A Blog by Robert Krulwich

An 80-Year-Old Prank Revealed, Hiding in the Periodic Table!

You wouldn’t know it, because it’s hiding down there at the bottom of the periodic table of elements, but it’s a prank—something a five-year-old might do—and the guy who did it was one of the greatest chemists in America. It’s pure silliness, staring right at you, right where I’ve drawn my circle, at element 94.

Periodic Table Courtesty of DePiep, CC
Periodic Table Courtesty of DePiep, CC

It says “Pu.”

“Pu” stands for plutonium, the element named for Pluto, back in 1941 the newest, teeniest planet in the solar system. The American chemist Glenn Seaborg came up with this name after his colleagues found neptunium (element 93) the year before. He and his team at Berkeley had a cyclotron that smashed particles together and so they had an incredible run of discoveries: americium (95), curium (96), berkelium (97), californium (98), einsteinium (99), fermium (100), mendelevium (101), nobelium (102), and finally (and he’s the only guy who got his name on an element while still alive), seaborgium (106).

[Learn more about plutonium and other man-made elements in “Twenty-Six New Elements.”]

Seaborg and his colleagues at Lawrence Berkeley Laboratory filled so many once empty boxes on the periodic table that it was said you could write him a letter addressed entirely in his own chemical elements, like this:

Illustration by Robert Krulwich
Illustration by Robert Krulwich

So the man knew his periodic table. But could he spell?

Let’s go back to Plutonium, which, I don’t have to tell you, is spelled P-L-U. There’s an “L” after the “P”. It’s not Puto, it’s Pluto. Now look back at the abbreviation on the Periodic Table. What happened? Why no “L”?

When Plutonium was discovered America was about to go to war. In 1942, Seaborg moved to Chicago to join the top secret U.S. effort to build an atomic bomb and helped produce a miniscule amount of plutonium fluoride (about a millionth of a gram). His team found that an isotope of plutonium, Pu-239, could be split, releasing an enormous amount of destructive energy. The Fat Man bomb, dropped on Nagasaki in 1945, had a plutonium core.

Glenn Seaborg
Glenn Seaborg
Photograph by Fritz Goro, Getty

The scientists who worked on the A-bomb were not allowed to call element 94 “plutonium.” Every ingredient in the bomb was top secret, so they gave it a false cover; they called it “copper.” When they had to use actual copper in some of their experiments, they called that “honest-to-God copper.” Only when the war ended was Seaborg allowed to publish his discovery, and that’s when plutonium became an official element.

Discoverers can not only name their elements, they can also choose the abbreviated symbol that goes onto the periodic table alongside the atomic number. It has to be very short, usually two letters.

There’s a naming committee that reviews and blesses the abbreviations, and so, Glenn Seaborg was free to choose.


He—nobody else—chose Pu. But why? Two colleagues, writing in Los Alamos Science, a journal published by the famous science lab, say he told them it was a crazy impulse. “The obvious choice for the symbol would have been Pl,” wrote chemists David Clark and David Hobart in 2000, “but facetiously, Seaborg suggested Pu, like the words a child would exclaim, Pee-yoo!” when smelling something bad.”

When I talked to Seaborg’s son Dave, he said the same thing. His dad had a weird sense of humor and “he just thought it would be fun” to treat this element as if it were stinky. You know the face kids make when they say pee-yoo (a la Calvin)? He wanted to sneak that into the periodic table.

Illustration by Robert Krulwich
Illustration by Robert Krulwich

It wasn’t an antinuke idea (though Seaborg opposed dropping an atomic bomb on Nagasaki and signed a letter saying so to President Truman). It wasn’t a comment on plutonium’s destructive power. It was just a prank.

What did the naming committee say when Seaborg handed in his abbreviation?

“Seaborg thought that he would receive a great deal of flak over that suggestion,” Clark and Hobart wrote. One imagines the members weren’t exactly a wild and crazy bunch, and yet, for reasons we will never know, “the naming committee accepted the symbol without a word.”

