Dubnium
| Dubnium | |
|---|---|
| |
| Atomic number | 105 |
| Symbol | Db |
| Group | 5 (vanadium group) |
| Discovery | JINR (Dubna) and LBNL (Berkeley), 1968–1970 |
| Electron configuration | [Rn] 5f14 6d3 7s2 |
| Cas number | 53850-35-4 |
| Period | 7 |
| Main isotopes | 268Db |
| Phase STP | Solid |
| Block | d |
| Oxidation states | +5, +4, +3 |
| Wikidata | Q1232 |
Dubnium (Db) is a highly radioactive synthetic element with atomic number 105. It is a d-block transition metal in period 7, group 5 of the periodic table (the vanadium subgroup) lying directly under tantalum (Ta, Z=73) and niobium (Nb, Z=41). In theory it shares the characteristic chemistry of niobium and tantalum: it should display a dominant +5 oxidation state (using all five valence electrons) in compounds. No stable isotopes of dubnium exist, so it has no standard atomic weight and no natural occurrence (it is produced only by nuclear reactions in the laboratory). The most stable known isotope, ^268Db, has a half-life on the order of 16 hours which has so far limited all studies to short-lived, one-atom-at-a-time experiments. Under ordinary conditions dubnium would be a solid refractory metal, likely silvery-gray in appearance and very dense (theoretically about 21.6 g/cm³ Its melting and boiling points are unknown but are expected to be extremely high (by analogy to tantalum and niobium). Dubnium has no commercial applications and is essentially of interest only for basic scientific research. It was first reported in 1968 by researchers at Dubna, Russia, and in 1970 by a team in California; the element was later named after Dubna, home of the discovery laboratory
Atomic Structure and Electron Configuration
An atom of dubnium has 105 electrons. Its electron configuration is predicted to be [Rn] 5f^14 6d^3 7s^2 meaning it has a radon-like core plus fourteen 5f electrons, three 6d electrons and two 7s electrons. The five outermost electrons (6d^3 7s^2) are the valence electrons that participate in bonding. This mirrors niobium and tantalum, which also have five valence electrons in the nd^2+(n+1)s^2 configuration (with n=4 for Nb, n=5 for Ta). Quantum relativistic effects are significant for such a heavy element: calculations indicate the 7s orbital of dubnium contracts (stabilizes) so much that the 7s electrons are held more tightly than expected In fact, dubnium is unusual in that its 6d electrons are predicted to be slightly easier to remove (ionize) than its 7s electrons, the reverse of the light homologs. The first ionization energy of dubnium is therefore estimated to be about 6.5–7.0 eV (around 640–680 kJ/mol), comparable to those of niobium and tantalum. Other periodic trends place dubnium’s atomic radius in the same range or slightly larger than tantalum’s: rough estimates give a covalent radius on the order of 1.4–1.5 Å Its electronegativity is expected to be somewhat lower than Nb and Ta (roughly 1.3 on the Pauling scale). In summary, dubnium’s electronic structure is continuous with the vanadium group pattern (five valence electrons, primarily forming +5 oxidation states) but modified by heavy-element relativistic effects.
Isotopes and Nuclear Properties
Dubnium has no stable isotopes. As a synthetic transactinide, it is known only through radioactive isotopes produced in nuclear reactions To date, about a dozen isotopes of dubnium (mass numbers roughly 255–270) have been identified The first to be made was ^261Db (in 1968); the heaviest observed is ^270Db (in 2009). All dubnium isotopes decay rapidly – generally in seconds to hours – with the most stable one, ^268Db, decaying with a half-life on the order of 16 hours (Some evaluations allow a ~30-hour half-life within statistical uncertainties but none of its isotopes lives much beyond a day.) Because of these short half-lives, dubnium atoms vanish almost as soon as they appear.
