Abstract on Intermolecular Forces

Van der Waals Forces - weakest

depends on: a. Surface Area

b. Polarizability

Dipole-Dipole

depends on: Dipole moment

1. Polarity of bonds -

electronegativity of atoms involved

size of atoms - bond length

2. Structure of molecule-

symmetry (do dipoles add or cancel)

Hydrogen-Bonding - strongest

depends on:

1. O-H bond or N-H bond being present (H-bond donor)

2. Lone pair of electrons (H-bond acceptor)

Problem Solving Strategy:

When deciding on what causes certain physical properties like boiling point or solubility look for the following

1. If Hydrogen bonding is possible it is almost certainly the cause since it is the strongest intermolecular force.

2. Look for a large dipole moment, the larger the dipole moment the larger the force.

3. Look for large atoms (3rd row or lower) if they are present the larger the atom the more polarizable and larger Van der Waals forces are possible (remember intermolecular interactions are the sum of all the forces).

4. If no large atoms look at the shape and size (i. e. surface area). The more contact between molecules the larger the Van der Waals forces.