You are right John, water vapor is already lighter than air. I wonder how I missed this point in the first place
The idea started in my mind to explain why the ocean/sea water is salty and specifically with NaCl.
Na and Cl are very special substances.
Na is a very light metal that cannot stay free in nature.
Cl is a rather heavy gas and also cannot stay free in nature.
Salty water is much easier to be decomposed than pure water.
In any case, an external energy is needed to decompose water.
Even a burning piece of coal can decompose water if immersed into it.
Usually ocean/sea water is continuously agitated. On the surface, we can easily notice in daylight bright spots like coming from tiny mirrors.
Finally, and perhaps I am imagining things, the random agitation of the water surface may form brief small concave mirrors and their focus could hit just a few molecules of NaCl ions and produce Na and Cl. But since Na is very light and Cl is heavy, they can quickly recombine at the surface while releasing H2 and O2 in the air.
What made me believe that this may occur is that O2 density over the oceans and seas are a bit higher than over lands. Obviously there might be other reasons for this phenomenon to exist but I was pleased thinking about the H2/O2 one to justify the huge salty water on our globe :-D
Kerim