicated class of minerals.
KAlSi3O8 is a feldspar

39. Sample problems
What kinds of bonds must be broken in order
to melt or boil each of these:
SiO2 KCl Cu CO C(diamond) BaSO4
NH3 NH4F C2H5OH N2 Fe HCl H2O Xe

40. Explain the difference in boiling points.
CH3OCH °C CH3CH2OH 79°C
HF 20°C HCl -85°C
CH3CH2CH2CH2CH °C
CH3CH2CH °C

41. Which of these has the highest mp or bp?
HCl, Ar, F2
H2O, NaCl, HF, C12H22O11
Cl2, Br2, I2
KO2 or SiO2

42. Classify as metallic, molecular,ionic or network covalent solid that
a. is a nonconductor, but conducts when melted.
b. dissolves in water to give a nonconducting
solution.
c. conducts electricity as a solid.
d. melts below 100°C to give a nonconducting
liquid.

43. Greatest
Order
Least
T2 > T1
Evaporation
Condensation

44. The equilibrium vapor pressure is the vapor pressure measured when a dynamic equilibrium exists between condensation and evaporation. It depends only on temperature.
H2O (l) H2O (g)
Rate of
condensation
evaporation =
Dynamic Equilibrium
11.8

45. Before
Evaporation
At Equilibrium
11.8

47. Clausius-Clapeyron Equation
Molar heat of vaporization (DHvap) is the energy required to vaporize 1 mole of a liquid.
ln P = -
DHvap RT
+ C
Clausius-Clapeyron Equation
P = (equilibrium) vapor pressure
T = temperature (K)
R = gas constant (8.314 J/K•mol)
11.8

48. The boiling point is the temperature at which the (equilibrium) vapor pressure of a liquid is equal to the external pressure.
The normal boiling point is the temperature at which a liquid boils when the external pressure is 1 atm.
11.8

49. What are two differences between boiling and evaporation?
A liquid boils at the temperature at which its vapor pressure equals the external pressure.
high elevation - pressure cooker
Boulder, CO 610 mm Hg is normal pressure – water boils at 94 °C
Climate? Storms?

50. The critical temperature (Tc) is the temperature above which the gas cannot be made to liquefy, no matter how great the applied pressure.
The critical pressure (Pc) is the minimum pressure that must be applied to bring about liquefaction at the critical temperature.
11.8

51. H2O (s) H2O (l)
The melting point of a solid or the freezing point of a liquid is the temperature at which the solid and liquid phases coexist in equilibrium
Melting
Freezing
11.8

52. Molar heat of fusion (DHfus) is the energy required to melt 1 mole of a solid substance.
11.8

53. 11.8

54. Calculate the amount of heat that
must be added to 2.50 moles of ice
At -40°C to convert it to 2.50 moles of steam at 130 °C .
Specific heats: ice J/g °C
steam 1.99 J/g °C , water J/g °C

55. H2O (s) H2O (g)
Molar heat of sublimation (DHsub) is the energy required to sublime 1 mole of a solid.
Sublimation
Deposition
DHsub = DHfus + DHvap
( Hess’s Law)
11.8

56. A phase diagram summarizes the conditions at which a substance exists as a solid, liquid, or gas.
Phase Diagram of Water
11.8

57. 11.8

58. Phase Diagrams for CO2 and H2O

59. Supercritical
fluid
I atm =
105 Pa
Phase diagram for water showing
different solid phases.

60. Use the following data to sketch
a phase diagram for ethylene.
bp at 1 atm °C
fp at 1 atm °C
critical pt °C and 50.5 atm
triple pt °C and atm

61. Fig

63. TA p395