[TeMPOraL]

And isotopes. And transient, unstable configurations that may exist for a brief moment before decaying into something that slots into the periodic table better.

And also elements aren't a thing, quantum fields are. This is why you sometimes see things that just don't fit the idea of distinct atoms. But then quantum fields also aren't a thing. We don't know what exactly is the thing. We only have increasingly sophisticated working models.

[rini17]

No need to go to such philosophical depths. We're only poor engineers trying to come up with workable model. The periodical table of elements was a true boon and it is unlikely these "foreign keys" will change, but still - it alone isn't fully suitable as data model for chemistry.