I am doing a project called science demos. We have had at least 4 presentations so far.I am very connfident that I am going to do a great job but, I still do not know why water expands when it freezes? Anyone a smart genius that know the answer to my question

I can't say it any better than this guy so here "http://en.allexperts.com/q/Science-Kids-3250/water-expand-freezer.htm"

Not necessarily a genius but, ice, like most other pure solids, has a crystalline structure. This means that the atoms are organized in a simple repeating structure. The crystalline structure of ice is a repeating arrangement of eight molecules of water. This arrangement is actually less dense than liquid water at 4 degrees Celsius! There are more molecules in the same amount of space in the cold liquid than there is in the solid form.So, water contracts until 4C and then expands. This is a unique property of water, as most chemicals have solid forms that are denser than their liquid forms. The arrangement of hydrogen and oxygen atoms in water results in this and other special chemical properties such as having a molecular weight of 18 and boiling at 100C.