Re: heated metal fluorides vs metal chlorides

Question NaCl=orange, KCl=purple, LiCl=red. What if fluorides were used 
rather than chlorides? Do they have a visible emission?

Cheryl, thanks for your question.  If I make one assumption, namely that 
when you say “heated” you really mean very hot, for example in a flame, 
the answer is simple.  This is because the colours your see are 
characteristic of the metals not the salts.  In a flame, the metal ions 
and halides introduced into the flame form part of the mixture of 
unionized and ionized molecules and atoms.  The colours are produced by 
visible light emissions due to electrons in the metal ions and atoms 
moving from higher energy levels to lower ones by ejection of photons.  
The colours introduced by the metal salts depend on the metals because the 
colours are due to the metals themselves. Whether the metal ions were 
originally associated with chloride ions or fluorides or anything else is 
not important.

So the straight answer to your question is … Yes, they have visible 
emissions, and the fluorides will have substantially the same emissions as 
chlorides.  There may be some differences in the visible emissions due the 
halides themselves but my guess is that this would not be significant.

For more on flames and plasmas you could look up another of my Madsci 
answers by searching using “Gareth” and “Plasma”.

I hope my assumption was right !  

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Admin note: although the fluorides will produce exactly the same colours as chlorides, you might not 
see any colours at all. It takes a much hotter flame to turn the fluorides into gas, and then plasma, 
than it does for chlorides. Putting fluorides in a very hot flame also produces extremely 
poisonous vapours. John C.