Wall Street Journal,
October 21, 2013
Book Review: A Tale of Seven Elements
by Eric Scerri
How seven elusive elements that completed the periodic
table were found.

By
PETER PESIC
At some point, many of us have gazed in idle wonder at a periodic table hanging on a
classroom wall. Some elements are familiar, but many are mysterious, down to their
abbreviations. What is Pm? What color is Hf? Is Fr dangerous? And what does this iconic
chart mean, arranging the chemical elements into an arresting graphic design?
In the 1860s, various investigators noticed that, when put in order by weight, elements
fell into recurrent groups with similar properties, visualized in the famous table
independently introduced in that decade by Dmitri Mendeleev and Julius Lothar Meyer.
In 1913, the English physicist Henry Moseley showed that the number of charged units in
the elements' nuclei (which increases by equal steps—1, 2, 3 . . . ) is a better ordering
principle than atomic weight (which doesn't). This reshuffling revealed seven gaps,
corresponding to then-unknown elements. Filling them in over the following decades
completed the table from hydrogen (element 1) to uranium (92), the last element then
known to occur naturally. In "A Tale of Seven Elements," Eric Scerri, a chemist and
philosopher of science at UCLA, tells the stories of how these elements—technetium,
promethium, hafnium, rhenium, astatine, francium and protactinium—were discovered.
A Tale of Seven Elements
By Eric Scerri
Oxford, 270 pages, $19.95
They had been missed because they are unstable, rare or, in some cases, hardly found on
earth at all—present only as traces in huge volumes of stone or seawater. Mr. Scerri
observes, for example, that there is a total of 1 ounce of naturally occurring astatine on
earth. It is so radioactive that a sample large enough to be visible would immediately
vaporize from the heat of its own decay. Yet the data and interpretation stored in the
periodic table made the missing elements treasures waiting to be discovered and
suggested clues to their properties. (We can surmise that elemental astatine would be
even darker than the purple of iodine, the preceding element in its group.)
The searchers struggled with false alarms and inconclusive sightings, such as an Italian
team's 1924 claim to have found promethium, which turned out to be so radioactive that
isolating it only became technically possible in the 1940s. Then too, many of these
elements come in different isotopes, alternate forms of the same element with various
degrees of instability. "Discovery" meant finding and analyzing the longest-lived isotope.
Not surprisingly, many claims and counterclaims swirled around each element, often
involving national rivalries. Consider Masataka Ogawa's disputed 1908 claim to have
observed what his partisans named "nipponium" (element 75). It is now called rhenium,
after the Rhine, having been officially discovered in 1925 by the German couple Ida and
Walter Noddack. Though Mr. Scerri and others don't accept it, the Noddacks claimed
also to find number 43 (technetium), the first element to be artificially produced, by
Emilio Segrè in 1937. Rather than regarding these controversies as incidental
embarrassments, Mr. Scerri considers them an essential part of science itself, an aspect of
its competitive nature.
Mr. Scerri writes clearly and calmly, without the impulse to overdramatize that can mar
popular books about science. "A Tale of Seven Elements" brings forward several
interesting and lesser-known female protagonists, such as the French physicist
Marguerite Perey, who discovered element 87 (francium) in 1939, though she didn't yet
have an undergraduate degree and wouldn't receive her doctorate until 1949. Like her
mentor, Marie Curie, Perey died early as a result of her work with radioactive materials
when their dangers weren't fully known.
Throughout, Mr. Scerri provides astonishing details almost in passing. For instance, in
1972 anomalies in the ratio of uranium isotopes found in Oklo, Gabon, led to the
deduction that a self-sustaining nuclear chain reaction had occurred at that site naturally,
two billion years before Enrico Fermi and others accomplished this feat artificially in
1942. This natural chain reaction lasted somewhere between 600,000 and 1.5 million
years, presumably limited by the supply of nuclear "fuel." Further, the Oklo "reactor"
produced a number of telltale elements (such as technetium and promethium) that
otherwise would have been absent from the earth's crust. Though Mr. Scerri doesn't go
into it, one certainly wonders to what extent this extraordinary phenomenon affected the
history of the earth.
I was also amazed to learn from Mr. Scerri that gold's characteristic color comes from the
effect of relativity on the inner shells of its electrons. I hadn't imagined that gold's color
(so different from its periodic neighbors, platinum and mercury) owed so much to
relativistic effects, which tend to be associated with much higher-energy phenomena than
atomic structure. Yet without relativity, gold would look like silver.
This example highlights an underlying tension that Mr. Scerri calls the "invasion of the
periodic table by physics." He takes pride in the continued integrity of chemistry as an
autonomous realm of thought. Though he presents the quantum-mechanical
underpinnings of atomic structure, Mr. Scerri wants to disabuse some physicists of their
arrogant delusion that chemistry is only a grubby applied subsidiary of their master
science. He stresses that there remain persistent questions about the periodic table that
aren't neatly resolved by basic physics, such as whether the relativistic causes of gold's
color will reappear in the new synthetic elements past number 112.
Mr. Scerri's outstanding book helps us understand the special spirit of chemistry, whose
contribution to science and human experience emphasizes the crucible of experiment.
The days of discovery aren't over: Beyond uranium, two dozen more elements have been
produced artificially. Mr. Scerri notes that chemists have no secure consensus about how
many elements are possible: Some say 137; others 173. The periodic table, as imposing
as it looks, is still a work in progress. What further surprises might it disclose?
—Mr. Pesic, tutor and musician-in-residence at St. John's College, is the author of "Sky
in a Bottle."