1. Intermolecular Forces
Main Concept:
Intermolecular forces play a key role in determining the properties of substances, including biological structures and interactions.

2. Intermolecular Forces Properties Affected by Intermolecular Forces
boiling point
surface tension
capillary action
vapor pressure
Intermolecular Forces Effects on Gases

5. - Many properties of liquids and solids are determined by strengths and types of intermolecular forces present
-boiling point
-surface tension
-capillary action
-vapor pressure

6. -vapor pressure: the pressure exerted by gas in balance with its solid or liquid form in a closed container at a given temperature
-capillary action: the ability of a liquid to flow through narrow spaces

7. -surface tension: the forces that occur between molecules that allows them to resist external forces
-boiling point: the temperature at which vapor pressure equals surrounding pressure and liquid changes to vapor

8. Question:
How would greater or weaker intermolecular forces affect each property below and why?
-boiling point
-surface tension
-capillary action
-vapor pressure

9. “like dissolves like”** ** This will not receive points on any exam
- Substances with similar intermolecular interactions tend to be miscible or soluble in one another (ex: polar soluble in polar vs nonpolar soluble in nonpolar)
“like dissolves like”**
** This will not receive points on any exam

10. I2 in Carbon Tetrachloride (CCl4)
This was taken from
Will it dissolve?
I2 in Water (H2O)
I2 in Carbon Tetrachloride (CCl4)

11. Solid Iodine Test I2
Nonpolar
Carbon
Tetrachloride
CCl4
Water
H2O

12. Will it dissolve? Sugar (C12H22O11) in Water (H2O)
Sugar (C12H22O11) in Carbon Tetrachloride (CCl4)

13. Sugar Test
C12H22O11
Polar
Carbon
Tetrachloride
CCl4
Water
H2O

14. Will it dissolve? Ethanol (C2H5OH) in Water (H2O)
Ethanol (C2H5OH) in Carbon Tetrachloride (CCl4)

15. Ethanol Test
C2H5OH
Polar and Nonpolar
Water
H2O
Carbon
Tetrachloride
CCl4

16. Will it dissolve? Acetone (C3H6O) in Water (H2O)
Acetone (C3H6O) in Carbon Tetrachloride (CCl4)

17. Acetone Test
C3H6O
Polar and Nonpolar
Water
H2O
Carbon
Tetrachloride
CCl4

18. I2 in Carbon Tetrachloride (CCl4)
Will it dissolve?
I2 in Water (H2O)
I2 in Ethanol (C2H5OH)
I2 in Acetone (C3H6O)
I2 in Carbon Tetrachloride (CCl4)

19. Solid Iodine Test I2
Nonpolar
Water
H2O
Ethanol
C2H5OH
Acetone
C3H6O
Carbon
Tetrachloride
CCl4

20. - presence of intermolecular forces among gaseous particles (including noble gases) leads to deviations from ideal behavior
- This can lead to condensation at sufficiently low temperatures and/or sufficiently high pressures

21. Question:
How would you explain why intermolecular forces cause condensation at low temperatures and/or high pressures?

22. - graphs of pressure-volume relationship for real gases can demonstrate the deviation from ideal behavior (usually at low temperatures and high pressures > 10 atm)
- deviations are caused by presence and strengths of intermolecular forces
At what pressures do most gases resemble ideal gases?

23. Which temperatures most closely resembles an ideal gas?

24. Question:
What kinds of forces would exist in this scenario and why do you think that?

25. Answer:
We could potentially expect London dispersion forces between the gases, and London dispersion forces between the gas and container. There are probably no dipole-dipole or dipole-induced dipole forces since none of the molecules are polar.

26. Question:
Based on the graph for nitrogen below, under which conditions would you expect helium to deviate from ideal behavior?
a) 100 K and 1 atm b) 100 K and 5 atm c) 300 K and 2 atm

27. - structure and function of many biological systems depend on strength and nature of various Coulombic forces
Substrate interactions with the active sites in enzyme catalysis
Hydrophilic and hydrophobic regions in proteins that determine three-dimensional structure in water solutions

28. What types of intermolecular forces are there? (in order of strength)1. 2. 3. 4. 5.

29. What types of intermolecular forces are there?
1. ion-dipole
2. dipole-dipole
3. ion-induced dipole
4. dipole-induced dipole
5. induced-dipole induced-dipole / London dispersion force (LDF)

30. What are some characteristics of hydrogen bonds?

31. What are some characteristics of hydrogen bonds?
Occur between hydrogen and lone pair of F, O, or N

32. What are some characteristics that affect polarity?1. 2. 3.

33. What are some characteristics that affect polarity?
1. Size  larger size, greater polarizability
2. Electronegativity differences
3. Symmetry/Lone Pairs

34. How do greater intermolecular forces affect the following properties
How do greater intermolecular forces affect the following properties? (for after this lesson…)
1. Boiling point
2. Surface tension
3. Capillary action
4. Vapor pressure

35. How do greater intermolecular forces affect the following properties?
1. Boiling point – higher
2. Surface tension – greater
3. Capillary action – greater
4. Vapor pressure – lower