Nobelium

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MELTING POINT: Unknown
BOILING POINT: Unknown
DENSITY : Unknown
MOST COMMON IONS : No ²⁺ , No ³⁺

The first claim for the discovery of the element nobelium was made in Sweden in 1957. However, neither American nor Soviet researchers could duplicate the original results, which are now known to have been interpreted incorrectly. The actual discovery of nobelium is credited to researchers in Berkeley, California, who in 1958 bombarded a curium target (95% ²⁴⁴ Cm and 4.5% ²⁴⁶ Cm) plated on a nickel foil with 60 to 100 MeV ¹² C ions, and detected both the 8.4 MeV α -particles created by the radioactive decay of ²⁵² No and the ²⁵⁰ Fm created from the α -decay of ²⁵⁴ No. Known isotopes of nobelium possess 148 to 160 neutrons and 102 protons; all are radioactive, with half-lives ranging between 2.5 milliseconds and 58 minutes, and decay by spontaneous fission , α -particle emission, or electron capture. ²⁵⁹ No has the longest half-life: 58 minutes.

Nobelium is a member of the actinide series of elements. The ground state electron configuration is assumed to be (Rn)5f147s2, by analogy with the equivalent lanthanide element ytterbium ([Kr]4f146s2); there has never been enough nobelium made to experimentally verify the electronic configuration. Unlike the other actinide elements and the lanthanide elements, nobelium is most stable in solution as the dipositive cation No ²⁺ . Consequently its chemistry resembles that of the much less chemically stable dipositive lanthanide cations or the common chemistry of the alkaline earth elements. When oxidized to No ³⁺ , nobelium follows the well-established chemistry of the stable, tripositive rare earth elements and of the other tripositive actinide elements (e.g., americium and curium).

SEE ALSO Actinium ; Berkelium ; Einsteinium ; Fermium ; Lawrencium ; Mendelevium ; Neptunium ; Plutonium ; Protactinium ; Rutherfordium ; Thorium ; Uranium .

Mark Jensen

Bibliography

Hoffman, Darleane C.; Ghiorso, Albert; and Seaborg, Glenn Theodore (2000). The Transuranium People: The Inside Story. London: Imperial College Press.