Hassium (108)

Hassium is a chemical element with symbol Hs and atomic number 108, named in honor of the German state of Hesse. It is a synthetic element (an element that can be created in a laboratory but is not found in nature) and radioactive; the most stable known isotope, ²⁶⁹Hs, has a half-life of approximately 9.7 seconds, although an unconfirmed metastable state, ^277mHs, may have a longer half-life of about 11 minutes. More than 100 atoms of hassium have been synthesized to date.

The interested reader should consult the on-line version of The Wonderful World of Atoms and Nuclei for a fascinating insight into research on "super-heavy" atoms.

Name: Hassium Symbol: Hs Atomic number: 108 Atomic weight: [ 277 ] (status unclear) Standard state: presumably a solid at 298 K CAS Registry ID: 54037-57-9

Group in periodic table: 8 Period in periodic table: 7 Block in periodic table: d-block Color: unknown, but probably metallic and silvery white or grey in appearance Classification: Metallic

Historical information

Hassium is not known to occur naturally on Earth because the half-lives of all its known isotopes are short enough that essentially none of any primordial hassium would have survived to the present day. However, this does not rule out the possibility of as yet unknown longer-lived isotopes or nuclear isomers existing, some of which could, if long-lived enough, still exist in trace quantities today. In the early 1960s, it was predicted that long-lived deformed isomers of hassium might occur naturally on Earth in trace quantities. This was theorized in order to explain the extreme radiation damage in some minerals that could not have been caused by any known natural radioisotopes, but could have been caused by superheavy elements

Physical properties

• The previous members of group 8 have relatively high melting points (Fe, 1538 °C; Ru, 2334 °C; Os, 3033 °C). Much like them, hassium is predicted to be a solid at room temperature, although the melting point of hassium has not been precisely calculated. Hassium should crystallize in the hexagonal close-packed structure (^c/_a = 1.59), similarly to its lighter congener osmium. Pure metallic hassium is calculated to have a bulk modulus (resistance to uniform compression) comparable to that of diamond (442 GPa). Hassium is expected to have a bulk density of 40.7 g/cm³, the highest of any of the 118 known elements and nearly twice the density of osmium, the densest measured element, at 22.61 g/cm³. This results from hassium's high atomic weight, the lanthanide and actinide contractions, and relativistic effects; although production of enough hassium to measure this quantity would be impractical, and the sample would quickly decay. Osmium is the densest element of the first 6 periods, and its heavier congener hassium is expected to be the densest element of the first 7 periods.

·         The atomic radius of hassium is expected to be around 126 pm. Due to the relativistic stabilization of the 7s orbital and destabilization of the 6d orbital, the Hs⁺ ion is predicted to have an electron configuration of [Rn] 5f¹⁴ 6d⁵ 7s², giving up a 6d electron instead of a 7s electron, which is the opposite of the behavior of its lighter homologues. On the other hand, the Hs²⁺ ion is expected to have an electron configuration of [Rn] 5f¹⁴ 6d⁵ 7s¹, analogous to that calculated for the Os²⁺ ion

Orbital properties

• Ground state electron configuration:  [Rn].5f¹⁴.6d⁶.7s² (a guess based upon that of osmium)
• Shell structure:  2.8.18.32.32.14.2
• Term symbol:   ⁵D₄ (a guess based upon guessed electronic structure)

Isolation

Only a few atoms of element 108, hassium, have ever been made. The first atoms were made through a nuclear reaction involving fusion of an isotope of lead, ²⁰⁸Pb, with one of iron, ⁵⁸Fe.

²⁰⁸Bi + ⁵⁸Fe → ²⁶⁵Hs + ¹n

Isolation of an observable quantity of hassium has never been achieved, and may well never be. This is because hassium decays very rapidly through the emission of α-particles.