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Re: IONS



SiO2 are real molecules, but when fused as in glass they form an unusual
structure called a network solid. I've only read a little about this and
you'll undoubtedly want to know more, but the gist is that the Si and O
atoms bond in such a way that the entire piece of glass becomes
essentially one huge complex molecule, in function if not in fact.

This apparently networks the electrons in such a way that under the right
circumstances the material becomes electrically conductive, as well as
accounting for some other weird properties of glass. If I recall
correctly, graphite is another network solid; nonmetallic and nonionic yet
conductive.

Best wishes,

Larry

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Larry Cartwright
Physics, Physical Science, Internet Teacher
Charlotte High School, 378 State Street, Charlotte MI 48813
<physics@scnc.cps.k12.mi.us> or <science@scnc.cps.k12.mi.us>
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On Mon, 21 Sep 1998, Ludwik Kowalski wrote:

The second is more fundamental. Why does the dielectric
material become a conductor? I suppose that SiO2 are real
molecules, not associations of ions, as NaCl. What is the
dissociation energy of SiO2 and why do Si and O atoms
become ions? The "dull glow" temperature is about 500 C
and this corresponds to k*T=0.066 eV. The bounding energy
of molecules, and bounding energies of electrons (in neutral
separated atoms) are probably about 100 times larger.

The rate of cooling of the glass rod at 500 C is probably
large, perhaps 30 W. This would mean that to sustain the
constant temperature the electric current must be large.
More specifically, i=30/120=0.25 A and R=480 ohms. Very
small in comparison with perhaps 10^9 ohms, or more, at
room temperature. Perhaps the "glass" chemists use is not
pure. But how can it be; they are in the best position to
know.