Take the 2-minute tour ×
Chemistry Stack Exchange is a question and answer site for scientists, academics, teachers and students. It's 100% free, no registration required.

I knew while learning about electrolysis that if the ionic compound is molten it becomes free moving ions.

If that is the case, what will happen if I continued heating till it reaches the boiling point so that the ionic compound evaporates?

Will it still be free moving ions?

Also, shouldn't the result be more efficient at electrolysis than in the liquid state due to increased mobility of ions? If not, why?

share|improve this question
The phase you describe is a plasma. –  Horba Nov 7 '12 at 12:07
I've incorporated your newer question into this one, they are nearly asking the same thing. –  ManishEarth Nov 19 '12 at 7:13

4 Answers 4

up vote 14 down vote accepted

Usually not. Boiling point rarely exceeds 4-5 thousands kelvin. A typical ionic bound energy is about 5 eV. 1 eV is roughly 11 thousands kelvin, so ions in low-temperature vapors are in molecules. When temperature becomes enough to break ionic molecules, it is enough to strip one-two electrons from atoms, so hight-temperature vapors will be plasma with electrons and positive ions.

share|improve this answer

I believe that gaseous ionic compounds such as NaCl are in fact diatomic NaCl. One can't create a plasma by simply boiling ordinary compounds. The forces between ions are way too strong.

share|improve this answer

To complete the previous answers: according to this article http://www.ncbi.nlm.nih.gov/pubmed/17579381 NaCl exists in the gas phase both as a monomer (NaCl), about 73% of atoms at 943K, and as a dimer where the four atoms are arranged in a wobbly square (the remaining 27%). Traces of Na${}_2$ and Cl${}_2$ are also observed. I expect that as the temperature goes up the proportion of the dimer drops, and that eventually, at a few thousand K, atomic Na and Cl predominate.

Since the boiling point of NaCl is 1,686 K at 1atm the study must have been conducted at low pressure or with the NaCl vapor mixed in with other gases.

The article also says (GED = gas-phase electron diffraction) :

The determination of the structure of sodium chloride vapor by GED dates back as far as 1937, when it was studied by heating salt to around 1000 K. As a consequence of the visual analysis methods in use at the time, only the predominant and expected monomer species was detected. It was not until the 1950s that the existence of associated species such as dimers (Na2Cl2) were discovered using mass spectrometry. Microwave spectroscopy has provided detailed information on the structure of the monomer, but the lack of a permanent dipole moment makes this impossible for the dimer.

share|improve this answer

In liquid state, NaCl become free moving ions but the overall system is stable because of the attractions between the oppositely charged ions. I believe that gaseous NaCl would exists as very polar covalent or ionic molecules with their overall affect being electrically neutral (no plasma).

This is a purely intuited answer and should be taken with a grain of salt as I could find no numbers to back it up. If someone could change this into a comment for me I would be much obliged.

share|improve this answer
It is actually individual Na+Cl- units in the liquid and gas states. What you are thinking of is dissolved NaCl and that would be Na+ and Cl- separate and thus free sodium and chloride ions. –  caters Aug 14 '14 at 4:43

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.