The dominant decay mode for dubnium isotopes is alpha decay (emission of a helium nucleus). Typically an alpha emission lowers the atomic number by two, so dubnium decays to lawrencium isotopes (element 103). For example, ^263Db and ^268Db decay by alpha emission to ^259Lr and ^264Lr respectively. Some isotopes also undergo spontaneous fission (splitting into lighter nuclei) or less commonly beta-decays (electron emission) and electron capture. A few metastable (isomeric) excited states (denoted by an “m”, e.g. ^257mDb) have been found, but they too decay in seconds. Nuclear spins and precise decay energies have been measured only for the easier-to-produce nuclides; for most dubnium isotopes these data are tentative. The nuclear properties of dubnium generally follow trends for heavy actinides and transactinides: as the nuclei get heavier, more neutrons are required for stability and many decay chains end in fission. None of the dubnium isotopes is suitable for use in radiometric dating or medicine due to their fleeting existence.
Allotropes and Typical Compounds
No allotropes of dubnium have been observed – an allotrope is a different structural form of the same element (like graphite vs diamond in carbon). Dubnium is a metal, so if bulk samples existed it would likely have one crystal form. Calculations predict that solid dubnium metal would adopt the same body-centered cubic structure as niobium and tantalum Otherwise there are no known allotropes or allotropic transitions.
Because dubnium is only made in trace amounts, its compounds have been studied only atom-by-atom. In chemistry, dubnium is expected to behave like niobium and tantalum in its compounds, especially in the +5 oxidation state. In this state it should form halides (e.g. DbCl5, DbBr5), an oxide Db2O5 (analogous to Ta2O5), and oxychloride or oxybromide species (e.g. DbOCl3, DbOBr3). For example, group-5 metals form pentachlorides (NbCl5, TaCl5) and corresponding oxychlorides; dubnium is predicted to form DbCl5 and DbOCl3. In a landmark experiment in 2021, a volatile dubnium oxychloride (DbOCl3) was actually created and detected by reacting single dubnium atoms with chlorine and oxygen in a gas-phase apparatus. This confirmed the expected group-5 chemistry: the measured properties of DbOCl3 matched the prediction that dubnium forms a +5 oxyhalide, analogous to NbOCl3 or TaOCl3.
Studies have used gas chromatography and solvent extraction to probe dubnium compounds. Early work (1970s) passed freshly made dubnium atoms over a reactor filled with chlorine gas. The observed behavior of the dubnium chloride compound was similar to niobium pentachloride (NbCl5) rather than hafnium tetrachloride This was one of the first chemical confirmations that element 105 behaved like an “eka-tantalum” (unseen Ta analog). Later experiments used bromine or oxygen to form DbBr5 or oxybromides. One thermochromatography study found that dubnium bromide was less volatile than niobium bromide and more like hafnium bromide suggesting strong bonding (perhaps formation of an oxybromide).
In aqueous solution, dubnium can form complex ions like the lighter group-5 metals. Experiments where dubnium ions were extracted from very strong HCl/HF acid showed that dubnium behaves chemically much like niobium or protactinium, forming anionic chloride complexes. Under these conditions, dubnium did not extract into certain organic solvents (such as methyl isobutyl ketone) that selectively bind some metals; its behavior was more similar to niobium (Nb) than to tantalum (Ta) These findings led chemists to conclude that dubnium forms negative chloride complexes (for example [DbCl6]^3– or ^2–) in concentrated acid, in analogy with Nb. Overall, the observed chemistry of dubnium agrees with periodic trends: its +5 state is the most stable, it readily forms halide and oxide species, and its bonding shows a slight increase in covalent character (more shared electrons) compared to tantalum No simple divalent or monovalent hydrides or salts have been isolated; dubnium’s chemistry is dominated by high-oxidation-state compounds.
Physical Properties
Physical properties of dubnium metal can only be estimated by analogy, since no bulk sample exists. It is expected to be a dense, hard metal with typical metallic thermal and electrical conductivity. Calculations predict a body-centered cubic lattice (like other group-5 metals) which is a strong, closely packed structure. The density has been calculated at about 21.6 g/cm³ (some older sources give ~29 g/cm³, but around 21.6 is considered more reliable). To compare, niobium metal is 8.6 g/cm³ and tantalum is 16.7 g/cm³, so dubnium would be among the heaviest.
