ElI5 what exactly happens in the freezing process that makes ice less dense than liquid water?
In: Physics
Ice is a special case. Water does a thing called hydrogen bonding. This is a weak intermolecular bond formed between hydrogen atoms in one water molecule and oxygen atoms in the adjacent molecule. This occurs because of dipoles within the water molecules – water is a covalent molecule, which means it’s atoms bond together by sharing electrons. Oxygen atoms are more attractive to electrons than hydrogen atoms, so the electrons float around closer to the oxygen than the hydrogen, which means effectively the centre of the molecule is slightly more negatively charged and the ends are slightly more positively charged. This makes them attract to each other like magnets.
Anyway, those hydrogen bonds become stronger and more numerous the more solid the water becomes. As a gas, there are no hydrogen bonds. In a liquid, there are a few. If allowed to freeze normally, hydrogen bonds in ice form a crystal lattice structure that creates a larger distance between molecules than there would be if water didn’t hydrogen bond. More empty space in a structure means it’s less dense, and so the structure has a higher total volume .
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