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A New (& little) take on the Periodic Table

I just read and enjoyed The Periodic Table: A Very Short Introduction, by Eric R. Scerri (Oxford 2012).

The periodic table of the elements is one of the icons of science. As author Eric Scerri writes, “The periodic table ranks as one of the most fruitful and unifying ideas in the whole of modern science, comparable perhaps with Darwin’s theory of evolution by natural selection. After evolving for nearly 50 years, …. the periodic table remains at the heart of the study of chemistry.”

But there have been roughly 1,000 versions of the table since Mendelev’s breakthrough in 1869. In modern times, we learn from Scerri, there have been Theodore Benfey’s spiral, Fernando Dufour’s three-dimensional tree, circles, ellipses, left step tables, and short forms, medium-long-forms, and long-forms.

Each version serves a different purpose, Scerri writes. “Whereas a chemist might favour a form that highlights the reactivity of the elements, an electrical engineer might wish to focus on similarities and patterns in electrical conductivities.”

Ironically, the one we all remember from high school is used because it’s convenient. Separating out the rare earth elements, as it does, makes the table narrow enough to fit the endpapers of chemistry books and the bulletin boards of labs and classrooms.

As old as the icon is, it’s still making discoveries, Scerri emphasizes. For example, the table was one of the primary principles used in the search for superconductivity; it was the clue that placed yttrium within a new set of superconducting compounds. Drugmakers, noting that gold and platinum sit next to each other on the table, replaced platinum atoms with gold atoms in various compounds and wound up with useful pharmaceuticals. And potassium, which is readily absorbed by the body, has been replaced in some molecules by rubidium, which lies below potassium and mimics it; the result is treatments for brain cancers.

Naturally, on the influence of physics on the table, Scerri sides with chemistry. He notes that Einstein’s theory of relativity explains the color of gold and the liquidity of mercury as relativistic effects due to fast-moving inner-shell electrons. But he emphasizes that quantum mechanics has had a profound influence on the periodic system.

The periodic table, he continues, has “served as a testing ground for the theories of atomic physics and for many early aspects of quantum theory and the later quantum mechanics. … But what seems to be forgotten in the current reductionist climate is that the periodic table led to the development of many aspects of modern quantum mechanics and so it is rather short-sighted to insist that only the latter explains the former.”

In short, he disapproves of modern textbooks that treat chemistry as “nothing but physics ‘deep down’ and [that say] that all chemical phenomena, and especially the periodic system, can be developed on the basis of quantum mechanics.” In fact, he argues that the explanation of the periodic system is still incomplete and far from perfect. For example, he writes that it is still unclear whether hydrogen should be placed with the alkali metals or the halogens — or whether it should “float majestically” atop the table, as a special case… above the law, very much like the British Royal family once was.”

In concluding his book, Scerri writes about some scientists today who believe that the table’s approximate repetition of the properties of the elements reveals, not an objective fact about the natural world, but a property imposed on nature by human agents. For them, of course, discovering the best periodic table is irrelevant.

Scerri, though, argues that the repetition of the properties of the elements — while neither constant nor precise — reveals an objective fact about the natural world. And for him, the best table would maximize the number of atomic number triads. Triads are groups of three elements where the atomic weight of one element is roughly the average of the other two. Using this system, for example, Scerri would sit hydrogen on top of the halogens.

So why is someone like myself, a non-chemist who just wrote a history of Bayesian statistics, interested in this book?

As a writer, I enjoyed reading about many interesting and to me unknown stories about the history of the table. Scerri’s historical depth also resonated with me because of my days as editor and writer about physics for the Encyclopaedia Britannica. One particular facet of the article I co-authored on “The Atom” comes to mind. A young English physicist Henry Moseley who died in World War I at the age of 26 put the periodic table on a rigorous basis by confirming experimentally that each element has a different atomic number. In our Encyclopaedia article, we brought out the then little-known fact that in all likelihood Moseley was directly influenced by Niels Bohr’s version of the atom because the two men had spent time together in the same laboratory.

Another aspect of the periodic table appeared in the history of the chemical industry that I wrote a while ago. One of the chapters is about Thomas Midgley, the inventor of leaded gasoline and CFCs, who carried a copy of the periodic table in his pocket. The table was the foundation — and extent — of much of Midgley’s chemical research.

Finally, this is a beautifully produced little book that’s ideal for gift-giving. It’s a summary of Scerri’s full-scale The Periodic Table: Its Story and Significance. It’s part of a series of “Very Short Introductions” published by Oxford University Press.

Its cover — “based on a concept by Philip Atkins,” whatever Oxford thinks that means — is an irresistibly silky-smooth landscape of greens and browns. At $12, it’s a pocket-sized book to give a chemist or a chemistry student — or simply a friend who likes science.
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