The melting point of dubnium is not measured; niobium melts at 2477 °C and tantalum at 3017 °C, and extrapolating down the group suggests dubnium would melt above 3000 °C. Its boiling point is similarly unknown but would be extremely high (tantalum boils ~5458 °C). Because only single atoms or tiny deposits are produced, these phase transitions have never been observed experimentally.
As a metal, solid dubnium would be a conductor of heat and electricity. Exact values (thermal/electrical conductivity, hardness, etc.) are unknown, but it would be expected to have properties akin to refractory transition metals. No visible spectral lines (atomic emission or absorption) have been measured for dubnium, as detection requires long-lived samples. The element’s electronic and lattice spectra remain entirely theoretical. In summary, dubnium’s physical nature is that of a heavy transition-metal solid: very dense, very high melting, and conductive, but all inferred rather than measured.
Chemical Reactivity and Trends
In chemical behavior, dubnium follows the pattern of the vanadium subgroup, with +5 as the predominant oxidation state. Its +5 state (Db(V)) is significantly more stable than lower states; Dubnium(IV) and Dubnium(III) compounds would be much less stable and have rarely been observed This mirrors niobium and tantalum (which have stable +5 and +3 states), but relativistic effects reinforce Db(V) while suppressing Db(III,IV) even further. Experiments confirm that the +5 state of dubnium is the only one readily accessible under normal conditions: for example, dubnium in solution behaves like other +5 metal ions and can be retained on cation-exchange resins with α-hydroxyisobutyrate (as niobium and tantalum are) whereas attempts to isolate a +3 or +4 state under similar conditions fail.
As a metal, dubnium would be very unreactive at room temperature. Like tantalum and niobium, a layer of oxide on the surface would likely render it inert to air or water. In practice, if exposed to air an oxidation layer of Db2O5 or mixed oxides would form instantly, passivating further reaction. It would not react with water or non-oxidizing acids (e.g. dilute HCl) except by slow oxidation. Strong halogen acids such as fluoride or chlorine could attack it by forming soluble complexes, similar to how Ta and Nb dissolve in HF or HCl+HF mixtures.
Redox-wise, dubnium is typically a strong oxidizing species in its +5 state. It would require vigorous conditions to reduce it to a lower state. For instance, niobium pentachloride (NbCl5) and tantalum pentachloride (TaCl5) react with reducing agents; by analogy, DbCl5 could in principle be reduced to DbCl4 or DbCl3, though no such reactions have been demonstrated due to the element’s short life. Standard reduction potentials for Db are not measured; it is expected to be less easily reduced (stronger oxidant) than Ta^5+.
Dubnium does form complexes typical of heavy metals. In solution, the Db^5+ ion (again a notional concept, since we only see it in trace) would strongly hydrolyze like Ta^5+, but somewhat less than Nb^5+. In acid media, dubnium associates with fluoride or chloride. For example, solution chemistry studies have shown that in concentrated HCl/HF mixtures, group-5 elements and protactinium form anionic chloro-complexes. Dubnium was observed to behave nearly like niobium, suggesting it too forms complexes such as [DbCl6]^3− (or [DbCl6]^2−, depending on counterions) In selective extraction experiments, Db(V) was not carried by neutral extractants in the same way as Ta(V), again indicating strong anionic complex formation.
In summary, dubnium’s reactivity trends are those of a refractory pentavalent metal: chemically it is moderately reactive (like its lighter congeners), forming stable +5 compounds but being difficult to reduce. There is no evidence of unusual chemical behavior beyond the slight relativistic nuances in bonding. In a reactivity series it would rank with niobium and tantalum as a very stable, corrosion-resistant metal. Theoretical models support that DbCl5, DbOCl3, and other Db(V) species should exist and behave analogously to NbCl5 or TaCl5, with minor increases in covalency
Occurrence and Production
Dubnium does not occur naturally in the Earth’s crust, atmosphere, or oceans. Any primordial dubnium (from the formation of the solar system) would have long since decayed away, and it is not a decay product of any naturally occurring radioactive element in the environment. The element has also not been found in meteorites or cosmic dust. In a very strict sense, tiny fleeting amounts of dubnium can be created by cosmic-ray spallation or neutron-bombardment of heavy elements, but these would decay almost immediately. Thus its natural abundance is effectively zero.
