London dispersion force, Dipole-dipole interaction, Ion-dipole interaction, van der Waals forces, Hydrogen bonding

1. Intermolecular forces
Dr. K. Shahzad Baig
Memorial University of Newfoundland (MUN)
Canada
Petrucci, et al. 2011. General Chemistry: Principles and Modern Applications. Pearson Canada Inc., Toronto, Ontario.
Tro, N.J. 2010. Principles of Chemistry. : a molecular approach. Pearson Education, Inc.

2. Intermolecular forces determine the macroscopic physical properties of
liquids and solids.
Macroscopic physical properties:
Density, Viscosity, Malleability,
Surface tension, Melting point,
Boiling point, Enthalpy of fusion,
Enthalpy of vaporization,
Resistance of conductor
London dispersion force
Dipole-dipole interaction,
Ion-dipole interaction,
van der Waals forces,
Hydrogen bonding

3. Gas
the KE of the molecules is
much greater than the
intermolecular attractions.
Solid
the KE of the molecules is less
than the intermolecular
attractions.
Major difference between liquid and solid is the freedom of motion.

4. States of Matter
Liquids
• High densities relative to gases.
• Indefinite shape:
takes the shape of their container.
• Definite volume:
cannot be compressed easily.
Solids
• High densities compared to gases
and liquids
• Definite shape.
• Definite volume
• May be crystalline (ordered) or
amorphous (unordered).

5. Dispersion Forces
Dispersion force is present in all molecules and atoms. Results from changes in e- locations

6. Instantaneous Dipoles
1
2
3
Charge separation in one creates charge separation in the neighbors.

7. Strength of Dispersion Forces
• Dispersion force strength depends on polarizability:
the ease with which the electron cloud is distorted by an external electrical field.
The greater the polarizability of molecules, the stronger the dispersion forces between
them.
Polarizability in turn depends on molecular size and shape.
• Heavier molecule =>
more electrons =>
a more- polarizable molecule [shape]

9. Dipole - Dipole Forces / Interactions
• A polar molecule has a positively charged “end” (δ+) and
a negatively charged “end” (δ–).
• When molecules come close to one another,
repulsions occur between like-charged regions of dipoles.
attractions occur between opposite charges
• The more polar a molecule, the more pronounced is the
effect of dipole–dipole forces on physical properties.

10. Effects can be seen in boiling and melting points