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xkcd #3200: Chemical Formula
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Title text:
Some of the atoms in the molecule are very weakly bound.
Transcript:
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Source: https://xkcd.com/3200/
There are exotic atoms in that chemical formula that aren't in the periodic table. Not even if you count the equivalent table of potential antimatter atoms.
Muonium is sure to exist in non-zero quantities at any one time, for example.
That's just impurities
"Approximate chemical formula"