Because water expands as it freezes.
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Tsk, tsk. That just begs the question. Why should liquid water behave differently than nearly all other materials?
I like keeping it short and simple ;) Oh- the "tsk, tsk" made me snort coffee out of my nose. Thanks.
:-D Did the coffee expand or contract as it cooled? ;->
I believe most of it was vaporized, and then the remainder was coughed out back into the mug.
Mmmmmm....second-hand coffee. Sounds delightful ;-P
...and slightly thickened.....
In liquid water, the molecules are in random disarray.As they cool and slow, the weak electrical forces between the different parts of the V-shaped molecule become more important, and the molecules arrange with the oxygen atoms of one molecule close to a hydrogen of another.This forces the molecules to "stack" point-of-V to end-of-V, which is a less space-saving arrangement, so the solid ice takes up more space than expected.
+1 "As water freezes, the molecules are forced to align themselves into a very particular structure – a hexagonal lattice that is the basis for the six-sided snowflakes." Source:http://expertvoices.nsdl.org/polar/2009/02/03/teaching-about-snowflakes-a-flurry-of-ideas-for-science-and-math-integration/
Hah, I gave my answer without resorting to the innertubes.
Water is "funny stuff" - it's mostly down to hydrogen bonding, the answer is in there. L
The space between the water molecules in crystal form is greater than in liquid form. This is also, of course, why water expands when it freezes.If you want to know why it's greater for water, unlike many other substances, you need to look at exactly how the molecules settle into the crystals.