1. Liquids
Forces Between Liquid Molecules and their Effect on the Properties of Liquids

2. Types of Forces Intramolecular-forces within a molecule-bonding types
examples: ionic and covalent
Intermolecular-forces between molecules
examples: ionic, dispersion, dipole-dipole,
and hydrogen bonding

3. Ionic Forces Exist between “molecules” that contain ionic bonds.
Result from the electrostatic charges within the
compound.
Opposite charges attract.
Strongest type of intermolecular force.

4. London Dispersion Forces
Exist between noble gas atoms and nonpolar molecules
Weakest
Temporary-as electrons move around the nucleus, a momentary asymmetrical distribution of electrons can occur (provides a temporary dipole)

5. London Dispersion Forces
The instantaneous dipole can induce a similar dipole in a neighboring atom

6. London Dispersion Forces (continued)
Large atoms with many electrons have stronger London Dispersion Forces
Larger nonpolar molecules have stronger LD forces

7. Which has the stronger LD force?
Cl2
Br2 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

8. Which has the stronger LD force?10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

9. Which has the stronger LD forceNe Ar Xe 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

10. Dipole-Dipole Forces Exist between polar molecules Permanent
Stronger than London Dispersion Forces
(1% as strong as ionic/covalent bonds)
Created through an unequal sharing of electrons which results in a partial negative and positive charge
Positive end of one molecule attracts the negative end of another molecule

12. Which of the following molecules have dipole-dipole forces present?
NH3
CH4
Both 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

13. Which of the following molecules have dipole-dipole forces?
CO2
H20
Both 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

14. Which of the following molecules have dipole-dipole forces present?
SF4
SF6
Both 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

15. Hydrogen Bonding A specific type of dipole-dipole force
Occurs when hydrogen atoms are bonded to highly electronegative atoms such as N, O, or F.
Created because of high levels of polarity and small size of hydrogen atoms (especially strong dipole-dipole attraction occurs)

17. Which of the following compounds has hydrogen bonding present?
CH3OH
Both 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

18. Which of the following compounds has hydrogen bonding present?
H2S
H2O
Both 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

19. Which of the following compounds has hydrogen bonding present?
HCl HF
Both 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

20. Review of Intermolecular Forces
Identify the most important type of interparticle forces present in each of the following substances. Ar
HCl HF
CaCl2
CH4 CO
NaNO3

21. What is the most importance type of interparticle force present in Ar?10
Ionic
London Dispersion
Dipole-Dipole
Hydrogen Bonding 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

22. What is the most important type of interparticle force present in HCl?10
Ionic
London Dispersion
Dipole-Dipole
Hydrogen Bonding 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

23. What is the most important type of interparticle force present in HF?10
Ionic
London Dispersion
Dipole-Dipole
Hydrogen Bonding 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

24. What is the most important type of interparticle force present in CaCl2?10
Ionic
London Dispersion
Dipole-Dipole
Hydrogen Bonding 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

25. What is the most important type of interparticle force present in CH4?10
Ionic
London Dispersion
Dipole-Dipole
Hydrogen Bonding 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

26. What is the most important type of interparticle force present in CO?10
Ionic
London Dispersion
Dipole-Dipole
Hydrogen Bonding 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

27. What is the most important type of interparticle force present in NaNO3?10
Ionic
London Dispersion
Dipole-Dipole
Hydrogen Bonding 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

28. CH3OH > CH3NH2>SO2>Cl2 Cl2>SO2>CH3OH>CH3NH2
Arrange the following molecules in order of decreasing intermolecular interaction: SO2, Cl2, CH3OH, CH3NH2 10
CH3OH > CH3NH2>SO2>Cl2
Cl2>SO2>CH3OH>CH3NH2
SO2>CH3NH2>CH3OH>Cl2
CH3NH2>CH3OH>SO2>Cl2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

29. Properties of Liquids

30. Surface Tension Resistance of a liquid to increase in surface area
Measure of the inward forces
Liquids with high intermolecular forces have high surface tensions

31. Viscosity A resistance to flow
Strong intermolecular forces result in high viscosity
Large molecules also have high viscosity due to greater LD forces
As temperature increases, viscosity decreases

32. Vapor Pressure Pressure of vapor above the surface of a liquid
Caused when the molecules on the surface break away and go into the gas phase
In order to break away, the molecules must possess a minimum amount of kinetic energy
High intermolecular forces result in low vapor pressures
Volatile liquids are liquids that evaporate rapidly resulting in high vapor pressures

33. Vapor Pressure (continued)
Substances with weak intermolecular forces tend to be volatile
As temperature increases, vapor pressure increases (more molecules possess the minimum kinetic energy and the rate of evaporation increases)

34. Calculating Vapor Pressure
The equation used to calculate the vapor pressure is:
ln (PvapT1) = ∆Hvap( )
(PvapT2) = R (T2 - T1)
∆H is the heat of vaporization in J/mol, T is Kelvin temperature, R is J/Kmol, and Pvap is vapor pressure

35. Practice Problem
In Breckenridge , Colorado, the typical atmospheric pressure is 520. torr. What is the boiling point of water (∆Hvap = 40.7 kJ/mol) in Breckenridge?

36. Capillary Action Spontaneous rising of a liquid in a narrow tube
Caused by cohesive and adhesive forces
cohesive forces-intermolecular forces
among liquid molecules
adhesive forces- force between the liquid
molecules and the container; occur when
the container is made of a polar substance

37. Example of Capillary Action
When water is placed in a glass graduated cylinder, the meniscus is concave
adhesive forces > cohesive forces (glass is polar)
When mercury is placed in the same graduated cylinder, the meniscus is convex
cohesive forces > adhesive forces (mercury contains only dispersion forces-nonpolar)

38. Melting Point and Boiling Points
Melting point- temperature at which the solid and liquid have the same vapor pressure
Boiling point-temperature at which the vapor pressure is equal to 1 atm (atmospheric pressure)
Melting and boiling points are higher when the intermolecular forces are stronger

39. Which of the following has the highest boiling point?HF HI
HBr 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

40. Which of the following liquids will be the most viscous?10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

41. B>C>A A>B>C A>C>B C>A>B
Arrange the following liquids, A, B, C, with vapor pressures at room temperature of 88, 680, and 155, respectively, in order of decreasing boiling points.
B>C>A
A>B>C
A>C>B
C>A>B 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

42. Knowing that solutes with a certain polarity are best dissolved in solutions with similar polarity, which of the following solvents would be optimal for the solvation of CH3COOH?
CH4
CH3OH
C2H6
C6H6 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30