A Tale of Seven Elements

We Are Seven

Quickly, what are technetium, promethium, hafnium, rhenium, astatine, francium, and protactinium? What do they have in common? Eric Scerri provides answers to these questions and many others in his recent book, "A Tale of Seven Elements" (2013). Dr. Scerri teaches chemistry at UCLA and specializes in the history and philosophy of science. Besides engaging in his own technical research, Scerri has written several books explaining difficult and important scientific principles to non-specialist readers. He has written two introductory studies of the periodic table, "The Periodic Table: Its Story and Its Significance", and "The Periodic Table: A Very Short Introduction" in addition to this new, more narrowly focused book.

Scerri's book discusses seven chemical elements, named above. But why, precisely, these seven and not others? Why not more familiar elements such as oxygen, carbon, gold, and more? And why not five elements, or eight? As the book unfolds, Scerri develops the reasons for the focus. Understanding the background for the choice of the seven elements is at least as important to this book as is the individual treatments of each.

After an extended introduction on the nature of science and scientific discovery, Scerri offers two background chapters on the historical development of chemistry. These chapters are critical to understanding the discussions of the seven elements that follows. Broadly speaking, in the late 1860s, Dimitri Mendeleev formulated what is essentially the modern periodic table and the periodic law. Then, in the early years of the 20th Century, a number of scientists did a great deal of revolutionary work in studying x-rays, radioactivity, modern atomic theory, and quantum physics. In 1913 -- 1914, a young scientist, Henry Mosely, synthesized the current knowledge to conclude that the chemical elements could be ordered by atomic number in a sequence that at the time ran from 1 .... 92. Prior to Mosely's discovery, the elements were ordered by atomic weight which resulted in some confusions and inaccuracies. Mosely developed a technique for ordering the elements which soon showed that seven elements were missing from the traditional periodic table which ends with uranium, element 92. These elements had atomic numbers 43,61,72,75,85,87,91 -- the seven elements with which this review began, listed in ascending numerical order.

In successive chapters, Scerri tells the story of the discovery of each of these elements and of their basic chemical and physical properties. He discusses the elements in the order of their discovery with each chapter beginning with a diagram of the periodic table with the element in question highlighted for a frame of reference. Scerri does indeed tell stories. He is interested in the historical, social element that led to the discovery of each element. After Mosley's findings became known, scientists competed with one another to discover the "missing links" in the periodic table. Scerri discusses these efforts for each of the elements and the differing techniques they used. Some scientists worked slowly and carefully, while other seemed to opt for flash-in-the pan approaches and, in a small number of cases, for an ethically questionable manipulation of data. Luck invariably also played a role in both the successes and the failures. Scerri focuses in particular on elements of nationalism among the competing scientists as most of the research on these seven elements took place during the WW I -- WW II years. Scerri uses substantial source material which shows the scientists and their respective supporters frequently arguing with each other about the merits of the research and about priorities in discovery. Scerri puts a human, halting face on the nature of scientific progress.

With all the emphasis on history and story, the discussion of the seven elements was the most interesting part of the book. Scerri develops the similarities and differences among the seven and tries to account for the properties of each element by the physical and chemical principles he develops beginning in the book's earlier chapters. He shows why each of the elements was rare and difficult of discovery. Of the seven elements, four are radioactive and inherently unstable. Two of the elements were discovered through synthesis rather than in nature. Of the seven elements, six bear odd atomic numbers, explaining their instability. With each element, Scerri shows the unsuccessful attempts at discovery and explains why these attempts failed while other succeeded. The discussion of the chemical and physical properties of the elements frequently is difficult for a lay reader such as myself. But with careful reading, I thought I increased my understanding of what chemistry was about.

Of the seven elements, Scerri seems most fascinated by no. 72, hafnium. The discovery of this element became intertwined with the earlier discovery of elements 70 and 71 as competing researches thought that element 72 would fit into different groups of elements. The ultimate discovery of the element owed a great deal to quantum physics leading some researchers to conclude that chemical properties ultimately were reducible to physical properties. In a section captioned "The Role of Hafnium in Philosophy of Chemistry", Scerri discusses this issue and concludes that the reducibility of chemical to physical properties has not yet been scientifically established.

Scerri has written a fascinating book about science, discovery, and philosophy of science that requires substantial effort to read. Scerri emphasizes historic and cultural and quirky factors influencing scientific research. Scerri, however, is neither a relativist nor a skeptic. Early in the book, he writes:

"Whereas theories and concepts that appear in textbooks are presented as being fully formed, real science is in a constant state of flux. When science is reported in the press, one seldom hears of the errors that led up to a discovery. In fact, actual science is full of mistakes and wrong turns. We don't ever reach the 'truth'. The best we can hope for is an approach to the truth, perhaps in an incremental fashion, meaning that current science is necessarily incorrect."

What comes through strongest in this book is the seriousness of the search for knowledge and understanding that manages to factor out to a degree competitiveness, human frailty, nationalism, and error. Science reaches results that form approximations to what is real through the processes of shared, disciplined inquiry.

I am grateful to OUP and to the author for the opportunity to read and review this book.

Robin Friedman