Structure actinide elements, electronic

There is no single best form of the periodic table since the choice depends on the purpose for which the table is used. Some forms emphasize chemical relations and valence, whereas others stress the electronic configuration of the elements or the dependence of the periods on the shells and subshells of the atomic structure. The most convenient form for our purpose is the so-called long form with separate panels for the lanthanide and actinide elements (see inside front cover). There has been a lively debate during the past decade as to the best numbering system to be used for the individual... 

Actinides, the chemical elements with atomic numbers ranging from 89 to 103, form the heaviest complete series in the Periodic Table. They are radioelements, either naturally occurring or synthesized by nuclear reactions. Their predominant practical application depends on the nuclear properties of their isotopes decay, spontaneous or induced fission. Their chemical and physical properties reflect a very complex electronic structure, and their study and understanding are a challenge to experimentalists and theoreticians. 

U is a member of the actinide series of elements which, together with the rare earths and the transition elements, possess a high heat of oxidation, a low oxide density compared with that of the metal, and the presence of an unfilled d shell in its electronic structure. While the reasons for the high pyrophoric potential of U are not clearly understood, they are thought to be related to these aforementioned properties (see under Pyrotechnics in Vol 8, P511 and Pyrophoric Incendiary Agents , P503-L)... 

The preceding discussion of the relationships between excited state electronic structure and photochemical reactivity focused primarily upon coordination compounds containing cP or low-spin cP transition metals. These relationships are generally applicable, however, to complexes of other d transition elements, the lanthanides and the actinides. A brief survey of the photochemical reactions of these latter systems is presented below. 

Scientific Committee of International Conferences First International Transplutonium Element Symposium, Argonne, IL, USA, 1963 Third International Transplutonium Element Symposium, Argonne, IL, USA, 1971 Fifteenth International Conference on Coordination Chemistry, Moscow, USSR, 1973 First International Symposium on the Electronic Structure of the Actinides, Argonne, IL, USA, 1974... 

Methods to calculate the electronic structures of very heavy element compounds are the same relativistic methods which can be applied to any relativistic systems. They were overviewed in application to transition elements [13], actinides [38], and transactinides [15-17]. They will, therefore, be only shortly described here with the accent put on those which were used for calculations of the transactinide systems. 

As a result of this disparity, many questions on the structure and bonding of the actinides center on the role of the 5f-electrons. The molecular orbital descriptions for the bonding of the actinide elements continue to evolve. One of the first general models used to describe the chemical bonding in d- and f-electron complexes is the FEUDAL model. FEUDAL is an acronym for f orbitals essentially unaffected d orbitals accommodate ligands . This model is represented in Figure 3, which depicts the molecular orbital... 

We also conclude from our ab initio DF SCF calculations that the 5d, 6d and 5f DFAOs (and their associated electrons) are definitely involved (due to relativistic effects in the electronic structure and bonding of the diatomics of the heavy third-row transition elements and actinides, and they present the formidable dual challenge to quantum chemists of the accurate calculation of the relativistic and electron correlation effects for such systems. 

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