## Chemistry Puzzle

Three elements were named after mischievous sprites. Two of them are real, while the third was just a mischievous trick played by Mother Nature herself. What are these elements, how did they get their names, and what was the trick?

### 35 Responses to Chemistry Puzzle

1. nyarlathotep says:

Nickel and Cobalt are the real ones, and I assume the difficulty was the early difficulties with extracting them from ore?

2. Blake Stacey says:

Fun fact: One of them was responsible for “beer drinker’s cardiomyopathy”.

3. streamfortyseven says:

OK, that’s cobalt. How about Niobium? named after Niobe – and Palladium, named after Pallas Athena (although I don’t think she’d be amused at being called a “sprite”)?

• John Baez says:

Yes, one of the mischievous trio is cobalt.

In German a goblin is called a “Kobold”. Miners called certain minerals “Kobold ore”, or goblin ore, because they were poor in known metals and gave poisonous arsenic-containing fumes when smelted. In 1735, such ores were found to contain a new metal – the first discovered since antiquity – and this metal was called cobalt

I don’t think of either Niobe or Athena as a “mischievous sprite”.

From the Wikipedia article Kobold:

The kobold (or kobolt) is a sprite stemming from Germanic mythology and surviving into modern times in German folklore. Although usually invisible, a kobold can materialise in the form of an animal, fire, a human being, and a mundane object. The most common depictions of kobolds show them as humanlike figures the size of small children. Kobolds who live in human homes wear the clothing of peasants; those who live in mines are hunched and ugly; and kobolds who live on ships smoke pipes and wear sailor clothing.

Legends tell of three major types of kobolds. Most commonly, the creatures are house spirits of ambivalent nature; while they sometimes perform domestic chores, they play malicious tricks if insulted or neglected. Famous kobolds of this type include King Goldemar, Heinzelmann, Hödekin. In some regions, kobolds are known by local names, such as the Galgenmännlein of southern Germany and the Heinzelmännchen of Cologne. Another type of kobold haunts underground places, such as mines. The name of the element cobalt comes from the creature’s name, because medieval miners blamed the sprite for the poisonous and troublesome nature of the typical arsenical ores of this metal (cobaltite and smaltite) which polluted other mined elements. A third kind of kobold, the Klabautermann, lives aboard ships and helps sailors.

• Tim van Beek says:

…and there is the Huck-Up known in my hometown Hildesheim, who jumps on the backs of thieves as a manifestation of a bad conscience (and just as a bad conscience he does not prevent the thievery itself, he only saddens the thief).

• John Baez says:

Interesting local mythology, Tim!

I just discovered that kobolds remain active in popular culture:

not to mention the Kobold Quaterly, or the ineffectual kobolds in D&D.

• Tim van Beek says:

Oh, now I understand why in the classic AD&D computer game Baldur’s Gate there are Kobolds that poison the iron in the iron mines of Nashkel.

And of course I forgot to mention one of the most well known Kobolds, the Nachtmahr (English “nightmare”).

Unfortunately all this brainstorming did not help me to remember the third answer, I give up :-)

• Blake Stacey says:

Palladium is named for Athena indirectly, via the asteroid Pallas. . . and on the subject of indirect naming, what are two stable chemical elements named (directly or otherwise) for non-mythological people?

• streamfortyseven says:

Sorry, the asteroid Pallas was named for Pallas Athena, the Greek Goddess of wisdom, who was a virgin and whose temple was thus named the Parthenon, on Acropolis Hill in Athens… see http://en.wikipedia.org/wiki/Athena

• John Baez says:

Blake wrote:

…what are two stable chemical elements named (directly or otherwise) for non-mythological people?

Hmm. So you’re not asking about curium, einsteinium, fermium, mendelevium, nobelium, lawrencium, rutherfordium, seaborgium, bohrium, meitnerium, roentgenium, or copernicium.

I hadn’t even heard of the last two until now!

By the way, digressing a bit further:

I’m actually sort of pleased that hahnium was renamed dubnium, given how shabbily Hahn seems to have treated Lise Meitner, who is one of my scientific heroes. And I’m very happy that meitnerium gives her some of the immortality she deserves!

