Transcript:

Water is unique in its behaviour. Let's look at phase transitions.

Let's look at a gas that has transitioned into liquid state. What it means is that the molecules of the gas that are far apart have now come close enough to touching each other, and it phase transitions to a liquid. In the liquid state, these molecules that are touching each other are free to roll over themselves. That's what a liquid is.

Now, when a liquid becomes a solid, these molecules that are free to roll over themselves are anchored to a fixed position. And usually, when things get anchored to a fixed position, they occupy a smaller volume — except for water.

Water is unique. When liquid water freezes to solid water, the distance between the molecules expands, and liquid is denser than the ice, which is why ice floats on the surface of the ocean. Which is also why, because there's an ice layer on top, you can still have marine life in the ocean, because the liquid phase remains.

It's an amazing molecule, water.