Editor’s Note: This is a column on the area’s watersheds by Blyden Potts and guest columnists, designed to spread awareness of the area’s tributaries and the efforts of local volunteers to keep them clean.
Water. Everyone knows about it. Ask your kids and you might get great answers like “Wet!” or “He puts out fires!” Health professionals will tell you that we cannot live without water, and your pastor may tell you that water is mentioned 722 times in the Bible. Evolutionary biologists will tell you that all life originated from it, and astronomers will tell you that water is the main criterion in the search for extraterrestrial life. However, if you ask a chemist, you will get a completely different answer.
Let’s start with a little history. The ancient Greeks, primarily Aristotle, considered water to be one of the four basic elements: water, fire, earth and air. Surprisingly, this view persisted for nearly 2,000 years before Henry Cavendish discovered in 1783 that water is made up of hydrogen and oxygen. After this discovery, it took another 22 years before the actual ratio of the elements was determined in 1805, when Joseph Louis Gay-Lussac and Alexander von Humboldt determined that water was composed of two parts hydrogen and one part oxygen.
The International Union of Pure and Applied Chemistry (IUPAC), which sets the rules for chemical names, defines the official name for water as “dihydrogen monoxide” or H2O, which of course no one uses unless they’re trying to sound technical. In addition to the formula, we know from X-ray crystal structures that two hydrogen atoms are bonded to an oxygen atom in a “curved” configuration with a 104.5 degree angle between the hydrogen atoms. Hydrogen-oxygen bonds are polar, with oxygen having a partial negative charge and hydrogen atoms having a partial positive charge. Water lines up around other molecules, orienting its polar oxygen next to other hydrogens and/or water’s hydrogens next to other polar atoms or ions. And bending allows water to wriggle into positions that would be impossible for a linear molecule.
Knowing its composition, let us dwell on three examples that distinguish water from any other substance. First, water is an excellent solvent. As mentioned earlier, water builds up around other molecules, separating them from their neighbors. Since physiologically we are approximately 60 percent water, this illustrates the importance of how staying hydrated helps transport nutrients into and out of our tissues. Its ability to dissolve is also the very reason why we wash clothes and dishes in water.
Second, water has what chemists call a high specific heat. This means that water can absorb a lot of heat. This is why it takes several minutes for a pot of water to boil. And since 71 percent of the earth’s surface is covered with water, it provides a huge radiator that regulates the temperature on our planet.
Third, when water freezes into ice, it floats because it is less dense. This property is unique to water and unlike any other liquid. When ice forms, water molecules line up in a hexagon shape with a water molecule at each corner. Consider packing your suitcase. If you roll up your clothes, you will be able to pack more into your suitcase, but if you try to arrange your clothes in hexagons, you will fit less. This is very important, because if the ice did not float, it would freeze and sink to the bottom, as a result of which reservoirs would accumulate ice from the bottom up, and aquatic life would die out in winter. Because ice floats, it stores water above the surface, which is an important issue when ice melts at the poles, causing sea levels to rise.
Water as a molecule seems very small and simple, but in fact it is an amazing and extremely important molecule.