5f Electrons in Transthorium Chemistry

Abstract

Electron configuration /Periodic Table/Transthorium elements/ Unsaturated quarks/Uranyl ion AbstractThe spectroscopic and chemical properties of 5f group compounds show several ramifications not exhibited by the lanthanides. When the oxidation state is M (III), they are indeed quite similar. Like M(IV) they vary their coordination number Ν rather indifferently, and available evidence from photo-electron spectra has modified our opinions on covalent bonding, weakening any idea of two electrons per bond. On the other hand, the uranyl ion and subsequent dioxo complexes have exceptional stereochemistry and electronic structure, of which all the details have not yet been clarified. Possible relations with unsaturated quarks and long-lived hypothetical "elementary" particles (such as technicolor hadrons) are discussed.Half a century ago, quantum chemistry had started with the gaseous species Hj and gone on with the complicated H 2 [1 ], and quarter a century ago, the controversy about the electronic structure of transthorium compounds was approaching its armistice. The two (equally absurd) extreme arguments had been that the presence of 5f electrons produces a propensity toward trivalency (like the 4f electrons in the lanthanides); and that the chemical stability of the oxidation states Pa(V), U(VI), Np(V) and Np(VI) shows the absence of 5f electrons, protactinium and uranium being 6d-homologs of the 5d-elements tantalum and tungsten. This whole discussion remains a clear-cut example of the much greater utility of induction from facts than of deduction in chemistry [2].It is worthwhile to analyze what we mean by 5f elements. Whereas the individual «/-values go back to the energy levels of atomic alkaline-metals studied by RYD-BERG in 1895, the explanation of the Periodic Table by an "Aufbau Princip" [3, 4] goes back to STONER in 1924 suggesting that each «/-shell is able to accomodate at most (4/ + 2) electrons. It is useful to concentrate our attention [5 -8] on gaseous ions M +z with charges from +2 to +6.Indicating the closed shell systems isoelectronic with noble gas atoms by double inequality signs, the shells are filled in the order ls^2s<2p^3s<3p«3d<4s<4p^4d<5s<5p ^4f<5d<6s<6p^5f<6d<7s...to which only five exceptions are known, all for M +2 with M=La(5d), Gd(4f 7 5d), Lu(4f 14 6s), Ac(7s) and Th(5f6d), where the electrons not belonging to the previous noble-gas configuration with Κ = 54 or 86 electrons are given in parentheses. Text-books frequently propose another sequence intended for neutral atoms, where the shells 4s, 5s, 6s and 7s follow immediately after Κ = 18, 36, 54 and 86. However, this sequence has 20 exceptions among the neutral atoms up to einsteinium (Z = 99) and is of much less relevance to transition-group chemistry [5,6] than (1). It is by no means trivial to define what the sequence (1) is meant to convey. The discrete energy levels of a monatomic entity are always characterized by / and (odd or even) parity. In most cases, adjacent /-levels can be bunched together in Russell-Saunders co...