Mushroom clouds. Glowing test tubes. Superheroes awakening. The rare elements at the bottom of the periodic table often bring to mind these kinds of pop culture images.
However, Thomas Albrecht-Schmitt, a chemistry professor and Director of the Department of Energy’s Center for Actinide Science & Technology at Florida State University, who studies these elements, says the truth of this part of the periodic table outstrips the fiction. These elements “are so complex and mystifying that we do not need to invent fanciful tales to remain a captive audience,” he says. Albrecht-Schmitt explains this perspective as the Guest Editor of “Actinide Chemistry at the Extreme,” a Virtual Issue from Inorganic Chemistry, which complies important basic and applied research on the actinides from a collection of recently published papers.
Actinides, as superheavy elements, are all firmly in the relativistic regime, Albrecht-Schmitt explains. Their inner electrons move at significant fractions of the speed of light, with increases in their effective mass of about 40%. This trait leads to pronounced differences in their properties, relative to other elements: “Actinides lie in an extreme realm where simple concepts concerning the nature of chemical bonds break down and where Occam’s razor—the philosophical approach that the simplest solution tends to be the correct one—leads to failure. Thus, our ability to use periodic trends as a predictive tool tend to unravel as we traverse the series from actinium to lawrencium.”
This Virtual Issue on actinide chemistry comes during a resurgence in the field. Twenty years ago, only a few f-block chemists remained of those who sought to understand and tame radioactivity during the period just before, during, and after World War II. Many nations had lost all of their actinide chemists, with no youth rising through the ranks, Albrecht-Schmitt says. But the field is no longer atrophying, he points out. Chemists are once again showing an interest in the field, due in part to its relevance to today’s needs in national security, energy production, and mitigating the environmental effects of Cold War nuclear weapons development and testing—as well as accidents such as Chernobyl and Fukushima.
New experimental ideas are being coupled with high-energy government research centers, characterization tools, and advances in theory, Albrecht-Schmitt says. These developments are allowing researchers to demonstrate that these elements are not humdrum metals with uninteresting chemistry and properties, but rather quite the opposite, going beyond traditional nuclear themes to include roles in catalysis, as luminescent probes, and as radiopharmaceuticals. “Now we understand that actinide elements display a vast array of structures, bonding, reactivity, and physical properties that we were seemingly unaware of before.”