Why does water expand when it freezes?

Why does water expand when it freezes?

Basically, the default thing for things to do is to shrink because normally, if you make something hotter, it’s vibrating more. It vibrates. It tends to take up more space. It tends to expand. Ice is very unusual that as it gets colder, it’s essentially vibrating less, it does expand. And the reason for that is due to the strange shape of water. If you’ve ever seen the picture of a water molecule, it looks like a Mickey Mouse head with a sort of oxygen molecule where Mickey Mouse’s face is and then two hydrogen atoms where his ears are and it’s bent basically. The oxygen atom is slightly negative and the hydrogens are slightly positive. And because of that bend, the way they tend to link together is actually a very open structure with big holes in it and that means, there’s quite a lot of extra, sort of basically vacuumspace in that structure. So when it freezes it, it releases a load of energy because it means lots of more extra strong bonds can be made. But it does take up more space. And so, ice expands when it freezes.