Lanthanides atomic numbers

The trend toward greater complex stability with increasing lanthanide atomic number (see Table 3 for EDTA, DCTA, and DTPA complexes) has also been demonstrated for lanthanide complexes with... 

Fig. 4.15 The system La(III) acetylacetone (HA) - IM NaC104/benzene at 25°C as a function of lanthanide atomic number Z. (a) The distribution ratio Hl (stars, right axis) at [A ] = 10 and [HA] rg = 0.1 M, and extraction constants (crosses, left axis) for the reaction Ln + 4HA(org) LnA3HA(org) + 3FE. (b) The formation constants, K , for formation of LnA " lanthanide acetylacetonate complexes (a break at 64Gd is indicated) circles n = 1 crosses n = 2 triangles w = 3 squares w = 4. (c) The self-adduct formation constants, for the reaction of LnA3(org) + HA(org) LnA3HA(org) for org = benzene. (A second adduct, LnA3(HA)2, also seems to form for the lightest Ln ions.) (d) The distribution constant Ajc for hydrated lanthanum triacetylacetonates, LnAs (H20)2 3, between benzene and IM NaC104. (From Ref. 28.)...

Note that the Lanthanide (atomic numbers 58-71) and Actinide (90-103) series elements, as well as the synthetic elements of atomic number greater than 87, are omitted from all the periodic tables in this text. With the possible exception of nuclear fuels such as uranium and plutonium, these elements are of little general engineering interest. 

Fig. 1.8. Effective extraction constant of the trisolvate (TBP)3-Ln(N03)3 versus lanthanide atomic number Z. Extraction system Ln(N03)3-H20-TBP 100 vol%.

The two rows beneath the main body of the periodic table are the lanthanides (atomic numbers 58 to 71) and the actinides (atomic numbers 90 to 103). These two series are called inner transition elements because their last electron occupies inner-level 4/orbitals in the sixth period and the 5/orbitals in the seventh period. As with the d-level transition elements, the energies of sublevels in the inner transition elements are so close that electrons can move back and forth between them. This results in variable oxidation numbers, but the most common oxidation number for all of these elements is 3+. 

Fig. 46. The thermopower at T = 273 K (Sot) vs. the lanthanide atomic number for the RAlj series together with the spin quantum numbers (S), orbital quantum numbers (L), and total quantum numbers (/).

Fig. 58. The thermal resistivity at T = 250 K (W250) together with the Curie temperatures for the RAI2 series as a function of the lanthanide atomic number (Sassik, 1981).

The experimental lattice parameters as a function of lanthanide atomic number show the famous lanthanide contraction, the decrease of the lattice parameter across the lanthanide series, with the exception of the two anomalies for Eu and Yb, as seen in Figure 1 (top panel). What is plotted there b actually the atomic sphere radius S (in atomic units) as a function of the lanthanide element A similar behaviour is abo observed, for example, for lanthanide monochalcogenides and monopnictides, whose lattice parameters are abo shovm in Figure 1 (middle and bottom panels). 

The jumps in the lattice constants in Figure 1, seen for the elemental Eu and Yb, as well as at the chalcogenides of Sm, Eu, Tm, and Yb, are due to the change in valence from trivalent to divalent. If a transition to the trivalent state were to occur, the lattice constant would also follow the monotonous behaviour of the other lanthanides, as seen in Figure 2, where the ionic radii of trivalent lanthanide ions are displayed. For the pnictides, only CeN shows an anomaly, indicating a tetravalent state, whereas all the other compounds show a smooth, decreasing behaviour as a function of the lanthanide atomic number. 

Lanthanide Atomic number Electron configuration Ionic radius (nm)... 

Fig. 1.2. Periodic table of the elements excluding lanthanides (atomic numbers 58 to 71) and actinides (atomic numbers 90 to 103). The crystal structures will be explained below.

Hexagonal Laves phases exhibit da values near to the ideal 1.63 value in compounds with Mn and Re and slightly higher values for RTci (1.65). These values for J Ru2 (1.69-1.67) and for ROs2 (1.67-1.65) are high, but decrease with increasing lanthanide atomic number. 

Under analogous conditions, the molecular constants of three lanthanide difluorides have been studied. The IR spectra of SmF2, Eup2, and YbF2 in nitrogen and argon matrices have been reported by DeKock et al. (1972). The v, and v, values for Eup2 coincide with those found by Hastie et al. (1971) however, the Vj frequency was not detected for any of these compounds (DeKock et al., 1972 Hastie et al., 1971). On the other hand, scrutiny of the available data (DeKock et al., 1972 Hastie et al., 1971) shows that the experimental values of v, and v, for the above three difluorides typically depend on the lanthanide atomic number, which makes it possible to assess unknovm frequencies by interpolation. 

Fig. 21.1. Concentrations of lanthanides and yttrium in a composite sample of 9 chondritic meteorites (Haskin et al., 1%8) are plotted against lanthanide atomic number in the lowest part of the figure. Relative lanthanide abundances for the solar atmosphere (Ross and Aller, 1976) and lanthanide concentrations for a composite of 40 North American shales (Haskin et al., 1968) are compared with the chondritic abundances in the middle and upper parts of the figure by plotting ratios of their lanthanide concentrations to those of the chondrites. Such comparison diagrams are used throughout this chapter.

Lanthanide distributions in individual specimens of granite-like rocks can vary markedly from the NASC distribution. Several examples are shown in fig. 21.13. Others are discussed in the reviews of Haskin et al. (1966a), and Herrmann (1968). Most) individual granites are relatively enriched in light lanthanides relative to chondrites, some not as much as the NASC, some more. Many show systematic enrichment with decreasing lanthanide atomic number extepding from the heaviest lanthanides to La. 

MHCOj" expressed in terms of as a function of lanthanide atomic number. Figure 2... 

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