There's a fundamental asymmetry which isn't always recognised here.
It's meaningless (or maybe just lazy) to ask markjo or Geoff (or whoever it was) what their atoms look like. Scepti, you have your own atoms, your own pressure, your own gravity, your own light, your own table of elements (nesting doll of elements?) and so on. But the outsiders here don't, we all subscribe to what has been demonstrated and what gets used in practical engineering. This isn't a philosophical debate between your atoms and his atoms. This is the weight of all human knowledge (which you can either be bothered to look up or you can't) being challenged by your intuition and gut feeling that "there can't be such thing as empty space" because you're pretty certain that there can't.
tldr: if you want to know what 'markjo's atoms' are, google it.
They exist everywhere and have been studied by everyone. They aren't only in his head. So while we do need to ask you specifically about your gas (or whatever), if you want to know about 'ours', you can always just look it up.