1. 2.4 Intermolecular Forces

2. Intramolecular Forces:
the attractive forces between atoms within a molecule
the attractive forces between ions within an ionic crystal
e.g. ionic bond, covalent bonds
strong
Intermolecular Forces:
the attractive forces between molecules
e.g. Van der Waals forces and 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
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

4. van der Waals Forces
Dipole-dipole
London dispersion

5. Dipole-dipole
forces of attraction between oppositely charged ends of polar molecules.
the strength of the dipole-dipole force is dependent on the polarity of the molecule

6. 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
strength depends on number of electrons in a molecule

7. Hydrogen Bonding
strong dipole-dipole force between the positive H atom of one molecule and the lone pair of electrons on the negative atom (N, O, or F) on another molecule

8. Properties of Gases and Liquids
very weak intermolecular forces acting on gases
in liquids, intermolecular forces account for some special properties.

9. Surface Tension
molecules in a liquid are attracted by molecules on all sides
Penny drop, alka seltzer

10. Cohesion and Adhesion Cohesion: The attraction between like molecules
Adhesion: The attraction between unlike molecules.
Adhesion between water and glass is higher than cohesion between water molecules.
Cohesion between mercury is higher than adhesion between mercury and glass