: why does water expand when frozen but not other liquids?

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: why does water expand when frozen but not other liquids?

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Note that ice expands compared to liquid water, but once it’s all solid, if you cool down the ice more and more it will contract.

The reason for ice having more volume than liquid water is that the molecules of liquid water are close to each other (like grains of sand), but to form ice they rearrange into a [hexagonal pattern](https://www.quora.com/If-cold-contracts-and-heat-expands-why-does-ice-expand) with a huge gap in the middle.

So density of a liquid vs. its solid form depends on the pattern that the atoms form when they go into their solid “arrangement”. Most materials [pack their atoms](https://i.pinimg.com/474x/0b/03/68/0b0368f4d6e909a6c0d31c4bfb07c7cc–electron-microscope-transmission.jpg) tightly, though some can form [more spaced out patterns](https://qph.fs.quoracdn.net/main-qimg-fa5e60ba2e4cf382b201346d80cf5b77).

Other liquids do, just maybe not ones we see everyday. Silicon is an example. The solid is less dense.

I might be misinformed, but I was explained that it is due to the polar nature of the water molecule. So a water molecule is kind of shaped like a Mickey Mouse head, where both of the (smaller) hydrogen atoms are closer together on the same side of the larger oxygen atom. The side with the hydrogen has a positive charge, and the side with the oxygen has a negative one, so the molecules kind of behave like magnets when they interact with each other — like charges repel each other, and opposite charges attract.

In liquid water, the molecules can all flow past each other freely. But when it freezes and becomes ice, the molecules can’t just be mashed together at any orientation. They have to turn to lock in with each other end-to-end in a specific crystalline structure, based on the charge of the molecules, which takes up more space.

The transition between liquid to solid allows atoms to pack closer together (less movement requires less space). Water is different from most molecules (in a lot of ways) because of hydrogen bonding.

Oxygen pulls on the electrons slightly harder than hydrogen in its bond (atoms pulling on electrons is how molecules are formed). Because more electrons are around the oxygen, it is slightly negative, and hydrogen is slightly positive.

As a liquid, water molecules can slide past each other and tumble about (rotate). However, when water freezes, that motion stops, and the molecules have to pick an orientation. The molecules organize to keep all those charges as balanced as possible; this leaves large gaps between the molecules. These gaps mean the water is taking up more space than it did before.

If it was not, there would be no life on earth. Ice would sink at the bottom of oceans and lakes and just accumulate until the earth would be a big snowball. Like some moon around Saturn and Jupiter.