Homework Help: APCHemistry

Posted by Kiki on Monday, April 26, 2010 at 8:07pm.

Hi
these are the posts from earlier---i just had a quetsion about your response:

""Apchemistry - DrBob222, Monday, April 26, 2010 at 7:10pm
Your thinking is ok. All ionic solids, although composed of ions, are locked into place by the crystal lattice structure of the compound. Thus the ions are not free to move about and they can not conduct electricity. """

*****my question is: even though the ions are not free to move about, don't they still have vibrational energy, if not translational and rotational? Doesn't the answer have to be related to electrons' movement? (i was thinking, in metallic solids, there is a sea of electrons, but in ionic solids, there is no such "sea" (?because the electrons are involved in the lattice structure of the ionic solid) so the electrons cannot freely flow so current cannot flow??

does this sound correct?
Thank you!!!!!

APCHemistry - DrBob222, Monday, April 26, 2010 at 8:20pm
I am a little confused; I think you may have contradicted yourself. I'll try to answer each part of your response.
Yes, the ions in a crystal lattice do posses some vibrational energy and I suppose it would not be outlandish to suggest that one or two of them (out of billions and billions and billions) might even have rotational and/or translational energy (IF they could break loose from the lattice). You are also correct that there is no sea of electrons as in a metallic conductor. The electrons; however, ARE moving (and moving very very fast). The ion itself is not moving from point to point but the electrons are moving in their respective shells and orbitals. Here is an example which I'm sure you have read about. An ionic crystal, such as NaCl, will not conduct electricity in the solid state precisely because the ions can't move and transport the electrical charge from one electrode to the other. BUT, what happens if we melt the NaCl, thus breaking the crystal lattice structure? I"m thinking the melting point of NaCl is about 800 C or so BUT in the molten state, the crystal lattice is broken, the ions are free to move more or less freely within the liquid, and it DOES conduct electricity, precisely because the ions CAN move from point A to point B.

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