Rebuilding the Periodic Debate — Eric Scerri

  • DOI: 10.1002/chemv.201000135
  • Author: David Bradley
  • Published Date: 02 November 2011
  • Copyright: Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
thumbnail image: Rebuilding the Periodic Debate — Eric Scerri

In June 2011, we published a feature entitled Periodic Debate that discussed the ongoing evolution, if not revolution, surrounding the periodic table of the chemical elements. It remains the most popular Research Highlight article on and continues to attract comments on the issues raised. In particular, from those who disagree with the standpoint that there could ever be a definitive two-dimensional table and that it is anything more than a tool or mnemonic to help chemists organize their understanding of the world around us.

I interviewed two of the people driving the debate, Philip Stewart and Eric Scerri. Here, I talk to Eric Scerri about his periodic inspiration.

Chemical Philosopher

After studying chemistry at the universities of London, Cambridge, and Southampton in the UK, Eric Scerri decided to follow his interests in the more conceptual aspects of the subject and did a Ph.D. in History & Philosophy of Science at King's College, London. He told ChemViews that he was lucky enough to work with Heinz Post, the son of the famous chemist, Fritz Paneth. Post was a highly respected historian and philosopher of science, steeped in scientific details. "This is something that I hope I have emulated in my own work," Scerri says. In his Ph.D. thesis, he questioned how successful the reduction of chemistry to quantum mechanics has been.

He undertook a postdoc in Karl Popper's old department at the London School of Economics, UK, and then took up a postdoc at Caltech (Califonia Institute of Technology, USA) where he worked mainly in the history of chemistry. Various brief appointments at a couple of universities in Mid-West USA then led Scerri to settle in Los Angeles as a lecturer in chemistry and history & philosophy of science.

"I have been one of a relatively small group of people trying to put the philosophy of chemistry on the map," he told us. "One of my own contributions was to start a journal called Foundations of Chemistry which is now in its twelfth year of publication and which I am still editing." 

Unifying Principle

As his work developed, he began to focus increasingly on the history and philosophy of the periodic table. "The periodic table is the main unifying principle in chemistry," Scerri says. "It's comparable to the role played by quantum mechanics and relativity in modern physics and Darwin's theory in biology." Scerri's 2007 book on the subject has, he told us, "opened up many new doors for me, including visiting many countries and being asked to appear, write and consult on radio and TV." He confesses that, "I enjoy that as much as doing basic research." A follow-up book, A Very Short Introduction to the Periodic Table will appear in December and he is now working on A Tale of Seven Elements, both to be published by Oxford University Press.

But what underlies Scerri's fascination with the periodic table? "I'm not quite sure why, but as long as I can remember, I have been enthralled by the idea of a single chart that summarizes, in principle, the whole of chemistry and brings order to the field by providing connections at many different levels." He points out that the periodic table acts as a bridge between the everyday reactions of the chemical elements and their atomic structure. However, as we discussed in Periodic Debate on ChemViews, despite his thrall, Scerri is not satisfied by the conventional, or medium-long, format of the periodic table. "One of the main problems concerns the placement of certain elements like H, He, La, Ac, Lu and Lr, all of which are debated in the scientific literature," he says.

Scerri is trying to answer the question of what are the best criteria for the classification of elements into particular groups. In terms of ordering the elements into a simple numerical sequence, the problem was solved about 100 years ago by Van den Broek and Moseley and it is, of course, done through the atomic number of each element. "Classification into groups is not quite so simple," he asserts, "and it is increasingly appreciated that the use of electronic configurations does not settle the issue in many cases."

Artificial Versus Optimal

Of increasing interest to Scerri is the notion of an "optimal" periodic table. "This very notion has met with resistance from some philosophers of science who argue that all classifications, even the periodic table, are artificial and therefore do not reflect the way the world actually is." Scerri is also surprised that a number of chemists also seem to subscribe to the view that there is no such thing as an optimal periodic table because, they claim, it depends on what particular feature about the elements one is trying to represent as to which version will be chosen. "If I am correct, there may be a sense in which we can claim the existence of a best table in terms of the most fundamental criteria instead of in terms of utility," Scerri adds. As such, although chemists are yet to find this elusive form of the periodic table, Scerri is searching for the new criterion that would provide us with a better classification than we currently have.

"I think that discussions about the foundations of the periodic table will begin to surface more and more and might serve to illuminate the profusion of periodic tables which continue to appear in articles and on websites," Scerri says. His current favorite is a format that places hydrogen among the halogens and maintains helium in the noble gases, contrary to the much discussed left-step periodic table which places helium at the top of the alkaline earth metals. However, he concedes that he has no hard evidence for this favored version, just some good plausibility arguments. "It would be useful if such questions could become more accessible to experimental verification and if more chemists would take an interest in the philosophical aspects of one of the central pillars of their own discipline."

In his spare time, Scerri abandons the formal and rigidity of academic work and plays flamenco and blues guitar and a little boogie-woogie piano. Perhaps the optimal periodic table will turn out to be a twelve-bar version ...

