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Name: Izabella
Status: student
Grade: 6-8
Location: MI



Question:
Does water have a crystal structure as a liquid?


Replies:
Water molecules do form predictable orientations depending on their temperature, but I would not say they are 'crystals'. Hydrogen bonds, formed between the hydrogen(s) of one molecule and the oxygen of another, strongly attract water molecules to each other -- it is this attraction that gives water its extremely unique properties. Water is constantly trying to lower its energy by rearranging itself, and it turns out water routinely arranges itself into some pretty complex shapes. However, those shapes are constantly changing and rearranging -- usually when we say 'crystal' we mean a more fixed architecture. While molecules in crystals occasionally jump around too, I think water is way too fluid (pardon the pun) to be called a crystal.

Hope this helps!
Burr Zimmerman


Hi Izabella,

Water has no crystal structure until it cools, freezes, and forms ice. This lack of crystal structure does not just apply to water, but to nearly all liquids.

Regards,
Bob Wilson


Izabella,

By definition "crystal structure" means an organized structure in which the particles involved in the structure have established and clearly defined positions. Also by definition, a liquid is made up of particles that are moving, in a fluid state. By these definitions, a liquid can not have a crystal structure. (There are exceptions such as the state known as liquid-crystals, but this is not the case for water.)

You may be thinking that liquid water has a crystalline structure because its density is higher than that of its solid form. However, this is true because of the difference in the type of intermolecular interaction of water in its liquid state than its solid state.

Greg (Roberto Gregorius)


Pure water in the liquid phase is disordered. I believe there is an average intermolecular distance, but any ordering of the polar water molecules is very short ranged. There does not appear to be any semi-ordered state between the liquid phase of water and ordered crystalline water. Water is however a large component of the solution for many liquid crystals.

---------------------------
Michael S. Pierce
Materials Science Division
Argonne National Laboratory



Liquid water does not have a crystal "structure" in the sense of "long range order" expected of a solid crystalline material. There is an "ice-like", lower density, ordered structure associated with the unusual behavior of water to increase in density between 0 C. and about + 4 C. Most solids just decrease in density (increase in molar volume) as the temperature increases from the melting point. This unusual behavior is related to the fact that the solid phase of water (ice) has a lower density than the liquid phase, which in turn is related to the unique orientation of the hydrogen atoms and the lone pairs of electrons in the case of water.

Vince Calder



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