I find her life story very moving, because she was so smart, worked so hard against so many obstacles, achieved so much, became head of an institute, became so absorbed in her work that she didn’t pay enough attention to the rise of the Nazis, then had to flee her country with only 10 marks in her purse, then managed to get a lousy job with a tiny lab and had to make her own experimental equipment… but then became the first to understand nuclear fission… but was then denied the Nobel prize for this discovery. Here’s a bit from my review of:

• Ruth Sime, Lise Meitner: A Life in Physics, University of California Press, 1997.

Meitner’s life was a fascinating but difficult one. The Austrian government did not open the universities to women until 1901, when she was 23. They had only opened high schools to women in 1899, but luckily her father had hired a tutor to prepare her for the university before it opened, so she was ready to enter as soon as they let her in. She decided to work on physics thanks in part to the enthralling lectures and friendly encouragment of Ludwig Boltzmann. After getting her doctorate in 1906, she went to Berlin to work with Max Planck. At first she found his lectures dry and a bit disappointing compared to Boltzmann’s, but she soon saw his ideas were every bit as exciting, and came to respect him immensely.

In Berlin she also began collaborating with Otto Hahn, a young chemist who was working on radioactivity. Since women were not allowed in the chemistry institute, supposedly because their hair might catch fire, she had to perform her experiments in the basement for two years until this policy was ended. Even then, she did not receive any pay at all until 1911! But gradually her official status improved, and by 1926 she became the first woman physics professor in Germany.

Meitner was one of those rare physicists gifted both in theory and experiment; her physics expertise meshed well with the analytical chemistry skills of Hahn, and as a team they identified at least nine new radioisotopes. The most famous of these was the element protactinium, which they discovered and named in 1918. This was the long-sought “mother of actinium” in the uranium decay series.

But to understand Meitner’s work in context, you have to realize that these facts only became clear through painstaking work and brilliant leaps of intuition. Much of the work was done by her team in Berlin, Pierre and Marie Curie in France, Ernest Rutherford’s group in Manchester and later Cambridge, and eventually Enrico Fermi’s group in Rome.

At first people thought electrons were bound in a nondescript jelly of positive charge – Thomson’s “plum pudding” atom. Even when Rutherford, Geiger and Marsden shot α particles at atoms in 1909 and learned from how they bounced back that the positive charge was concentrated in a small “nucleus”, there remained the puzzle of what this nucleus was.

In 1914 Rutherford referred to the hydrogen nucleus as a “positive electron”. In 1920 he coined the term “proton”. But the real problem was that nobody knew about neutrons! Instead, people guessed that the nucleus consisted of protons and “nuclear electrons”, which made its charge differ from the atomic mass. Of course, it was completely mysterious why these nuclear electrons should act different from the others: as Bohr put it, they showed a “remarkable passivity”. They didn’t even have any spin angular momentum! But on the other hand, they certainly seemed to exist – since sometimes they would shoot out in the form of β radiation!

To solve this puzzle one needed to postulate a neutral particle as heavy as a proton and invent a theory of β decay in which this particle could decay into a proton while emitting an electron. But there was an additional complication: unlike α radiation, which had a definite energy, β radiation had a continuous spectrum of energies. Meitner didn’t believe this at first, but eventually her careful experiments forced her and everyone else to admit it was true. The energy bookkeeping just didn’t add up properly.

This led to a crisis in nuclear physics around 1929. Bohr decided that the only way out was a failure of conservation of energy! Pauli thought of a slightly less radical way out: in β decay, maybe some of the energy is carried off by yet another neutral particle, this time one of low mass. Two mysterious unseen neutral particles was a lot to stomach! In 1931 Fermi called the big one the “neutron” and the little one the “neutrino”. In 1932 Chadwick realized that you could create beams of neutrons by hitting beryllium with α particles. The neutrino was only seen much later, in the 1950s.

[…]

When Hitler gained power over Germany in 1933, her life became increasingly tough, especially because she was a Jew. In May of that year, Nazi students at her university set fire to books by undesirable writers such as Mann, Kafka, and Einstein. By September, she received a letter saying she was dismissed from her professorship. Nonetheless, she continued to do research.

In 1934, Fermi started trying to produce “transuranics” – elements above uranium – by firing neutron beams at uranium. Meitner got excited about this and began doing the same with Hahn and another chemist, Fritz Strassman. They seemed to be succeeding, but the results were strange: the new elements seemed to decay in many different ways! Their chemical properties were curiously variable as well. And the more experiments the team did, the stranger their results got.

