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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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