In the fall of 1983 I was applying to go to college and was invited to come to the University of Delaware to write an essay to help determine if I would be admitted to the honors program.  For my younger readers, 1983 was just the very beginning of the e-mail age and you could not attach a file.  So to submit my essay I actually had to go there.  Yes, it was the Dark Ages. 
The honors program candidates assembled in the room, were handed one of those little blue composition books (remember those?), and took out our freshly sharpened number 2 pencils.  They handed out the essay question and it read “Is God a Mathematician”? I immediately felt deflated and, to be honest, a bit aggrieved.  As a non-church-attending secular-humanist, I seriously considered writing an essay about how a religious-themed question was an inappropriate device for determining who should be admitted to the honors program.  But I calmed myself, decided to be pragmatic, answered “yes”, and wrote about water.   Whatever the forces are that govern the universe, water is quite unique compared to other molecules, and without these unique qualities humans would not exist.
To start with, water is way too small of a molecule to be a liquid.  (By the way if any of the upcoming discussion about chemical formulas or molecular weights gets confusing, follow this link to a discussion of these topics in “The World’s Greatest Cheat Sheet”.)  Consider this table below showing molecular weights and physical states of some common compounds.

Molecule Formula Molecular Weight Physical State
Hydrogen H2 2 Gas
Methane CH4 16 Gas
Oxygen O2 16 Gas
Water H2O 18 Liquid
Ethane C2H6 30 Gas
Propane* C3H8 44 Gas
Carbon Dioxide CO2 44 Gas
Butane C4H10 58 Liquid

*The propane for your gas grill is pressurized in the tank to liquefy it.
With one notable exception, molecules with molecular weights of less than 50 are gases at ambient temperatures and pressures.  Larger molecules are liquids.
So why is water, with its rather paltry molecular weight of 18, a liquid?  The reason for this anomaly is the shape of the water molecule.  If you look at the graphic at the top of the page, you will see that the three atoms in the water molecule are not arranged in a straight line, but rather make a 104.45o angle.  There is a long and complicated explanation for why water is shaped this way which I will not cover, but the implications are important.  Since the water molecule is not straight, the distribution of electrons in the molecule is non-uniform, which makes water molecules act like small magnets.  Imagine the part of the water molecule with a higher population of electrons as the north pole of the magnet and the part with a lower population of electrons as the south pole.  Due to this magnetic-like property, water molecules clump together in groups, which then take on the properties of a larger molecule and condense into a liquid.  As I will explain below, this little chemistry lesson is pivotal in understanding life on Earth.
Life evolved in water.  The human body is about 60% water.  Photosynthesis and all plant life depend on liquid water.  If water molecules did not stick together to make a liquid, they would exist as a gas and earth would be lifeless.  You should already be impressed by our little friend the water molecule. But there is another feature of water which is even more unique from my perspective, which is also responsible for life on Earth, ice floats.
Consider the process of freezing for a moment.  The molecules in a liquid are moving around and bumping into each other.  As you reduce the temperature of the liquid the molecules slow down, bump into each other less vigorously, and eventually clump together into solid particles.  This is what freezing is.  With one exception (I suspect you can guess what it is) the solid particles are denser than the liquid so they fall to the bottom where they then aggregate into one solid mass.
Water is the exception to this. In liquid form, water molecules, acting like little magnets, exist in very close proximity to each other, which makes water a rather dense liquid.  As you reduce the temperature to where you begin to form solid particles (ice), the water molecules begin to organize themselves into small solid crystals which are less dense than the liquid, so they float to the top.  The particles then aggregate into an ice sheet which completely covers the liquid layer.  Ice is a rather efficient insulator, so the ice layer protects the water below from the cold air above and helps to trap in heat which is coming from the ground below.  Therefore, even with sustained bitter cold temperatures, you have a pocket of liquid water below the ice.
If water was a “normal” liquid and the ice sank, then the cold air would keep freezing liquid water at the surface, the ice would keep falling to the bottom, and in a short time, the entire body of water would be a solid block of ice.  Perhaps some species of bacteria could have evolved to live through the winters with this scenario, but the complex and varied species that inhabit the earth today would never have come to be.
So back to Delaware. I wrote an essay extolling these unique features of the water molecule as evidence that God was, in fact, a mathematician.  Apparently my essay was a good one and I was admitted into the honors program and was well on my way to becoming a Fighting Blue Hen.  Soon thereafter I was accepted at the University of Virginia, which expressed no interest in my religious perspective, and headed to Charlottesville to become a Cavalier.
In addition to being a remarkable molecule, water is going to be an increasingly important topic locally, nationally, and globally as the 21st century proceeds.  This is the first of several columns I’m planning on water.  Also, I have the great honor and privilege to fill-in for D.G. Martin on Who’s Talking on AM 1360 WCHL which airs Tuesday through Friday at 6:15 pm and 10:00 pm.  To get more information and perspective on local water issues follow these links to listen to my conversations with Ed Holland, Planning Director for OWASA and Robin Jacobs and Kathy Lee of the Eno River Association.
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