No doubt this is part of why Meitner took so long to flee Germany. Another reason was her difficulty in finding a job. For a while she was protected somewhat by her Austrian citizenship, but that ended in 1938 when Hitler annexed Austria. After many difficulties, she found an academic position in Stockholm and managed to sneak out of Germany using a no-longer-valid Austrian passport.

She was now 60. She had been the head of a laboratory in Berlin, constantly discussing physics with all the top scientists. Now she was in a country where she couldn’t speak the language. She was given a small room to use a lab, but essentially no equipment, and no assistants. She started making her own equipment. Hahn continued work with Strassman in Berlin, and Meitner attempted to collaborate from afar, but Hahn stopped citing her contributions, for fear of the Nazis and their hatred of “decadent Jewish scence”. Meitner complained about this to him. He accused her of being unsympathetic to his plight. It’s no surprise that she wrote to him:

Perhaps you cannot fully appreciate how unhappy it makes me to realize that you always think I am unfair and embittered, and that you also say so to other people. If you think it over, it cannot be difficult to understand what it means to me that I have none of my scientific equipment. For me that is much harder than everything else. But I am really not embittered – it is just that I see no real purpose in my life at the moment and I am very lonely….

What is a surprise is that this is when she made her greatest discovery. She couldn’t bear spending the Christmas of 1938 alone, so she visited a friend in a small seaside village, and so did her nephew Otto Frisch, who was also an excellent physicist. They began talking about physics. According to letters from Hahn and Strassman, one of the “transuranics” was acting a lot like barium. Talking over the problem, Meitner and Frisch realized what was going on: the neutrons were making uranium nuclei split into a variety of much lighter elements!

In short: fission.

I won’t bother telling the story of all that happened next: their calculations and experiments confirming this guess, the development of the atomic bomb, which Meitner refused to participate in, how Meitner was nonetheless hailed as the “Jewish mother of the bomb” when she came to America in 1946, and how Hahn alone got the Nobel prize for fission, also in 1946. It’s particularly irksome how Hahn seemed to claim all the credit for himself in his later years….

And from the Wikipedia article:

Meitner was part of the team that discovered nuclear fission, an achievement for which her colleague Otto Hahn was awarded the Nobel Prize. Meitner is often mentioned as one of the most glaring examples of women’s scientific achievement overlooked by the Nobel committee. A 1997 Physics Today study concluded that Meitner’s omission was “a rare instance in which personal negative opinions apparently led to the exclusion of a deserving scientist” from the Nobel. Element 109, Meitnerium, is named in her honor.

[…]

When Adolf Hitler came to power in 1933, Meitner was acting director of the Institute for Chemistry. Although she was protected by her Austrian citizenship, all other Jewish scientists, including her nephew Otto Frisch, Fritz Haber, Leó Szilárd and many other eminent figures, were dismissed or forced to resign from their posts. Most of them emigrated from Germany. Her response was to say nothing and bury herself in her work (she later acknowledged, in 1946, that “It was not only stupid but also very wrong that I did not leave at once.”).

After the Anschluss, her situation became desperate. In July 1938, Meitner, with help from the Dutch physicists Dirk Coster and Adriaan Fokker, escaped to the Netherlands. She was forced to travel under cover to the Dutch border, where Coster persuaded German immigration officers that she had permission to travel to the Netherlands. She reached safety, though without her possessions. Meitner later said that she left Germany forever with 10 marks in her purse. Before she left, Otto Hahn had given her a diamond ring he had inherited from his mother: this was to be used to bribe the frontier guards if required. It was not required, and Meitner’s nephew’s wife later wore it.

Meitner was lucky to escape, as Kurt Hess, a chemist who was an avid Nazi, had informed the authorities that she was about to flee. However, unknown friends only checked after they knew she was safe. An appointment at the University of Groningen did not come through, and she went instead to Stockholm, where she took up a post at Manne Siegbahn’s laboratory, despite the difficulty caused by Siegbahn’s prejudice against women in science. Here she established a working relationship with Niels Bohr, who travelled regularly between Copenhagen and Stockholm. She continued to correspond with Hahn and other German scientists.