And there it remains. So any time you like, you can look at one of humanity’s greatest intellectual creations, posted in classrooms all over the world, a table that organizes all the stuff of the cosmos into a coherent map, and smack dab at the bottom, somebody’s whispering, “pee-you!”

Periodic Table Courtesty of DePiep, CC
Periodic Table Courtesty of DePiep, CC

82 thoughts on “An 80-Year-Old Prank Revealed, Hiding in the Periodic Table!

  1. Really, that’s it!? The whole story about it being called copper and no mention that copper has the similar (not to mention odd) abreviation of Cu? No connection?

    1. Jeremy, Copper is what we might call an old-world element. It has been used by humanity for some 10,000 years. Because of this, there is no documented discoverer and the “Cu” abbreviation is just a shortening of “cuprum,” the Latin word for Copper. This is true for many of the elements: Au for gold comes from the Latin word “aurum,” also meaning gold, and Pb for Lead (Latin: plumbum).

      1. Patrick Hobbs: It is true that Pb comes from ‘plumbum,’ meaning lead.

        But then really, we could ask how come LEAD isn’t Pl (or Pu for that matter?)

      2. I am pretty sure that Jeremy does not need a history lesson. I am fairly confident that he, like I, saw the play-on-abbreviation potential with Copper and he’s not asking “Why is Copper CU?”

      1. Tomas, apologies. I misread your comment, thought you’d asked about Plutonium. I couldn’t figure out how to delete it!

      1. Ha! You guys surprise me. When researching this, I got to wondering if maybe whovever discovered Platinum, element 78, had already jumped on “Pl” so that combo was taken, but if you look, you’ll see Platinum is “Pt” (why? why choose the ‘t’?), and then there’s potassium which has a “p” and “t” but gets called “K” — derived, apparently, from a neo-latin word, kalium — which goes to show you that when it comes to naming your baby, as in life, so in chemistry, the parent can do whatever the parent wants to. That guy in the Johnny Cash song who names his boy Sue is the closest I can come to what Glenn Seaborg did here (of course plutonium can take care of itself no matter what it’s called…but I’m blabbering on.)

        Potassium is a chemical element with symbol K (derived from Neo-Latin, kalium) and atomic number 19. It was first isolated from potash, the ashes of plants, …

        Platinum is a chemical element with symbol Pt and atomic number 78.

          1. As do we in Swedish. Although Davy discovered the element, potassium was given its abbreviation by a Swedish chemist, Jöns Jacob Berzelius. The name kalium is neo-Latin but goes back to an old Arabian word al-qalyah meaning plant ash, a root it shares with alkali.

      2. I’m surprised nobody bothered to mention that the Latin word is predated by the Greek word for copper. Just like most things, the Romans merely stole that name from the Greeks. Copper in the Greek world mostly came from Cyprus, so it was called metal-of-Cyprus: aes cuprium.

        I immediately thought of the possible like to Cu when Robert mentioned that they used copper as a Euphamism for Plutonium… I’m surprised none of his interviewees had any comments about that apparent coincidence.

      1. That’s not the point that Jeremy was making. He was saying that it was odd that the author was stressing ‘pee-you’ as the sybol for plutonium, due to it sounding rude, when the symbol for copper (which was masquerading as plutonium) is Cu anyway. i.e. he was saying it was perfectly natural to give plutonium the symbol Pu without resorting to childish lavatorial humour.

    2. Jeremy I am not sure if anyone has said this but it seems that Cu comes from cuprum. I hope you were asking about this.

  2. In some languages, such as Bahasa (used in Malaysia), the chemical elements are still based of the ‘sciency’ chemical name, e.g.

    Ferum (Fe) for Iron
    Natrium (Na) for Sodium (from Soda)
    Kalium (K) for Potassium (from Potash)
    Kuprum (Cu) for Copper..

    So, when we first heard ‘pig iron’, it was quite interesting to know the chemical formula (as English isn’t our 1st language)

    1. And in other languages, of course, very few of the common names have any connection to the symbols. In Czech:

      H – Vodík
      O – Kyslík
      C – Uhlík
      K – Draslík
      Mg – Hořčík
      Si – Křemík

      and so on.

