Article: Shadhrah 4.

Why does ice float on water?

When al-Biruni asked this question in a letter to Ibn Sina almost a thousand years ago, he did not have the tools now used to study molecular structures, hence he did not know that in a water molecule, two atoms of hydrogen are attached to one atom of oxygen at an angle of 104.5 [degrees], and that therefore, upon freezing, water molecules cannot stack upon each other to form compact layers as they would if this angle was 180[degrees]. Of course, he was also unaware of the important role played by the mutual attraction between hydrogen and oxygen atoms--and the resultant hydrogen bonding--in the structure of this most important of all ...

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