Water: A Very Special Molecule
—Eli Schaffer, Environmental Educator
With arctic temperatures invading the Rye area, all of the water around us will change into ice. Have you ever wondered why water expands and gets all slippery when it freezes? And while we're wondering, what's the big deal with water anyways? Sure, our bodies are two-thirds water which basically makes us walking, talking water balloons. And it's true that water covers over 70% of the Earth's surface, giving our home its "Blue Planet" nickname. But, really, what gives! What makes water so special!?
To find the answer we have to ask the water. Unfortunately we won't hear the answer in the crash of waves. We have to ask an individual water molecule. Since a drop of water is actually holding over 1 thousand billion molecules, we have to zoom in... a lot. A water molecule is made up of one big oxygen atom with two little hydrogen atoms stuck to its sides. When atoms bond together, they try to line up totally even, but when water (H2O) is formed, the hydrogen atoms get squeezed onto just one side of the oxygen. This imbalance, called polarity, makes the water molecule have a positive side, and a negative side, kind of like a battery or a magnet. Finally, we arrive at our answer!
The off-balance water molecule is just fine being a little uneven. Unless, you try to tell it where to go. When water is liquid or gas, most of the molecules just bounce off each other and go on their way. But something very special happens when it gets too cold for the water to stay liquid. The water molecules will only freeze if their positive side is lined up perfectly with the negative side of their neighbor. This pickiness takes up a tiny bit more space than when the water is liquid. That means that as water freezes, it expands. This makes water really good at breaking things apart in the winter. If you need proof, go for a drive and notice that there are more potholes in the road this time of year. Or if you want to do a home experiment, fill a (plastic!) bottle with water, and put it in the freezer.
Polarity makes water so important to life because if something has the same amount of stuff, but takes up more space, it floats. Water freezes at the top because ice is less dense than liquid water. The turtles, fish and other aquatic life that live in frozen ponds are able to continue living in the chilly, liquid water underneath. While life thrives below, we can skate across the surface above; but how? Because of polarity of course! The water molecules line up so well, that the surface turns into a flat sheet just right for slipping and sliding. This polarity also causes surface tension to do some pretty cool stuff (think water-skiing or skipping stones). With such nifty tricks, it's no wonder H2O is so special.
