Why does water expand when it freezes?
When water in its liquid state, the molecules move quickly enough that hydrogen bond between adjacent molecules quickly break. Consequently, there is no large structure to the molecules in liquid water.
Water expands when freezes, unlike other substances
In one word you can say, it is all because of hydrogen bonding.
Typically, when something is cold, it shrinks. That’s because temperature describes atomic vibration — the more vibration, the more space it takes, hence expansion. Water is an exception. Even though it vibrates less when it’s frozen, the ice occupies more volume. That’s due to the strange shape of the water molecule. This means the electron density is greater on one side of the molecule than it is on the other side.
you can see in image, the oxygen atom and the hydrogen atom share electrons, they don't share evenly.The oxygen atom has much stronger pull on electrons than the hydrogen atom do, so the shared electrons tend to gravitates towards the oxygen atom.
Water is a polar molecule.
Water is a polar molecule.
Since hydrogen atoms are so small.
When two water molecules approach each other, the partially positive hydrogen atoms of one water molecule can closely approach to the partially negative oxygen atom of the other.As they get closer together the electrostatic attraction between them gets even stronger.This extra strong attraction between molecules that have hydrogen atoms bonded to electrons like oxygen is called hydrogen bonding.
When water in its liquid state, the molecules move quickly enough that hydrogen bond between adjacent molecules quickly break. Consequently, there is no large structure to the molecules in liquid water.
But take away thermal energy and the water molecules slow down hydrogen bonds form between molecules and snap into place ,with a particular geometry.And this geometry takes up more space,because empty spaces between water molecules.
When water freezes it releases energy because a lot of extra strong bonds can be made. But it does take up more space. And so, ice expands when it freezes. So that's why water expands when it freezes.Hydrogen bonds between molecules cause the molecules to get into 3D shape that is less efficiently packed than the molecules in liquid water.
Another interesting fact worth mentioning is that hot water freezes faster than cold water.
Thank you😊
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