The Lanthanoid Series

Part of the absorption spectrum of an aqueous solution of neodymium(iii) -configuration/ - is shown in Fig. 10-4. The situation shown there is quite typical of the whole of the lanthanoid series i.e. we could have chosen any/" configuration equally well to illustrate the main characteristics of the spectra of lanthanoid complexes. We shall focus on three main features splittings, band widths and absolute excitation frequencies. 

Samarium is one of the rare earth elements found in Row 6 of the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. The rare earth metals are not really very rare in Earth s surface. The name comes from the fact that these elements were once very difficult to separate from each other. For a long time, chemists knew very little about the individual elements. A more correct name for these rare earth elements is the lanthanoid series. It is named after the element lanthanum, the first element in the series. 

Groups 1,2, 17, and 18 are often identified with the group names shown on the table to the right. Groups 3 through 12 are called the transition metals. The lanthanoid series is contained in period 6, and the actinoid series is in period 7. The two series together are called the inner transition metals. The locations of the transition and inner transition metals in the periodic table are discussed further in Skill 1.1b. 

Lanthanum hydroxide, though sparingly soluble, is a strong base and absorbs CO2, giving the carbonate. Base strength and solubility decrease on crossing the lanthanoid series, and Yb(OH)3 and Lu(OH)3 dissolve in hot concentrated NaOH (equation 24.14). 

In accordance with the variation observed in their successive ionization potentials. Table 2-1, the (3+) oxidation state is a common characteristic chemical feature of the lanthanoid series. With a few exceptions, typically associated with elements having a relatively low fourth ionization potential (Ce, Pr, Tb), Table 2-1, the (3+) oxidation state exhibits a high stability. In the case of the three elements mentioned above, the (4+) oxidation state is very relevant as well. In particular, higher oxides, i.e. dioxides and mixed-valent (+3/+4) compounds are well known for... 

As deduced from the equilibrium data (Ph2o) reported in Table 2-3, the hydration process would be favorable, at room temperature, for most of the rare earth oxides. Moreover, experimental hydration studies carried out on sesquioxides belonging to the second half of the lanthanoid series Sm203 [107,110,111], H02O3... 

J and gj for ground states are both larger in the second half than the first half of the lanthanoid series. 

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