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The Disappearing Actinides, and Other Frustrations from the Bottom Row of the Periodic Table of the Elements


I bought three copies of Sam Kean’s The Disappearing Spoon: And Other True Tales of Madness, Love and the History of the World from the Periodic Table of the Elements. I left the first one in the seat-back pocket of Delta flight 188 from Beijing to Detroit. The second one is sandwiched between ROCK and GEM and The Poisoner’s Handbook on an end table in my living room. The third is a Kindle edition that I purchased so that I could quickly search the text.

When I started reading my first copy of The Disappearing Spoon at 2 am local time in a Beijing hotel room, I was fascinated. I followed Kean readily into the introduction, beginning what I could only imagine would be a tantalizing journey through the periodic table.

I signed on for the prerequisite section ORIENTATION: COLUMN BY COLUMN, ROW BY ROW. We thought back to our first encounters with the periodic table, commiserated about high school exams, and pictured the blank table as a castle. We quickly moved on through our tour—mercury, bromine, top to bottom, east to west, periodic trends! And then, the F-shell elements! Lanthanides, lanthanides, lanthanides, atomic structure, Goeppert-Mayer, the end?! Where are the actinides, my beloved actinides?

It’s ok, I thought, it’s cool. A small oversight. I’m sure he’ll mention the actinides in the text. He must, I mean, really, how can you write about elemental hard-hitters like Marie Curie and Glenn Seaborg without mentioning the actinides? Kean will undoubtedly affirm the four years that I’ve spent in graduate school double-gloving over plastic sleeves, wearing a dosimeter, and stepping onto a hand-and-foot monitor for the sake of better understanding those pesky actinides, right?!

Wrong. Rather than acknowledge the actinides as an independent collection of elements with intriguing properties that have been used to do very big things although they are very much still full of mystery, Kean lumps them together with the lanthanides. He uses the word “actinide” exactly twice, but it is only used in conjunction with the word “lanthanide” when pointing out the two rows at the bottom of the periodic table. Sure, he briefly mentions individual actinide elements—thorium, uranium, and plutonium mostly—in later chapters with some assessment of how they were discovered and how they’ve been used, but he never even dips his toes into the still relatively uncharted waters of the bottom row.

Maybe, though, it’s not his fault.

According to Thomas Albrecht-Schmitt, a professor at the University of Notre Dame who teaches a graduate level course on the chemistry of lanthanides and actinides, the treatment of the actinide elements in The Disappearing Spoon is comparable to the level of recognition that they receive in introductory level college chemistry courses.

“[Kean’s] book is symptomatic of how we educate people, even a chemistry major,” says Albrecht-Schmitt. “In a freshman chemistry course sequence, students learn nothing about actinides, and all they are told about lanthanides is that they are similar to one another.”

In light of worldwide emphasis on the future of energy, crippling incidents like Fukushima, and policies that leave the U.S. wondering what to do with decades worth of waste, the lack of attention given to the bottom row of the periodic table is a bit troubling.

“It’s mind-boggling,” says Albrecht-Schmitt, “that nearly 20 percent of the world’s energy is generated by uranium, but we don’t teach anything about uranium in freshman chemistry.”

The Reappearing Actinides: An Introduction

The modern study of actinides began more than 70 years ago reaching a climax during the Manhattan Project. In that time, they’ve played a vital role in weapons development, nuclear energy, and space exploration.

The most basic definition of the actinide series, comprised of elements 89 through 103, is that it results from the sequential filling of the 5f electron shell. All fifteen elements in the series are radioactive and have half-lives ranging from fractions of seconds to billions of years.

The radioactivity of the actinide elements is caused by their nuclear instability. In order to become more stable, the nucleus of an actinide element undergoes radioactive decay, releasing gamma rays, alpha particles, beta particles, or neutrons. This process of decay produces new daughter elements, which may be stable or radioactive. For example, the transformation of U-235 used in nuclear reactors results in the formation of radioactive, long-lived Np-237 through a process of neutron capture, gamma emission, and beta decay.

Understanding what may seem like the tiniest details about the actinides has important implications for environmental remediation of radioactive contaminants. Unlike the lanthanides, which occur primarily in the +3 oxidation state, the actinides generally have a large range of oxidation states—from +3 to +7. This becomes the most important distinction, a reason why the actinides must be studied independently of the lanthanides, in consideration of the environmental mobility of actinides.

If you would like to know more about what’s happening on the bottom row of the periodic table, check out recent research highlighted in Actinide Research Quarterly, a publication of the G. T. Seaborg Institute for Transactinium Science.

The views expressed are those of the author and are not necessarily those of Scientific American.

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