1. Intermolecular Forces

2. Intramolecular Forces:
The attractive forces between atoms and ions within a molecule
e.g Ionic bond, covalent bonds (e.g. polar, nonpolar, double, triple)
Relatively strong
Intermolecular Forces:
The attractive forces between molecules
E.g. London dispersion, Van der Waals forces: dipole-dipole forces, hydrogen bonds
Weak (in comparison to intramolecular forces)
I.e. much less energy to melt H2O (inter) than for it to decompose into H2 and O2 (intra)

3. Intermolecular Forces & Physical Properties
The strength of the intermolecular forces determines:
State
Melting point and boiling point
Surface tension
Hardness/texture
Solubility

4. Intermolecular Forces
If covalent bonds were the only forces at work, most molecular compounds would be gases as there would be no attraction between molecules strong enough to group the molecules as liquids or solids

5. van der Waals Forces
Dipole-dipole
London dispersion
Hydrogen bonding

6. Dipole-dipole
Forces of attraction between oppositely charged ends of polar molecules.
Relatively strong intermolecular force
Dipole-dipole force

7. London Dispersion
Attractive forces between all molecules, including nonpolar molecules
Result of temporary displacements of the electron cloud around atoms in a molecule (extremely short-lived dipoles)
Therefore weaker than dipole-dipole

8. Hydrogen Bonding
Strong dipole-dipole force between the positive hydrogen atom of one molecule and highly electronegative atom of another molecule (O, N, F)
H-bond

9. Discussion/Recap:
Rank the intermolecular forces from weakest to strongest.
How might intermolecular forces affect physical state?
How might intermolecular forces affect melting point?

10. Surface Tension
Molecules in a liquid are attracted by molecules on all sides
But, molecules at the surface are only attracted down or sideways.
Penny drop, alka seltzer