Dubnium (Db)

Otto Hahn, who found nuclear fission, has no element. He was nominated for three separate squares of the periodic table over a period of thirty years, and each time the name went elsewhere. The square where he came closest is element 105, which American chemists called hahnium and wrote as Ha for roughly a quarter of a century before IUPAC settled the matter against them.

Three near misses

The pattern is worth setting out, because it is not a single unlucky vote.

• Element 105. Berkeley's discovery paper in 1970 proposed hahnium, and the name entered American textbooks, journal articles and reference tables. It stayed there until 1997.
• Element 108. IUPAC's 1994 draft recommendation put hahnium on element 108 instead — moving the name to a different square as part of a rebalancing that satisfied nobody.
• Element 110. When the naming of element 110 came up in 1997, the American side proposed hahnium once more. It was not adopted.

The 1944 chemistry Nobel went to Hahn on his own, and he died in 1968 — two years before the first proposal that would have put his name on the table.

Two claims, and the names attached to them

Dubna reported element 105 in 1968, from an americium target under a neon beam, and proposed nielsbohrium. Berkeley reported it in 1970, from californium under a nitrogen beam, identifying the new nuclide through its alpha decay chain, and proposed hahnium.

The Transfermium Working Group's 1992 assessment gave shared credit: both laboratories had made element 105, and neither had made an airtight case ahead of the other. IUPAC's 1994 draft then proposed joliotium for the square, after Frédéric Joliot-Curie — a third name, from a third country, for an element two laboratories had already named twice.

The 1997 resolution gave element 105 the name dubnium. The reasoning was openly political rather than technical. Dubna had been assessed as sharing or holding credit for several elements in this region and had ended up, in the draft settlements, with nothing named for it. Awarding 105 to the town where the Joint Institute for Nuclear Research sits was the compensation that made the whole package acceptable to both sides.

That makes dubnium unusual: not a name honouring a discoverer, a place of discovery, or an idea, but a name awarded as part of a negotiated settlement.

Following niobium instead of tantalum

Element 105's chemistry has been probed enough to show that it belongs in group 5, beneath vanadium, niobium and tantalum, and enough to show that it does not sit there comfortably.

The expectation from ordinary periodic logic is that dubnium should most closely resemble tantalum, its immediate neighbour above. Experiments on the extraction of dubnium halide complexes from acid solution found something else: dubnium behaves more like niobium, and in some systems more like protactinium, than like tantalum. The order in the group is scrambled.

The explanation is relativistic. In an atom with 105 protons the inner electrons move fast enough that the 7s and 7p₁/₂ orbitals contract and the 6d orbitals expand, altering how readily the metal forms the particular chloride and bromide complexes these experiments depend on. Group membership survives; the within-group ordering does not.

Dubnium's oxide and oxychloride behaviour, studied in the gas phase, similarly places it as a group 5 element that has stopped obeying the smooth trends the lighter members set.

Twenty-eight hours

The isotope worth knowing about is dubnium-268, which lasts around twenty-eight hours — an extraordinary figure in this part of the table, where survival is usually counted in seconds. It does not have to be made directly. It appears at the bottom of the decay chain of element 115, so every successful synthesis of moscovium deposits a dubnium atom that then sits around for the best part of a day before splitting in half.

That longevity has been genuinely useful. Because the atoms persist long enough to be moved and chemically processed, dubnium produced this way has been separated and identified by its chemistry rather than only by its decay — which in turn confirms the atomic number at the top of the chain. An element that hangs around for a day is, in this neighbourhood, a laboratory in itself.