# Why are isotopes of hydrogen the only ones with special names?

Why does no other element but hydrogen get special names for its isotopes?

• Because D has different organic chemistry perhaps. physlink.com/Education/AskExperts/ae685.cfm Aug 25 '15 at 17:43
• The isotopes of hydrogen are much more commonly used in the laboratory and in chemical discussion then the isotopes of other elements.
– ron
Aug 25 '15 at 23:47
• Dare I suggest the simple answer is that we can't name everything, or we'd run out of names ? Jan 26 '17 at 16:53

## 4 Answers

Harold Urey and George Murphy used spectroscopy to identify deuterium late in 1931, announcing it at the 1931 Christmas meeting of the American Physical Society. Picking up out of 'From Nuclear Transmutation to Nuclear Fission, 1932-1939" by Per F. Dahl:

If anything, the naming of the new isotope proved more problematic than its isolation. At a special session on heavy hydrogen at the general June meeting in 1933 of the APS in Chicago, organized in conjunction with the Century of Progress Exposition, the ensuing discussion on its naming 'threatened to become acrimonious,' according to Francis Aston of the Cavendish Laboratory - the great authority on atomic weight measurements and a guest speaker at the discussion. The argumentation had to do with whether to retain the name 'hydrogen' for the isotope, as Niels Bohr preferred; after all, it was not a new element and had the atomic number 1. Both Gilbert Lewis and Ernest Lawrence opted for 'dygen' for the H$^{2}$ isotope and 'dyon' for its nucleus, wheras Rutherford preferred 'diplogen' and 'diplon' instead. In the end, Urey had the last word, as he was entitled to, settling on 'deuterium' for the isotope and 'deuteron' for its nucleus.

Given the heavyweights in the field wanting a separate name for the isotope, even Neils Bohr could not hold back the tide. Again, though, you have to remember that this was in the very early days of nuclear physics. While the existence of the nucleus dated back to Rutherford's experiments pre-WWI, they were still very unclear just what the nucleus was constructed out of.

This was all occurring just as Cockroft and Walton were using their new ion accelerator to perform the first human-induced nuclear fission ($^{7}$Li + p -> 2 $^{4}$He), published in the Proceedings of the Royal Society on July 1st, 1932. Alpha, beta, and gamma particles had been identified since the late 1800s, and natural sources were used for nuclear physics experiments. It was readily recognized that a source of energetic protons would be highly desired.

Also, remember that 1932 was the year that Chadwick discovered the neutron as a separate entity. Thus, also from Dahl:

The discovery of the neutron would soon revise Urey's view of his deuteron as consisting of two protons and an electron. However, as late as October 1932, it was still not obvious among physicists that the deuteron consists of 'one proton and one Chadwick neutron' instead of two protons and one electron.

Against this rapid-fire series of experiments on nuclear physics, it really isn't unusual that deuterium got a separate name - it was still not universally appreciated that it wasn't something weird. Than, once it was accepted, it was too useful to readily distinguish experiments with protons vs deuterons vs tritons to revert their names back to normal isotope nomenclature.

• This is obviously the most correct of the answers given since unlike the others it is not a post-factor rationalization of isotope naming but an actual account of how deuterium came to be named. It should be the accepted answer, IMO. Aug 26 '15 at 23:17
• It is probably the most accurate non-ex-post-facto account of the naming of deuterium, but OP actually asks for the absence of names for all the other isotopes (for which, I believe, there is no "real" reason to pinpoint but only rationalization)
– ste
Sep 5 '15 at 13:50

In addition to the reasons ste listed, the isotopes of hydrogen have the greatest differences in mass compared to other elements. Consider that deuterium is twice as heavy as protium, and tritium is three-times as heavy as protium. Isotopes of all elements can be used in kinetic isotope experiments. The dramatic differences in mass among the hydrogen isotopes gives the most pronounced isotope effects. This type of difference in reactivity likely made it easiest to discover the different isotopes, and these differences explain the continued usage of the trivial names even more systematic descriptors are available.

• This answer describes interesting chemistry but is unfortunately wrong, given the history provided by Jon Custer. Deuterium was named because it was discovered first, and was discovered before we knew much about neutrons. So kinetic isotope effects had little to do with how names were chosen. Aug 26 '15 at 23:04
• @CurtF. I agree that my answer does not explain where the names came from, but I think it does provide some value in explaining why the historical names for the hydrogen isotopes have persisted when more systematic descriptors are available. If this is edging on opinion, I'm happy to remove my answer. Aug 27 '15 at 1:17

I think there are two reasons. First, it is more convenient to categorize them under the actual element-name to which they belong. If I say "15-Beryllium" everyone knows immediately, what I'm talking about. If we add hundreds of isotope-names, it would be quite a mess. Leading to the second reason: Xenon for example has over known 30 isotopes. There are just too many to name them all.

Hydrogen has, by the way, 7 known isotopes, of which only 3 have names:
1-Hydrogen: Protium (rarely used)
2-Hydrogen: Deuterium (D)
3-hydrogen: Tritium (T)

IUPAC discourages using the abbreviations to avoid confusion with other elements. Although, I see a lot of "D" in the organic literature.

Addendum:
I just saw, that in the novel The Mouse That Roared the isotope 4-Hydrogen has been named quadium (Q). This is neither used nor "official" though.

• That immediately raises the question, though, of why hydrogen does get special names. Perhaps not all isotopes should get special names, but why don't certain isotopes from other elements have special names as hydrogen does? (e.g. carbon 14)
– R.M.
Aug 25 '15 at 14:32
• Yes, why hydrogen? I think, as many things in trivial nomenclature, there is not a really specific reason behind it but tradition and conventions. For deuterium, I see a lot of use in organic skeletal formulae, because it's probably the most used radioacive marker. Instead of then having a mess of abbreviations, one decided to use a formal nomenclature, as 14C. I don't rule out, that there is more to it, though.
– ste
Aug 25 '15 at 14:48
• Actually, it seems to go back to the beginnings of nuclear physics, where they (Rutherford et al.) were not completely sure what the particle twice as heavy as a proton actually was ('From Nuclear Transmutation to Nuclear Fission, 1932-1939", Per F. Dahl, is a nice book covering this era in physics history). Aug 25 '15 at 17:09
• I like @JonCusters answer. This answer is a good post-facto rationalization of current isotope naming practices, but doesn't describe the causal reason for the deuterium isotope name discrepancy (DIND?) Deuterium was named because it was discovered first, and was discovered before we knew much about neutrons. So convenience had little to do with how names were chosen. Aug 26 '15 at 23:06
• @R.M. Hydrogen is quite special. It's very easy to ionise it completely (since it only has a single proton and electron), which basically leaves you with a "naked" proton - extremely reactive (that's how most acids work). Unlike other elements, hydrogen isotopes have a significant effect on chemistry, despite the fact that chemistry mostly cares about outer shell electrons. The chemical and mechanical differences between hydrogen and deuterium are bigger than for any other element. Since other isotopes are interchangeable in chemistry, deuterium and tritium stand out quite a bit. May 5 '17 at 8:52

This is not true. There are more isotopes that had (and have now) its own name. For example: 210Po - RaF (Radium F); 218Po - RaA (Radium A); 218Pb - RaB; 227Th - RdAc (Radioactinium); and much more Some of the names are still widely used (f.e. RaF)

• Maybe this is country/field dependent, but these don't seem to really be used any more. Most of them were placeholder names that just describe how the isotope was produced. Can you point to a recent example that still uses these names? The most recent I could find was a 1968 paper about Radium A Jul 11 '20 at 15:42