    1. Einsteinium was discovered by Albert Ghiorso and used for a thermodynamic bomb in 1952, but it’s name was revealed and announced in 1955 after Einstein had died for the reason that it is used for a bomb.

  3. I met Seaborg in the early 1990s at UCLA and talked to him for a few minutes. He was a nice man and wished me well in my scientific career.

  4. And here I was thinking that Seaborg backtracked it from plutonium fluoride, and wanted to make it PuF (in my head, read as: poof!). :/

  5. Who finds this amusing? I feel a part of me dies ever time I see this kind of garbage published. I’m at a loss as to what to even say about it; juvenile…not really, it’s too lame to even consider immature. A whole article about a coincidence of two letters and an unfounded assumption to make a joke that that only a simpleton would find in the least bit humorous. The internet and so many of the once respected publications are little more than spam at this point wasting peoples time and corroding knowledge.

    1. Thank you Jason.
      I have worried about the NatGeo since Rupert Murdoch took it over.
      And seeing what they are publishing….this article is Beyond stupid. And pointless…

      1. On another article, the paragraph concerning bacteria out-smarting scientists again says a virus infects pigs, pork, and people. I think we may be suffering from a terminal case of stupidity.

  6. That is it? do you really think committee liked that it was not PL ( already Plumbum is PB, that could have been abbreviated to PL as well ). This actually removed a serious confusion NO PL for lead or plutonium. so there

  7. In the world outside the U.S., the two elements Sodium (Na) and Potassium (Ka) are called Natrium and Kalium, respectively. Do the element table abbreviations make more sense now?

    Another U.S. oddity: they insist calling Aluminium (Al) “Aluminum”! Why? I guess someone made the mistake long ago, and nobody ever stepped up to correct it.

    1. Actually Aluminum was the original name for the element, however shortly after it was named it was decided to change it to Aluminium as ‘ium’ was more commonplace in the periodic table than ‘um’. While most of the world accepted this change in America it was felt unnecessary so they kept the initial spelling.

      1. You mean aluminium is not the British spelling? Like colour? These people that talk about vee-ta-mins don’t always spell the way we do.

  8. So why is lead (“plumbum”) Pb, and platinum Pt, I wonder? It couldn’t possibly be because it’s hard to tell a lowercase L from an uppercase I in a san serif font (the sort of font that’s regularly used in, ohh, say, periodic tables of the elements), could it?

    I mean, there’s no possible chance the naming committee considered any confusion that might arise between a hypothetical element “Pl” and the perfectly real compound potassium iodide (PI), if someone’s reading a formula quickly, right? Surely not.

    1. Yay! @Steve (and @Jeremy above),,, a couple of voices of reason on this discussion. Sheesh! As anyone who has ever tried to distinguish between l (ell, lower case) and 1 (number 1) and I (upper case i) in any sort of typing, coding, or layout, it’s important to avoid possible confusion.

      “Pee-yoo” that the author seems to think is a childish reason for abbreviating it as Pu just makes no sense for me. I can’t imagine a professional scientist ever considering trying to insert “pee”, referring to urine, into any name or abbreviation.

      1. I personally know a Russian theoretical physicist who invented a term that was translated into English as “pipiation” (meaning “multiplying each term in a nonanalytic series by pi-squared in order to make the series analytic”). In the hallway, he snickered as he asked me if I knew what “pi-pi” meant in English (Russians pronounce the Greek letter pi as “pee”). I expect such humor from physicists.

  9. You ever spent time with a 4 year old? Trust me, PU is funny. And when that 4yo gets to high school, or junior high, then Chemiker’s research is funny, too. And a great many of us never outgrow silliness. Even scientists are allowed to be silly–the creativity that comes with it is what allows them to think outside the box and discover things the rest of the world never thought of. That’s the true beauty of science–it’s refusing to ‘grow up’ and think like the rest of the world, even after you’re educated.

