The Lanthanide Elements

Using tables of free energies of formation it is clear that most metals will react with most HX. Moreover, in many cases, e.g. with the alkali metals, alkaline earth metals, Zn, A1 and the lanthanide elements, such reactions are extremely exothermic. It is also clear that Ag should react with HCl, HBr and HI but not with HF, and... 

Table 30.1 The discovery of the oxides of Group 3 and the lanthanide elements ...

Figure 30.1 Flow diagram for the extraction of the lanthanide elements.

The very slight differences that do exist among these elements are due to small changes in size brought about by increase of nuclear charge. The separation of the lanthanide elements from each other is based upon clever exploitation of these slight differences in properties. Table 23-1 shows a comparison of some of the properties of the various lanthanide elements. As can be seen, +3 is the common oxidation number and is most characteristic of the chemistry of these elements. Another thing to note is the steady decrease in... 

The most important minerals of the lanthanide elements are monazite (phosphates of La, Ce, Pr, Nd and Sm, as well as thorium oxide) plus cerite and gadolinite (silicates of these elements). Separation is difficult because of the chemical similarity of the lanthanides. Fractional crystallization, complex formation, and selective adsorption and elution using an ion exchange resin (chromatography) are the most successful methods. 

Recent advances in the chemistry of the less common oxidation states of the lanthanide elements. D. A. Johnson, Adv. Inorg. Chem. Radiochem., 1977, 20, 1-133 (599). 

Recent Advances in the Chemistry of the Less-Common Oxidation States of the Lanthanide Elements D. A. Johnson... 

Here 1 is the third ionization enthalpy of the lanthanide element and I(MCln,s) is AH for the following reaction ... 

Table 1—Oxidation states, electronic configurations, and radii of the (III) ion of the lanthanide elements and yttrium...

Data on the absorption of simple salts of the lanthanide elements injected intramuscularly into rats are summarized in Figure 10.4 The dependence of the fraction remaining at the injection site on the administered mass is apparent. When the amount injected was less than 0.01 jug, about 0.5 was absorbed in the first few days another 0.4 was absorbed with a half-time of about 25 days and the remaining 0.1 left the injection site with a half-time of 100 to 200 days. As the total mass injected was increased, the fraction absorbed in the first few days declined, and the amounts associated with the lower absorption rates increased. If 100 jug or more were injected, only 0.05 to 0.1 was absorbed during the first few days, and absorption was very slow thereafter. 

Baybarz, R. D. (1965). Dissociation contents of the transplutonium chelates with diethylenetriaminepentaacetic acid (DTPA) and the application of DTPA chelates to solvent extraction separations of transplutonium elements from the lanthanide elements, J. Inorg. Nucl. Chem. 27,1831. 

On the basis of properties, explain why is yttrium frequently found with the lanthanide elements. 

The results in the three preceding subsections conform fairly well to a consistent pattern. However, there are gaps and inconsistencies that require further thermochemical, and in some cases chemical, study. The series of solution enthalpies for the lanthanide trichlorides is satisfactory, but disagreements over the value for the enthalpy of solution of yttrium trichloride in water need resolving, and a modern value for scandium trichloride (at 25°C) would be welcome. The complete absence of enthalpies of solution of tribromides of the lanthanide elements and yttrium is regrettable, as is the lack of a value for scandium triiodide. 

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