Hahn and Meitner met clandestinely in Copenhagen in November to plan a new round of experiments, and they subsequently exchanged a series of letters. Hahn and Fritz Strassmann then performed the difficult experiments which isolated the evidence for nuclear fission at his laboratory in Berlin. The surviving correspondence shows that Hahn recognized that fission was the only explanation for the barium, but, baffled by this remarkable conclusion, he wrote to Meitner. The possibility that uranium nuclei might break up under neutron bombardment had been suggested years before, notably by Ida Noddack in 1934. However, by employing the existing “liquid-drop” model of the nucleus, Meitner and Frisch were the first to articulate a theory of how the nucleus of an atom could be split into smaller parts: uranium nuclei had split to form barium and krypton, accompanied by the ejection of several neutrons and a large amount of energy (the latter two products accounting for the loss in mass). She and Frisch had discovered the reason that no stable elements beyond uranium (in atomic number) existed naturally; the electrical repulsion of so many protons overcame the “strong” nuclear force. Meitner also first realized that Einstein’s famous equation, $E = mc^2$, explained the source of the tremendous releases of energy in nuclear fission, by the conversion of rest mass into kinetic energy, popularly described as the conversion of mass into energy.

A letter from Bohr, commenting on the fact that the amount of energy released when he bombarded uranium atoms was far larger than had been predicted by calculations based on a non-fissile core, had sparked the above inspiration in December 1938. Hahn claimed that his chemistry had been solely responsible for the discovery, although he had been unable to explain the results.

It was politically impossible for the exiled Meitner to publish jointly with Hahn in 1939. Hahn and Strassman had sent the manuscript of their paper to Naturwissenschaften in December 1938, reporting they had detected the element barium after bombarding uranium with neutrons; simultaneously, they had communicated their results to Meitner in a letter. Meitner, and her nephew Otto Robert Frisch, correctly interpreted their results as being nuclear fission and published their paper in Nature. Frisch confirmed this experimentally on 13 January 1939.

Meitner recognized the possibility for a chain reaction of enormous explosive potential. This report had an electrifying effect on the scientific community. Because this could be used as a weapon, and since the knowledge was in German hands, Leó Szilárd, Edward Teller, and Eugene Wigner jumped into action, persuading Albert Einstein, a celebrity, to write President Franklin D. Roosevelt a letter of caution; this led eventually to the establishment several years later of the Manhattan Project. Meitner refused an offer to work on the project at Los Alamos, declaring “I will have nothing to do with a bomb!” Meitner said that Hiroshima had come as a surprise to her, and that she was “sorry that the bomb had to be invented.”

[…]

In 1944, Hahn received the Nobel Prize for Chemistry for the discovery of nuclear fission. Some historians who have documented the history of the discovery of nuclear fission believe Meitner should have been awarded the Nobel Prize with Hahn.

• Tom Leinster says:

That’s a moving story, John.

On a different note, I’ve realized that the reason why I couldn’t solve your puzzle is that I was using the wrong periodic table.

• G.R.L. Cowan says:

Searching by atomic number … well, I’m pretty sure rhodium wasn’t named after Cecil Rhodes. Oh, it’s going to be one of the rare earths, isn’t it … samarium. *And* gadolinium, which makes two, so I don’t have to worry about Rhodes.

• The puzzle remains what links cobalt, beer and cardiomypathy. Now I googled it out: There was once a heart failure epidemic among beer drinkers in parts of U.S., Canada, and Belgium. It turned out to be due to the addition of tiny amounts of cobalt chloride by some breweries to improve the foaming quality of their beer.

4. Blake Stacey says:

The one which turned out to be a trick on Nature’s part would have been close to the other two on the Periodic Table, until a better way of organising said Table made the need for the new element vanish….

• John Baez says:

Okay, so Blake has proved he could easily win this game if he wanted. Don’t let him intimidate you: I want someone to actually answer the puzzle!

• Gremlinium? Impium?

Was the reorganization of the periodic table due to the discovery of Nature’s trick?

Could it be masurium? No, masurs don’t seem to be minor evil spirits.

Near in the periodic table … how near?

• John Baez says:

Gremlinium? Impium?

Close! Much closer than you probably realize!

5. Johann Leida says:

Nickel was also named after a sprite.

