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04.5˚

B

e Curious

What is

water? 104.5˚

104.5˚

By Ashley Stewart

Water covers 71% of the surface of the Earth. It is ubiquitous in our poems, songs, and dreams. It makes up about 4/5 of my body and 72% of my husband’s. I have stood in awe of the ocean, cursed the rain, and savored a bath. Water is all around me, and it is me. But, what is water? On the face of it, the answer is less than poetic. Its chemical name is dihydrogen oxide—also known in chemistry circles as the universal solvent. It is the most common chemical on Earth. Make no mistake, though: this chemical is exceptional. In order to understand just how extraordinary this molecule is, please indulge a crash course in organic chemistry. An element is a nucleus of protons (positive charge) and neutrons (no charge) that is surrounded by an equal number of electrons (negative charge). The electrons are arranged in pairs (more stable in terms of chemistry) in a sort of orbit around the nucleus. The smallest, closest orbit holds a single pair of electrons. The next level has the capacity to hold four 104.5˚ pair, or eight additional electrons. The third orbit holds sixteen electrons, and so on. Just like a magnet, particles of the same charge repel one another. Therefore, in the second orbit, assuming all electron slots are full, the four pairs naturally form a quadrahedron, which looks something like a teepee:

12 Longleaf Style Summer 2010

Oxygen has eight protons and eight electrons. Two electrons occupy the first orbit, leaving six for the second orbit. The most stable configuration for oxygen, then, is to have two pairs of electrons and two single electrons in that orbit, like this:

Conveniently, hydrogen has one proton and one electron. If two hydrogen electrons fill the empty slots in the oxygen’s second orbit, the result is water. Now—here is where the peculiarities come in. Hydrogen is a small molecule, but it balances out the charge in the electron pair. This allows for two things to happen: The two unopposed electron pairs are stronger in terms of charge, and they push the two hydrogens together. In a perfect quadrahedron, the angle between each electron pair is 109.4 5 degrees, but in water, the angle is 104.5 degrees. Also, the much larger oxygen molecule tends to pull the negative charges toward itself, with the end result being a

Longlead Summer 2010  

The Summer 2010 issue of Longleaf

Longlead Summer 2010  

The Summer 2010 issue of Longleaf

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