inorganic chemistry – Will gaseous ionic compounds be free moving ions?

The Question :

25 people think this question is useful

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?

The Question Comments :
  • The phase you describe is a plasma.
  • I’ve incorporated your newer question into this one, they are nearly asking the same thing.

The Answer 1

23 people think this answer is useful

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

The Answer 2

11 people think this answer is useful

To complete the previous answers: according to this article 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.

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.

The Answer 3

9 people think this answer is useful

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.

The Answer 4

3 people think this answer is useful

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.

Add a Comment