Note : The following essay was dictated to me by the late Dr. Isaac Asimov
in the summer of 1998, during a séance.
[ ;;;-) HHOJ wink-wink (and more of the same) ]
Of course my first idea was that she was pulling my leg, but these are strange times, and I hesitated. Maybe she meant it? Maybe the proton rule reminded her of another hateful prominence, maybe she saw the periodic table as yet one more chauvinist pig sty. So I just tried to reply quietly that it was the number of protons which determined the number of electrons, hence the chemical properties, which after all are the whole point of the table. Neutrons didn't play a role at all. She listened to me with a nasty smile and asked, "Oh no? Then what about deuterium and tritium? Why are they left out?" And she vanished before I could answer. I have decided since then that she must have been playing with me, but who knows? If you ever hear of a Neutron Anti-Defamation League led by a Ms. Paula Whatshername, you'll know where it all started.
Anyway, this led me to think that the periodic table, a subject that I
thought pretty much exhausted, actually wasn't. More: the table even
made the news recently! Well, not the headlines, so you might have
missed it. But you know how I love to share all this with you.
Brace yourselves, here it comes!
From here on, I'll take for granted that you are familiar with the periodic table and all basic notions behind it. If you aren't... better stop reading.
The periodic table is now kind of a classic, even though it was not known to the ancient Greeks. (I bet you didn't think that I could place a mention of ancient Greece in this essay.) But it exists for more than a century and, apart from a few details, it was frozen to its current aspect decades ago. In fact, it is not too difficult--I could do it quickly when I was a kid--to memorize once for all the hundred-odd names of elements along with their chemical symbols. Once you've done it, no chemical formula should puzzle you any more ever after. "NaCl"? Ah, yes, Na is sodium and Cl is chlorine.
Right? Right... roughly. But get ready for surprises, for once you look around sharply enough, you're bound to trip on a number of symbols not on your table.
Thus, there are 'meta-symbols'. When a chemist want to speak generally of 'oxides of all kinds', it is tempting to write that 'MO' or 'MxOy', where 'O' stands for 'oxygen' and 'M' for 'just any metal'. Similarly, organic chemists speak of 'radicals', and like to write 'R-CH3' to refer to methyl-anything, I mean any complex molecule ending with one methyl. Besides, they like to use 'pseudo-symbols' to denote a few dozens of most frequently used building blocks, like 'Me' for methyl (although methyl is really CH3), 'Et' for 'ethyl' (really C2H5), 'Ph' for 'phenyl' (really C6H5)... And there was a time, not so long ago, when cyanogen, really CN, was written 'Cy' since it behaved a lot like a monoatomic element.
You might yell that I'm cheating with my meta-symbols or pseudo-symbols. OK, drop them and go back to the table itself. And as the song goes, "Let's start with the very beginning, a very good place to start."
The table starts at element number one, that is hydrogen. But couldn't we imagine an element zero? No, please don't shout. Ms. Paula gave you a hint. Say there is an element zero, and let's give it a name, 'nullium', with a symbol, 'Nu'. So what would be its isotopes?
Well, zero proton and 'n' neutrons make a cluster of neutrons. Now (unless of course we are ready to consider exotic environments like neutron stars) such a cluster couldn't exist without a proton to make these neutrons stick together. (The reverse is true: no cluster of protons can exist without any neutron--that's why helium-2 or lithium-3 cannot exist.) There is, of course, one exception and that's nullium-1, i.e. one isolated neutron.
So: element zero does exist, and that's the neutron! Also note how it fits beautifully our suggested symbol, 'Nu'. (Much less seriously, element zero is also the subject of a hilarious spoof on the Web. To quote it partly, it speaks of the "discovery of the heaviest element ever known. Tentatively named administratium, or Ad, it has no protons or electrons, which means that its atomic number is 0. However, it does have one neutron, 125 assistants to the neutron, 75 vice-neutrons and 111 assistants to the vice-neutrons, giving it a mass number of 312. Its absence of electrons makes it inert, but it can be detected indirectly because it slows down considerably every reaction in which it is present.")
