Thread: Question about water ice.

How many molecules of H20 need to be stuck together a 0 degrees C to call it ice? When does it go from being water to being the expanded less dense version of ice, when in terms of the number of molecules added. When you go from some magic number to the next, the whole thing boings out a bit?

In my opinion at least, you could really have as few as 2 molecules... The temperature of 0^oC would slow them down and allow them to hold together via hydrogen bonds and be solid and more stable. I'd consider that ice, or to look at it another way, the solid phase of water, personally.

You would need as many moelcules as make up a unit cell of an ice crystal. There are several forms of ice and I do not recall the crystal structure of any of them, but it should be easily googled.

Actually you need something like tens to hundreds of building blocks to overcome the Keimbildungsarbeit (don't know the exact phrase in english and too lazy to look it up) as the surface to volume ratio is indded pretty high so this requires a lot of energy. Thus you only get crystallization from highly saturated solutions or supercooled liquids because the entropy in the solution has be higher than the entropy within the crystal otherwise nothing happens. For water methinks the minimum H2O molecules is at the lower end of the range stated above as it's apretty simple molecule and you have hydrogen bonds helping the formation of ice.