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As the Chase For New Elements Slows, Scientists Focus on Deepening Their Understanding of the Superheavy Ones They Already Know (nature.com)
From a report: The quest to extend the periodic table is not over, but it is grinding to a halt. Since Russian chemist Dmitri Mendeleev published his periodic table 150 years ago, researchers have been adding elements to it at the average rate of one every two or three years. Having found all the elements that are stable enough to persist naturally, researchers started to create their own, and are now up to element 118, oganesson. Although they still hope to find more, they agree that prospects of venturing beyond element 120 are dim.
"We're reaching the area of diminishing returns in the synthesis of new elements, at least with our current level of technology," says Jacklyn Gates, who works on heavy-element chemistry at the Lawrence Berkeley National Laboratory in California. As a result, research on the edge of the periodic table is shifting focus. Rather than chasing new elements, scientists are going back to deepen their understanding of the superheavy ones -- roughly speaking, those with an atomic number above 100 -- that they have already made.
Studying the chemical properties of these elements could show whether the most massive ones obey the organizing principle of the table -- which sorts elements into groups with similar behaviours on the basis of periodically recurring patterns of chemical reactivity. And although the heaviest elements decay in less than the blink of an eye, researchers still hope that they might arrive at the fabled 'island of stability': a hypothesized region of element-land where some superheavy isotopes -- atoms that have the same number of protons in their nucleus, but differing numbers of neutrons -- might exist for minutes, days or even longer.
"We're reaching the area of diminishing returns in the synthesis of new elements, at least with our current level of technology," says Jacklyn Gates, who works on heavy-element chemistry at the Lawrence Berkeley National Laboratory in California. As a result, research on the edge of the periodic table is shifting focus. Rather than chasing new elements, scientists are going back to deepen their understanding of the superheavy ones -- roughly speaking, those with an atomic number above 100 -- that they have already made.
Studying the chemical properties of these elements could show whether the most massive ones obey the organizing principle of the table -- which sorts elements into groups with similar behaviours on the basis of periodically recurring patterns of chemical reactivity. And although the heaviest elements decay in less than the blink of an eye, researchers still hope that they might arrive at the fabled 'island of stability': a hypothesized region of element-land where some superheavy isotopes -- atoms that have the same number of protons in their nucleus, but differing numbers of neutrons -- might exist for minutes, days or even longer.
Basically it's mainly a quantum effect that makes larger nuclei unstable, specifically the Pauli-Exclusion-Principle. It's the same thing that hinders the electrons of an atom to all go to the lowest possible energetic state. They have to occupy different "orbitals", which pushes electrons to successively higher energy levels if they'd be added one at a time to a nucleus to form an atom.
The same happens to neutrons and protons in an atom core, and it's the reason why it isn't possible to just add an arbitrary number of neutrons to any atom core (they wouldn't be repelled due to electric forces and just "bond" with strong forces to other nucleons, so their contribution to the binding energy should be positive).
In the "Semi-Empirical Mass Formula" this contribution is called (a)symmetry term:
https://en.wikipedia.org/wiki/...
This formula works quite well, and the asymmetry term (penalizing different numbers of protons and neutrons) is what hinders nuclei with arbitrary numbers of added neutrons to be stable. Without this contribution the model can't (approximately) reproduce what we find in nature, and any model of the nucleus needs some explanation for this. Somehow there must be some reason why that is so, and the best reason we found so far is the Pauli-Exclusion-Principle applied to nucleons, which is basically quantum mechanical.
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