Dubnium – facts and properties
- Symbol
- Db
- Atomic number
- 105
- Atomic mass
- 268 u
- Period
- 7
- Group
- 5
- Category
- transition metal
- Electron configuration
- [Rn] 5f¹⁴ 6d³ 7s²
- Valence electrons
- 5
- State at standard conditions
- solid
- Discovered
- 1967
Dubnium is a radioactive element with atomic number 105. It is named after the Russian town of Dubna, home of the Joint Institute for Nuclear Research. Dubnium is a superheavy element that exists only as single atoms made in accelerators. As a member of group 5 it should behave like niobium and tantalum. The few experiments so far show that it does not fall into line as neatly as its place in the periodic table suggests.
Position in the periodic table
Occurrence and extraction
There is no natural dubnium. The longest-lived known isotope, dubnium-268, is reported in the literature with a half-life of about 16 hours. That is long for a superheavy element, but the figure is uncertain. Many other isotopes decay within seconds.
The name commemorates a place, not a person. Dubna lies on the Volga north of Moscow. The Joint Institute for Nuclear Research was founded there in 1956, a shared facility of several states of the former Eastern Bloc. Around 1967, a team at the institute fired neon ions at americium and reported the first signs of the new element. In 1970 Berkeley followed with a result from californium and nitrogen ions. The names caused a row: Berkeley wanted hahnium, after the chemist Otto Hahn, while the Dubna group had nielsbohrium in mind. The quarrel was part of the wider Transfermium Wars. Only in 1997 did the International Union of Pure and Applied Chemistry settle on dubnium, which recognises the institute's role.
Today dubnium arises in fusion reactions or as a daughter nucleus when heavier elements decay. For some years Dubna has also run a facility with a very intense beam, called the factory for superheavy elements.
Properties and reactions
Dubnium is in period 7 and group 5, below tantalum, with niobium above that. The electron configuration [Rn] 5f¹⁴ 6d³ 7s² is predicted, and so is almost everything else. Nobody has held the metal in their hands. The atomic mass is given as 268 u, the mass number of dubnium-268.
From its place in the table one expects the oxidation state plus five and compounds like those of niobium and tantalum, such as an oxide of formula Db₂O₅. The experiments confirm the general direction but show deviations. In tests with hydrochloric and hydrofluoric acid, dubnium forms complexes like the elements above it, yet it does not act like tantalum. Depending on the test it resembles niobium more closely, and in some systems even protactinium from the actinoid row. Volatile oxide chlorides were also studied in the gas phase, and there dubnium proved less volatile than niobium.
With atoms this heavy, relativistic effects change the energies of the electrons, and the trend within a group can shift. Dubnium decays by alpha radiation, electron capture or spontaneous fission. Experimenters need radiation protection; for everyone else the element is irrelevant, given the minute amounts.
Research and synthesis
Dubnium is used only in basic research. It is a touchstone for two questions: does the periodic table hold at the far edge of the known elements, and can methods be developed for doing chemistry on atoms that live only minutes to hours?
The answers come from experiments with very few atoms. They are produced in an accelerator, separated from everything else in a gas stream or a liquid, and identified by their decay. Each atom is counted. From comparatively few atoms emerges a picture of the chemistry that can be set beside that of niobium and tantalum, which people handle by the gram.
For nuclear physics dubnium is interesting as a way station. It appears in the decay chains of still heavier elements, and knowing its properties helps in assigning such chains. No device uses the element.
Quick question
What is the atomic number of dubnium (Db)?
FAQ
What is dubnium named after?
After the Russian town of Dubna, where the Joint Institute for Nuclear Research is based. Important work on the discovery was done there, and the international union chose the name in 1997 as a tribute.
Does dubnium behave like tantalum?
Only partly. It forms similar compounds, but in tests it departs from tantalum and, depending on the system, resembles niobium or protactinium more. The data come from very few atoms.
How long does dubnium last?
That depends on the isotope. Some halve within seconds, and about 16 hours is quoted for dubnium-268. So a sample can never be accumulated.