May the Force Be with You !

1. Intermolecular ForcesForces that hold molecules together! Not to be confused with forces that hold atoms together to form a molecule (intramolecular). May the Force Be with You!

2. Dipole – Dipole page 489 • Polar molecules are attracted to each other • Like a magnetic field • “sticking power” of the molecules • Not as strong as ionic or covalent bonds • Insignificant in gases because molecules are so far apart

3. Hydrogen bonding page 490 • Strong dipole forces between molecules in which hydrogen is bonded to a very electronegative atom such as N, O, or F. • Electronegative atom “hogs” hydrogen’s only electron leaving it pretty much a proton that is very attracted to any unshared electrons on a molecule that happens by. • A type of dipole-dipole attraction

4. London Dispersion Forces • Forces that exist among noble gas molecules and nonpolar molecules • Electrons are not really equally distributed at every instant • Have “moments” of attraction – induced or instantaneous dipole • Weak and does not last long • More significant as the size of molecules increases

5. Type of Force Determines Properties • If the molecules have a lot of “sticking” power, they will be solids or liquids at room temperature. • If the molecules don’t stick together, they are gases. • Molecules that don’t stick together very well have low melting and boiling points. • Size of molecule is also a factor – generally, smaller, lighter molecules have lower mp & bp’s.