    1. In high school we decided to have an awards day at the end of our Chemistry and Physics classes, (Chemmy and Physie awards) and I and a classmate emceed the proceedings and saw fit to take our stage names from the periodic table. I was FeCoNiCu TaWReOs, and he was GaGeAsSe PaUNpPu. Were it not for Pu, it would not have worked quite as well.

  10. Does this guy produce anything beyond this kind of contrived inanity? I’ve yet to see a piece of actual scientific information emerge here. Guess this was just another “little thing” that caught his eye and then just naturally got “bigger, richer and much more compelling”…

    The other contributors to Phenomena manage to be a lot more grown-up and a hell of a lot more interesting.

    1. Google for Robert Krulwich. You’ll find he’s a longtime science reporter, quite respected, and a co-host of the brilliant NPR program Radiolab.

      Sometimes he writes about silly things. There are silly things in the world. Don’t get all agitated when he writes about something you don’t think is funny.

      1. Hi Chris

        1] I’m not agitated.

        2] You’re quite right – Robert Krulwich is an accomplished individual. However, I stand by my opinion that the other contributors are doing a better job in this setting.

  11. Some elemental symbols and even the cations are from Latin:
    Hg, mercury, from hydrargyrum, which is used to be called. AKA quicksilver. Quite toxic.
    Copper: Cu from cuprum. The classical names of the cations are cupric and cuprous, with cuprate used in transition metal complexes. Co is cobalt.
    Silver: Ag from argentum. Argentate when used in a transition metal complex. Si is silicon.
    Gold: Au from aurum. Aurate when used in a transition metal complex.
    Potassium: K from kalium. Po is polonium.
    Sodium: Na from natrium.
    Lead: plumbum, also seen plumbarius. Classical names of cations are plumbic and plumbous. What did plumbers work with in the old days? Probably lead, then copper, now PVC piping quite often.

    Tungsten (heavy stone or lodestone, Swedish): W, from German, Wolfram.
    On and on we could go.

  12. At a guess, there was one occasion when the abbreviations for then known elements were agreed and standardised, and that happened at a date when everybody was already familiar with lead and platinum, so they chose abbreviations which wouldn’t confuse one with the other.

  13. If nothing else, middle school students would enjoy something like this as they love working on codes and figuring them out. What better to get them thinking that science is cool because possibly more mysteries are lurking around every corner and hiding behind each turn of the pages of their text books? The Pu is a great “hook”.

  14. Know what’s crazier than this? Having to work with radioisotopes in a college lecture. I had to use a nuclide generator to demonstrate radioactive decay. I didn’t want to, but I wasn’t given a choice: “We all do this,” or something like that.

  15. “The obvious choice for the symbol would have been Pl”
    Perhaps. As much obvious as the choice for the symbol of platinum, which instead is Pt and of lead (plumbum, in Latin), which instead is Pb.

    This article only contributes to the stereotype of physicists as people with a lame sense of humor.

    1. I guess that’s like the movie Forrest Gump. You can’t understand all the humor unless you were alive in the 1960s. In fact, you won’t even recognize all the characters. You might recognize JFK and LBJ, but do you recognize Abbie Hoffman or Bobby Seale? If not, then some of the movie goes over your heads.

  16. PLATINUM is called like that because it is the latinization of the Spanish word Platino. It was called like that in the description of the Spaniard Antonio de Ulloa in the 1730s due to the superficial similarity with Silver (Plata in Spanish). Both elements were very often confused at the time.

    In order to be called PlatinIUM instead of PlatinUM, as some comments point out, the Spanish word should had been PlatnIO instead of PlatinO.

  17. 15 Phosphorus = P
    19 Potassium = K
    46 Palladium = Pd
    59 Prasodymium = Ps
    61 Promethium = Pm
    78 Platinum = Pt
    82 Lead = Pb
    84 Polonium = Po
    91 Protactinium = Pa

    I’m thinking calling Plutonium as PL would be confusing with Polonium and Platinum. Pu is good for uniqueness. There’s a lot more elements starting with P than I remembered. Praseodymium? Really? I’d missed that one before. Granted, it’s an odd-duck Lanthanoid, but still, funky name.

