1. Intermolecular Forces

2. Solids, Liquids, and Gases

4. Intermolecular Attractions

5. Intermolecular Vs Intramolecular forces
Intermolecular forces are much weaker than intramolecular forces.
Example:
We need about 41kJ to vaporize 1 mole of water at its boiling point (to overcome intermolecular forces), but about 930 kJ are needed to break the two O-H bonds.

6. Ion – Dipole interaction

8. Dipole – Dipole Interaction

10. London Dispersion Forces (instantaneous dipoles)

11. Polarizability: the ease with which the electron distribution around an atom or molecule can be distorted. Dispersion forces increases with:
1. polarizability 2. atomic or molecular mass 3. number of electrons

12. Van der Waals Forces Dipole – dipole forces
Dipole – induced dipole forces
Dispersion forces (London forces)
But not ion-dipole forces or hydrogen bonding

14. Example: Correlate intermolecular forces to mp
Melting point, oC
Compound
-182.5
CH4
-150.0
CF4
-23.0
CCl4
90.0
CBr4
171.0
CI4

15. Which is greater: dipole dipole or dispersion forces?
CH3F has a dipole moment of 1.8 Debye, while CCl4 has no dipole moment. The boiling point of the two compounds are and 76.5 oC. Although CH3F has both dipole – dipole forces and dispersion forces, it has a much lower BP (smaller intramolecular forces) than CCl4 which has dispersion forces only. However this is not always true.

18. Example: What types of intermolecular forces exists between the following pairs:
a. HBr and H2S
Cl2 and CBr4
I2 and NO3-
NH3 and C6H6
CH3Cl and CCl4
KBr and H2O

19. Intermolecular forces
Polarity of molecules
Dipole – dipole (+Dispersion)
Polar - polar
Dipole – induced dipole (+Dispersion)
Polar - nonpolar
Ion – dipole (+Dispersion)
Polar + ion
Ion – induced dipole (+Dispersion)
Nonpolar + ion
Dispersion
Nonpolar + nonpolar
Ionic bonds (Strongest)
Ionic compounds

20. Hydrogen Bonding

21. A hydrogen bond can form when:
We have molecules containing one of the following groups:
N-H
O-H
H-F
And O, N, or F atoms in the same molecule or other molecules

25. Density of water

27. Highest density occurs at 4oC.
From 0 – 4oC, trapping prevails which results in an increase in density
Above 4oC, thermal expansion predominates resulting in a decrease in density