Hassium

Hassium
Atomic number	108
Symbol	Hs
Group	8
Electron configuration	[Rn] 5f14 6d6 7s2
Period	7
Main isotopes	269Hs, 270Hs, 271Hs
Discovery	1984 (GSI, Darmstadt)
Block	d
Oxidation states	+8, +6, +4
Wikidata	Q1252

Hassium is a synthetic, ultra-heavy element (atomic number 108) named after the German state of Hesse. It is a member of group 8 of the periodic table, directly below osmium, and belongs to the 7th period and the d-block of transition metals. Hassium is radioactive and extremely short-lived: no stable isotopes are known, and it is produced only in particle accelerators. Only a few dozen atoms have ever been made. Because of its fleeting existence, Hassium’s properties are inferred largely from theory and from tracer experiments on single atoms. All evidence indicates that Hs behaves like a heavier homologue of osmium. Pure metallic hassium (if bulk amounts could be made) is predicted to be a very dense, silvery metal with strong chemical reactivity towards oxygen. In fact, chemistry experiments have detected hassium forming a volatile oxide HsO₄, analogous to osmium tetroxide (OsO₄). Overall, Hassium’s chemistry and physics fit the expectations for a group 8 element, with the dominant high oxidation state being +8.

Overview and Key Facts

• Symbol: Hs
• Atomic number (Z): 108
• Group/Period/Block: Group 8, Period 7, d-block (transition metal)
• Standard oxidation states: predicted +8 as the most stable (plus likely +6, +4, +2 as in lighter group-8 congeners)
• Phase at STP (predicted): solid (metallic), silvery-gray metal
• Category: synthetic (transactinide) transition metal
• Discovery: first synthesized in 1984 (GSI Darmstadt, Germany)

Hassium is entirely man-made; it does not occur naturally. Its most common oxidation state is expected to be +8 (forming HsO₄), like osmium. In smaller oxidation states it would resemble osmium and ruthenium, possibly forming various oxides, halides, or complex ions, but those have not been observed. Because hassium atoms decay in seconds, its macroscopic physical and chemical properties (melting point, appearance, etc.) are known only from calculations. For example, hassium is expected to have a hexagonal close-packed crystal structure and a very high density (around 40 g/cm³), making it the densest of all elements. The name “hassium” comes from Hassia, the Latin name for Hesse, the region in Germany where it was discovered.

Atomic Structure and Electron Configuration

Hassium’s electrons fill the shells up to atomic number 108. Its ground-state electron configuration is expected to be [Rn] 5f¹⁴ 6d⁶ 7s². In other words, it has the same valence-shell configuration as osmium (which is [Xe] 4f¹⁴ 5d⁶ 6s²), but with one extra filled inner (7th) shell and the 5f subshell complete. The valence electrons are thus six in the 6d orbitals and two in the 7s orbital, giving a total of eight valence electrons. Relativistic effects (the influence of high nuclear charge on electron motion) are strong for hassium; they stabilize the 7s electrons more than the 6d electrons. As a result, when hassium loses its first electron (forming Hs⁺), a 6d electron is removed rather than a 7s electron – the opposite of lighter group-8 elements. The next ionization (forming Hs²⁺) then removes the second 7s electron. These details match advanced calculations.

Because it lies below osmium in the periodic table, hassium follows the general trends of group 8 elements with relativistic modifications. The atomic radius of Hs is predicted (by theory) to be about 126 pm (picometers) for the neutral atom – slightly smaller than osmium’s atomic radius (approx. 135 pm) due to the so-called lanthanide and actinide contraction of inner shells. Electronegativity and ionization energy cannot be measured directly for hassium, but theoretical estimates suggest they are similar to osmium’s values. Osmium’s first ionization energy is about 8.7 eV, and hassium’s is expected to be in the same ballpark. Likewise, hassium’s electronegativity is predicted to be moderately high (on the Pauling scale, perhaps around 2.3–2.4) due to contracted valence orbitals, comparable to osmium (≈2.2). In summary, Hs’s electronic structure is that of a heavy, highly charged nucleus whose valence electrons are strongly bound, giving it chemistry analogous to osmium but with noticeable relativistic shifts.