Wikipedia says:

In medieval Germany, a red mineral was found in the Erzgebirge (Ore Mountains) which resembled copper ore. However, when miners were unable to extract any copper from it they blamed a mischievous sprite of German mythology, Nickel (similar to Old Nick) for besetting the copper. They called this ore Kupfernickel from the German Kupfer for copper. This ore is now known to be nickeline or niccolite, a nickel arsenide. In 1751, Baron Axel Fredrik Cronstedt was attempting to extract copper from kupfernickel and obtained instead a white metal that he named after the spirit which had given its name to the mineral, nickel.

Not sure about the third trickster. Fun puzzle!

• Tim van Beek says:

The only stories of the Erzgebirge that I have been told revolve around the sprite “Rübezahl”, who got his nickname after he was tricked into counting turnips by a cunning princess he had held captive, who used this distraction to flee his realm. (The turnips were scheduled to be used in a magic trick that would create playfellows for the princess, and the princess claimed that she would need the exact number of turnips to plan ahead what friends she would like to have the turnips turned into).

But I have never heard of “Nickel”.

6. John C says:

Another one is nickel… Nickel was named after a mischevious German sprite, Nickel, after miners blamed him for being unable to extract any copper from what they thought was copper ore, but which actually contained nickel.

7. David Corfield says:

Nickel seems to be named for a sprite which prevented copper emerging from what miners took to be its ore.

• John Baez says:

Yes, kupfernickel, which means roughly ‘goblin copper’, was revealed in 1751 to contain a new element: nickel.

Johann L and John C beat you to it, David, but their comments hadn’t gone through moderation by the time you posted yours. So, all three of you get an equal share of glory.

8. Physicalist says:

Sprite, or not a sprite?

9. John Baez says:

Physicalist wrote:

Sprite, or not a sprite?

Interesting! I’d say goddess, not sprite.

In any event, vanadium is not the third element I had in mind for this puzzle. Nor is it titanium! My wife Lisa was wondering if that element was named after Titania, queen of the fairies in A Midsummer Night’s Dream. But no, it was named after the titans, in 1795, by Klaproth—the same guy who named ‘uranium’.

And while we’re talking gods, I also don’t mean uranium, neptunium or plutonium!

After nickel and cobalt were discovered, a third element was postulated, with a closely related name. But later, scientists realized this element does not exist! It turned out they’d been fooled by a mischievous trick of Mother Nature. For more clues, ponder the words of Blake Stacey.

We have now reached the heart of the puzzle:

• Thorbear says:

This was difficult, but gnomium and the atomic weight not being monotonic w.r.t. atomic number is the trick.

10. David Corfield says:

Was the element postulated by Mendeleev? Is the trick that increasing atomic numbers don’t always mean increasing atomic weights, as with cobalt and nickel?

11. Simon Willerton says:

The only “element” I can find that was on Mendeleev’s original table is didymium, which was later found to consist of two seperate elements neodymium and praseodymium. But I don’t see how that can be the correct answer as the root of didymium seems to be the Greek word for ‘twin’.

12. Simon Willerton says:

Oops, by ‘”element”‘ I meant a thing that was later found to be not an element.

13. It seems with some lucium I googled my way out of the nebulium: Now methinks the puzzle wasium about GNOMIUM!

14. So I had to grow quite old to learn that chemistry could be fun… Apropos Mendeleev’s table and Hund’s rules: I hated this stuff at school and university. And I found out why: There’s a totally unknown but very pretty alternative periodic table drawn by Helmut Lindner, e.g. in his excellent book Grundriss der Atom- und Kernphysik (Leipzig, GDR, 1984). (Just needed to mention it lest this jewel gets lost. (Someone tell wikipedia))

15. John Baez says:

Thorbear and Florifulgurator solved the puzzle! I guess it takes a mythological being to find a nonexistent element named after a mischievous sprite!

After nickel and cobalt, the third element named after a mischievous underground sprite is gnomium!

The problem is that while:

• iron has 26 protons,
• cobalt has 27 and
• nickel has 28,

the atomic weights of these elements don’t rise along with the number of protons:

• the atomic weight of iron is 55.845,
• the atomic weight of cobalt is 58.9331,
• that nickel of is 58.6934.

As far as I know, this is the only place in the periodic table where such a ‘glitch’ occurs!

