Transeinsteinium actinides

The transeinsteinium actinides, fermium (Fm), mendelevium (Md), nobelium (No), and lawrencium (Lr), are not available in weighable (> ng) quantities, so these elements are unknown in the condensed bulk phase and only a few studies of their physicochemical behavior have been reported. Neutral atoms of Fm have been studied by atomic beam magnetic resonance 47). Thermochromatography on titanium and molybdenum columns has been employed to characterize some metallic state properties of Fm and Md 61). This article will not deal with the preparation of these transeinsteinium metals. 

There has not been any solid-state chemistry reported for pure bulk forms of the transeinsteinium elements, due to the small amounts of the elements that have been available and their short lives. The most abundant of these elements is Fm [nanograms of a very short-lived (20 h) Fm-255 isotope] and the above limitations have precluded studying its oxide. When reaching the end members of the actinide series, the availability of isotopes is a much greater problem e.g., only a few atoms of a short-lived isotope of Lr can be produced. 

It is not feasible to consider conventional-type studies (structure, vaporization behavior, etc.) for the transeinsteinium oxides, given their scarcity and short lifetimes. Presumably their oxide chemistry would be very similar to that of the lanthanide oxides, especially for the trivalent oxidation state. However, there is an increased tendency for actinides in the second half of the series toward divalency. This suggests that the monoxides of the higher actinides (e.g., transeinsteinium elements) could be potentially more stable, perhaps approaching the stability of Eu monoxide. With No (element 102 homolog of Yb), the monoxide could be its most stable oxide. 

Except for a study of a few reactions of Pu, most early work with the actinide cations was limited to long-hved naturally occurring Th and U. Beginning in the mid-1990s, specialized mass spectrometers with unique sample-handling capabihties were developed to enable systematic studies of ion chemistry for all of the actinides from Th to Es. The actinides beyond Es— Em, Md, No, and Lr—are available in insufficient quantities (< 1 pg) to effectively produce gas-phase ion sources the short half-Uves of these transeinsteinium isotopes (<1 day) further hinder progress in the extension of gas-phase ion chemistry studies beyond Es by conventional approaches. 

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