Going one step too far, you even have nullium-0: no proton and no neutron, a possible worthy candidate for a science hoax. And going yet further: could one imagine elements with negative numbers, say an 'element -1'? No? What about atoms made of antimatter? Mightn't we say that an anti-hydrogen atom, made of an antiproton with an orbiting positon, could be a nominee for 'element -1'? Nice enough... except there's the antineutron. Minus zero is equal to plus zero, while a neutron is NOT the same as an antineutron. So let's not go overboard there and return to the safety of positive numbers.
Back to Ms. Paula: could one 'redraw' a periodic table organized around the number of neutrons? Answer: yes and no. Yes, you can make a table, but no, it wouldn't be 'periodic', meaning that nothing useful would recur on successive lines, like chemical properties do for the proton- based table. Agreedly, by making lines end on 'magical numbers' (2, 8, 20, 28, 50, 82...), there would be some common point to line ends, namely an abundance of stable 'isotopes', but that's all, and not enough. A neutron-based table would just be useless. Chauvinist pig protons needn't fear to lose their first place.
But what about deuterium and tritium? Here one did take the trouble to make up names and symbols, D and T, for 'mere isotopes'. Well, they do play an important role in nuclear industry, and the presence of neutrons has specific impacts on their properties, because for such light nuclei one neutron can make a difference. Thus, the density of heavy water (D2O) is 10% larger than that of 'light' water (H2O), and molecular deuterium (D2) is twice heavier than light hydrogen (H2). (This is easy to understand, just count nucleons, they make most of the mass.) But notice how the notion of symbol is getting fuzzy: we just used 'H' here to denote the neutronless hydrogen-1, while 'H' should stand for any isotope of hydrogen. In order to speak specifically of hydrogen-1, we would really need a separate name for it. Going back to Greek roots, the logical name next to 'tritium' (i.e. 'third') and 'deuterium' (i.e. 'second') should be 'protium' (i.e. 'first'). But which symbol could be used for it? All possible symbols seem to be preempted, 'P' by phosphorus, 'Pr' by praseodymium, 'Po' by polonium, 'Pt' by platinum... Only the unconvincing 'Pi' is free. Or call it 'protonium' to use 'Pn'?
There was a time when other 'mere isotopes' at the high end of the table did get specific names, but I explained that at length in another essay (Overflowing the Periodic Table, in Science Past - Science Future). By the way, one of the most striking cases of isotope naming among heavy elements is one that I later changed my mind about. (Yes, this happens, although not too frequently.) I'm referring to the 'emanation' gases, i.e. the following three isotopes of element 86: 222 (radon, Rn), 220 (thoron, Tn) and 219 (actinon, An). I wrote then, "the element is today called radon, but some people wonder if a better name might not be 'emanon,' covering all three 'emanations' and not preferring one to the other." It came to my mind later that, after all, all three isotopes do come from radium, only from different varieties of radium, so 'radon' is an adequate common name. Radon 222 just came from the first discovered variety of radium, the one generated by the decay of uranium 238--so, if you need to give it a specific name, why not call it 'uranon', 'Un'? And you might have noticed a 'hole' in the set of radons: to fill it, just throw in the fourth and last radioactive family, the one which is less known because its ancestor, neptunium-237, is not long-lived enough to have survived in significant amounts. So, add radon 221, and call it 'neptunon', 'Nn'!
OK, let's be serious: I do not recommend, now or later, to go on with particular names for specific isotopes. It can only create confusion. I would accept grudgingly deuterium and tritium, but just because it's much too late to kick them out. Let us stop at that. Thoron and actinon--and ionium and brevium and mesothorium and such--belong to the history of science, not to its present or future.
If we now forget individual isotopes and go up to the bulk of the table, we find some fuzziness when we compare periodic tables coming from different times or different countries. You would expect holes--after all, some elements were discovered pretty recently--but you would not expect unusual names or chemical symbols. However, this happens, for a number of reasons.
