Baby It's Cold Outside

Its effing freezing outside and I don’t do cold very well. As I was walking into my building and saw ice, I did start thinking about ice skating.

One of my favorite topics I have ever covered is the chemistry of water. Yup, it’s official – I’m a huge nerd. This sounds a little random, but it’s actually really crazy how perfectly created the water molecule is. It has properties that allow it to do things nothing else can. That’s the reason it is so essential to life.

So what makes water so great for ice skating?

First we have to back up – what does it mean to float? Something floats if it is less dense than what it is floating on top of. A rock is much denser than water, so it sinks. Oil is much less dense than water, so it floats. To float an object must displace as much weight of the fluid as its own weight. Very basic. If you don’t know this, you need to get off the plane and back into elementary school.

Water is a tricky little devil and it’s due to the makeup of the water molecule. Water is comprised of 2 hydrogen atoms attached (covalently bonded) to 1 oxygen atom. The arrangement looks like the Mickey Mouse head. This arrangement makes water a polar molecule – meaning it has a slight charge because the electrons all tend to hang out with the oxygen more than the hydrogen atoms. With electrons always visiting, the oxygen has a slightly negative charge and each hydrogen has a slightly positive charge. When water cools, the molecules lose energy, move closer together and arrange themselves such that the negative oxygen of one molecule comes in close contact with the positive hydrogen of another molecule. This close arrangement is known as a hydrogen bond (that’s a really shitty definition of a hydrogen bond, but you get the basic idea). Hydrogen bonds are weak and water has a lot of energy in a liquid state, so the bonds can be broken easily.

Water reaches its peak density at ~40°F. At this temperature, water molecules are super close together (as dense as they are ever going to get). Once water starts to freeze, water molecules lose energy and water’s density decreases because the hydrogen bonds become stronger than the water molecules are able to hold the oxygen molecules apart. Ice actually takes up 9% more space than liquid water because of the hydrogen bonding. The ice is lighter and less dense, so it is displaced by the liquid water and floats.

So who cares? Fish sure do! If ice didn’t have this property, lakes and rivers would freeze on the top and the ice would then sink to the bottom. This would continue until the lake or river was a solid block of ice. All of the little fishes and other water animals would be killed – trapped in a block of ice – if this happened. I guess we would still be able to ice skate, but you get the point I’m trying to make…