[ifyoubuildit]

I appreciate all that, but I think I might not have been clear with my question.

If our understanding is complete (in other words there is nothing else to know about flourine) then not having a known mechanism of action would be a good proof. But when is our understanding ever complete about anything?

It seems a lot easier to know things like "in the presence of x, fluorine does y" because you can easily observe that isolated thing under test. It's harder to know "fluorine does not do x in any circumstance" because the tests for that are infinite. How do we know we just haven't tested the right case yet?

Again, I'm a layman, so I can only try to logic my way through this. I acknowledge that it may be a dumb question.