All known amounts of dubnium have been produced artificially in nuclear laboratories. The usual method is a heavy-ion fusion reaction, where a beam of one type of ion is smashed into a target of heavier atoms. The first synthesis was reported in 1968–70 by two groups: researchers at JINR Dubna (bombarding americium with neon ions) and at Lawrence Berkeley Lab (bombarding californium with nitrogen ions) In modern experiments, various target-projectile combinations have been used. For example, ^243Am + ^22Ne → ^265Db (releasing 0–1 neutron), or ^249Cf + ^15N → ^264Db, among others “Cold fusion” reactions with lead or bismuth targets and vanadium, titanium, or chromium beams have also made isotopes in the range A=259–263. Specialized facilities (cyclotrons or linear accelerators) provide the high-energy beams. Production rates are extremely low: typically only a few atoms of a given dubnium isotope are produced per day or per week of beam time.
Once created, dubnium atoms are rapidly separated for study. Techniques include gas-phase thermochromatography (where a dubnium compound is volatilized and trapped on a cooled surface) and liquid chromatography or solvent extraction (separating Db ions from other reaction products). The Dubna and Berkeley teams (and later GSI Darmstadt) have been the main producers of dubnium. No industrial-scale production is possible. Major laboratories that have contributed to dubnium synthesis include JINR Dubna (Russia), Lawrence Berkeley National Laboratory (USA), and the GSI Helmholtz Centre (Darmstadt, Germany). Each new isotope typically requires a specially designed experiment.
Because there are no dubnium deposits or ores, the only “refining” is the physical separation of single atoms after synthesis. No commercial or geological source exists. All dubnium production is research-oriented, and only micrograms are produced annually worldwide (and those in total; each “world supply” experiment deals with picograms at best).
Applications and Technology
Dubnium has no applications in technology, industry, or medicine. Its extremely low production rate and very short half-lives preclude any practical use. Even if bulk dubnium metal could somehow be made, its intense radioactivity would make it useless. So far, the only “use” of dubnium is in fundamental research.
In nuclear science, dubnium is studied to improve our understanding of superheavy elements and nuclear stability. Each new isotope of dubnium adds data points on how nuclei behave when they are very large. In chemistry, dubnium serves as a test that periodic trends hold true. For example, confirming that dubnium forms +5 compounds analogous to Nb and Ta validates the predictive power of quantum chemistry for the heaviest elements
Because of this, dubnium has been used as a calibrant or target in experiments that probe the chemistry of transactinides. Its single atoms might be used (along with its neighbors rutherfordium and seaborgium) to test methods of one-atom chemistry (such as gas chromatography on surfaces or partitioning between solvents). No large-scale material applications exist. No electronics, no catalytic processes, no structural roles. There are no uses in batteries or alloys or catalysis – those applications are impossible with at most a few dozen atoms.
Occasionally, longer-lived heavy isotopes (though none for Db yet) are sought for potential nuclear fuel or medicinal isotope uses, but dubnium’s isotopes are simply too short-lived. In summary, dubnium’s role is purely as an object of scientific curiosity.
Biology, Environment, and Safety
Dubnium has no known biological role. It is far too unstable and rare to have any biochemical interactions. As a heavy actinide-like metal, if it were somehow introduced into the body it would be expected to be highly toxic, but in practice humans and other organisms never encounter it. There is no evidence of any dubnium in the environment outside laboratories.
Safety concerns with dubnium are related entirely to its radioactivity. Any, even microscopic, amount delivers intense radiation. For example, ^268Db decays by alpha emission of ~8–9 MeV; this energy is highly damaging to cells at very short range. Inhaling or ingesting a dubnium atom would be lethal at the cellular level, but in reality no one is exposed to dubnium outside a fully protected lab. There are no established exposure limits for dubnium specifically; handling follows the same guidelines as for other actinides or transuranic radionuclides.
