Hydrogen bonding opens a hexagonal lattice in ice, so solid water takes more space and floats. Most substances pack tighter when they freeze; water is the famous exception.
That quirk saves aquatic life in winter: ice lids form on top while denser liquid water stays below. Lakes freeze from the surface down, not solid from the bottom up.
Climate, shipping, and cold drinks all ride on the same molecular accident. A floating cube in your glass is a miniature version of polar ice sheets.
Shahzad Mahota
Ice is less dense than liquid water
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