Actinides valency

F-Block Element the lanthanides and actinides, valence electrons in the f orbitals Feedstock a process chemical used to produce other chemicals or products Fine Chemicals chemicals produced in relatively low volumes and at higher prices as compared to bulk chemicals such as sulfuric acid, includes flavorings, perfumes, pharmaceuticals, and dyes First Law of Thermodynamics law that states energy in universe is constant, energy cannot be created or destroyed First Order Reaction reaction in which the rate is dependent on the concentration of reactant to the first power... 

Choice of Semiconductor Material for Actinide Valence Control. 467... 

Choice of Hole Scavenger for Actinide Valence Control. 470... 

Photochemical manipulation of actinide valence states has been studied as a means towards a salt-free method for actinide separation during fuel processing. This section summarises the points of relevance to photocatalytic valence manipulation and places them in the context of the dark redox reactions of actinide ions in aqueous solution. 

Similar arguments can be used to discount ZrC>2, HfC>2, Si, SiC, Ge, ZnO, PbC>2 and CdS. However, inspection of the Sn-H20 potential-pH diagram indicates that SnC>2 may find wide utility as a photo catalyst in actinide valence control. 

The electron donor/hole scavenger to be used in actinide valence control must have two properties. The first is that it is capable of undergoing an irreversible oxidation, either by valence holes formed by the photo-excitation of the semiconductor photocatalyst or by means of the hydroxide radicals generated by the oxidation of water by the same valence band holes. Suitable materials include organic acids, alcohols, aldehydes, amino acids, and hydrazine and its oxidation products, such as hydroxylamine and dihydrox-ylamine. 

Factors found to be contributory to efficient actinide valence control include ... 

Continuing this pattern, the first and second lEs of the actinides are less sensitive to increasing atomic number than the third lEs (Figure 2.6). However, owing to the similarity in energies between the 6d and 5f subshells, the behaviour of the third lEs is less simple than for the lanthanides, although maxima do appear at Am and No ". The behaviour of the actinide elements is also complicated by the effects of relativity. These result in a contraction of the 7s and 7p orbitals but an expansion and destabilization of the 6d and 5f orbitals. As a consequence, the actinide valence shell 6d and 5f electrons are more easy to ionize than would be predicted by a non-relativistic model. 

For the actinide valence states of most interest to chemists, 1 -I- through 7 -I-, very few gaseous free-ion spectra have been sufficiently analyzed to provide a... 

A further consequence of 5f-Sf overlap and hybridization in metallic actinides is a reduction of the importance of valence as a useful concept. In most of the light actinide metallic materials there is no clear separation between Sf electrons and bonding electrons. Unlike 4f electrons, the 5f electrons may enter into the bonding. There are, however, cases where the concept of actinide valence is useful, particularly when the magnetism has a local-moment character. Many properties of each system must be examined and reconciled before simplifying concepts such as localized magnetism and valence can be used correctly. Chan and Lam [19]... 

FiUaux C, Berthet JC, Conradson SD, Guilbaud P, Guillaumont D, Hennig C, et al. Combining theoretical chemistry and XANES multi-edge experiments to probe actinide valence states. C R Chimie. 2007 10 859-871. 

Thor, Scandinavian god of war) Discovered by Berzelius in 1828. Much of the internal heat the earth produces has been attributed to thorium and uranium. Because of its atomic weight, valence, etc., it is now considered to be the second member of the actinide series of elements. 

If pure, the carbides of Groups 1 and 2 are characterized by their transparency and lack of conductivity. The carbides of Group 3, ie. Sc, Y, the lanthanides, and the actinides, ate opaque. Some, depending on composition, show metallic luster and electroconductivity. The cation may exist in the MC2 phases of this group, and the remaining valence electron apparendy imparts pardy metaUic character to these compounds. 

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... 

In what follows we briefly review some of the previous attempts to analyze the available spectra of plutonium (6). In addition, we estimate energy level parameters that identify at least the gross features characteristic of the spectra of plutonium in various valence states in the lower energy range where in most cases, several isolated absorption bands can be discerned. The method used was based on our interpretation of trivalent actinide and lanthanide spectra, and the generalized model referred to earlier in the discussion of free-ion spectra. 

As was the case with lanthanide crystal spectra (25), we found that a systematic analysis could be developed by examining differences, AP, between experimentally-established actinide parameter values and those computed using Hartree-Fock methods with the inclusion of relativistic corrections (24), as illustrated in Table IV for An3+. Crystal-field effects were approximated based on selected published results. By forming tabulations similar to Table IV for 2+, 4+, 5+ and 6+ spectra, to the extent that any experimental data were available to test the predictions, we found that the AP-values for Pu3+ provided a good starting point for approximating the structure of plutonium spectra in other valence states. However,... 

The Table shows a great spread in Kd-values even at the same location. This is due to the fact that the environmental conditions influence the partition of plutonium species between different valency states and complexes. For the different actinides, it is found that the Kd-values under otherwise identical conditions (e.g. for the uptake of plutonium on geologic materials or in organisms) decrease in the order Pu>Am>U>Np (15). Because neptunium is usually pentavalent, uranium hexavalent and americium trivalent, while plutonium in natural systems is mainly tetravalent, it is clear from the actinide homologue properties that the oxidation state of plutonium will affect the observed Kd-value. The oxidation state of plutonium depends on the redox potential (Eh-value) of the ground water and its content of oxidants or reductants. It is also found that natural ligands like C032- and fulvic acids, which complex plutonium (see next section), also influence the Kd-value. 

Hexavalent Pu—See Valence states Hexyl hexyl- V, V-diethylcarbamoyl-methylphosphinate, actinide... 

Most of the known borides are compounds of the rare-earth metals. In these metals magnetic criteria are used to decide how many electrons from each rare-earth atom contribute to the bonding (usually three), and this metallic valence is also reflected in the value of the metallic radius, r, (metallic radii for 12 coordination). Similar behavior appears in the borides of the rare-earth metals and r, becomes a useful indicator for the properties and the relative stabilities of these compounds (Fig. 1). The use of r, as a correlation parameter in discussing the higher borides of other metals is consistent with the observed distribution of these compounds among the five structural types pointed out above the borides of the actinides metals, U, Pu and Am lead to complications that require special comment. 

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