Water breaks the rules
Most substances
- Shrink as they cool
- Solid is heavier than liquid
- Frozen chunks sink
Water
- Is heaviest at 39 °F (4 °C)
- Expands about 9% as it freezes
- Ice floats on top
Why it happens
- Water molecules are V-shapedWith a slightly charged end on each side
- As water freezes they lock togetherHeld by hydrogen bonds
- They form an open honeycombWith more empty space than liquid water
- More space means lighterSo ice floats
Why it matters
Lakes stay alive
Ice forms a lid on top; fish live in 39 °F water below
Icebergs hide
About 90% of an iceberg sits underwater
Pipes burst
Freezing water expands with great force
Rocks split
Water freezing in cracks breaks stone apart
Remember
If ice sank, lakes would freeze solid from the bottom up.
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Answer key
- At what temperature is water heaviest?39 °FWater is densest at about 39 °F (4 °C).
- How much does water expand when it freezes?About 9%About 9%, which is why ice floats.
- Why does ice have more empty space?Molecules lock into an open honeycombHydrogen bonds hold molecules in an open pattern.
- How much of an iceberg is underwater?About 90%Only about a tenth shows above the surface.
- How do fish survive a frozen lake?Ice forms on top and they live in 39 °F water belowThe ice acts as an insulating lid.