Liquid Water and Crystal Structure

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

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

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Michael S. Pierce
Materials Science Division
Argonne National Laboratory
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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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