The
attractions between water molecules are more than just the attractions
of one tiny dipole for another. Each hydrogen atom with its partial
positive charge is attracted to one of the lone pairs on an oxygen
of a neighbor molecule, by a weak ionic attraction known as a hydrogen
bond (right). Hydrogen bonds can be formed whenever a hydrogen atom
with a partial positive charge is near a small N, O, or F atom carrying
an excess of negative charge. Such bonds, although weak, are important
in holding molecules such as proteins together because there are so
many of them. We will discuss the occurrence of hydrogen bonds in
living organisms in Chapter 22. For example, the most central process
in all living organisms, the coding of genetic information in molecules
of DNA, also depends on hydrogen bonds for the preservation of the
message.