However, because most biomolecules form many hydrogen bonds, they make a significant contribution to the stability of biomolecules. Because of its highly polar character, water also interacts favorably with ions. Hydrophilic or Polar molecules are soluble in water because they interact favorably with water by formation of hydrogen bonds or via ionic interactions. Hydrophobic or Nonpolar molecules do not have ionic groups and can not form hydrogen bonds. Also, the presence of hydrophobic molecules in water causes the water molecules to organize around the hydrophobic molecule in the form a Clathrate .
Clathrate formation causes the order of the water molecules to increase.
This corresponds to a decrease in Entropy , an unfavorable process. The combination of the lack of favorable hydrogen bonding interactions between hydrophobic molecules and water, and the unfavorable entropy combine to explain the very low solubility of hydrophobic molecules in water. Amphipathic molecules have a hydrophilic polar head group and a hydrophobic nonpolar tail. Such molecules have an identity crisis - the polar head group interacts favorably with water but the hydrophobic tail does not. This crisis is solved by the formation of a Monolayer , a Micelle or a Bilayer .