Water Clusters: The Real Truth About Water Molecules
Chemists have long recognized water as a substance having unusual and unique properties that one would not at first sight expect from a small molecule having the formula H2O. It is generally agreed that the special properties of water stem from the tendency of its molecules to associate, forming short-lived and ever-changing polymeric units that are sometimes described as "clusters". These clusters are more conceptual than physical in nature; they have no directly observable properties, and their transient existence (on the order of picoseconds) does not support an earlier view that water is a mixture of polymers (H2O)n in which n can have a variety of values. Instead, the currently favored model of water is one of a loosely connected network that might best be described as one huge "cluster" whose internal connections are continually undergoing rearrangement.