Hassium – facts and properties
- Symbol
- Hs
- Atomic number
- 108
- Atomic mass
- 277 u
- Period
- 7
- Group
- 8
- Category
- transition metal
- Electron configuration
- [Rn] 5f¹⁴ 6d⁶ 7s²
- Valence electrons
- 8
- State at standard conditions
- solid
- Discovered
- 1984
Hassium is radioactive and artificial, with atomic number 108. Its name goes back to the German state of Hesse, where GSI in Darmstadt, the laboratory that discovered it, is located. As a member of group 8 hassium stands below osmium, and an experiment with only a few atoms showed that it forms a similarly volatile tetroxide. Nuclear physicists also care about it because the isotope hassium-270 is regarded as an especially stable nucleus. Almost every property of the element, though, is only predicted.
Position in the periodic table
Occurrence and extraction
Hassium is not found on Earth outside laboratories. All known isotopes are radioactive. The longest half-lives reported in the literature range from seconds up to about a minute, and the exact values are uncertain. Other isotopes halve within milliseconds.
The element was discovered in 1984 at GSI. A team around Peter Armbruster and Gottfried Münzenberg bombarded lead-208 with iron-58 ions and detected three atoms that could be assigned to the new element through their decay chain. Dubna also recorded fission events that year, which were later judged very probably to belong to this element. The international working group that examined the claims gave the larger share of the credit to GSI.
The name comes from Hassia, the Latin name for Hesse. Darmstadt is in Hesse, and the state is a shareholder of GSI. GSI proposed the name in 1992, IUPAC first wanted to introduce hahnium instead, and only in 1997 was hassium settled for good.
Properties and reactions
Hassium is in period 7 and group 8, below osmium, with ruthenium and iron higher up. The electron configuration [Rn] 5f¹⁴ 6d⁶ 7s² is predicted and corresponds to that of osmium one period higher. The atomic mass entry is 277 u. That is the mass number of a single isotope, not an average like those for elements with stable isotopes.
No sample of hassium exists. Calculations predict a very high density, even above that of osmium, the densest known element. It remains a calculation. Melting point, boiling point and electronegativity are unknown.
Its chemistry was studied in 2001 at GSI. Hassium atoms were made from curium and magnesium ions and carried into a stream of oxygen. Seven atoms were detected in the form of a volatile compound, interpreted as hassium tetroxide, HsO₄. Osmium forms the matching tetroxide, OsO₄, and the hassium compound behaved similarly. That fits its place in the group and is a clear indication, though not full proof, because the number of atoms was small.
Osmium tetroxide is a poisonous, easily volatile compound. Of hassium tetroxide only single molecules ever formed, and they pose no danger.
Research and synthesis
Hassium serves research and nothing else. Nuclear physics focuses on the isotope hassium-270. Nuclei behave somewhat like electron shells: certain numbers of protons and neutrons, the magic numbers, make them especially stable. In hassium-270 the proton number of hassium meets the neutron number 162, both magic numbers for deformed nuclei. Calculations predict an especially stable nucleus for this combination, elongated rather than spherical in shape. Measurements suggest that hassium-270, with a half-life of some seconds, really is long-lived for its size.
This should not be confused with the island of stability, which theory expects at still heavier nuclei with about 184 neutrons. Hassium-270 is better described as a small patch of stability where shell models can be checked. The isotope forms, for instance, from curium and magnesium ions, but even then only single atoms result.
Quick question
What is the atomic number of hassium (Hs)?
FAQ
Why is it called hassium?
The name derives from the Latin Hassia, the name for Hesse. The German state is home to GSI in Darmstadt, where the element was discovered.
Is hassium like osmium?
An experiment with seven atoms says so. Both form a volatile tetroxide that attaches to surfaces in a similar way. Nothing more has been measured, and the rest is predicted.
What is special about hassium-270?
It is regarded as a nucleus with an especially stable proton and neutron number, the neutron number being 162, and its decay is comparatively slow for such a heavy isotope. It is still not seen as the large island of stability that theory expects.