Liquid Water and Crystal Structure
Does water have a crystal structure as a liquid?
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
Hope this helps!
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.
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
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.
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Update: June 2012