Nobelium (No)

Nobelium is named after a result that nobody was ever able to reproduce. The 1957 experiment that gave the element its name did not, on the best modern assessment, detect element 102 at all. The name survived anyway, because by the time the record was straightened out it had been in print for three decades and no one wanted to renumber the literature.

An experiment that failed, and a name that did not

In 1957 an international group working at the Nobel Institute of Physics in Stockholm bombarded curium with carbon ions and reported an alpha emitter of about 8.5 MeV with a half-life near ten minutes. They assigned it to element 102 and proposed the name nobelium, after Alfred Nobel and the institute that bore his name.

Berkeley tried to reproduce it in 1958 and could not. Dubna tried and could not. Neither could anyone else, and no isotope of nobelium with those properties has ever been found. The Stockholm group had almost certainly been looking at something else in their decay data.

What they had done, unrepeatably, was attach a permanent label. The symbol No entered textbooks immediately, and stayed.

Who actually made element 102

The IUPAC/IUPAP Transfermium Working Group examined the competing claims in 1992 and reached a conclusion that pleased nobody entirely. Only the 1966 work at Dubna, which produced nobelium-254 from uranium under a neon beam and correctly identified both the isotope and its decay daughter, met the standard for a discovery. Berkeley's 1958 and 1959 experiments very probably did produce nobelium, but the assignments made at the time were not correct, and correctness at the time is what the working group weighed.

So the credit went to Dubna, for an element carrying a Swedish name derived from an American and European claim that was wrong. The Dubna group, having won the priority, proposed replacing the name — joliotium was their suggestion — and IUPAC declined, ruling that thirty years of established usage outweighed the tidiness of matching the name to the discovery. It is the only element on the table whose name commemorates a laboratory that did not discover it and an experiment that did not work.

The one actinide that prefers +2

Set the history aside and nobelium has a chemical distinction that is entirely its own.

Every other actinide, and every lanthanide bar a couple of exceptions, sits in solution as a tripositive ion. Nobelium does not. Its stable aqueous state is +2, and getting it to +3 requires a strong oxidising agent — the opposite of the situation everywhere else in the f-block.

The reason is a filled shell. Removing two electrons from nobelium leaves 5f¹⁴: fourteen electrons in seven f orbitals, every one paired, the most stable arrangement the shell can adopt. Taking a third electron would have to break into that closed configuration, and the energy cost is more than aqueous chemistry can usually pay. Ytterbium, directly above nobelium in the lanthanides, does something similar for the same reason, but nobelium's preference is far more pronounced.

The practical consequence is that nobelium behaves nothing like its neighbours in a separation. The No²⁺ ion has a radius close to that of calcium and strontium, and it follows the alkaline earths through ion-exchange columns rather than the actinides. That is a useful diagnostic — an element that turns up in the wrong fraction is identifying itself — and it was one of the earliest clear signals that the second half of the actinide series is genuinely f-block chemistry rather than an extension of the transition metals.

Laser light on a single atom

Nobelium holds a record that has nothing to do with its discovery. In 2016 a team led by Mustapha Laatiaoui at Darmstadt performed laser resonance ionisation spectroscopy on nobelium — the first optical spectroscopy ever done on an element beyond fermium.

The difficulty is not subtle. Optical spectroscopy normally means shining tunable light through a vapour and looking for absorption, which requires a great many atoms and some idea of where the transitions are. Nobelium had to be studied atom by atom, as nuclei arrived one at a time from an accelerator, were stopped in a gas cell, and were probed with laser light scanned across a range where theory said a transition ought to be. Detection was by ionisation: an atom that absorbed the right photon could be ionised by a second and counted.

They found the transition, at a wavelength that let them pin the atomic level structure of element 102 experimentally for the first time, and follow-up work derived its first ionisation energy from the same data. This matters beyond nobelium itself. Every prediction about the chemistry of the elements above depends on relativistic atomic calculations, and until 2016 those calculations had almost no experimental anchor this far up the table.

Isotopes, and how little of any of them there is

Twelve or so isotopes are known and all are short-lived. Nobelium-259 is the most durable at 58 minutes; the isotope most used in experiments, nobelium-255, lasts about three minutes, and the one Dubna identified in 1966 lasts under a minute. The element has never existed as a substance, only as individual atoms in flight or in solution, so its metallic form, its density and its melting point are all figures the literature computes rather than reports. Everything above is known from atoms counted individually as they arrived and decayed.