Actinide transition series

Element 103, lawrencium, completes the actinides. Following this series, the transition elements should continue with the filling of the 6d orbitals. There is evidence for an element 104 (eka-hafnium) it is believed to form a chloride MCl4, similar to that of hafnium. Less positive evidence exists for elements 105 and 106 attempts (so far unsuccessful) have been made to synthesise element 114 (eka-lead). because on theoretical grounds the nucleus of this elemeni may be stable to decay by spontaneous fusion (as indeed is lead). Super-... 

Fig. 1. Oxidation numbers for - d-transition series , - f-transition series (lanthanides and actinides) (non-common or uncertain oxidation numbers have been put between brackets)...

Absorption spectra of ions of the lanthanide and actinide transitions series differ substantially from those shown in Figure 26-3. The electrons responsible for absorption by these elements (4f and 5f, respectively) are shielded from external influences by electrons that occupy orbitals with larger principal quantum numbers. As a result, the bands tend to be narrow and relatively unaffected by the species bonded by the outer electrons (see Figure 26-3). 

First/-transition series (lanthanides) Second/-transition series (actinides) ... 

Actinide elements (Z = 89 - 103) include the heaviest natural and most of the synthetic transuranium elements. They form a series of transition elements, characterized by the filling of an inner - the 5f-electron shell. The elements from Ac (Z = 89) to Es (Z = 99) are available in quantities sufficient for solid state studies. Elemental actinides are metallic. The methods of metal preparation and characterization have been improved to yield samples of known purity and crystal structure, sometimes in the form of single crystals. Recent measurements of structural, thermodynamic and electronic properties have emphasized elements in the beginning and in the centre of the actinide series. 

The dodecahedron requires a larger radius ratio than the antiprism (i.e., 0.665 versus 0.645), and it is tempting to say that it is favored over the antiprism as a coordination type for the larger (with respect to the d-transition series) actinide elements. The lack of a sufficiently large number of well-determined structures makes such a suggestion tenuous at this time. However, there is some support for this thesis among the one dimensional polymers, as explained in the following section. 

Compounds of the stoichiometry MCp 2X2 provide an opportunity to compare actinides with block elements. Several such species have been studied both by gas phase PE experiments as well as by theoretical approaches. Thus, the first comparative study of the PE spectra of a series of transition metal and actinide organometallic compounds with exacdy the same ligand array was carried out on MCp 2X2 (M = Zr, Th, U, and X = CH3 and Cl) complexes. Comparable bonding was found along the series with smaller differences than encountered in the parent series involving transition elements. The major differences between Zr and the actinides are due to the involvement of yin the bonding. 

Transition metals lanthanide series, actinide series... 

Seaborg GT (1954) Coordination of properties as actinide transition series. In Seaborg GT, Katz JJ (eds) The actinide elements. McGraw-Hill, New York, pp 733-768... 

Her actinides are more similar to a series of transition elements, but beyond the half-filled stage of the 5f orbitals the series become similar to the oxides of the corresponding lanthanides. The lower oxidation states are basic, the higher ones acidic, with intermediate oxidation states being amphoteric. 

In spite of the fact that the f-block elements, the members of the lanthanide and actinide transition series, have no known essential role in life processes (Williams 1988), they pose some of the most fascinating, challenging and important chemical and biochemical problems of all the inorganic elements of the periodic table. 

Second/transition series (actinides, 5/orbitals occupied) 90Tb through losLr... 

The sum of the two contributions is a skew parabola with its minimum moved towards the beginning of the series. Further, the skewness and the distance of the minimum from the centre of the series increase as the strength of f-p hybridization increases, as shown in fig, 59. A model similar to that summarized in fig. 58 may also be used for actinide transition metal compounds, with d bands replacing the p bands of the chalcogenide or pnictide. The resulting state densities are then similar to those in fig. 40, modified to include f states in the bands, as in sect. 5.3 for cerium compounds. 

This chapter is intended to provide a unified view of selected aspects of the physical, chemical, and biological properties of the actinide elements. The f block elements have many unique features, and a comparison of the lanthanide and actinide transition series provides valuable insights into the properties of both. Comparative data are presented on the electronic configurations, oxidation states, redox potentials, thermochemical data, crystal structures, and ionic radii of the actinide elements, together with a miscellany of topics related to their environmental and health aspects. Much of this material is assembled in tabular and graphical form to facilitate rapid access. Many of the topics covered in this chapter, and some that are not discussed here, are the subjects of subsequent chapters of this work, and these may be consulted for more comprehensive treatments. This chapter provides a welcome opportunity to discuss the biological and environmental aspects of the actinide elements, subjects that were barely mentioned in the first edition of this work but have assumed great importance in recent times. 

As regards the transition elements, the first row in particular show some common characteristics which define a substantial part of their chemistry the elements of the lanthanide and actinide series show an even closer resemblance to each other. 

Evidence other than that of ion-exchange favours the view of the new elements as an inner transition series. The magnetic properties of their ions are very similar to those of the lanthanides whatever range of oxidation states the actinides display, they always have -1-3 as one of them. Moreover, in the lanthanides, the element gado-... 

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