Europium atomic radius

These are listed in Table 2.3 and shown in Figure 2.4. It will be seen that the atomic radii exhibit a smooth trend across the series with the exception of the elements europium and ytterbium. Otherwise the lanthanides have atomic radii intermediate between those of barium in Group 2A and hafnium in Group 4A, as expected if they are represented as Ln + (e )3. Because the screening ability of the f electrons is poor, the effective nuclear charge experienced by the outer electrons increases with increasing atomic number, so that the atomic radius would be expected to decrease, as is observed. Eu and Yb are exceptions to this because of the tendency of these elements to adopt the (+2) state, they have the structure [Ln +(e )2] with consequently greater radii, rather similar to barium. In contrast, the ionic radii of the Ln + ions exhibit a smooth decrease as the series is crossed. 

Density The density depends upon the atomic weight, atomic radius and the structme of the aggregate. It is a general trend in a periodic family that density increases with increase in atomic weight. This trend is observed in lanthanides also. The reason is that the increase in atomic weights in lanthanides is comparatively larger than the increase in volumes of individual atoms, since the lanthanides have almost the same atomic radii. The exceptions are europium (Eu) and ytterbium (Yb). 

An interesting effect of the half-filled and filled 4/ shell is shown when a graph is made of the melting point of the elements. Such a graph is shown in Figure 11.6. Although it is not shown, a plot of atomic radii for the metals shows a large increase in size for Eu and Yb. For example, the radii of Sm and Gd are approximately 180 pm, but Eu, situated between them, has a radius of 204 pm. The difference in size between Yb and the atoms before and after it also amounts to about 20 pm. Europium and ytterbium... 

The lanthanide or rare earth elements (atomic numbers 57 through 71) typically add electrons to the 4f orbitals as the atomic number increases, but lanthanum (4f°) is usually considered a lanthanide. Scandium and yttrium are also chemically similar to lanthanides. Lanthanide chemistry is typically that of + 3 cations, and as the atomic number increases, there is a decrease in radius for each lanthanide, known as the lanthanide contraction. Because bonding within the lanthanide series is usually predominantly ionic, the lanthanide contraction often determines the differences in properties of lanthanide compounds and ions. Lanthanide compounds often have high coordination numbers between 6 and 12. see also Cerium Dysprosium Erbium Europium Gadolinium Holmium Lanthanum Lutetium Praseodymium Promethium Samarium Terbium Thulium Ytterbium. 

Gschneidner [28,29] showed that the enthalpies of formation of several classes of lanthanide compounds can be correlated systematically as a function of atomic number. He pointed out [30] that the correlations for europium and ytterbium are anomalous because they are divalent in their metallic state but trivalent in the compounds. As shown in Figure 1, the enthalpies of formation of the lanthanide sesquioxides (or of any other class of compounds of R ) do not change in a smooth fashion as a function of Z or of the ionic radius of R. These enthalpies of formation correspond to the reactions that appear to be similar throughout the rare earths,... 

There are two apparent artifacts in this correlation. First, one would not expect based on these arguments that the acidic phosphoric acid esters HDOP, HDBP, and HDEH P (bars U, V, and W) would demonstrate as great a selectivity for europium as is observed. Similarly, there is no apparent reason for the enhanced selectivity demonstrated by 100% TBP for americium for extraction from 13 M HNOj (bar G). In the case of the phosphoric-acid extractants, the apparent anomaly is a manifestation of the steep slope of the linear relationship between distribution ratios and atomic number (cation radii) as shown in figs. 4 and 5, and a mismatch of the ionic radii of americium and europium. It is generally believed that the cation radius of americium is more nearly comparable to that of promethium or neodymium than europium (see table 1). The logSi J calculated from the the same data is —0.35. 

Fig. II. (L t-hand side) Lm absorption spectra of Ce, Pr, Gd, Tb and Yb (solid lines) ligned up with the Lm absorption spectrum of Eu (dashed lines) at g. o defines intersection of the atomic-like absorption lines with the average absorption at high energies. Right-hand side) The same spectra as on the left side, however, the energy axis is scaled with R/R ). R denotes the metallic radii in A, Rgu metallic radius of europium from Matthias etal. (1967).

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