Ytterbium 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... 

Most trace elements have values of D< C 1, simply because they differ substantially either in ionic radius or ionic charge, or both, from the atoms of the major elements they replace in the crystal lattice. Because of this, they are called incompatible. Exceptions are trace elements such as strontium in plagioclase, ytterbium, lutetium, and scandium in garnet, nickel in olivine, and scandium in clinopyroxene. These latter elements acmally fit into their host crystal structures slightly better than the major elements they replace, and they are therefore called compatible. Thus, most chemical elements of the periodic table are trace elements, and most of them are incompatible only a handful are compatible. 

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,... 

The first neutral lanthanide(II) silyl complex (Ph3Si)2Yb(THF)4 was synthesized by the reaction of PhsSiCl with metallic ytterbium in THF. The solid complex has a cen-tros3munetrical octahedral structure with a Yb atom bonded to four oxygen atoms of the THF molecules in the equatorial positions and to two Si atoms of the SiPhs fragment in the axial positions. The Yb—Si distance of 3.158(2) A is 0.1 A larger than the Sm—Si distance in Cp2 SmSiH(SiMe3)2 which is in agreement with the difference in ionic radius between Ln(II) and Ln(III) complexes. ... 

The difference in activity among the lanthanide salts was further demonstrated by the fact that para-nitrobenzaldehyde was not acetalized after 20 hr in the presence of erbium chloride, but was completely converted when ytterbium chloride was the catalyst. This is consistent with the observation that acetalization yields increased with increasing atomic number (decreasing ionic radius), a phenomenon related to the Lewis acidity (or degree of hardness) of the cations. The role of the lanthanide catalyst is not well-defined, however. 

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