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Liquid electrolytes ionize and hence a current can pass through them. So if a gas can ionize, can it conduct electricity too? If so, what are a few such gases?

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When gases get ionized, they're no longer gases, really, they're plasma. In fact, it's definition of plasma in physics that it's ionized gas. Plasma is conductive, of course, and heavily responds to electromagnetism. – Luboš Motl Sep 29 '12 at 11:30
The degree of ionization can be very different. It is not always 100%. Low pressure gases conduct currents at low voltage and are mostly gases than plasmas. – Vladimir Kalitvianski Sep 29 '12 at 17:45
up vote 8 down vote accepted

At atmospheric pressure, air and other gases are poor conductors (Insulators) of electricity. Because, they don't have any free electrons to carry current. But, once the free electrons are produced in gas by ionization (they become plasmas), electric discharge occurs.

This could be done in many ways such as by applying a large potential difference across a gas column at very low pressure, or by allowing high frequency EM-waves such as the X-Rays through the gas. This question is not proper to ask. Indeed, gases become plasmas once they're ionized!

All dielectrics have a certain value of breakdown potential. In most of them like air, ceramics, etc. (including semiconductors like Silicon), this potential provides sufficient energy to ionize a few atoms. The free electrons formed as a result of this ionization are energized enough to bump the neighborhood atoms, break some covalent bonds and produce more free electrons.

These free electrons are then accelerated by the applied electric field and they collide and ionize the other atoms to produce more free electrons (multiplication by collision). Now, there are large number of free electrons available for current flow. Thus, an electric arc is produced!

However, this isn't applicable for all gases. As @mikuszefski has mentioned, there are a few other cases such as the noble gases which are mono-atomic (and are used in most of the discharge tubes), whose breakdown potentials are only meant to ionize them!

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Are you sure that getting free electrons requires breaking of covalent bonds? What about noble gases? – mikuszefski Feb 19 '15 at 10:01
@mikuszefski: No, the noble gases don't have covalent bonds. In that case, ionization occurs directly! (Thanks! I've updated my answer). – Waffle's Crazy Peanut Feb 19 '15 at 11:05
You're welcome. However, I still don't think the covalent bond story is good. See e.g. here: ...This also explains why the ionization energy of F2 is less than that of an F atom... So it stays an F2 molecule but is ionized. You wouldn't count the anti-bonding electron states as covalent bond and those provide the electrons that are removed by ionization first. Highest energy goes first and that is most likely not the bonding electron pair. I hope I made my point clear. – mikuszefski Feb 19 '15 at 13:15
I also wonder: Considering the critical point in water, one cannot really distinguish between liquid and gas unless in a situation where both phases and an according phase boundary are present. So lets consider pure water for a second as gas. Here I can conduct electricity by swapping hydrogen bridges. So there is in ionization and actually the charge going in on one side has nothing to do with the one leaving on the other. Can one think of such a process in other gases? – mikuszefski Feb 19 '15 at 13:23
Yes, sorry for being so persistent. I think the new version is much better than before (I really had some problems with the covalent bonds). Cheers. – mikuszefski Feb 20 '15 at 13:03

Gases do conduct electricity, as all materials do. However, they conduct electricity so poorly that we consider them insulators. "Electricity" requires the movement of electrons. In a gas, these electrons are too dispersed to provided any measurable current. The "lightning" example is slightly different. This refers to capacitative discharge. When the two sides of a capacitor (i.e. the ground and the clouds) store too much charge, that charge eventually jumps the dielectric (i.e. the stuff in between the ground and clouds). We still don't say that the dielectric "conducts" electricity, although it obviously does. The best insulators in the world could not stop a discharge of sufficient strength. The defining quality of a conductor is that it conducts electricity "more easily" than most substances. There is no perfect conductor or perfect insulator. In short, gases can conduct electricity, but they are considered insulators for the most part.

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Gas on its own cannnot conduct electricity but it can be made to conductor electricity by subjecting it under LOW PRESSURE and HIGH VOLTAGE.

Gas can conduct electricity under two condition using a discharge tube; (1)low pressure (about ~0.01mmHg) (2)high voltage (>1000v)

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Should you perhaps combine this with your other answer, and expand it a little? Maybe explain why gases can't conduct electricity? – HDE 226868 Dec 6 '14 at 20:36

Carbon is the only gas, when solidified, that can conduct electricity. This is of the form Graphite, when it only has 3 bonds between the atoms. This leaves electrons to flow through the network structure.

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If it's solidified, it's no longer a gas, is it? And once solidified, all metals conduct electricity so carbon certainly is not the exception. – MSalters Feb 19 '15 at 10:20

protected by dmckee Feb 20 '15 at 21:33

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