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Phases of Matter VIII - The Wonder of Water 1

Crossposted at Dailykos.com

None of us should be alive. We are only because of water. Water. Everyone knows about it, everyone uses it, but few understand it. Every schoolchild knows that water is H20, but few scientists realize the ramifications of that simple formula.

Water has a molecular weight of 18 atomic mass units (amu, the mass of a proton or neutron, roughly) since the common isotope of oxygen has a a mass of 16 amu, and that of the most common type of hydrogen has a mass of one amu.

Water looks sort of like Mickey Mouse, in that the two hydrogen atoms make an angle through the H-O-H bond of about 104.45 degrees.

Water, at 18 amu, should be a gas. Nothing with that molecular weight is a solid except for lithium, and it is a metal, and metallic bonds are special. I wrote about that earlier in this series.

All of the atmospheric gases weight more, on a molecular basis, than water. Ammonia, water’s close cousin, is a gas at STP (standard temperature and pressure, one atmosphere at 20 degrees C). Both ammonia and water share a special property, but water does it better.

The secret is the hydrogen bond. It turns out, due to both electrostatic and quantum mechanical considerations, that hydrogen (the lightest and smallest element) when bonded to nitrogen, oxygen, or fluorine (the most electron hungry elements in the second row of the periodic table) is “special”.

We should all be dead, and water should not exist. But the hydrogen bond changes everything. More in future, if any interest. I will hang around a bit to answer comments and stave off flames. Warmest regards, Doc.

What is water, anyway?

We all know that water is H2O, two hydrogen atoms to one oxygen atom. On a molar basis, water is two thirds hydrogen. On a mass basis, it is only 16/18ths hydrogen, since oxygen weighs 16 to hydrogen only one. But that is not the wonder of water.

Most compounds that have a molecular weight of 18 are gases. Nitrogen is 28, and boils at 77 kelvins, cold enough to freeze a banana into a hammer. Pretty much the same with oxygen, and argon. Carbon dioxide, with a molecular weight of 44, liquefies at higher temperatures. Read more »