Is water is the only liquid that expands when it freezes? Yes.Water is most dense at 4 degrees Celcius. That's why lakes freeze at the top and you would never find frozen pockets of ice at the bottom of the sea - the pressure would force it to be in the liquid state.
All substances expand when you heat them, as the particles vibrate more the average space between them increases. Water is no exception, but it's only when it freezes that the strange stuff happens:
Science bit: "The reason water expands when frozen is the crystalline structure that forms, and the strong O-H bonds. The hydrogen atoms have a very strong attraction for the unbonded electrons in the nearby molecules. In an ice crystal, each oxygen atom has it's own 2 electrons, and grabs hold of 2 more electrons from the water molecule next door. And so they crystallize into a big hexagon shape, which takes up more space than the same molecules do when the water is in liquid form. An ice crystal's form is called a 'network structure.' Same molecules, but takes up more space."
Source: http://en.allexperts.com/q/Science-Kids-3250/water-expand-freezer.htm
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