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Crystal Lattice and Boiling Point
Name: Rachael
Status: student
Grade: 12+
Country: United Kingdom
Date: Winter 2009-2010
Question:
What do crystal lattices have to do with atoms and their boiling
points?
Replies:
Hi Rachael,
Atoms do not have boiling points -- the concept of 'boiling' only makes
sense in the context of macroscopic quantities of material. Typically,
boiling refers to materials that go from a liquid phase to vapor, but
a crystal lattice normally refers to a solid material, not a liquid.
Some solids (such as ice) can go directly from a crystal to a gas (but
that is known sublimation, not boiling).
So I guess I need a little help understanding your question here --
can you provide more context for what you're trying to understand?
Hope this helps,
Burr Zimmerman
Hi Rachael,
A crystal lattice is a specific, regular arrangement of atoms, repeated over
and over. For example, ordinary table salt has a basic crystal arrangement
with one atom at each of the 8 corners of an imaginary submicroscopic
cube. This pattern is repeated endlessly to build up a visible
crystal of salt.
The cube-shaped basic crystal structure is why visible crystals (or crystal
lattices) of table salt also look like miniature cubes. The basic cube-shaped
8-atom salt crystal is repeated over and over, building up a visible crystal
lattice (salt crystals) whose shape closely resembles the original
8-atom salt
crystal.
On the other hand, crystal lattices have nothing whatsoever to do with a
crystalline material's boiling point. This should be fairly obvious, since a
substance must be melted to liquid form in order to boil, but
crystal lattices
are solids. For example, water ice is a crystalline substance, but ice cannot
boil because it is a solid. You have to melt it first, which destroys the ice
crystals. The resulting water will boil when heat is applied, but
liquid water is
obviously not crystalline and contains no crystal lattices. So you
can see that
crystal lattices cannot possibly have any effect on boiling point of
a liquid,
because liquids cannot contain any crystal lattices.
Regards,
Bob Wilson
Rachel,
In brief, crystal lattices can be a measure of how closely packed
atoms are. If you were to arrange four marbles, say, in a square and
put each square directly on top of one another so that you have four
columns of marbles, you would not be able to fit as many marbles in
this arrangement as when you arrange marbles in hexagons and fit
hexagons on top each other so that one marble from one hexagon is
always partially in the hole formed by another hexagon.
You can then imagine that the more tightly packed atoms are, the
higher will be its melting point.
Now, as to their boiling point - I do not see any real relationship
because the crystal lattice will have been destroyed (as the
substance melts) before it can boil (liquid to gas). Moreover, the
important factors in boiling points (the intermolecular or
interatomic attraction), while a factor in how well an atom might
pack, is not the only factor in packing.
Greg (Roberto Gregorius)
Canisius College
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