1. Section 10.1 Intermolecular Forces
DHfus = 6.02 kJ/mol
DHvap = 40.7 kJ/mol
Answer
Now
Based on the enthalpy values and what you know of solids, liquids, and gases, which two states of matter are most similar? Which is most unique?

2. Liquids and Solids
Chapter 10

3. Types of Intermolecular Forces
Dipole-Dipole
Molecules must have dipole
Opposites attract
Attractions weaken as distance between dipoles increase.
Hydrogen Bonding
Type of Dipole-Dipole
Between H and any highly EN atom. (ie: F, Cl, O)
Extremely strong attraction

4. Types of Intermolecular Forces, 2
London Dispersion Forces
Noble Gases and Non-Polar Molecules
Temporary Dipoles form
Sometimes called Induced Dipole Forces
Weaker than Dipole-Dipole
In molecules with large atoms, dispersion forces are often more important than dipole forces.

5. Properties and Intermolecular Forces
What properties do intermolecular forces affect?
Boiling Point
Freezing Point
Vapor Pressure
Surface Tension
Capillary Action
Viscosity

6. Practice Problems
Identify the most important types of intermolecular forces present in each of the following substances:
In each of the following group of substances, pick the one what has the given property and justify your answer:
Highest boiling point:
HCl, Ar, or F2
Highest freezing point:
H2O, NaCl, or HF
Lowest Boiling Point:
CH4, CH3CH3, or CH3CH2CH3 Ar
HCl
CH4 CO
NaNO3

7. Vapor Pressure
Vapor Pressure of a liquid occurs when some particles are vaporized just above the surface of the liquid.
Volatile liquids have higher vapor pressures
REMEMBER:
Patmosphere = Pvaporization + PHgColumn
The heat of vaporization (DHvap) is the amount of heat required to change 1 mole of liquid to gas.
Endothermic values

8. Vapor Pressure Relationships
Molar Mass
Temperature
Vapor Pressure
Intermolecular Forces
Vapor Pressure

9. Vapor Pressure Calculations
lnPvap = -(DHvap/R)(1/T)
Use J/Kmol for R.
The vapor pressure of water at 25oC is 23.8 torr and the DHvap of water is always 43.9 kJ/mol. Calculate the vapor pressure of water at 50oC.
Try Me Problem

10. Heating Curve
When a solid is heated, it will absorb energy (increase temp) until it begins to melt.
At melting point and at boiling point, the two states of matter are present.
No change in temperature occurs until all particles are converted.

11. Phase Diagrams
Relate the temperature, pressure, and state of matter for a substance.
Triple Point is the point at which all three states of matter are present.
Critical Point is the last temperature and pressure combination at which it is possible to condense particles to a liquid.

12. Phase Diagram of Water
Melting
Evaporation
Sublimation

13. What IS Boiling Point?
Myth
Fact

14. Special Cases UNSTABLE !
Superheated liquid: A liquid that is heated so rapidly that it is actually at a temperature that is above the boiling point, but has not evaporated.
Supercooled liquid: A liquid that is cooled so rapidly that it is actually at a temperature that is below the freezing point, but has not solidified.
UNSTABLE !

15. Section 10.3 Structures and Types of Solids
Ionic solids
Molecular solids
Atomic solids
All types of solids form crystal lattices.
The smallest repeatable unit inside a crystal lattice is a unit cell.

16. Unit Cells Simple cubic: one atom at each vertex. Polonium metal
Basic format
Binary Compound

17. Unit Cells, 2
Body centered cubic: at each vertex and in the center. Uranium metal
Basic Format
Binary Compound

18. Unit Cells, 3
Face centered cubic: at each vertex and in the center of each face. Also called Cubic Closest Packing structure because each new layer of atoms nests into the holes from the layer below.
Basic Format
Binary Compound

19. Unit Cells, 4
Hexagonal Close Packed: each atom in the second layer lays in a dimple between the atoms in the sandwiching layers.
Basic Format
Binary Compound

20. Section 10.5 Atomic Solids Carbon as diamond Carbon as graphite
Physical Properties
Structure
Bonding
Carbon as graphite
Physical Properties
Structure
Bonding

21. Section 10.6 Molecular Solids
Covalent bond length within molecule is shorter than the distance between attracted molecules.
Low melting points, relatively weak IMF’s
Examples of molecules that form Molecular Solids:
Water
Carbon Dioxide
Any other covalently bonded molecule

22. Section Ionic Solids
The large ions define the shape of the crystal lattice. Smaller ions fit in the holes between the larger ions.
Stable
High Melting Point
Strong Intermolecular Forces (because ions have good dipole moments!)
Examples of things that form ionic solids:
NaCl
CsCl
Any other ionic compoud