Mixing Oil and Water
Name: Melinda H.
What role do intermolecular bonds play in why water
and oil don't mix?
Intermolecular bonds are exactly the reason why they don't mix.
Water molecules have strong bonds with one another, called
"hydrogen bonds." This consists of an extraordinarily strong
attraction that the hydrogens of one H2O have for oxygens of nearby
H2O molecules. Oil molecules also have very strong bonds with one
another, but not hydrogen bonds. Oil molecules are bonded to
one another by what are called "London forces," or sometimes
"dispersion forces." This is a little harder to explain in
simple terms, but basically the large oil molecules tend to
clump together because of these forces. However, an oil molecule
does not hydrogen bond with a water molecule, and an oil molecule's
dispersion attraction to a water molecule is weak compared to
the oil-oil attraction. So, the water stays separate from the oil,
giving rise to the old chemistry saying "like dissolves like."
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Update: June 2012