Firstly, some symbols took some time to reach their final form, so you could find 'Yt' instead of 'Y' for yttrium, or 'Ur' instead of 'U' for uranium. But that's just a small detail.
Secondly, a few elements once had another name. Niobium (Nb) was once known as columbium (Cb), and beryllium (Be) as glucinium (Gl). Another interesting case is nitrogen (N). Nitrogen was studied by various scientists, but especially by the illustrious French chemist Antoine Laurent de Lavoisier, who called it 'azote', meaning 'no animal (life)', since mice suffocated when put into it (nitrogen is not toxic, but it doesn't support breathing either--you need oxygen to breathe). The French insisted to use this name, along with the symbol 'Az' and names like 'azotate' instead of 'nitrate', well into the present century. After the Second World War, they accepted to move to symbol 'N' and to words like 'nitrate', although they still cling to 'azote' as the name of the element. But 'Az' disappeared for good from French periodic tables.
Thirdly, you might also find an unusual name and symbol that were added only briefly, then dropped from later tables. Typically, this happened when chemists believed that a new element had been discovered, but later studies proved this discovery to be false. An example is 'masurium' (Ma) for element 43. Element 43 was later found not to exist in nature at all; it had to be synthetized in the laboratory, hence its name, 'technetium' (Tc), meaning 'artificial'. Another interesting case is didymium (Di): this rare earth metal had been discovered shortly before Mendeleev made his original table--where didymium actually appears--but it was later proved to be really a mixture of the two elements 59 and 60, praseodymium (Pr) and neodymium (Nd).
But the worst confusion in the periodic table came in modern times, and in fact quite recently, in the upper part of the table, starting from element 104. Indeed, you might find in various tables this very element 104 diversely called rutherfordium (Rf), kurchatovium (Ku), dubnium (Db) or unnilquadium (Unq); and the same with the next-heavier elements, so that you might wonder what happened. Well, you know that heavy elements beyond uranium (element 92) did not exist in nature and had to be made artificially. (Sure, once elements 93 and 94 had been synthetized, they were discovered in nature as minute traces, but only because one then knew from the lab what to look for.) A fierce competition soon rose between research centers of various countries to be the first to make the next-heavier element. America took the lead, as witnessed by the name of element 95, americium (Am), but the Soviets and the Europeans followed close. Even the Swedish had their hour of fame with element 102, which they called 'nobelium' (No), even though their claim was shaky. The Americans expressed their skepticism by calling element 102 'nobelievium' as an inside joke, and indeed the Swedish find was later proved wrong. But the Americans, even though their claim won, gracefully let the name 'nobelium' stay.
As heavier elements were made, the fight grew more bitter. Mind you, the race was mostly for glory: the heavier the element, the shorter its period and the more insignificant the amount that you can make, so that no element beyond (say) 98 can have any practical use. Nevertheless, as illustrated by the case of nobelium, a consensus of sorts could be reached for the names of elements up to and including element 103, lawrencium (once Lw, now Lr). But then it all blew up. Element 104 was claimed by the Americans as rutherfordium and by the Soviets as kurchatovium, and similar struggles affected the following elements. Contenders then turned to the International Union for Pure and Applied Chemistry (IUPAC), an organization which had until then recorded new names without all that trouble. The IUPAC created a committee, the Transfermium Working Group, to settle the dispute and reach agreement. Pending its conclusions, it suggested using temporary 'neutral' names. Thus, element 104 could be referred to as 'unnilquadium' (Unq). No, that's simple, really: un-nil-quad-ium, that is, from Latin roots, one-zero-four-ium. Got it?
The committee spent several painful years in search of a compromise about elements 104 to 108 (more about the 109 and higher up later). In fact, they were still busy when I died, a sad occurrence which did not stop me to follow their proceedings. (No, I'm not allowed to give details on that, even if I can understand your disappointment.) Thus in 1994, they came with a first proposal--which, by the way, attributed to element 104 yet another name, 'dubnium' (Db), in honor of the formerly-Soviet-and-now-Russian research center of Dubna.
