Professor Eric Scerri, University of California, Los Angeles, USA, is well-known for his research on the history and philosophy of the periodic table. Dr. Francesca Novara spoke with him for ChemViews Magazine about his fascination with the periodic system, how discoveries are made, what makes Mendeleev unique, and why first discoverers are overestimated. They met at Mendeleev 150: 4th International Conference on the Periodic Table in Saint Petersburg, Russia.
How important was the discovery of the periodic table?
The discovery of this table was extremely important because it provided a connection between all the elements for the first time. It is one overarching principle that provides the unification.
Starting from the time it was discovered, it meant that we could better understand the properties of the elements and we could simplify the study of chemistry. To put it very generally, if a chemist knows the properties of a typical element within any column on the periodic table, he or she can predict the properties of other elements within the same column. Nothing quite like this kind of visual generalization exists in any of the other branches of science.
Mendeleev attended the first international congress in chemistry held in 1860 in Karlsruhe, Germany. How important was this for him and how did it affect his later career?
At the time of the Karlsruhe conference Dmirti Mendeleev was a virtually unknown chemist who happened to be studying in Germany under the great Robert Bunsen. One might say that Mendeleev happened to be at the right place at the right time. He was certainly not invited to the conference because of his fame since he had none at the time.
The conference was to be an extremely important meeting because many important chemical concepts became clarified. The atomic weights of elements and how to measure them became standardized. The basis of the periodic table is that all the elements have increasing atomic weights. Before this congress, there were different systems of atomic weights. Actually, it would not even have been possible to have the periodic table before this congress.
But the periodic table is more than a one-dimensional sequence. It depends on the recognition of the approximate recurrence in element properties after regular intervals within this sequence.
Another chemist who attended the conference was Julius Lothar Meyer, who would become Mendeleev’s most vocal competitor in the debate as to who had really discovered the periodic system.
There are several versions of how Mendeleev came up with the idea of the table. Some say the idea came to him in a dream, some others say that he was playing cards. Which one is correct?
Yes there are various legends as to how Mendeleev arrived at his discovery. According to some, Mendeleev was playing a game of solitaire or patience. This account is probably apocryphal since no such playing cards were ever found among his possessions. When Mendeleev realized he was becoming famous – and he realized that quite soon – he kept all of his papers, and nobody has found a single card.
Alternatively there is the story that it all came to him in a dream which also seems rather unlikely. Yet another popular story is that the idea of the periodic table coming to Mendeleev all at once over the course of a single February day in 1869.
The less Romantic version is that there was a period of about ten years during which the idea gradually developed in the mind of Mendeleev and several other scientists working independently at about the same time. It was a slow process of accumulation and gradual understanding.
How about the other chemists who worked on the periodic table? Who was the closest?
We can say that there are at least six discoverers of the periodic table. They include Alexandre-Émile Béguyer de Chancourtois (1820 – 1886) in France. He was the one who first discovered chemical periodicity or the repetition in the properties of the elements that the periodic table represents graphically. He was a geologist, who published in a French journal, which omitted to include a diagram of his three-dimensional system known as the telluric screw. Not surprisingly, this discovery was almost universally unnoticed.
Then there was Gustavus Detlef Hinrichs (1836 – 1923) a Danish political refugee who had emigrated to the United States. Hinrichs published some rather ambitious analogies between the elements and astronomical bodies in the course of arriving at his spiral periodic system. Again this had little impact on the scientific community of the time.
John Alexander Reina Newlands (1837 – 1898) working in London published a number of consistent periodic tables over a period of several years. However, in the course of presenting his ideas to the London Chemical Society, he made an analogy between music and the elements and announced his “Law of Octaves”. The general idea is essentially correct since musical notes recur after regular intervals in much the same way that element properties do. However, to the rather conservative British chemists of the time this seemed too fanciful and idea. They dismissed Newlands proposal, and it was not published in the journal of the society, although Newlands did succeed in publishing his ideas in other publications.
