Hassium is a synthetic, highly radioactive transactinide metal in group 8. Only a few atoms have ever been made in particle accelerators. Its chemistry is expected to resemble osmium, including a highest oxidation state of +8, but most macroscopic properties remain unknown.
Hassium (Hs) is a synthetic transactinide element with atomic number 108. It belongs to Group 8 (the iron–ruthenium–osmium family) and lies in period 7. Because it does not occur in nature, it is produced atom-by-atom in particle accelerators.
Hs isotopes are made in fusion–evaporation reactions where a heavy target is bombarded with a lighter ion. A classic route is:
\(^{208}\mathrm{Pb}(^{58}\mathrm{Fe},\,n)\,^{265}\mathrm{Hs}\)
The compound nucleus cools by evaporating neutrons (\(n\)) to form a specific Hs isotope, which is transported within milliseconds to a detector.
Newly formed Hs atoms recoil from the target into a separator and are implanted into position-sensitive detectors. Identification relies on time-correlated decay chains with characteristic energies (mainly \(\alpha\)-decay and sometimes spontaneous fission):
\(^{A}_{108}\mathrm{Hs} \;\xrightarrow{\alpha}\; ^{A-4}_{106}\mathrm{Sg} + \alpha \;\to\; \cdots\)
By analogy with osmium (Os), Hs is expected to reach a +8 oxidation state and to form volatile tetroxides. Single-atom gas-phase studies indicate formation of hassium tetroxide, HsO4, analogous to OsO4, under oxidizing conditions.
Relativistic calculations and periodic trends support a ground-state configuration close to [Rn] 5f14 6d6 7s2. The involvement of 6d and 7s electrons (with strong relativistic effects) underpins its Group-8-like chemistry.
Experiments produce only a few atoms at a time, and these atoms decay quickly. As a result, macroscopic samples cannot be prepared, so properties like density, melting point, or crystal structure are inferred from atom-at-a-time chemistry and theoretical calculations rather than direct measurements.
Several short-lived isotopes (mass numbers around 265–277) have been reported. Dominant decay modes are alpha decay and spontaneous fission, with half-lives typically from milliseconds to minutes, depending on the isotope.
Yes—evidence from single-atom thermochromatography indicates a volatile HsO4 species analogous to OsO4. Such behavior supports Hs’s placement in Group 8 and its ability to access the +8 oxidation state under strongly oxidizing conditions.
Direct aqueous chemistry is extremely limited due to scarcity and short half-lives. By Group-8 analogy, high-valent oxo species would be expected, but most evidence for Hs chemistry currently comes from gas-phase single-atom experiments.
Production (stylized):
\(^{208}\mathrm{Pb}(^{58}\mathrm{Fe},\,n)\,^{265}\mathrm{Hs}\)
Generic \(\alpha\)-decay step:
\(^{269}\mathrm{Hs} \;\to\; ^{265}\mathrm{Sg} + \alpha\)