My notes and thoughts from Biology 111, for Wednesday, September 3, 2008. The entire series can be found here.
We left off before the Labor Day break with polarity and the ability to form hydrogen bonds.
The polarity of the water molecule, having an oxygen to one side and the two hydrogen atoms to the other, gives the molecules a slight attraction to charged molecules, since the oxygen end is going to have a slight negative charge and the hydrogen end is going to have a slight positive charge. This is caused by the unequal sharing of valence e- between the oxygen and the two hydrogens. Because the oxygen pulls harder on the shared e-, they are going to spend more time toward the oxygen, increasing its negative charge a little, and away from the hydrogens, increasing their positive charge a little (actually decreasing their negative charge a little, to be accurate).
That little bit of polarity will cause the oxygen end of one water molecule to be attracted to the hydrogen end of another water molecule (or any other positively charged molecule), and though the effect is small in one pair of molecules, it adds up with millions of molecules.
(More below the fold)