for electrons than the two hydrogen atoms,
and so the shared electrons are held closer to
the oxygen than to the hydrogens. As a result,
there’s an overall negative charge in the
vicinity of the oxygen, and an overall positive
charge around the hydrogen atoms. This
unequal distribution of charge, together with
the geometry of the covalent bonds, results in
a molecule with a positive end and a negative
end. Such a molecule is called polar because
it has two separate centers, or poles, of
charge.
A hydrogen bond results from the attraction
between oppositely charged ends of polar
molecules (or portions of molecules). This
kind of bond is important because it’s very
common in materials that contain water,
because it brings different kinds of molecules
into close association, and because it’s weak
enough that these molecular associations can
change rapidly at room temperature. Many of