Eric Scerri, UCLA, USA

Professor Eric Scerri was born in 1953 in Malta. He obtained his bachelors and masters degrees in chemistry from the universities of London, UK, and Southampton, UK, and his Ph.D. in the history and philosophy of science from King's College, London. He moved to the US for a postdoctoral fellowship at Caltech sixteen years ago and has remained in the US ever since. For 12 years, he has taught chemistry and philosophy of science at the University of California, Los Angeles, USA, and is one of the founders of the field of philosophy of chemistry as well as the founder and editor of the journal Foundations of Chemistry, now in its twelfth year of publication.

Scerri has authored more than 100 journal articles in chemistry, chemical education, and the history and philosophy of science. In recent years, he is turning increasingly towards working in the TV and radio media and to presenting his work to the general public.

Selected Publications


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Valery Tsimmerman wrote:


Jess,__ thanks for giving me opportunity to comment on triads, unless you are setting me up for the conflict with Eric (just kidding). I agree with Eric that triads played important role in the past to alert early chemists about relationships between the elements. I think that in our tetrahedral theory triads also play important role as a confirmation of its validity.___As Eric wrote in his famous book, triads are products of doubling the periods. For example, in traditional periodic table, triad Ar-Kr-Xe exists because 4th and 5th periods have same lengths 18 elements each. In other words, triads exist because, starting with second period, lengths of periods recur: 8,8,18,18,32,32. The problem of the traditional periodic table is its inconsistency in regard to the length of its 1st period: 2,8,8,18,18,32,32, as well as placement of He. In traditional periodic table He and Be are members of triads (He-Ne-Ar, Be-Mg-Ca) and Hydrogen, as well as all other group first elements are not members of triads! Something is terribly wrong with this picture. It shows that in traditional PT He and Be are the exclusions. But this happens only because of period length rule violation. If lengths of the periods were made consistent 2,2,8,8,18,18,32,32, He and Be would not be members of the triads therefore they would cease to be exclusions from the general rule.____ Some time ago Jess has noticed that atomic numbers of Be, Ca, Ba and Ubn match every other tetrahedral number and atomic numbers of the rest of the alkaline earths are exact arithmetic means of the atomic numbers of their neighbors in the group. Guess what? I was able to match all the atomic numbers of the alkaline earths exactly by stacking spheres of two colors or by modifying pascal triangle by suppressing every even number in the sequence of natural numbers and multiplying the forth sequence by factor of two to account for S=1/2 spin._____ Therefore, Eric, I argue that instead of trying to increase number of triads, we should optimize number of triads by re-arranging the Periodic Table to have period lengths 2,2,8,8,18,18,32,32...___Valery Tsimmerman

Fri Nov 18 15:10:03 UTC 2011

Philip Stewart wrote:


Jess's comment about nickel 62, the most stable of all nuclei, suggests the way to the 'island of stability'. Ni 56 has a half life of 6 days, but in the explosion of a supernova it can reach Ni 62 by neutron capture. To get enough neutrons on to the heaviest nuclei we need to create them in a neutron flux like that of a supernova. Remember the neutron bomb?! Dangerous, but perhaps do-able.

Fri Nov 18 08:20:57 UTC 2011

Jess Tauber wrote:


I left off my story of the development of the Pascal math so that Valery could chime in with the explanation he came up with for element triads after the discovery of the tetrahedral number explanation- why only HALF possible triads actually work within-group in the PT. How about it??

Thu Nov 17 18:03:32 UTC 2011

Jess Tauber wrote:

Tetrahedral jackets

It is another property of tetrahedra of close packed spheres that once you establish a core of 20 in a tetrahedral arrangement (20 being a tetrahedral number) every surrounding 'jacket' uses the same formula for count, being the sum of two contiguous squares of even integers. That is, 20 is 4+16, and the next jacket of 100 has 36+64. This relates directly to tetrahedral diagonal numbers, but doesn't stacked triangular layers.

Thu Nov 17 17:52:15 UTC 2011

Valery Tsimmerman wrote:

Explanation. Post 4 of 3.

So, to make it even more simple and to avoid references to the Pascal triangle, following procedure can be used: In order to build geometric representation of atomic sequences in the periodic system, buy bunch of red and green marbles. Take one red marble, write H and He on it and put it on top of table, then take two green spheres and put them next to the red to form a triangle. Take another red sphere and write Li and Be and put it on top of the triangle. Take three more red spheres and put them on the table next to two green. Write B, C and N on them, then write O an the marble marked with B, F on the marble marked with C and Ne on the marble marked with N (this is to account for Hunds rule). Take two green spheres and place them next to red sphere in second row. Then, take one one red sphere, put it on top to complete the tetrahedron. Mark it with Na and Mg____ Start new layer by putting 4 green spheres on top of the table next to three red spheres. Put three red spheres on top of green in the second layer and write Al, Si, P and then write S next to Al, Cl next to Si and Ar next to P. Place two green spheres in the third layer on top of three red and then put one green sphere on top of third layer to complete the tetrahedron. Mark last red sphere with K and Ca. Continue this procedure for the rest of the elements of the periodic system. I am sure you will enjoy it.__ Best, Valery.

Thu Nov 17 17:35:03 UTC 2011

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