1. Intermolecular Forces
What are they?
Forces of attraction between molecules that…
vary in strength
are weaker than bonds that…
join atoms in molecules,
ions in ionic compounds,
or metal atoms in solid metals.

2. Intermolecular Forces
Why are they important?
Intermolecular forces, kinetic energy (temperature) of the molecules, and external forces (gravity) determine…
1) the properties of solids, liquids and gases, and
2) whether a molecular compound is a solid, liquid, or gas, at a given temperature.

3. What are the different types?
Dipole - dipole Forces
London Dispersion Forces
Hydrogen Bonds

4. London Dispersion Forces
Weakest of all intermolecular forces
Caused by the motion of electrons
strength increases with the number of electrons in the molecule
Act among noble gas atoms and non-polar molecules. Example: halogen diatomic molecules
Account for the low boiling points of molecular compounds.

5. Dipole Interactions (dipole-dipole forces)
An electrostatic attraction between polar molecules (+ to -)
similar to ionic bonds, but weaker
Stronger than dispersion forces
Explain high boiling points in compounds

6. Hydrogen Bonds
Only occur in molecules where Hydrogen is bonded to a strong electronegative element such as oxygen, nitrogen, or fluorine.
Are the strongest of the intermolecular forces
The hydrogen is attracted to the unshared pair of electrons of the electronegative atom in a nearby molecule.
Are responsible for the unique properties of water.

7. Copyright©2000 by Houghton Mifflin Company. All rights reserved.
Figure 13.6: (a) The polar water molecule (b) Hydrogen bonding among water molecules
Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8