This proposal raised havoc in the United States for several reasons. On one hand, it seemed to mirror the internal balance of the IUPAC more than the reality of discoveries. On the other hand, it rejected the American-proposed name 'seaborgium' (Sg) for element 106, under the pretext that Glenn Seaborg was still alive. Now Seaborg had always been the motor behind heavy element research in the U.S. He was the father or grandfather of more elements than anyone else, and element 106 had been named from him as a logical and well-deserved tribute. And this 'sorry-not-yet-dead' rule, which had never been invoked before in the story of chemistry, looked a bit too much like a trick to make room for other (late) stars of IUPACland.
The roar of dissent from America put IUPAC back to work, and a second compromise was ready in 1997. Here are in a nutshell the three views for elements 104 to 108:
- the U.S. view: rutherfordium (Rf), hahnium (Ha), seaborgium (Sg),
nielsbohrium (Ns), and hassium (Hs)
- IUPAC's first try: dubnium (Db), joliotium (Jl), rutherfordium (Rf), bohrium (Bh), and hahnium (Hn)
- IUPAC's second try: rutherfordium (Rf), dubnium (Db), seaborgium (Sg), bohrium (Bh), and hassium (Hs)
Looking at this, you get the feeling that IUPAC chemists, being badly prepared for such wrangling, cared more for compromise than for coherent conclusions. In two cases, they suggested a same name for two different elements: dubnium for 104 then for 105, rutherfordium for 106 then for 104... and, last but not least, they proposed hahnium for 108 as Hn while it had been proposed for 105 as Ha, before dropping it altogether. The first-name-or-not quarrel around element 107 is also worth noticing.
Hopefully, tensions should now subside. The future will be quieter, if only by lack of contenders. There remains now just one main player in the game, the GSI ('Gesellschaft für Schwerionenforschung', i.e. 'Heavy Ion Research Society') at Darmstadt, Germany, the undisputed maker of the heaviest nuclei. Thus, everyone agreed upon the name 'meitnerium' (Mt) for element 109, in honor of Lise Meitner, who thus became the only woman having an element named from herself only. (Curium was named from both Pierre and Marie Curie, and possibly also from their daughter Irene Curie--who, by the way, married Frederic Joliot, a brief nominee for element 105.) But this womanly element was also the most unstable ever made, a coincidence that I'm sure Ms. Paula would resent.
Later, the GSI synthetized elements 110 to 112, but, with understandable cautiousness, refrained from proposing names yet. Consequently, these elements are today referred to as (yecch!) ununnilium, unununium and ununbium, but everyone hopes that this won't last. So the poor Otto Hahn might have a last chance after all to get an element named after him. I personally would suggest element 111 as the ultimate hahnium, after the stepping stones at 105 and 108.
The heaviest nucleus at the time of writing is ununbium-277. Its period is only a fraction of a millisecond, and one might think that the very limit of the feasible is almost reached. However, the structure of nuclei is complex and there exist 'magical' numbers of protons and neutrons which make some nuclei less unstable. A 'stability island' might exist around element 114, and more precisely around the nucleus ununquadium-298. Such nuclei might have periods of years or more, instead of fractions of a second. A few optimists even expect to find there a few stable isotopes, although this appaears highly unlikely, no such elements having ever been found in nature.
Even the idea of relatively high stability might make you incredulous, seeing the short-short--and what's worse, shorter-shorter--lives of superheavy isotopes obtained so far. Aren't we now, with element 112, very close to this alleged island, with still no sign of increased stability?
