Breaking the rules: Heavy chemical elements alter theory of quantum mechanics

October 3, 2017 by Kathleen Haughney, Florida State University
Thomas Albrecht-Schmitt is the Gregory R. Choppin Professor of Chemistry at Florida State University. Credit: Bill Lax/FSU Photography Services

A series of complicated experiments involving one of the least understood elements of the Periodic Table has turned some long-held tenets of the scientific world upside down.

Florida State University researchers found that the of does not adequately explain how the heaviest and rarest elements found at the end of the table function. Instead, another well-known scientific theory—Albert Einstein's famous Theory of Relativity—helps govern the behavior of the last 21 elements of the Periodic Table.

This new research is published in the Journal of the American Chemical Society.

Quantum mechanics are essentially the rules that govern how atoms behave and fully explain the chemical behavior of most of the elements on the table. But, Thomas Albrecht-Schmitt, the Gregory R. Choppin Professor of Chemistry at FSU, found that these rules are somewhat overridden by Einstein's Theory of Relativity when it comes to the heavier, lesser known elements of the Periodic Table.

"It's almost like being in an alternate universe because you're seeing chemistry you simply don't see in everyday elements," Albrecht-Schmitt said.

The study, which took more than three years to complete, involved the berkelium, or Bk on the Periodic Table. Through experiments involving almost two dozen researchers across the FSU campus and the FSU-headquartered National High Magnetic Field Laboratory, Albrecht-Schmitt made compounds out of berkelium that started exhibiting unusual chemistry.

They weren't following the normal rules of quantum mechanics.

Specifically, electrons were not arranging themselves around the berkelium atoms the way that they organize around lighter elements like oxygen, zinc or silver. Typically, scientists would expect to see electrons line up so that they all face the same direction. This controls how iron acts as a magnet, for instance.

However, these simple rules do not apply when it comes to elements from berkelium and beyond because some of the electrons line up opposite of the way scientists have long predicted.

Albrecht-Schmitt and his team realized that Einstein's Theory of Relativity actually explained what they saw in the berkelium compounds. Under the Theory of Relativity, the faster anything with mass moves, the heavier it gets.

Because the nucleus of these heavy atoms is highly charged, the electrons start to move at significant fractions of the speed of light. This causes them to become heavier than normal, and the rules that typically apply to electron behavior start to break down.

Albrecht-Schmitt said it was "exhilarating" when he and his team began to observe the chemistry.

"When you see this interesting phenomenon, you start asking yourself all these questions like how can you make it stronger or shut it down," Albrecht-Schmitt said. "A few years ago, no one even thought you could make a berkelium compound."

Berkelium has been mostly used to help scientists synthesize new elements such as element 117 Tennessine, which was added to the table last year. But little has been done to understand what the element—or several of its neighbors on the tables—alone can do and how it functions.

The Department of Energy gave Albrecht-Schmitt 13 milligrams of berkelium, roughly 1,000 times more than anyone else has used for major research studies. To do these experiments, he and his team had to move exceptionally fast. The element reduces to half the amount in 320 days, at which point it is not stable enough experiments.

Explore further: Chemists explore outer regions of periodic table

More information: Mark A. Silver et al. Electronic Structure and Properties of Berkelium Iodates, Journal of the American Chemical Society (2017). DOI: 10.1021/jacs.7b05569

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Jim4321
5 / 5 (2) Oct 04, 2017
This is very provocatively titled. Are they saying that relativistic quantum mechanics is unable to account for the chemistry -- this would be a breakthrough of immense importance. Or are they saying that ordinary nonrelativistic quantum chemistry is unable to account for what they saw?
Nik_2213
not rated yet Oct 04, 2017
Wasn't this invoked some years ago to explain some of the 'bizarre' properties of gold & lead, among others ??

Would you get the same effect by replacing inner electrons of 'lighter' elements with muons ??
physman
5 / 5 (1) Oct 04, 2017
@Jim4321 I think they're saying that for lighter atoms they use "simplified" quantum mechanics only models with good predictive power. However, these models become insufficient for heavier atoms because the mass component of the nucleus is no longer neglibile - leading to non-negligible relativistic effects.

"Because the nucleus of these heavy atoms is highly charged, the electrons start to move at significant fractions of the speed of light. This causes them to become heavier than normal, and the rules that typically apply to electron behavior start to break down."

This is an interesting article: https://eic.rsc.o....article
Da Schneib
not rated yet Oct 04, 2017
@physman and @Jim, I think it's not the mass of the nucleus, but the masses of the electrons, and I think the reason the electrons get mass is because they go so fast because of the high charge on the nucleus, not its mass. So the relativistic effects are on the electrons, not on the nucleus. But other than that I think @physman got it right.
Jim4321
5 / 5 (1) Oct 04, 2017
physman and da schneib -- thank you. But relativistic effects have been included in ab initio atomic energy calculations for at least 20 years. So what is really new -- just that the chemistry follows unexpected empirical rules because of the relativistic effects?. Or does the self-consistent field approach of Density Functional Theory fail? You would think self-consistent field together with the Dirac Equation would probably be enough to get the right answers.
Da Schneib
not rated yet Oct 04, 2017
@Jim, sounds like you're ahead of me just knowing DFT. I'll poke around and see if I can find anything out but I won't be surprised if you already knew it.
Da Schneib
not rated yet Oct 04, 2017
From what I've seen so far I think maybe the relativistic effects included in DFT didn't account for relativistic mass gain of electrons. But you'll have to judge. I'll have to let this all soak in a while.

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