4.                                 

        Ice

 


       Water shows its strangest property when it transforms from a liquid to a solid.  In the transformation to ice, it becomes less dense than liquid water.  At temperatures above 4 Celsius, water behaves like other liquids by expanding as it warms and contracting as it cools.  At temperatures below 4 Celsius, water begins to freeze and the molecules slow to a point where they do not break their hydrogen bonds.  A crystalline structure forms at temperatures near 0 Celsius, with each water molecule bonded to a maximum of four others.  By holding molecules at a distance, it is the hydrogen bonds that make ice less dense than liquid water (Fig. 7).

 


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