What causes it? Since the weight comes from both protons and neutrons, you’ll want to know how many protons and neutrons these elements have. This depends on which isotope we’re talking about:

• the most common isotope of iron has 56 protons and neutrons. (About 92% of iron on Earth is iron-56.)

• the only stable isotope of cobalt has 59 protons and neutrons. (All the cobalt on Earth is cobalt-59.)

• the most common isotope of nickel has 58 protons and neutrons. (68% of nickel on Earth is nickel-58, but 26% is nickel-62, and other isotopes are also present.)

As you can see, the most common isotope of nickel has fewer protons and neutrons than the most common isotope of cobalt! That’s part of the explanation, but it’s more complicated than that.

First, the atomic weight is the average weight, averaged over different isotopes according to how common they are: so, nickel’s atomic weight is pushed up by the large amount of nickel-62 on Earth.

Second, the atomic weight is not just the sum of the weights of the protons and electrons; thanks to E = mc2, we must also subtract the binding energy divided by the square of the speed of light. The binding energy is how much energy it takes to pull the nucleus apart into separate nucleons (protons and neutrons). Iron, cobalt and nickel have among the highest binding energies per nucleon of all elements:

Here’s a deeper puzzle: Is it a coincidence that the glitch in atomic weights happens near the peak of the binding energy curve, or not?

I honestly don’t know.

Anyway, in the late 1800’s, scientists noticed this glitch in the periodic table. At first they blamed the problem on errors in the measured atomic weights. But after the atomic weights of cobalt and nickel were established more precisely, the contradiction remained.

To understand the situation, you should remember that neutrons and protons were not known at this time, nor even the fact that atoms have nuclei: atomic weight was a mystery.

In 1889, Gerhard Krüss and F. W. Schmidt proposed a solution to the problem: an element, very similar and very hard to separate from cobalt, but with a lower atomic weight, so that its mixture with cobalt would be lighter than nickel. For reasons that should be obvious by now, they named this proposed element gnomium!

• Gerhard Krüss and F. W. Schmidt, Ein neues Element, welches neben Kobalt und Nickel vorkommt, Zeitschrift für Analytische Chemie 28 (1889), 340.

Alas, it turned out not to exist.

(And another small puzzle: what portion of what I just said doesn’t make sense? I got it from a Wikipedia article.)

• John Baez says:

John wrote:

(And another small puzzle: what portion of what I just said doesn’t make sense? I got it from a Wikipedia article.)

Since nobody seems to be trying this puzzle, I think I’ll answer it before I forget to fix the Wikipedia article!

There’s a ‘glitch’: the atomic weight of cobalt is higher than that of nickel. And I said:

In 1889, Gerhard Krüss and F. W. Schmidt proposed a solution to the problem: an element, very similar and very hard to separate from cobalt, but with a lower atomic weight, so that its mixture with cobalt would be lighter than nickel. For reasons that should be obvious by now, they named this proposed element gnomium!

That doesn’t make sense! Either we need gnomium to be very similar to cobalt but heavier than nickel,… or very similar to nickel but lighter than cobalt.

It took me surprisingly long to notice this mistake. I got it from Wikipedia:

A theoretical solution would have been an element, very similar and nearly inseparable from cobalt, but with a lower atomic weight, so that its mixture with cobalt would be lighter than nickel.

Is gnomium like cobalt but heavier, or like nickel but lighter? Luckily, Wordnik breaks the tie:

In chem., a supposed new metal having a high atomic weight, which Krüss announced in 1892 as associated with nickel and cobalt, and the presence of which he believed to be the cause of the assignment of too high a value to the atomic weight of cobalt. It has been shown that the supposed discovery was an error.

So, now I’ve fixed the Wikipedia entry…
So, I’ll fix the Wikipedia entry now.

16. David Corfield says:

As far as I know, this is the only place in the periodic table where such a ‘glitch’ occurs!

Argon 18 39.948
Potassium 19 39.098?

And tellurium-iodine.

• John Baez says:

Oh, okay!

(This is not the thing I said that does not make sense.)

Maybe I once knew about the potassium-argon glitch, or maybe I’m just vaguely remembering the fact that radioactive potassium decays into argon.

I wonder if the glitches you mention created as much puzzlement as the cobalt-nickel glitch. A curious extra twist in that glitch lies in the fact that cobalt and nickel are chemically similar, unlike the pairs you mention.

