Why does water expand when frozen?

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Why does water expand when frozen?
« on: 09/09/2009 11:30:03 »
martin asked the Naked Scientists:
Why does water expand yet other things contract when frozen?

What do you think?


Offline Cooljeffct2

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Why does water expand when frozen?
« Reply #1 on: 09/09/2009 20:57:55 »
Water expands when it freezes due to molecular geometry and the fact that it is a very polar molecule. The water molecule is shaped like an upside-down "v". Due to this shape, when water freezes it make a hexagonal shape such that the slightly negatively charge oxygen atoms are aligned with the slightly positively charge hydrogen atoms -- this is the most stable configuration. (Less polar molecules do not configure themselves in this way because there is less of a reduction in energy if the molecule is not as polar) This orientation leaves space in the middle of the frozen water molecules. That is why water expands when it freezes.