Intermolecular Forces and Solubility

1. Intermolecular Forces and Solubility Tuesday review session October 4, 2010

2. Intermolecular Forces • Definition: Forces between molecules • Intermolecular forces are much weaker than intramolecular forces • There are three different types • London Dispersion Forces/ Van der Waals • Dipole-Dipole Interactions • Hydrogen Bonds

3. London Dispersion Forces Also referred to as Van der Waals forces Occurs because of momentary dipole (uneven distributions of electrons in a molecule causing a partially negative end and a partially positive end) These are the weakest intermolecular forces

4. Dipole-Dipole Interactions Occurs when polar molecules align so that their oppositely charged ends are attract each other This bond is stronger than Van der Waals forces

5. Hydrogen Bonding A type of dipole-dipole bond that occurs when hydrogen is bonded to a highly electronegative atom (O, F, N) This is the strongest intermolecular force

6. Intermolecular Forces Trends • Compounds with stronger intermolecular forces will be harder to separate therefore they will have larger melting points and boiling points • This means compounds with weak intermolecular forces are more likely to be found in gaseous form, while compounds with stronger molecular forces are more likely to be found as liquids or solids