Pour yourself a nice glass of water, and take a close look at it. Seems pretty boring, right? It’s clear, doesn’t have a taste or smell, and just sits there. It you were trying to come up with the most ordinary thing imaginable, water might be right up there with shoelaces or potato chips. But behind it’s bland appearance, a wonderfully weird substance is hiding in plain sight. In this episode of Brains On, we explore some of the weird things water can do, like move against gravity! Or cut right through rock! We learn some of the reasons why water is so weird, and fill you in on how you can learn more about the water in your neighborhood.
How is water weird? Let’s start with a water oddity that’s easy to see. Ice, the solid form of water - floats on it’s liquid! Substances can exist in 3 forms or phases: gas, liquid, and solid. These phases are different because the atoms or molecules, what makes up all the stuff in the universe, are arranged differently. Gas molecules move around really quickly, and have lots of space between them. Liquid molecules are much closer together, but still moving and flexible. Solids are packed tight, the atoms right up next to each other. Almost everything gets denser as it moves from gas to liquid to solid. But not water! When water solidifies into ice, it becomes less dense and floats!
Another weird factoid - hot water seems to freeze faster than cold water! That’s right, in a race to the icy finish line, hot water will get there faster than cold water, despite having further along the thermometer to travel! This phenomenon is known as the Mpemba effect, named after Erasto Mpemba, a Tanzanian high school student who observed this phenomenon while making ice cream! Scientists still aren’t confident they know why this happens.
Water is what’s called a “universal solvent” which means it is really good at dissolving stuff. Table salt? No problem. Vitamins and minerals? Easy peasy. A vertical mile of rock? Give water enough time and it can carve the Grand Canyon. Water can climb upwards against gravity, absorb an unusually high amount of heat energy, and transport essential nutrients throughout our body.
Why is water so weird? Well it turns out that it boils down to the forces that hold water together. Like everything, water is made up of atoms, those tiny-building blocks that make up all the stuff in the universe. Atoms combine to form molecules, and in the case of water, two hydrogen atoms combine with one oxygen atom to form H2O!
Every H20 molecule has an end with a positive charge and an end with a negative charge, just like a magnet does. The Oxygen atom has a small negative charge, and the two Hydrogen atoms have an even smaller positive charge. And just like a magnet, negative and positive ends attract one another. These small attractions are called hydrogen bonds, and are indicated by the dotted lines in this picture.
These attractions are called hydrogen bonds because they only form between hydrogen atoms and other charged molecules. These Hydrogen bonds between the different water molecules are a lot weaker than the bonds that hold the two hydrogen atom to the oxygen atom of a single H2O molecule. It’s kind of like the difference between a firm, long lasting handshake and a quick high-five. Plus, Hydrogen bonds exist for just a fraction of a second, 10 picoseconds to be exact (a picosecond is to one second, what one second is to 31,700 years!)
So you’ve got all these water molecules zooming around, “high-fiving” their neighbors, and being pulled together just a little bit more by hydrogen bonds. This little extra pull means water molecules can to stick really well to each other. And it helps them stick to other stuff without getting stuck, since the hydrogen bonds are so easily broken. It also explains why water expands when it freezes, since these H-bonds get “stuck” below 32 ℉, leaving more room between the molecules and making ice less dense than liquid water!
Check out this video to learn more:
What makes water so weird is also what makes it so essential for life. In fact, in addition to supporting life by transporting nutrients and energy, helping our cells do their work, filling the gaps between cells, and even making up the bulk of our bodies (about 70%!), water was likely a crucial player in the origin of life itself! Listen to the podcast to hear all about it!
This episode was powered by the Water Main, a new initiative from American Public Media focused on connecting people to their water resources. Find out more at www.watermain.org