1. Intermolecular Forces
Bonding Unit
Intermolecular Forces

2. Intermolecular Forces
Forces of attraction between different molecules rather than bonding forces within the same molecule.

3. Forces and Phases of Matter
Substances with very little intermolecular attraction exist as gases
Substances with strong intermolecular attraction exist as liquids
Substances with very strong intermolecular (or ionic) attraction exist as solids

4. Polar Covalent Bond The two atoms do not share the electrons equally.
One atom takes on a slight (partial) negative charge and the other atom taking on a partial positive charge.
The molecule has a positive end and a negative end, called a dipole (think of a magnet).
The little Greek symbol by the charges refers to a partial charge.

6. - water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.

8. These molecules are not polar.

10. How to tell if a molecule is polar.

11. Electronegativity Difference
If the difference in electronegativities is between:
1.7 to 4.0: Ionic
0.3 to 1.7: Polar Covalent
0.0 to 0.3: Non-Polar Covalent
Example: NaCl
Na = 0.8, Cl = 3.0
Difference is 2.2, so
this is an ionic bond!

12. Determining polarity of a molecule based on the symmetry of the molecule.

14. Types of Intermolecular Forces
1. Hydrogen Bond (strongest)
Bonding between hydrogen and more electronegative neighboring atoms such as oxygen and nitrogen.
IT IS NOT A BOND. A H … B or
A & B are N, O, or F
11.2

15. Types of Intermolecular Forces
2. Ion-Dipole Forces
Attractive forces between an ion and a polar molecule
Ion-Dipole Interaction
11.2

16. 11.2

17. Ion-Dipole Forces

18. Types of Intermolecular Forces
3. Dipole-Dipole Forces
Attractive forces between polar molecules
Orientation of Polar Molecules in a Solid
11.2

19. Types of Intermolecular Forces
4. Dispersion Forces – van der Walls forces/London forces (weakest)
Attractive forces that arise as a result of temporary dipoles induced in atoms or molecules
ion-induced dipole interaction
dipole-induced dipole interaction
11.2

20. Summary: Intermolecular Forces
Formed by the
attraction between …
Examples
Ion-dipole
an ion and a polar molecule
Na+ and H2O
Hydrogen bond
molecules which have H on N, O, or F atoms
H2O and H2O; H2O and CH3CH2OH
Dipole - Dipole
two polar molecules
CH3Br and ICl;
CH3Br and H2O
Ion - Induced dipole
an ion and a nonpolar
Fe2+ and O2
Dipole - Induced
dipole
a polar molecule and a
nonpolar molecule
HCl and Cl2
London (dispersion)
forces
two nonpolar
molecules
CH4 and CH4; F2 and F2; CH4 and F2