Isotopes and Nuclear Properties

Hassium has no stable or naturally occurring isotopes. It is highly radioactive: its known isotopes have mass numbers roughly from 263 to 277. All decay in fractions of a second to minutes, mainly by alpha emission and some by spontaneous fission. The longest-lived isotope observed so far is about Hassium-²⁷⁷ in a metastable excited state (277m) with a half-life of roughly 130 s, though that is not fully confirmed. Ground-state ^269Hs (N=161) has a half-life on the order of 10 seconds, and ^270Hs (N=162) was measured around 3–4 seconds. These relatively long half-lives for such a heavy element reflect a local “island of stability” near neutron number N≈162. For comparison, many other superheavy isotopes live only milliseconds. The alpha particles emitted have energies on the order of 8–10 MeV.

Hassium isotopes are produced one atom at a time in fusion reactions. For example, bombarding a curium-248 target with magnesium-26 yielded ^269Hs and ^270Hs, which were then studied chemically. Each atom of ^269,270Hs decays via a chain of alpha emissions eventually leading to lighter nuclei. These decay chains have allowed scientists to measure irradiation cross-sections (a few picobarns, meaning tens of picograms of ^269Hs per week of beam) and to confirm new isotopes. The isotopes also have various nuclear spins in their ground states, but detailed spectroscopy of Hs nuclei is not possible beyond these decay studies.

Because Hs is so short-lived, it has no role in radiometric dating or tracing. There is no known application of Hs isotopes outside research. (Some theoretical work speculated about extremely long-lived isomeric states of hassium or transuranium elements possibly surviving in nature, but no solid evidence exists.) For practical purposes, ^269Hs can serve as a reference in decay-chain experiments to identify heavier transactinides and test nuclear models on neutron-rich heavy nuclei.

Allotropes and Typical Compounds

In bulk (if it could be made), hassium would have the same crystal structure as osmium: a hexagonal close-packed (hcp) metal lattice. No surface allotropes (like different crystalline forms) are known or expected, since even a few-nanogram sample is far beyond reach.

Because only single atoms of Hs have been produced, the only chemical compounds observed involve gas-phase short-lived chemistry. The hallmark is hassium tetroxide, HsO₄. In the GSI experiments (2001–2004), a handful of Hs atoms were rapidly oxidized in a helium–oxygen atmosphere to HsO₄, and this molecule proved to be volatile. By tracing the decay of Hs atoms along a temperature gradient, researchers detected what must have been HsO₄ arriving on a cold detector surface. This compound is analogous to osmium(VIII) oxide (OsO₄) and ruthenium tetroxide (RuO₄), all group-8 tetroxides with +8 metal centers. The observation of HsO₄ confirmed that hassium can attain the 8+ oxidation state and form a tetroxide, as predicted by periodic trends.

Another known species assigned to hassium chemistry is sodium hassate(VIII), Na₂[HsO₄(OH)₂]. In one experiment, small amounts of HsO₄ were reacted with NaOH vapor in situ; the resulting product behaved like a sheet of sodium hydroxide capturing an Hs-containing molecule. The chemistry is analogous to the behavior of osmium tetroxide with base, forming sodium osmate(VIII), Na₂[OsO₄(OH)₂]. The reaction 2 NaOH + HsO₄ → Na₂[HsO₄(OH)₂] demonstrates that HsO₄ is a strong acid anhydride (in water it would form hassic acid H₂[HsO₄ and that hassium follows osmium’s chemistry in acid/base reactions.

No other hassium compounds have been directly observed. However, by analogy with the group-8 homologues, one can predict likely candidates: for example, ruthenium and osmium form halides like RuCl₆²⁻/RuCl₃ and OsCl₆²⁻/OsCl₄, as well as fluorides (RuF₆, OsF₆) and oxides (RuO₂, OsO₂, etc.). Thus, hassium might form HsCl₄ or HsCl₆ in principle, and HsF₆ may be possible, or lower oxides like HsO₂, if it were stable enough; and H₂emitted by Hs might form a hydride analogous to osmium hydrides. None of these are accessible in practice. In summary, the only chemically characterized compound of hassium is HsO₄ (and its related oxy-anion), and it mirrors the known chemistry of osmium tetroxide.

Physical Properties

Because hassium samples can never be made in larger quantities, its physical constants are theoretical. Density: Computations predict an extraordinarily high density around 40–41 g/cm³ for solid Hs metal. This would be about 1.8 times the density of osmium (≈22.6 g/cm³), making hassium the densest element of the periodic table. The enormous density arises from its high atomic mass (≈270 u per atom) and the contraction of its electron cloud under relativistic effects. Crystal structure: Predicted to be hexagonal close-packed (hcp, similar to osmium) with a c/a ratio around 1.59. This is the same structure adopted by osmium and technetium, consistent with Hs’s placement in that column.