The argon-potassium glitch must have been discovered later. Argon was only isolated in 1894 (by Lord Rayleigh and Sir William Ramsay), though its existence had been suspected for a long time.

I see that tellurium was discovered in the 1780s, and iodine in 1811, but I have no idea when their atomic weights were measured with enough accuracy to note a glitch.

Tellurium was sufficiently confusing that its discoverer called it aurum paradoxium and metallum problematicum.

Ah, for the good old days, when there were plenty of elements left to discover. And plenty of false ones, too. I’d known about nebulium and coronium as a kid, and my beloved CRC handbook included charmingly obsolete isotope names like mesothorium, radiothorium, brevium and thoron. But only now, thanks to Wikipedia, did I learn about carolinium, pelopium, hesperium, sequanium…

• John Baez says:

It turns out that the tellurium-iodine glitched caused quite a lot of hand-wringing! Here’s a quote from:

• Joseph William Mellor, A Comprehensive Treatise on Inorganic and Theoretical Chemistry, Vol. 1, page 45.

which is part of a 16-volume book published perhaps sometime around 1922. Emphasis mine:

G. Krüss and F. W. Schmidt (1889) attributed the difficulty with cobalt and nickel to the presence of a hitherto undiscovered element in nickel which they named gnomium. This explanation, however, had to be discarded. It did not survive the ordeal remorselessly applied to conjectures of this kind. No gnomium has yet been found.

Again, the case of iodine and tellurium has been studied with relentless vigour stimulated largely by D. I. Mendeleeff’s prediction: “The atomic weight of tellurium must be between 123 and 126, and cannot be 128.” Iodine most certainly belongs to the same group as the other halogens, and tellurium undoubtedly belongs to the selenium group; these elements are accordingly placed among their own family relations in spite of the fact that if their atomic weights were alone considered tellurium would be ranked with the halogens, and iodine with selenium.

B. Brauner (1889) suggested that ordinary tellurium is a complex containing a- and jS-tellurium; and it was inferred that true tellurium say a-Te has an atomic weight 125, and that the other form of this element has a higher atomic weight, and will find a place in the periodic system in the valency below tellurium. D. I. Mendeleeff cafled this undiscovered element dwi-tellurium, Dt, and he sketched some of its physical and chemical properties; but tellurium, said G. Wyrouboff, has been tortured in every conceivable manner: it has been melted, sublimed, oxidized, hydrogenized, phenylated, dissolved, crystallized, fractioned, and precipitated; yet nothing but failure has followed all attempts to get an atomic weight lower than iodine or to fraction the element into two others.

Nothing has developed which would warrant a belief in Mendeleeff’s “must.” Hence, in spite of the fact that “the laws of nature admit of no exception,” faith in the law has led chemists to allocate these discordant elements according to their chemical properties and not according to their atomic weights.

To put the matter bluntly, the procedure runs: It is necessary either to reject the periodic law or to reject the number 127.5 for tellurium; the periodic law cannot be rejected because it is the very embodiment of truth, nay, truth itself; ergo, in spite of all evidence to the contrary, the number 127.5 must be wrong.

Bode’s law of astronomy successfully predicted the asteroids and allocated their proper place in the solar system; but the subsequent discovery of Neptune did not agree with Bode’s law. The law was accordingly abandoned and it is now regarded as a curiosity. Mendeleeff’s law may have to go the same way. B. Brauner’s assumption that tellurium is a mixture of true tellurium with a higher homologue, may be a good working hypothesis for stimulating experiments on this element, but to maintain the thesis against all evidence to the contrary “may afford an easier way out of the difficulty than by working steadily at the cause of the discrepancy, but it affords at best a feeble and undignified cover for one’s retreat.” This method must be dubbed unscientific, but the circumstantial evidence justifies the procedure in the expectation that a consistent system will ultimately grow from the truth and error engrafted into the “law.” It is not very probable that the principle underlying the periodic law will be abandoned because it is founded on a vast assemblage of facts of different kinds; and because it seems to be plastic enough to fulfil subsequent requirements.

The central problem in inorganic chemistry, said W. Ramsay (1904), is to answer the question: Why this incomplete concordance?

And of course the answer was to understand nuclear physics.

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