1. Intermolecular Forces of Attraction

2. IMFAs  Intermolecular Forces of Attraction  Forces that exist between molecules  By knowing the strengths of the IMFAs we can predict physical properties of molecules.  The stronger the IMFAs, the more the molecules want to stick together.  This affects Boiling & Freezing Points, Evaporation Rate, and Miscibility.

3. Ion-Ion (Ionic Bonding)  Ionic Compounds are all Solids at RT.  This is because the attraction between ions within the compound is so strong – like a bunch of Magnets sticking together.  Ionic compounds tend to dissolve in Polar solvents

4. Ion-Dipole  Charged ions are attracted to the opposite charge of a polar covalent molecule.  These are very similar to Ionic bonding.  These forces occur when an ion is Dissolved in a Polar liquid.

5. Dipole-Dipole  Similar to ionic bonding, the Partial Charges of a Polar molecule line up with the opposite charge of another polar molecule.  Polar compounds will be Miscible in polar solvents.

6. Hydrogen Bonding  Strong Dipole-Dipole force:  When H is in a polar molecule and bonded with:  Nitrogen  Oxygen  Fluorine  It produces a very strong dipole-dipole attraction between different molecules.

7. H-Bonding (cont’d)  Because of hydrogen bonding, a very small & light molecule like Water (H 2 O) is a liquid while a Heavier compound, H 2 S, is a gas.  So, if the molecules are polar and hydrogen is having FON, then it will have hydrogen bonding.

8. London Dispersion Forces  Nonpolar molecules cannot have any of the previously mentioned forces of attraction since they do not have any dipole Moment or Charge.  Instead, the only forces available to these compounds are induced Dipoles.  LDFs arise when the electrons of one molecule are Pushed away by the electrons of another molecule.

9. LDFs (cont’d)  A whole bunch of molecules doing this together create Temporary dipoles in otherwise nonpolar molecules.  These are by far the Weakest of the intermolecular forces.

10. LDFs (yet again)  These are the only forces available to Noble Gases.  These are the forces at work when we are able to Liquefy or Solidify them.

11. LDFs (one last time)  All Molecules have LDFs in addition to any of the other forces already mentioned  Except Ionic Compounds since they have permanent poles already.

12. Size and Weight  If the molecule is Big & Bulky, it’s going to get stuck on other molecules when it moves around – kind of like Spaghetti.  For this reason, big molecules, even when they are Nonpolar, tend to be liquids or solids.  If the molecule has some really heavy atoms in it, it’s going to need more energy to get it moving around.

13. Strength of IMFAs 1.Ion-Ion 2.Ion-Dipole 3.H-Bonding 4.Dipole-Dipole 5.London Dispersion Forces  The stronger the IMFAs, the more likely a compound will be a solid or liquid.