Bulk mechanical properties would also be extreme: calculations suggest a bulk modulus on the order of 440 GPa, comparable to that of diamond, implying very high hardness and resistance to compression. Melting/boiling point: Not measured or accurately calculated, but as a heavy homolog of osmium and platinum-group metals, Hs would likely have very high temperatures of fusion and boiling – perhaps well above 3000 °C for the melting point. (For reference, osmium melts at 3033 °C.) Appearance: Pure hassium metal would be expected to look silvery-white metallic, again by analogy to osmium and ruthenium, though no sample has ever been seen.

Electrical and thermal conductivity: As a transition metal, hassium should conduct electricity and heat like a metal. Group-8 metals (Fe, Ru, Os) are good conductors; Hs would likely be similarly conductive or possibly slightly poorer due to relativistic band effects, but data do not exist. Spectroscopy: No atomic emission or absorption spectrum lines have been measured for Hs because it has only been produced atom-by-atom. Any spectroscopic study would require trapping atoms longer. Theoretical work could predict shifts in spectral lines, but this is beyond current capabilities.

In summary, Hs’s physical nature as a dense, hard, high-melting metal is inferred from its position in the periodic table, with no direct experimental characterization of bulk properties.

Chemical Reactivity and Trends

Hassium’s chemistry is governed by its group-8 position and strong oxidation ability. The production experiments show that Hs atoms oxidize almost immediately. In the gas-phase chemistry setup, freshly formed Hs atoms (in a helium stream) reacted with oxygen to give HsO₄. This indicates a strong preference for the +8 oxidation state under those conditions. By analogy to Os and Ru, Hs would also be able to exist in +6, +4, and +2 states (though +8 is the most stable high state). The +8 state (Hs(VIII)) means hassium can form powerful oxo-compounds: HsO₄ in particular is likely a strong oxidizer, akin to OsO₄, which is known to oxidize organic compounds vigorously. Any Hassium metal exposed to O₂ or ozone would likely form a protective oxide layer of HsO₄ or lower oxides, analogous to a passivation.

The experimental observation of Hassiate(VIII) (the anion [HsO₄(OH)₂]²⁻) shows that hassium tetroxide behaves like a strong acid in water, forming a stable anion in basic solution. This is parallel to osmate chemistry (H₄[OsO₄] + base → [OsO₄(OH)₂]²⁻). It suggests that HsO₄ is less volatile (more strongly adsorbed) and perhaps more covalent than OsO₄; indeed, the experiments found HsO₄ adsorbing to surfaces at higher temperature than OsO₄ does, a subtle reversal of the volatility trend (i.e., HsO₄ is somewhat less volatile than OsO₄, indicating stronger bonding, due to relativistic effects). Fully relativistic calculations predicted an adsorption enthalpy for HsO₄ of about –46 kJ/mol, compared to –39 kJ/mol for OsO₄, matching the experimental findings.

Corrosion and acid/base behavior: no bulk Hs exists to test, but one can infer that as a platinum-group metal it would resist attack by acids (like most noble metals), but in oxidizing conditions it would form HsO₄. As noted, OsO₄ is very volatile and toxic, while lower oxides OsO₂, OsO₃ are non-volatile solids often used in catalysis. If analogous Hs oxides could be isolated (like HsO₂, HsO₃), they would likely be insoluble refractory types. Osmium and ruthenium also form coordination complexes (e.g. RuCl₂(PPh₃)₃); one expects Hs could form very heavy coordination compounds, but none have been studied.

Reactivity series: hassium cannot be placed in the usual reactivity series of metals in water, since it decays too quickly. It is predicted to be chemically active (as many heavy metals are) in forming oxides/halides, but inert (like platinum) regarding simple reactions at room temperature. No systematic study of acid/base or salt formation has been done, except the noted tetroxide chemistry. In summary, hassium’s chemical reactivity trends match those of osmium and ruthenium, with an extreme case of strong +8 oxidation due to its high nuclear charge.

Occurrence and Production

Natural Occurrence: None. All known isotopes of hassium have half-lives far too short to exist on Earth today in any appreciable amount. If hassium were produced in nature (for example, in supernova nucleosynthesis), it would have long since decayed. Environmental mining or separation is impossible; only speculative searches for ultra-trace long-lived isomers have been tried (for example, looking for long-lived ^{271m}Hs in minerals), but so far with no confirmed success. In short, hassium does not occur in nature in any usable quantity.

Astronomical abundance: Similarly negligible. All hassium atoms that may form in stellar processes would decay via alpha emission or fission on timescales much shorter than the age of the universe (except hypothetical isomers, which remain unproven). There is no known geological or biological reservoir of Hs, and cosmic-ray spallation does not produce such heavy elements.