There was another discoverer in London: William Odling (1829 – 1921) published a perfectly respectable periodic table with 57 elements but moved onto other research projects and did not attempt to develop his table to any extent. And then there was Julius Lothar Meyer in Germany who had attended the Karlsruhe conference.
And then there was Justus Lothar Meyer in Germany. Lothar Meyer arrived at what might be termed the mature periodic system earlier than Mendeleev, starting with some tables of 1864.
Mendeleev was in fact the sixth and last of discoverers of the periodic system, although his contributions appear to have had the greatest impact. How much of this is due to a perfectly natural tendency of wanting to identify one single heroic discoverer is something that is still being discussed among historians and philosophers of chemistry.
Why is Mendeleev regarded as the most important discoverer?
There are several reasons for this. The most commonly given reason for why Mendeleev is regarded more highly than the other discoverers, is that Mendeleev alone made predictions as to the properties of elements that appeared to be missing from his system. He did not just leave empty spaces. He predicted quite precisely the properties of three elements that subsequently became known as gallium, germanium, and scandium, including their melting points, boiling points, and their atomic weights. Within a period of 15 years, these three elements had been isolated and identified with Mendeleev’s predictions.
However, there are other more philosophical reasons for why Mendeleev may deserve more credit. One of these reasons is that he believed that there were two senses of the concept of an element: First, there is the element in the obvious sense of something that can be isolated and placed in a beaker or a test tube. But there is also an abstract concept of an element as the bearer of properties and something that survives when an element such as chlorine enters into a chemical combination. In his writings, Mendeleev states categorically that the periodic table is primarily a classification of this more philosophical sense of elements. This conception may have allowed Mendeleev to sometimes go beyond the facts. For example, there was an active debate as to which group beryllium should be placed in. Many believed it should be placed in group 3 but Mendeleev correctly determined that it belonged in group 2 by somewhat ignoring certain chemical properties while concentrating on others. I believe this to be an equally important aspect of Mendeleev’s approach than his ability to make predictions.
Moreover, there is a debate among philosophers of science about whether predictions should really count in science. Psychologically, of course, a prediction is very impressive. When a scientist predicts something and it turns out to be correct, we have the idea that the scientist somehow knows the future and knows the secrets of nature. However, the ability to explain what is already known, sometimes called retrodiction, can be equally impressive. If this is correct then we should not give all the credit to Mendeleev because of his successful predictions. We should examine who accommodated the elements in the most effective way. And if we do that, Lothar Meyer comes out slightly ahead of Mendeleev. So it is a complicated question.
Was there a discussion about who first discovered the table?
There has been a big priority dispute among the two leading discoverers Lothar Meyer and Mendeleev. This dispute has many aspects, such as the fact that Lothar Meyer was not keen on claiming priority in the same way that Mendeleev was. He even said at some point that he lacked the courage to make predictions, although he had in fact predicted the existence and the atomic weight of the element that became known as germanium.
There is another important fact that should be considered: Lothar Meyer was working in Germany, which at the time had a very conservative chemical society in which speculations and predictions were not looked upon favorably. Mendeleev, on the other hand, was working here in St. Petersburg at a time of big change. Here the new Russian Chemical Society had just been formed. They were looking for new articles to put in their journal and they were encouraging speculations. So one of the reasons why Mendeleev made predictions and Lothar Meyer did not, is just the result of these differences in the professional milieu that these chemists worked in.
Why is it so important to be the first in science?
Well, scientists like everybody else are human, and it is considered important to be the first. But it may not be so important for science as a whole. My most recent book, A Tale of Seven Scientists, is partly about the question of scientific priority. In it I propose that precedence is important to scientists because they devote much time and effort to making discoveries. But science as a whole doesn’t care who made the discovery.