Laboratories that create dubnium use remote handling and heavy shielding. Dubnium is typically stored (for the few seconds or minutes it exists) on metal foils or in aqueous solutions inside shielded hot cells. After experiments, any waste containing Dubnium is treated as high-level radioactive waste. Dubnium decays into lighter isotopes (lawrencium, rutherfordium, etc.), which themselves are radioactive, so a decay chain of hazards must be managed. In ecological terms, dubnium does not cycle through the environment: it is produced and then decays away in the lab. There are no groundwater contamination issues or uptake by organisms. Standard nuclear lab safety (gloves, fume hoods, HEPA filters, etc.) suffices for the tiny quantities involved.
In summary, from a public health viewpoint dubnium is negligible because it cannot exist outside of a lab. In a laboratory, safety procedures assume it poses an extremely high radiological hazard.
History and Etymology
Dubnium’s discovery was part of the “transfermium wars,” a mid-20th-century competition over elements beyond fermium (Z>100). In 1968, a Soviet team at the Joint Institute for Nuclear Research (JINR) in Dubna reported the creation of element 105 by bombarding americium-243 with neon-22 ions They observed decay chains they attributed to isotopes ^260Db and ^261Db. In 1970, a team at Lawrence Berkeley Laboratory (LBL) in the USA announced they had made element 105 by bombarding californium-249 with nitrogen-15 ions Both groups performed chemical tests on the decay products, indicating the new element behaved like a heavy niobium/tantalum. For example, the Dubna team concluded that a volatile chloride they observed matched niobium pentachloride rather than hafnium chloride
Each group proposed a name: LBL initially suggested hahnium (Ha) after Otto Hahn, while the Dubna group eventually suggested nielsbohrium (Ns) after Niels Bohr (they had even briefly proposed “bohrium” before). For several years both names were used unofficially. In 1974 IUPAC recommended temporary systematic names; element 105 was called unnilpentium (Unp, from the Latin/Greek for “one-zero-five”). However, this was ignored by the discoverers. Over the 1970s and 1980s, experimental data accumulated, and a joint IUPAC–IUPAP Transfermium Working Group in 1993 evaluated the claims, concluding that JINR and LBL should share credit for the discovery.
Finally, in 1997 IUPAC announced official names for the disputed elements. Element 105 was named dubnium (symbol Db) in honor of Dubna, Russia This decision recognized the Dubna laboratory in the discovery and resolved the long naming conflict. (The name “dubnium” had briefly been used in a 1994 recommendation for element 104, but that was later changed.) American scientists accepted the name, and “hahnium” was dropped. Since then, dubnium has been the internationally recognized name.
Etymology: The name dubnium honors the town of Dubna, Russia, home of the JINR. The suffix -ium follows the convention for metallic elements. The chemical symbol Db derives from the name. There is no meaning beyond this geographical tribute.
Data Table
| Property | Value |
|---|---|
| Symbol | Db |
| Atomic number (Z) | 105 |
| Element category | Synthetic transition metal (group 5) |
| Period, Group | 7, 5 (d-block) |
| Electron configuration | [Rn] 5f^14 6d^3 7s^2 |
| Valence electrons | 5 (6d^3 7s^2) |
| Oxidation states | +5 (dominant); +4, +3 predicted |
| Standard state (STP) | Solid (predicted metallic) |
| Density (calculated) | ≈21.6 g/cm³ |
| Crystal structure | Body-centered cubic (predicted) |
| Melting point | Unknown (estimated >3000 °C) |
| Boiling point | Unknown |
| Atomic/covalent radius | ~1.39 Å (atomic radius) ~1.49 Å (covalent, est.) |
| Electronegativity | ~1.3 (Pauling, estimated) |
| First ionization energy | ~664 kJ/mol (≈6.88 eV, estimated) |
| Most stable isotope | ^268Db (half-life ≈16 h) |
| Discovery year | 1968 (JINR); 1970 (LBL) |
| Discoverer(s) | Joint Institute for Nuclear Research (Dubna); Lawrence Berkeley Lab |
| Named after | Dubna, Russia (site of JINR) |