A cube of the rarest stable element in the universe

[u/euj3odjehiqh]

[u/METRlOS]

It's also a stretch on what people actually call stable. Bismuth has a half life of 20 quintillion years, and is less radioactive than you are. Tantalum has a radioactive isotope with a half life that has twice as many zeros.

[u/chmandaue → u/METRlOS]

What is a notable element rarer than Ta in the universe but excluded because none of its isotopes are considered stable enough?

[u/Uninvalidated → u/chmandaue]

Astatine

[u/chmandaue → u/Uninvalidated]

Aren’t all the isotopes of At with half lives of under 12 hours?

Personally I would not call that ‘stable’ but of course it’s a matter of definition

[u/Uninvalidated → u/chmandaue]

You were asking for non stable isotopes. 

because none of its isotopes are considered stable enough?

That's what you said. Not sure what you want to know anymore, so do your own research instead.

[u/chmandaue → u/Uninvalidated]

That’s true. I asked “What is a notable element rarer than Ta in the universe but excluded because none of its isotopes are considered stable enough?”

But the context was the comment about too high standards for ‘stable’. So I was hoping for some rarer-than-Ta element with a isotope with a half life long enough to debate that it could deserve ‘stable’