Locking into a pattern
What Happens When Water Freezes?
Freezing locks water molecules into an open lattice — which is why ice expands.
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Step 1 of 5
Cooling slows molecules down.
Temperature is molecular motion. Removing heat means removing movement, until attraction between molecules can finally win.
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Step 2 of 5
At 0°C they lock into place.
Molecules stop sliding and settle into fixed positions. That transition is freezing, and it happens at one specific temperature.
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Step 3 of 5
The pattern is deliberately open.
Water molecules link at 120-degree angles, which forces a hexagonal lattice with gaps in it. The gaps are why ice takes more room.
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Step 4 of 5
So ice takes up more space than water.
About 9 percent more. That is why bottles crack in the freezer and why frozen pipes burst — the expansion is unstoppable.
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Step 5 of 5
Which is why ice floats.
The same mass in more space means lower density. Ponds freeze from the top down, leaving fish alive in liquid water below.
If ice sank, ponds and lakes would freeze solid from the bottom and most freshwater life would not survive.
The short version
Freezing locks water into an open hexagonal lattice, so ice expands and floats — which keeps lakes liveable.
Try it yourself
Fill a plastic bottle to the brim, cap it and freeze it. It bulges — the expansion is genuinely unstoppable.
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