Clathrate, Hydration Shell

[physgirl]

What's the difference between a clathrate and a hydration shell?

Is it right that in a hydration shell the water molecules are coming in and out, replacing the molecules that were already a part of the shell, "dynamic", but in a clathrate, everything is fixed and ordered (no replacement of molecules going on)?

I'm not really sure if I follow my book's descriptions of the two...

[Jammerz]

You're mostly right...

a hydration shell is the result of a polar solvent (in this case water) orienting itself around ions due to the charge. The ions are essentially surrounded by a "shell" of water. The "shell" is not fixed, and molecules may move around, about, in and out... but they all orient themselves around the ion based on its charge.

A clathrate structure is a lattice structure... fixed and ordered like you said. Solid water (aka ice) forms a clathrate structure.