The long debate over adding ununbium to the periodic table of the elements.

The state of the universe.
June 12 2009 3:59 PM

Periodic Discussions

Element 112 was discovered more than a decade ago. Why wasn't it given a place on the periodic table until now?

Ununbium. Click image to expand.
Ununbium in the extended periodic table

The periodic table added its 112th official element Wednesday, when scientists in Darmstadt, Germany, announced they had received official approval for ununbium from an international body of chemists. But the discovery of the new element wasn't news to anyone—it was first announced back in 1996, when the Darmstadt scientists claimed to have created two atoms of the stuff in a 400-foot particle accelerator. It's just taken 13 years of formal reviews and appeals for their colleagues around the world to believe them. How did the most basic question of science— what are the fundamental materials that make up our universe?—turn into the science equivalent of a Supreme Court decision?

It seems as if the makeup of the periodic table would be as rudimentary as apples falling down, not up. There's evidence for elements like oxygen, iron, and silicon all around. Heck, you're made of evidence. But that's not true for the dimmer corridors of the table that run along its very bottom, where elements like ununbium sit. No one has ever seen element 112 with their own eyes—we've only assumed its existence based on a smattering of computer blips stored on a couple of hard drives around the world. How to interpret those blips has become a matter for endless committee meetings and debates over whether it's OK to add a new square to the most precious real estate in science.

It wasn't always that way. In the old days, scientists got visible, earthy samples of new elements by sifting through exotic minerals. Marie and Pierre Curie boiled down a few thousand pounds of uranium ore to isolate a few grams of polonium and radium—the latter of which happened to glow in the dark. By 1940, scientists had exhausted all of nature's easily accessible elements. From then on, they would extend the periodic table only by creating elements—by hurling bits of matter at heavy-element targets. If they stuck—if the nuclei of the smaller bits fused with the nuclei of the targets—they'd have a new, extra-heavy element to add to the list.

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But it's not easy to tell when you've created a new element by these means—three-quarters of all elements are gray metals, after all. So to confirm they'd discovered something new, scientists studied its radioactivity. All heavy elements are unstable, and their nuclei spew atomic shrapnel as they decay. Since each one breaks apart in its own unique way, scientists can spot brand-new heavy elements by looking for novel radioactive signatures in their data. Chemists could later double-check the discovery by creating (often after years of work) a larger sample of the potential element that might be quickly washed in chemicals to see whether it reacted like its prospective neighbors on the periodic table. Confirming the presence of berkelium, for example, can be as easy as watching a vial of the element turn yellow-orange in a chemical bath.

That method allowed us to authenticate elements up to an atomic number of around 107 or 108. But elements even heavier than that fall apart too quickly to allow the chemists to do their work. It's still possible to use radioactivity data, but the further down the periodic table you push, the less reliable that method gets, too: When you're only dealing with one or two atoms of the new element, and when each was created months or even years apart during messy shoot-and-scatter experiments, it's almost impossible to separate the signal from the noise using traditional methods.

Scientists now must search for the faint traces of new elements using a combination of old-fashioned physical detection and new-fangled computer filtering. And instead of looking only for an atom of the new element, they trace the "daughter products" of radioactive decay. When element 112 decayed, it turned into element 110 (darmstadtium), which in turn decayed to element 108 (hassium), and so on. Each step in the process leaves its own signature, and the chain can be reconstructed to guess what the original product must have been. The computer software has to sort through reams of spurious data and determine the probability that a promising signal might be true.

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