Elements of mystery

The international hunt for chemistry’s ‘missing links’ makes for an engrossing tale, finds Alan Rocke

August 15, 2013

In 1789, a year marked by scientific as well as political revolution, the great French chemist Antoine Lavoisier proposed the first list of chemical elements in the modern sense. He would lose his head in the Reign of Terror five years later, but his list of 33 “simple substances” survived. The race for new discoveries was on: by 1860, about five dozen elements were recognised. In 1869 Dmitri Mendeleev systematised this increasingly chaotic menagerie into his periodic table of the elements. From then on, chemists had at least a rough idea where to look to fill the holes in Mendeleev’s tableau.

The periodic table of the late 19th century was organised according to increasing atomic weights, a good but (as it turned out) imperfect principle. Shortly before the Great War erupted, a young English physicist named Henry Moseley developed an instrumental means that could provide an unambiguous ordinal scale for the elements, soon to be called “atomic number”. Moseley was killed in action in 1915, but others using his method quickly deduced that there were exactly seven mysteriously “missing” elements that formed random gaps in the table, between the lightest, hydrogen (number 1), and what was then the heaviest known, uranium (number 92). Their modern names are protactinium, hafnium, rhenium, technetium, francium, astatine and promethium. A highly competitive international hunt uncovered them all over the course of the interwar period and the Second World War.

Eric Scerri offers us a fascinating account of the discovery of these seven elements. Author of The Periodic Table: Its Story and Its Significance (2007), Scerri is superbly qualified for this task: chemist, philosopher of science and historian, he is the foremost contemporary analyst of the periodic table. The cast of his engrossing tale includes dozens of scientists in many countries, avidly pursuing these last remaining prizes in the classic table of the elements. Scerri organises the story in the most logical way, element by element. Each chapter recounts the history of the discovery, the frequent false leads and mistaken claims, and the personal stories of rivalry and collaboration; each concludes with a contemporary update on the science and technological applications of the element.

There are many intriguing, surprising and often ironic commonalities in these stories. One expected theme is the sometimes heated quarrels over legitimacy and priority of discovery; in the hyper-nationalistic interwar period it is unsurprising that hafnium was named after Copenhagen, rhenium after the German Rhine, and francium after – well, you know. Less expected is the gratifying number of women in the list of protagonists: the Austrian Lise Meitner, the German Ida Noddack, and the Frenchwomen Marie Curie, her daughter Irène Joliot-Curie and her former student Marguerite Perey. Another surprise is the truly astonishing number of claims of discovery subsequently shown to be erroneous. Tom Lehrer could have a field day composing an additional verse of his song The Elements with the mythical substances alabamium, brevium, davyum, canadium, celtium, helvetium, ilinium, moseleyum, nipponium, pluranium and uralium.

As a professional historian of chemistry who thought that he already knew these stories, I was surprised by how much novel and interesting material Scerri has unearthed in this admirable book. He offers corrections to many long-standing textbook errors, both historical and scientific, and presents a fresh, thoroughly researched understanding of a complex web of interacting research during a period of about 30 years. It is a shame that the book is marred by an unfortunate number of typographical and editing slips, some of them more than trivial – the fault of Oxford University Press’ editorial production, not Scerri’s scholarship. That said, chemists, historians and philosophers of science, as well as educated laypeople, will unquestionably find this book an entertaining and highly instructive read.

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