  18. IMO, the assertion that “Pl” would have been the single most obvious choice is flawed from the outset.

    I can’t quite pin it down, but after being exposed to them for a while, most element abbreviations started to make sense to me. Ar-gentum, Man-ganese, Molyb-denum, Ber-kelium, Ytter-bium… possibly a linguist could extract a pattern, something phoneme-based perhaps. To my ear, the most obvious would have been Pt, which was already taken.

    Though wouldever “rule” I try to come up with, there’d be numerous exceptions. So, to repeat, I don’t see why “pl” should have been obvious or why anything else needs an explantion, much less do I understand why that explanation should be a juvenile joke.

    Unless someone discovers a letter from the old man himself, I say the pee-you explanation is nonsense. You had your clicks, and -congratulations!- the world now has another urban myth. Thank you very much.

  19. Regarding the I/l/1 font confusion comment, Pl honestly just reminds me of Pi. (Not that it’s ever spelled out in usage… Nor is it used frequently in chemistry to my recollection.)
    All that being said, I swear I remember hearing this joke 15-20 years ago. Nothing new.
    On a side note, this discussion has made me want to brush up on my knowledge, so thanks for that! (Chemistry was never my strong suit.)

  20. No one here seems to have commented that if spoken as a syllable instead of two letters, it sounds like ‘poo’. P U!

  21. Thank you for a respectful (for the most part) and interesting discussion. Very rare these days. A lot of folks who read Nat Geo are like me. Long time fans who are not scientists or “geeks” , for lack of a better word, who love these interesting tidbits. As a middle school reading teacher, I can tell you my kids will love this, and learn something in the process. I’ll use it when their science class works on the periodic table. Thanks NAT GEO!

  22. Actually, the element gallium was named after its discoverer, Le Coq, while he was still alive. He told the committee that he wished to honor the country of his birth, France. But “francium” was already in the periodic table, as he well knew. So he said “gallium” to honor Gaul.

    After it was decided, he told them that he named it after himself. “Gallus” is “rooster” in Latin, and Le Coq is, well, “rooster”.

    I met Seaborg in Hawaii thirty years ago. He and my father were in the same chemistry class back in 1930 or so at UCLA. Seaborg was dumbfounded that I could tell him the name and nickname of his chem prof.


  23. Speaking of the names of chemical elements where on earth is Humphrey Davy? There are physicists & astronomers but not the chemist & epic humanitarian, Humphrey Davy. After all, he discovered at least 5 elements: Barium, Calcium, Boron, Strontium, and Magnesium. Come on, Ladies & Gentlemen let us honour one of the greatest chemists of all time. Humphridium, perhaps?

  24. I see nothing unusual about the choice of Pu as the abbreviation for Plutonium, so when I saw “Pu” circled in the article, I didn’t think of anything other that it being a standard type of abbreviation. I think the only prank here is the one being played on all of us by the author.

  25. One would have expected something extraordinary from the heading of the article. But it was a let down. After all, what is in a name, let alone an abbreviation.

  26. Have enjoyed the refresher course – 80yo and still learning; also for what it’s worth:
    And so we ask why is it so
    And we answer we don’t know
    But if you tell us we’ll believe
    That you’re not trying to deceive
    Until another we denote
    And then your answer we’ll demote
    Until another’s on the scene
    Then all foregoing we’ll demean
    And so on, so forth ‘til the end
    When It may drive us round the bend
    – well almost

  27. As Horace once wrote,
    “Misce stultitiam consiliis brevet:
    Dulce est desipere in loco,”
    which can be translated as “Mingle a little folly with your wisdom; a little nonsense now and then is pleasant.”

    And Roald Dahl rephrased it (via Willy Wonka):
    “A little nonsense now and then
    Is relished by the wisest men.”

    I agree with both of them.

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