I have proposed that science evolves as an organic entity, or as one unified process that I have compared with a biological organism. So yes, we are all different, we are all individuals but really science is one. So in that scenario, there are no winners and there are no losers. And not just the six discoverers I mentioned but all the others, even students and laboratory technicians, have a role in this organic process. I have called this view Sci-Gaia by analogy with Lovelock’s view that the earth is a living unified organism
What got you interested in the history of the periodic table?
It is a long story. I studied in England and at the time had to make an early choice between humanities and sciences. I liked chemistry and physics so I took the scientific direction, but I had to give up subjects that I liked such as history, geography, literature, and languages. This decision continued to nag at me, particularly as I had a deep interest in history. All my early university training was as a chemist but I eventually discovered the history and philosophy of science and wrote my Ph.D. on the subject.
Fifteen years later this thesis morphed into my first book, The Periodic Table, Its Story and Its Significance, which incidentally has just been published as a revised 2nd edition this year. I am pleased to say that it has become the standard reference of the periodic table.
Do you think that there is anything comparable to the periodic table in other disciplines?
No, there is nothing else comparable. As I said earlier, there is no analogous chart in other disciplines.
Learning chemistry can be very confusing. I remember when I was first presented with the periodic table, at about age 15. Suddenly I could see the connections and could see a system, and I could breathe more easily. Chemistry was no longer a matter of just learning isolated facts but there was some logic to it. I have the kind of mind that likes order. For example, as a young boy, I collected stamps and I loved trying to impose order on them. Similarly, the deep order provided to the elements by the periodic table resonates with me.
A question about the name: Some countries like Germany adopt the word “system” rather than “table”. Which one do you prefer?
I think that system is better than table because system is the abstract idea that all the elements are connected or related. A table is a representation on a piece of paper or a model. So in my book, I actually make the distinction between periodic law, periodic system, and periodic table. Periodic table is the most restrictive one and it is the most specific one. It is also the best-known term, but it is a representation of the periodic law of the periodic system.
Could you comment on the expression “cracks in the periodic table”?
As we create more elements today, it is beginning to look like the periodic law is threatened. This is a problem for the periodic law and this happens because some of the very heavy elements, which have been created in Russia, the United States, and Germany, do not behave in a way that is expected from their group in the periodic table. And this is because of relativistic effects. The theory of relativity becomes important for the super-heavy atoms. And if that is the case then the period table seems to be breaking down.
Will a new periodic table appear or will the law change?
We don’t know. There could be one more general periodic table. At the moment we have the traditional periodic table that works for the light elements. For the heavy elements, the table may have to be modified because we cannot always make predictions in the way that we could before these super-heavy elements were created. So this is a period of uncertainty.
Do you believe that science goes through revolutionary breakthrough moments, or that it happens as a slow process of adding and adding, or that the process cannot be generalized at all?
In my most recent book, I argue against Thomas Kuhn [an American historian of science] who made his reputation on the idea of revolutions in science. I claim that there are no revolutions in science. As I see it, there is evolution, not revolution. And evolution usually progresses gradually.
I was talking to David Seaborg a biologist and the son of Glen Seaborg who is here at this conference. He was saying that there are a few cases of revolutions in biology while, generally speaking, evolution is gradual. I think the same is true in science. So, as I was saying earlier, all the apparently minor contributors count just as much as the well-known, heroic discoverers in the overall evolutionary trajectory of science as a whole.
Eric Scerri, born in 1953 in Malta, obtained his bachelor’s and master’s 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 did a postdoctoral fellowship at the London School of Economics abd the California Institute of Technology (Caltech), Pasadena, USA. Since 2000, Eric Scerri has taught chemistry and philosophy of science at the University of California, Los Angeles, USA.
Eric Scerri 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.
- Webpage of Eric Scerri
- The Periodic Table – Its Story and Its Significance,
2nd Edition, Oxford University Press, UK, 2019.
- A Tale of Seven Scientists and a New Philosophy of Science,
Oxford University Press, UK, 2016.
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