Production: All hassium is produced artificially in nuclear facilities. The first synthesis (1984) was at GSI Helmholtz Centre (Darmstadt, Germany) by bombarding a lead-208 target with an iron-58 beam:

\[ ^{208}\mathrm{Pb} + {}^{58}\mathrm{Fe} \to {}^{265}\mathrm{Hs} + 1\,\mathrm{n}. \]

Three atoms of ^265Hs were detected, each decaying by alpha emission. The discovery is credited to Peter Armbruster and Gottfried Münzenberg’s team. Prior attempts in the USSR (Dubna) had not been conclusive. Later, other reactions have been used to make different Hs isotopes, such as ^263–270Hs, for example:

• \(^{208}\mathrm{Pb} + {}^{54}\mathrm{Cr} \to {}^{262}\mathrm{Bh} \to{}^{262}\mathrm{Hs} \) (indirect),
• \(^{238}\mathrm{U} + {}^{34}\mathrm{S} \to {}^{272}\mathrm{Hs} + 4\,\mathrm{n}\) (reported in 2009),
• \(^{248}\mathrm{Cm} + {}^{26}\mathrm{Mg} \to {}^{270}\mathrm{Hs} + 4\,\mathrm{n}\),
• \(^{248}\mathrm{Cm} + {}^{26}\mathrm{Mg} \to {}^{269}\mathrm{Hs} + 5\,\mathrm{n}\).

The ^26Mg+^248Cm reactions were used in the chemistry experiments (yielding ^269,270Hs) because they produce isotopes with half-lives of seconds, long enough to do chemistry.

Each production run yields at most a few atoms of Hs per day (often much less). The reactions have cross-sections on the order of picobarns (10^-36 cm²), reflecting the extremely low yield. These atoms are separated from beam and reaction products by physical systems like the SHIP and TASCA separators, and then delivered one by one into chemistry apparatus.

Major producers: Hassium is produced only in very specialized research laboratories. The main groups are GSI (Germany) and Dubna (Russia). There are no commercial producers. The international nuclear research community collaborates on such work. No country or company “supplies” hassium as a material – it’s made for each experiment.

Extraction/Refining: Not applicable. There are no ores or expected chemical routes to extract hassium. The only “production” is via nuclear reactions, and the products (atoms) are detected almost instantaneously or filtered out. Because only atomic-level samples exist, no chemical extraction or purification is needed beyond rapid, gas-phase chromatographic separation on the fly.

Applications and Technology

Hassium has no practical applications outside scientific research. Its fleeting existence and minute quantities make it impossible to use like ordinary elements. There is no industrial or commercial use. Even in science, hassium’s role is strictly fundamental.

Primary uses include:

• Fundamental research in nuclear physics: Hassium isotopes help scientists study the limits of nuclear stability. Each new Hs isotope discovered (or measured from decay of heavier elements) tests theoretical nuclear models and the predicted “island of stability.”
• Systematics of the periodic table: Chemists study hassium to confirm that even superheavy elements follow periodic trends. The HsO₄ experiments, for example, showed that periodic classification still holds for Z=108.
• Calibration and detection: Hassium decay chains serve as benchmarks. In discovering elements 114–118, detecting the characteristic alpha energies of Hs isotopes (269, 270, etc.) in the decay chain is crucial. In that sense, hassium acts as a stepping stone in identifying higher elements.
• Technology development: The extreme challenge of making hassium has driven advances in accelerator and detection technology (e.g., high-intensity beams, fast on-line chemistry, sensitive detectors). This is an indirect benefit.

There are no known uses of hassium in materials science, catalysis, medicine, electronics, or energy (like reactors or lasers) because almost no stable atoms exist. Occasionally, the study of HsO₄ provides insight into the volatility of heavy oxides, which might find an abstract parallel in high-temperature chemistry (though Hs itself is not used). Hassium’s only “application” is to expand human knowledge of the heaviest elements.

Biology, Environment, and Safety

Hassium has no biological role – it has never been known to enter any living organism. Because it is so short-lived, it would decay before being metabolized. Its chemistry (like the volatile tetroxide) suggests it would be extremely toxic in molecular form, but this is irrelevant since it cannot accumulate.

In terms of toxicity, if a quantity of hydrogenst has somehow deposited in the environment (which never occurs naturally), it would pose a radiation hazard rather than a chemical one. All Hs isotopes are alpha emitters; any biological exposure would entail damage from intense alpha radiation. However, in practice the only exposure risk is for the scientists producing it in labs. Those researchers handle any traces of hassium only remotely, behind shielding, because the amounts are vanishingly small but highly radioactive.

