Re: Solubility of covalent bonded compounds.

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.