Well... yes and no. We may be close 'proton-wise'--112 vs. 114--but we aren't 'neutron-wise'--165 vs. 184. You see, the neutron-to-proton ratio giving the least instability grows with the weight. It is 1-to-1 for light nuclei, like in carbon-12, nitrogen-14 or oxygen-16, but about 1.6-to-1 for heavy nuclei like thorium-232 or uranium-238. Now how do you synthetize superheavy elements? Starting from thorium or uranium and adding one nucleon at a time was practical as long as the nuclei you dealt with survived years or even days, enough to leave you time to jump from one stepping stone to the next. But what do you do when your intermediate nuclei decay in a minute fraction of a second? The only other way--the way used with success by GSI today--is to do it in one step, by hurling middle-sized ions onto heavy nuclei in order to cause 'gentle fusion'. Thus, GSI produced ununbium-277 by having zinc-70 ions fuse with lead-208, in such a way that only one neutron would spill over in the process. GSI expects to go further, to elements 113 and 114, by replacing the target by bismuth-209, or the 'missile' by germanium-76, thus producing ununtrium-278 and ununquadium-283. The catch is that the neutron-to-proton ratio of the end result is of course lower than that of the target, while we would like it higher to get better stability. A process to produce high-neutron-ratio nuclei is yet to discover.
There is no particular reason to expect that 'future' superheavy elements would display any extraordinary properties, and yet such expectations do exist in a part of the general public. Indeed, the collective mind remembered a long time the glamorous discovery of radium in the 1890's, and it was tempting to capitalize on these memories, whether in science fiction or in pseudo-science. What turned out as common heavy elements of today did feed SF dreams in the 1930's. In Donald Wandrei's story Blinding Shadows (1934), element 95, rhillium, extends itself into 4-D space, and a complex mirror built from it brings back murderous ghost-like hyperbeings who make New York City a place of terror. Or take Nat Schachner's Ultimate Metal (1935). Here element 93, evanium, is obtained "with heavy neutron bombardment from sulphur," only to vanish 35 seconds afterwards into "a gas identified as uranium X." However, it can be 'stabilized' by mixing it "in minute traces with beryllium and titanium." This fabulous alloy, "harder than diamond but malleable," shines of its own light, enough to make artificial lighting superfluous in a 150-floor tower that is quickly built of it by a greedy tycoon. Alas, it turns out that the stabilization is temporary, and the tower eventually vanishes into thin air, dropping its 50,000 tenants to their deaths. I gave you some 'scientific' details here--and I left out the most appalling ones about evanium's 'metallic life'--to show how fiction much outweighed science in such tales.
Superheavy elements of today happily fill this glamor niche. Thus, fans of Star Trek and the like have extended the periodic table well beyond 112 with, in this order, celebium, colladium, algobarium, irillium, topaline, zienite, dilithium, rubindium... Most of these were (are to be?) supposedly discovered on various planets, satellites, and asteroids in the solar system. The fact that they are 'discovered' suggests that they are stable or almost stable, so that one wonders why they weren't found on Earth, but then where would be the glamor? An answer of sorts is given by dilithium, "discovered on Jupiter's fifth moon," which has four-dimensional properties--like its paper ancestor, rhillium--but does exist on Earth... as crystals which were mistaken for mere quartz. (Seemingly, spectroscopes weren't invented on Star Trek's Earth).
I should also mention element 115, and specifically its isotope 271, because it was the focus of lots of attention recently. It is supposed to be the fuel of flying saucers, I mean extraterrestrial UFOs, which were captured by the U.S. Air Force and are being reverse-engineered in a secret base. No, not Roswell. Go look by yourself. Just search the Web for "Bob Lazar." You'll learn that 115 is the key to anti-gravity and anti-matter. Wow!
To conclude on a more serious note, physicists might someday prove from
theoretical considerations that there is an ultimate heaviest element,
one that cannot ever be outweighed. The race to be the first to get it
would be something. Personally, I would find it poetic that it be
element 123, that is one-two-three-ium! Eventually, this element would
get a 'real' name. I just hope it wouldn't be Schwerionenforschungium...
but then, wouldn't that present a unique, and ultimate, opportunity to
have a chemical symbol fit to please all science fiction fans... "Sf" ?