No environmental cycling of hassium occurs; it has no presence in air, water, or soil. If an atom of Hs forms (e.g., in a cosmic event, extremely unlikely), it will decay within seconds and its daughter nuclide will follow its own decay chain. There are no known permissible exposure limits or standards, because there is no commercial use. The Laboratory practice is to handle hassium as a fume: real-time observation by detectors, but no physical “handling.”

In summary: biologically inert because absent, but highly radiotoxic if concentrated (comparable to any heavy actinide). Standard radiological safety (glove-boxes, vacuum lines, remote detectors) is used by experimentalists. There are no special ecosystem or disposal concerns beyond those typical for short-lived radionuclides.

History and Etymology

The story of hassium begins in the late 1970s-1980s during the race to synthesize the heaviest elements. In 1963, a Soviet scientist once claimed to find element 108 (dubbed sergenium) in nature, but this “discovery” was discredited. The real progress came with heavy-ion accelerators. Starting in 1978, researchers at the Joint Institute for Nuclear Research (JINR, Dubna) attempted to create element 108 by bombarding lead-208 with chromium-54 and iron-58, yielding some tentative evidence. However, these were inconclusive at the time.

In 1984, a team at GSI Helmholtz Centre in Darmstadt (Germany) led by Peter Armbruster and Gottfried Münzenberg reported clear production of element 108. They used a lead-208 target and an iron-58 beam to produce ^265Hs, detecting three atoms via their alpha decay chains. This is widely credited as the first undisputed synthesis of hassium. (A complicated review by the IUPAC/IUPAP Joint Working Party later officially recognized GSI’s synthesis.)

The name hassium was proposed by the GSI team. It comes from Hassia, the Latin name for Hesse, the federal state in Germany where Darmstadt is located. This honored the region of discovery. In the intervening years, various placeholder names were used. For a time in the 1980s, before any official name, element 108 was called eka-osmium (in Mendeleev’s nomenclature) or simply “element 108.” In 1979, IUPAC had provisionally assigned the systematic name unniloctium (symbol Uno, meaning one-zero-eight), but this was never popular among chemists. In 1992, IUPAC controversially proposed “hahnium” (symbol Hn) after Otto Hahn, but after protests by the discoverers and the chemical community, the name hassium (Hs) was finally adopted internationally in 1997.

Since discovery, hassium has featured in several notable experiments. In 2002, Christoph Düllmann and coworkers famously demonstrated the chemistry of hassium by creating HsO₄ molecules and showing they behave like osmium tetroxide. That Nature paper was the first to chemically characterize a transactinide element beyond mere existence. In 2004, further studies showed the formation of hassate ion from HsO₄. These achievements underscored how hassium actually fits the periodic table pattern. No industrial or cultural uses exist; Hs is mentioned only in scientific literature.

Data Table

Property	Hassium (Hs)
Atomic number (Z)	108
Symbol	Hs
Atomic mass	~269 (for longest-lived isotope); no stable atomic weight
Group	8
Period	7
Block	d-block (transition metal)
Electron configuration	[Rn] 5f¹⁴ 6d⁶ 7s²
Valence electrons	6d² + 7s² (eight total)
Oxidation states (common)	+8 (most stable), +6, +4, +2 (predicted)
Standard state	Solid (predicted metal) at STP
Density (predicted)	~40.7 g/cm³ (highest of elements)
Crystal structure	hexagonal close-packed (hcp, predicted)
Atomic radius (predicted)	~126 pm (covalent radius)
Melting point	— (unknown; predicted very high, >3000 °C)
Boiling point	— (unknown; predicted very high)
Thermal conductivity	— (not measured; metal-like behavior expected)
Electrical conductivity	— (not measured; behaves as a metal)
Electronegativity	— (theoretical ~2.2–2.4, similar to Os)
First ionization energy	— (theoretical ~9 eV, like osmium)
Most stable isotopes	^269Hs (T₁/₂ ≈ 10 s), ^270Hs (T₁/₂ ≈ 3.6 s)
Predominant decay modes	α decay (to seaborgium, rutherfordium) and spontaneous fission
Discovery year	1984 (GSI Darmstadt, Germany)
Named after	Hassia (Latin for Hesse, Germany)

Note: Hassium is synthetic and has no standard atomic weight or stable isotopes. Many properties above are predicted by theory or analogies to osmium (element 76) and have not been directly measured.