Chandler Group - The Two Faces of Water. H 2 O, is repellent to oil. In reality, demixing of oil and water at ambient conditions is not due to the fear of water on the part of oil molecules, but rather to especially favorable bonding between water molecules. Each water molecule can simultaneously participate in four such bonds, sharing its two hydrogen atoms with two neighboring water molecules and sharing two other hydrogen atoms associated with two other neighbors. Ice is a tetrahedral ordered array of such hydrogen bonded waters.
Liquid water is a disordered network of such bonded waters.
Computer rendered picture showing the disordered hydrogen bonding network typical of liquid water. The blue spheres are oxygen and the white spheres are hydrogen. The dotted lines show the hydrogen bonds with which the water molecules attract one another. Oil and water molecules actually attract each other, but not nearly so strongly. Mixing enough oil with water therefore leads to a reduction in favorable bonding.