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Yesterday I asked a question at Chemistry SE, which is if the molten NaCl molecules have enough energy to break into free moving ions, won't be the Na Cl vapor contain free moving ions? So, I've got this answer telling me that that's what we call plasma. But after reading about plasma, I've read that "plasma is a gas which received enough energy to be ionized so ions and electrons can coexist ". In my question there will be ionization, but this ionization will take place when the ionic compound is melting breaking down to positive and negative ions not positive ions and electrons. So basically I need to know if Na Cl vapor is ionized "into positive and negative ions" or it will turn to plasma.

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2 Answers 2

up vote 6 down vote accepted

You're presumably thinking that vaporised NaCl would consist of Na$^+$ and Cl$^-$ ions, but this isn't what you get. At temperatures just above the boiling point (1413c) you get neutral NaCl molecules and Na$_2$Cl$_2$ dimers, and possibly bigger polymers. Amazingly someone has measured this: see this paper for details (it's behind a paywall I'm afraid but you can see the abstract).

So the answer is no, the vapour is not a plasma. You'd have to heat it to much higher than the boiling point to get a plasma.

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It may sound strange, but Sodium Chloride exists as a molecule in vapourosed form. It is the only ionic compound in this world that exhibits this strange property.

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Wouldn't most salts behave this way? –  Kevin Kostlan Aug 30 '13 at 12:09

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