Atomic number 105

Dubnium

Db
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Shells Orbitals 5f 6d 7s

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105 electrons in 7 shells: 2, 8, 18, 32, 32, 11, 2.

Shells are a teaching model: an electron does not travel on a ring at a fixed distance.

Category: Transition metal
Period: 7
Group: 5
Block: d
Atomic mass: 268.126 Da (longest-lived isotope, estimated)
Electron configuration: [Rn] 5f¹⁴ 6d³ 7s² (predicted)
Phase at 25 °C: solid (predicted)
Discovered: 1967 (Dubna) and 1970 (Berkeley); credit disputed, Soviet team at Dubna (reported by G.N. Flerov); A. Ghiorso's team at Berkeley

Neighbours in the table

Rf Sg

Dubnium is named after Dubna, Russia, home of the Joint Institute for Nuclear Research, although the detection Los Alamos calls the first conclusive one was made in Berkeley, California. Credit for the discovery is still under debate, Jefferson Lab says. The Soviet team at Dubna reported possible atoms of element 105 in 1967 and fuller work in 1970. A Berkeley team announced its own positive identification that same year, and A. Ghiorso’s group there later tried and failed to confirm the Soviet findings, Los Alamos adds.

The Soviet group put forward no name, according to Los Alamos. Berkeley proposed hahnium, symbol Ha, after the German scientist Otto Hahn, who lived from 1879 to 1968. An IUPAC panel (International Union of Pure and Applied Chemistry) recommended dubnium instead. Under the rules for naming new elements hahnium cannot return, although some scientists kept using it because it had been current for about 25 years.

PubChem gives the mass of its longest-lived isotope, dubnium-268, 268.126 Da. The element has no stable isotope at all, Jefferson Lab records.

Where it is found

Dubnium has no estimated abundance in the crust or the oceans; Jefferson Lab marks both as not applicable. It is made by fusion, in which two nuclei meet with enough combined energy to overcome the repulsion between them, Los Alamos explains. At Dubna, a Soviet team fired neon-22 at americium-243 and may have produced a few atoms of dubnium-260 and dubnium-261, Los Alamos reports. Jefferson Lab adds that the first formed with five free neutrons and the second with four.

The Dubna evidence rested on the timing and energies of alpha particles, helium nuclei whose energy identifies the atom that emitted them. At Berkeley, Ghiorso, Nurmia, Haris and K.A.Y. and P.L. Eskola aimed 84 MeV (million electronvolts) nitrogen nuclei from the Heavy Ion Linear Accelerator at californium-249, Los Alamos reports. Nitrogen’s seven protons and californium’s 98 add up to 105.

Each nitrogen-15 nucleus absorbed shed four neutrons and left dubnium-260. Its half-life, the time for half a sample to decay, is 1.6 seconds in Los Alamos’s figures and 1.52 seconds in those of the Atomic Mass Data Center (AMDC). Los Alamos dates the first conclusive detection to 5 March 1970.

Why it matters

Dubnium-268 is the most stable of dubnium’s isotopes, with a half-life of about 32 hours in Jefferson Lab’s account. AMDC gives 29 hours and the International Atomic Energy Agency (IAEA) 28 in its evaluation. Spontaneous fission, the nucleus splitting unprompted, accounts for about 100 per cent of its decays in AMDC’s and IAEA’s figures. Its other routes, electron capture (the nucleus taking in an electron) or beta-plus decay (positron emission) and alpha decay, have no measured share in those figures.

Dubnium-261 gives off 8.93 MeV alpha particles and becomes lawrencium-257; its half-life is about 1.8 seconds, according to Los Alamos. AMDC gives 4.7 seconds, with 73 per cent of decays by fission and 27 per cent by alpha emission. Dubnium-262 turns into lawrencium-258 over about 40 seconds, Los Alamos says, while AMDC gives 34 seconds, 52 per cent fission and 48 per cent alpha decay. Beta-plus decay is a further route, with no measured share.

In group 5 and period 7, dubnium’s predicted configuration is [Rn] 5f¹⁴ 6d³ 7s². Los Alamos lists +5 as its oxidation state, the charge an atom would carry if every bond were ionic, with +4 and +3 as predictions. Only small amounts are produced and its half-life is short, so dubnium has no uses outside basic scientific research, according to Jefferson Lab.

Properties

Properties of dubnium Standard atomic weights from IUPAC/CIAAW (abridged, 2024); other values from PubChem's periodic table, kelvin converted to °C.
Property	Value	Unit	Source
Atomic number	105
Atomic mass	268.126 Da	Da	PubChem, longest-lived isotope, estimated
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f¹⁴ 6d³ (predicted)
Phase at 25 °C	solid (predicted)

This element has no standard atomic weight; the atomic mass shown is that of its longest-lived isotope, as PubChem gives it.

That mass is an estimate by the IAEA's Atomic Mass Data Center, not a measurement.

The electron configuration and the phase of this element are predictions, not measurements.

Safety

Dubnium’s hazard is ionising radiation: it has no stable isotope. It is produced only in small amounts, Jefferson Lab notes, so there is none to handle, and in AMDC’s figures its isotopes last from 54 milliseconds to 29 hours. PubChem’s record for elemental dubnium, CID 56951718, is the reference for the substance.

Questions

Who discovered dubnium?

Credit is still under debate, in Jefferson Lab's words. In 1967 G.N. Flerov reported that a Soviet team at Dubna may have made a few atoms by striking americium-243 with neon-22, Los Alamos records. In 1970 A. Ghiorso's group at Berkeley announced a positive identification of element 105, made from californium-249 and nitrogen-15, and later could not reproduce the Soviet results.

What is the half-life of dubnium?

It depends on the isotope. Dubnium-268 lasts longest: about 32 hours according to Jefferson Lab, 29 hours in the Atomic Mass Data Center's table and 28 hours in the IAEA's evaluation. At the short end, that table gives an excited state of dubnium-255 just 2.8 milliseconds. Dubnium-260, the Berkeley isotope of 1970, lasts 1.6 seconds per Los Alamos and 1.52 in the table.

What is dubnium used for?

Nothing outside basic scientific research, according to Jefferson Lab, because only small amounts are produced and its half-life is short. At Berkeley its atoms were made in the Heavy Ion Linear Accelerator, where a light nucleus such as nitrogen-15 or oxygen-16 struck a heavy target such as californium-249 or berkelium-249 and was absorbed, Los Alamos reports. In AMDC's figures, the products then split, give off alpha particles or undergo beta-plus decay.

Is dubnium a metal?

Jefferson Lab classes it as a metal, and PubChem places it among the transition metals, in group 5 and period 7 of the d-block. It is expected to be a solid, and its predicted configuration is [Rn] 5f¹⁴ 6d³ 7s². Los Alamos lists an oxidation state of +5, predicts +4 and +3, and estimates an atomic radius of 139 pm.