H2O, water

water
"Water is without doubt the most abundant, the most accessible, and the most studied of all chemical compounds. Its omnipresence, its crucial importance for human survival, and its ability so readily to transform form the liquid to the solid to the gaseous states has ensured it prominence in human history. Water plays a prominent role in most creation stories and has a symbolic purifying or regenerating significance in many great religions even to the present day. ...Water is distributed very unevenly and with very variable purity over the surface of the earth. Less than 2.7% of the surface water is fresh and most of this is locked up in the Antarctic ice cap." (Greenwood and Earnshaw, Chemistry of the Elements page 726.)
Bonding in H2O
Chemistry
The graphic above shows the electrostatic potential map of H2O. Note the high amount of negative charge on the O (red) and the postive nature of the two hydrogens (H) This illustrates the polarity of water.
(Calculated using Gaussian92 with SPARTAN software on a SGI Indigo2 at Millikin's chemistry dept.)

Of course, it is the polarity of water that accounts for its uniqueness. It is ionic enough to be able to separate and insulate some cations from corresponding anions producing a solution where the cations are surrounded by a cage of water molecules. It is polar enough to interact with a wide variety of similar molecules, molecules having OH, NH, C=O or N=C groups with which water hydrogen-bonds. These kinds of molecules are hydrophilic "water lovers". On the other hand, molecules with nonpolar regions are hydrophobic, "water haters". Water haters tend to cluster together to avoid water. As water haters cluster, the water has more places to be; its entropy increases. It is the entropy increase in water that accounts for this hydrophobic effect.

molecular orbitals in water
orbital 5
the highest occupied MO
B1 symmetry
E = -0.3917
orbital 4
A1 symmetry
E = -0.45488
 orbital 3
B2 symmetry
E = -0.61418
orbital 2
A1 symmetry
E = -1.2675
orbital 1
A1 symmetry
E = -20.243

top[Back to homepage]