Lanthanide elements, actinides compared

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... 

The ilillerent ranges of oxidation stales of the actinides in aqueous solution were described, discussed and compared with the much narrower ranges displayed by the lanthanide elements. 

A comparable temperature dependence of resistivity was obtained for a mixed phase sample of Cel2. The formation of apparently metallic phases for only the iodides of five lanthanide and actinide elements is considered in terms of the stoichiometry, the electronic structure of the cation, the possible nature of the band, and the role of the anion. In contrast, the intermediate Lai2.1,2 phase exhibits semiconduction. Its magnetic data between 80° and 300° K. can be best accounted for if the reduced component is considered to be La ", [Xe]5d with a ground term, a spin-orbit coupling constant A — 050 cm. and only small covalency and asymmetry parameters. 

In this chapter, we learned about the transition metals, which are located in Groups 3 through 12 in the periodic table. Compared to other metals, the transition elements are more stable and are therefore more often found pure in nature. The transition metals also include the lanthanides and actinides, two groups that are often displayed separately in the periodic table. The actinides contain the three heaviest naturally occurring elements in the periodic table—thorium, protactinium, and uranium. 

The structures are formed only by the transition, lanthanide and actinide elements, and not by other metals of comparable atomic radius and electronegativity. 

Since the ionic sizes are comparable for both series, the formation of complex ions and their stability constants are similar, so that it is difficult to separate actinide from lanthanide elements, though it can be done, as described below (page 1111), by ion-exchange or solvent-extraction procedures. 

Fig. 11 shows that the IR of the 4d and 5d elements are, as expected, almost equal due to the well-known lanthanide contraction (of 0.020 A) which is roughly 86% a nonrelativistic effect The diminished shielding of the nucleus charge by the 4f electrons causes the contraction of the valence shells. The IR of the transactinides are about 0.05 A larger than the IR of the 5d elements. This is due to an orbital expansion of the outer 6p3/2 orbitals responsible for the size of the ions. The IR of the transactinides are, however, still smaller than the IR of the actinides due to the actinide contraction (0.030 A, being larger than the lanthanide contraction) which is mostly a relativistic effect The 5f shells are more diffuse than the 4f shells, so that the contraction of the outermore valence shells is increased by relativity to a larger extent in the case of the 6d elements as compared to the 5d elements. This has first been shown for elements 104-118 by DF and DS calculations of atomic and ionic radii by Fricke and Waber [20]. 

It is neither intended nor possible to give a comprehensive review of relativistic density functional calculations on small molecules. To be able to compare the methods described in Sec. 2, we will primarily discuss molecules for which computational results from a variety of different methods are aveulable. Molecules containing heavy elements from the left half of the periodic table (including lanthanides and actinides) will not be discussed, as most of this is covered in the eirti-cle by V. Pershina in this volume. Likewise, only calculations of molecular spectroscopic constants such as bond lengths (r ), (harmonic) vibrational frequencies ((0 ) and binding energies (D ) are... 

Speciation and reactivity of actinide compounds comprise an important area for quantum chemical research. Even more so than in the case of lanthanides, f-type atomic orbitals of actinides can affect the chemistry of these elements [185,186] the more diffuse 5f-orbitals [187] lead to a larger number of accessible oxidation states and to a richer chemistry [188]. The obvious importance of relativistic effects for a proper description of actinides is often stressed [189-192]. A major differences in chemical behavior predicted by relativistic models in comparison to nonrelativistic models are bond contraction and changes in valency. The relativistic contribution to the actinide contraction [189,190] is more pronounced than in the case of the lanthanides [191,192]. For the 5f elements, the stabilization of valence s and p orbitals and the destabilization of d and f orbitals due to relativity as well as the spin-orbit interaction are directly reflected in the different chemical properties of this family of elements as compared with their lighter 4f congeners. Aside from a fundamental interest, radioactivity and toxicity of actinide compounds as well as associated experimental difficulties motivate theoretical studies as an independent or complementary tool, capable of providing useful chemical information. 

The dilTcrcnl raiiiies ol oxidation stales ol lire actinides in a(. ueous solution weie dcscribal. discussal aiul compared with the much narrower laimes tiisplayed b the lanthanide elements. 

In actinides, the distance between the outer (valence electrons) orbitals and the inner electron orbitals is much greater when compared that of the lanthanide elements. In actinide, the distance between the 5f orbitals (outer orbital) and the 7s7p orbitals is greater than the distance between the lanthanide 4f orbitals and the 6s6p orbitals. 

Comparable recent detailed reviews of the actinide halides could not be found. The structures of actinide fluorides, both binary fluorides and combinations of these with main-group elements with emphasis on lattice parameters and coordination poly-hedra, were reviewed by Penneman et al. (1973). The chemical thermodynamics of actinide binary halides, oxide halides, and alkali-metal mixed salts were reviewed by Fuger et al. (1983), and while the preparation of high-purity actinide metals and compounds was discussed by Muller and Spirlet (1985), actinide-halide compounds were hardly mentioned. Raman and absorption spectroscopy of actinide tri- and tetrahalides are discussed in a review by Wilmarth and Peterson (1991). Actinide halides, reviewed by element, are considered in detail in the two volume treatise by Katzet al. (1986). The thermochemical and oxidation-reduction properties of lanthanides and actinides are discussed elsewhere in this volume [in the chapter by Morss (ch. 122)]. 

It is our purpose to present a summary of the compounds formed with oxygen and the lanthanide and actinide elements in such a way as to facilitate comparisons and contrasts. It is hoped that for many readers this summary will, in itself, prove useful by presenting an updated account of some relevant research concerning the lanthanide and actinide oxides. Beyond this, it will be found that the oxides afford a substantial platform upon which to assemble a comparative collage of lanthanide/ actinide chemistry. 

As stated in the opening section of this chapter, the objective is to discuss and compare the solid-state chemistry and physics of the lanthanide and actinide element oxides. The topics of discussion have been limited to binary oxides of these elements. Therefore, a discussion of the many complex (ternary, mixed, etc.) oxide systems for these f elements, and oxides of actinides representing oxidation states above four that do not have lanthanide counterparts, are not present. 

The objective of this section of the chapter is to compare the properties and behaviors of the binary oxides of the lanthanide and actinide elements. The trends and the differences between the binary oxides of each series of elements are reviewed but a discussion of the more complex (e.g., ternary or larger) oxides that these elements are known to form is excluded. Essentially this section offers a comparison of the monoxides, sesquioxides, dioxides and binary oxides with 0/M ratios intermediate to those found in these three oxides. Since the lanthanide elements do not form oxides with higher O/M ratios than 2.0, actinide oxides with higher oxygen stoichiometries are not discussed in this section. 

In contrast to the now relatively extensive metal-metal bonded chemistry of sub valent Mg, Al, and Zn, homomet2Jlic bonds involving the 6s and 7s orbitals of the lanthanide and actinides elements are rare (diatomic overlap between the 5f orbitals in Uj and other cases is discussed later). Their absence is largely a consequence of the rdatively low second and third ionization energies (compared to Al), which reduce the stability of the -i-l and +2 oxidation states. Examples... 

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