It’s colourless, odourless and ubiquitous, covering 74 percent of the Earth’s surface. But even though water is one of the most common substances on the planet (although it doesn’t seem that way some years in Saskatchewan), in terms of its special properties, it’s also one of the most uncommon.
It’s a good thing, too, because if water didn’t have all those special properties, we wouldn’t exist–at least, not in this form.
Chemically, water is a very simple compound, written as H2O or H-O-H, indicating that it consists of two hydrogen atoms bound to an oxygen atom. But it’s the way those two hydrogen atoms bind to the oxygen atom that makes water special. They form a V-shape, with an angle of 105 degrees.
This means that a water molecule is not symmetrical, either in shape or in electrical charge. The atoms in water molecules are bound to each other covalently, which just means that they share electrons, the tiny particles that each carry a negative electrical charge. However, oxygen atoms attract electrons more strongly than hydrogen atoms, so the point of the molecule’s V-shape–the oxygen atom–ends up with a slight negative charge, because the electrons prefer to hang around at that end of the molecule, while the two arms of the V–the hydrogen atoms–are left with slight positive charges. Water is therefore called a “polar” molecule, because, like a magnet, it has a positive and negative pole.
Those two positively charged hydrogen atoms are naturally attracted to the negatively charged ends of other water molecules in the vicinity, forming what are termed “hydrogen bonds” (not to be confused with “hydrogen bombs”). This relatively weak hydrogen bonding is what keeps water liquid rather than gaseous over a wide range of temperatures, unlike most substances.
It’s also what makes ice float; the V-shape of the water molecules means that the arrangement of molecules in ice is very loose, actually looser than in cold liquid water, and therefore less dense than the liquid. That’s why water expands when frozen, unlike other substances, which shrink and become more dense when they go from liquid to solid.
All of these characteristics of water are important to you and me and every other form of life on Earth.
For example, water’s polar nature ensures that it is able to attract ions–charged molecules–of other substances, as well as other polar molecules. Because of this, water comes close to being a universal solvent, one that can dissolve absolutely anything. Given enough time, even the hardest stone will yield.
Water’s ability to dissolve things makes it ideal for transporting the substances that make life possible. Most of the reactions in a living cell occur in a water solution. In fact, cells consist of about 70 percent water, which is why the fact water remains liquid over such a wide range of temperatures is so important. You can imagine how limited life would be if water remained a liquid only within a range of, say, 20 degrees, instead of 100.
Water’s unique expansion upon freezing is also vital to life. That may sound strange, since the expansion of freezing water in living cells is what kills plants when frost hits, made your cat’s ear fall off last winter and makes it highly unlikely that any of the cryogenically frozen dear departed will be in much shape to dance the lambada upon being thawed out. However, consider this: if ice did not expand, and therefore did not float, every year the ice that formed on the surface of lakes and the ocean would sink to the bottom. Life could not exist in any body of water where that happened; it would be buried in the ice, and any deep body of water would soon be reduced to a vast lake of ice with a little meltwater on top during the warmest months. The whole planet would be gripped in a permanent Ice Age.
(Although water shrinks when heated from freezing to about 4 degrees, above that temperature it begins to expand as it is heated, and from there on up acts like other substances.)
Water has other interesting properties, as well. It is both a weak acid (a substance that can provide hydrogen ions for chemical reactions) and a weak base (a substance that can accept hydrogen ions) boosting its versatile and vital role in the myriad chemical reactions of life.
It conducts electricity, which may not seem immediately important to the life process but will quickly become so if you drop the radio in the bathtub.
It is surprisingly incompressible (another effect of hydrogen bonding), which is why flat rocks can be skipped on it, exploding mines can sink ships without actually touching them, and belly-flops hurt.
As noted at the beginning, it is odourless (certain Saskatchewan lakes notwithstanding), colourless (ditto), and, when pure, tasteless; but it’s the one liquid you’d most like to drink when you’re really, really thirsty. Unspectacular in appearance though it is, it’s still a heck of a lot of fun to wade, splash and swim in, and to boat, water-ski and windsurf on.
It is also depressingly vulnerable to pollution (remember, it dissolves almost anything, including all kinds of nasty man-made additives) and, despite covering three quarters of the globe, it is alarmingly scarce in some areas, including ours at times.
Maybe because it is so common, we tend not to give it the respect it deserves until we’re suddenly short of it. But conservation and protection of our water resources is something that can never begin too early. In some places it’s already too late.
Water may be the most remarkable substance in the universe, not only because of its unique chemical properties, but because of what those properties allow to exist: us.
I don’t know about you, but any substance on which my existence is based gets my utmost respect, colourless and odourless or not.
