1. Intermolecular Forces:
- Attractive forces between molecules and ions, based on polarity
- Determine bulk properties of matter example – solid vs. liquid vs. gas
- Much weaker than intramolecular forces such as covalent bonds and ionic bonds

2. Intermolecular Forces 01
Type of Intermolecular Forces:
Dipole–dipole
Hydrogen Bonds
London Force (instantaneous induced dipole)

3. Intermolecular Forces 03
Ion–Dipole: Between polar molecules and ions. “opposites attract”

4. Intermolecular Forces 02
Dipole–Dipole: Between polar molecules. Polar molecules:

5. Intermolecular Forces 05
Hydrogen Bond: Molecules containing N–H, O–H, or F–H groups, and an electronegative O, N, or F.
This type of dipole-dipole force is especially strong, since the partial positive charge on H is high.
The H on the electronegative element is δ+, and is strongly attracted to the lone pair of electrons in a different molecule.
H-bonding is a special type of dipole-dipole force that is especially strong.
It is an intermolecular force,

6. Intermolecular Forces 05
Hydrogen Bond: Molecules containing N–H, O–H, or F–H groups, and an electronegative O, N, or F.
Strength of hydrogen bonds can be observed by looking at boiling points of various compounds.

7. Intermolecular Forces 05
Boiling points for different compounds of Group 4A, 5A, and 6A.

8. Intermolecular Forces 04
The element bromine is a liquid, composed of Br2 molecules.
A molecule of Br2
Bromine is a liquid, but non-polar. What holds bromine molecules together as a liquid?

9. Intermolecular Forces 04
London Dispersion Forces: Attraction is due to instantaneous, temporary dipoles formed due to electron motion.

10. Review: Cl2 CH3OCH3 Cl-NH2 Ar CH3CH2CH3
What intermolecular forces will operate between molecules in the substances below?
Cl CH3OCH Cl-NH2 Ar
CH3CH2CH3

11. Intermolecular Forces 06
very
very weak

12. Intermolecular Forces 07
Effect on Boiling Point
CH4 110 K
SiH4 160 K
GeH K
SnH4 215 K
H2O 373 K *
H2S 215 K
H2Se 225 K
H2Te 270 K
Force:

13. Intermolecular Forces 08
Surface Tension is the resistance of a liquid to spread out and increase its surface area.
Surface tension results from intermolecular force differences between molecules in the interior of a liquid and those on the surface.

14. Intermolecular Forces 09
Viscosity is the measure of a liquid’s resistance to flow. It is related to the ease with which molecules move around and thus to intermolecular forces.
High Viscosity
Low Viscosity

15. Phase Changes 01

16. Phase Changes 02
Molar Heat of Fusion (∆Hfus): The energy required to melt one mole of solid (in kJ).
Molar Heat of Vaporization (∆Hvap): The energy (in kJ) required to vaporize one mole of liquid.

17. Phase Changes 02

18. Phase Changes 04
Sublimation: The process in which molecules go directly from the solid into the vapor phase.
Deposition: The process in which molecules go directly from the vapor into the solid phase.
Molar heat of sublimation (∆Hsub): The energy (kJ) required to sublime one mole of solid. D H
sub =
fus +
vap

19. Phase Changes 06
Vapor Pressure: The pressure exerted by gaseous molecules above a liquid.