|MadSci Network: Chemistry|
The interactions of nonpolar compounds with each other are based on dispersion (or Van der Waals) forces. These are weak attractive forces that arise from temporary dipoles that form in nonpolar compounds. These temporary attractive forces arise from the attraction of temporary oppositely charged poles of the temporary dipoles. For more information on disperaion forces see http://www.chemguide.co.uk/atoms/bonding/vdw.html. These are the forces that hold I2 molecules together in iodine solid. These are also the type of forces that would attract an I2 molecule to a glycerol molecule. In water, there are disperaion forces, strong diple-dipole forces and even stronger hydrogen bonding forces. The combination of all of these make the water molecules so attracted to each other that the I2 molecules (or other nonpolar molecules) canot break in between the water molecules to dissolve; they are kept apart as a separate nonpolar phase. I2 is only very slightly soluble in water. The polar and hydrogen bonding forces are not as strong in glycerol, so I2 has a better chance of breaking in between the glycerol molecules and interact with them favorably through the dispesion forces. Incidently, I2 can be rendered soluble in water by having I- ion dissolved in the water. Then the I2 molecules are converted to I3- ions which are soluble because of the ion/dipole attractions with water, as is the case with the Na+ and Cl- ions.
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