1. INTERMOLECULAR FORCES
Chap. 13: Day 2
INTERMOLECULAR FORCES

2. Type of Bond determines Forces
Generally strongest
“Interparticle”
Ionic Bond
Ion-ion force
Metalic bond
Electronic force
Generally weaker
“intermolecular forces”
Covalent bonds
Polar molecules
Dipole forces
Nonpolar molecules
London
Disperson
Induced dipole forces

4. Molecules will be polar if
Molecular Polarity
Molecules will be polar if
a) bonds are polar
AND
the molecule is NOT
“symmetric”

5. Compare CO2 and H2O. Which one is polar?
Polar or Nonpolar?
Compare CO2 and H2O. Which one is polar?

6. Polar or Nonpolar?
Consider AB3 molecules: BF3, Cl2CO, and NH3.

7. B—F bonds in BF3 are polar. But molecule is symmetrical and NOT polar
Molecular Polarity, BF3
B atom is positive and F atoms are negative.
B—F bonds in BF3 are polar.
But molecule is symmetrical and NOT polar

8. Molecular Polarity, HBF2
B atom is positive but H & F atoms are negative.
B—F and B—H bonds in HBF2 are polar. But molecule is NOT symmetrical = POLAR.

9. Methane is symmetrical
Is Methane, CH4, Polar?
Methane is symmetrical
and is NOT polar.

10. C—F bonds are MUCH more polar than C—H bonds.
Substituted Ethylene
C—F bonds are MUCH more polar than C—H bonds.
Because both C—F bonds are on same side of molecule, molecule is POLAR.

11. Why do the intermolecular forces vary between nonpolar molecules?
What causes the differences in intermolecular forces between molecules?
Why do the intermolecular forces vary between nonpolar molecules?

12. Solid
Liquid
WHY?

13. Bigger Molecules interact more

14. DISPERSION FORCE
Nonpolar Molecules

15. Why do the intermolecular forces vary between polar molecules?

16. Molecules—such as HCl and H2O— can be POLAR (or have a dipole).
Molecular Polarity
Molecules—such as HCl and H2O— can be POLAR (or have a dipole).
They have a DIPOLE MOMENT. The polar HCl molecule will turn to align with an electric field.
Figure 9.15

17. DIPOLE FORCE
Polar Molecules

18. More polar stronger force

19. Why different?
liquid
gas

20. ?

21. Dipole force with Hydrogen
SOME POLAR
Molecules
Have “special”
Dipole force with Hydrogen
HYDROGEN
FORCE or
HYDROGEN BOND

22. NEED TO BE POLAR & H is attached to N, F, or O
HYDOGEN BOND
NEED TO BE POLAR &
H is attached to
N, F, or O

23. ALL have LONDON DISPERSION force

24. Melting Point
Energy needed over come the intermolecular forces between molecules in the solid phase
Temperature at which molecules in a solid gain enough potential energy to change position (become L)

26. Boiling Point
Energy needed over come the intermolecular forces between molecules in the liquid phase
Temperature at which molecules in a liquid gain enough potential energy to change position (become gas)

27. POLAR vs NONPOLAR

28. Graphing: Intermolecular Forces
See handout
4 different Families
Boiling point vs period
100 C
Boiling point
-200 C 4
period 7