The Lanthanide Series

Theoretically, an atom may have the following electron shells K, L, M, N, O, P, and Q or 1, 2, 3, 4, 5, 6, and 7 where K (or 1) is the most inward and P (or 7) is the most outward. The electrons in the outer shells are most important for determining the chemical behavior, and how they behave as conductors. 

Every shell has also subshells. These are composed of atomic orbitals. The electron subsheUs of an atom are labelled s, p, d, and f, which is short for sharp, principal, diffuse, and fundamental (Jensen 2007). The first shell (K) has one subsheU, called Is. The second shell (L) has two subshells called 2s and 2p. The third shell (M) has 3 subsheUs (3s, 3p, 3d). The fourth shell (N) has 4 subshells (4s, 4p, 4d, 4f). 

The numbers of possible electrons per orbital is given in Table 3.1. 

The order in which these orbitals are fiUed is given by the n -i- f mle (also known as the Madelung rule (Madelung 1943). 

The Madelung Rule is also caUed the Aufbau principle (from German Aufbau meaning build-up, fabric, structure ). This describes electron configuration and the filling of atomic orbitals. 

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Another characteristic change across the lanthanide series is that of the paramagnetism of the ions this rises to a maximum at neodymium, then falls to samarium, then rises to a second maximum at gadolinium before falling finally to zero at the end of the series. 

Therefore the extent of extraction or back-extraction is governed by the concentration of X ia the aqueous phase, the distribution coefficients, and selectivities depending on the anion. In nitrate solutions, the distribution coefficient decreases as the atomic number of the REE increases, whereas ia thiocyanate solutions, the distribution coefficient roughly increases as the atomic number of the REE increases. The position of yttrium in the lanthanide series is not the same in nitrate and thiocyanate solutions, and this phenomenon has been used for high purity yttrium manufacture in the past. A combination of extraction by carboxyUc acids then by ammonium salts is also utilized for production of high purity yttrium. 

Catalysts for SW tube formation are not confined to the iron-group metals. Some elements of the lanthanide series can catalyze the formation of SW tubes. 

Scandium is very widely but thinly distributed and its only rich mineral is the rare thortveitite, Sc2Si20v (p. 348), found in Norway, but since scandium has only small-scale commercial use, and can be obtained as a byproduct in the extraction of other materials, this is not a critical problem. Yttrium and lanthanum are invariably associated with lanthanide elements, the former (Y) with the heavier or Yttrium group lanthanides in minerals such as xenotime, M "P04 and gadolinite, M M SijOio (M = Fe, Be), and the latter (La) with the lighter or cerium group lanthanides in minerals such as monazite, M P04 and bastnaesite, M C03F. This association of similar metals is a reflection of their ionic radii. While La is similar in size to the early lanthanides which immediately follow it in the periodic table, Y , because of the steady fall in ionic radius along the lanthanide series (p. 1234), is more akin to the later lanthanides. 

Rare earth (RE) is a generic name for 14 metallic elements of the lanthanide series. These elements have similar chemical propenies and are usually supplied as a mixture of oxides extracted from ores such as bastnaesite or monazite. 

Rare Earth is a generic name used for the 14 metallic elements of the lanthanide series used in the manufacturing of FCC catalyst to improve stability, activity, and gasoline selectivity of the zeolite. 

In the lanthanide series, the equivalent values are much reduced by the retreat of the 4f electrons into the xenon core. This is so whether we consider processes that involve the condensation of gaseous ions, or conventional reactions. Table 1.3 includes data for the change... 

Sc(naphthenate)3/ROH/AlR3 (1/2/7) has been found to exhibit an activity similar to the lanthanide series catalyst [114], The cis PA film obtained with it showed an electrical conductivity of 14.4 S cm 1 when the polymer was doped with I2 at a ratio of (CHI0.04)n, and the TEM measurement suggested the formation of ca. 20-30 nm fibrils. 

Cerium, an element in the lanthanide series, has a number of radioactive isotopes. Several of these are produced in abundance in nuclear fission reactions associated with nuclear industry operations or detonation of nuclear devices. This report summarizes our present knowledge of the relevant physical, chemical, and biological properties of radiocerium as a basis for establishing radiation protection guidelines. 

Metal ions that have a high charge-to-size ratio (charge density) undergo hydrolysis to produce acidic solutions. As a result of the decrease in size of the +3 ions across the lanthanide series, there is a general increase in acidity of the aquated ions as a result of the reaction... 

As idealized computational models of metal hypovalency, let us therefore consider the early second-series transition-metal hydrides YH3, ZrH4, and NbfL (avoiding both the complications of lone-pair-bearing ligands and those associated with the lanthanide series). Figure 4.54 shows optimized structures of these species, and Table 4.33 summarizes the bonding (omh) and nonbonding (nM ) orbitals and occupancies at the metal center. 

Lanthanum is considered a member of the lanthanide series for the purposes of this review we shall also from time to time include yttrium and scandium within the generic term "lanthanide. ... 

Enthalpies of solution of the series of chloride hydrates in aqueous hydrochloric acid (approximately 0.1 mol dm-3) are listed in Table IX (190). In Fig. 1, the trend in these values across the lanthanide series is compared with the trends for enthalpies of solution of the hydrates and of the anhydrous salts in water. 

The situation for the triiodides is only slightly better than for the tribromides. There is only one set of values, obtained many years ago at 20°C (292). These are listed, and compared with the analogous set of solution enthalpies for the trichlorides obtained under analogous conditions by the same workers, in Table XI (and see Fig. 1). As for the chlorides, the solution enthalpies for the iodides must be subject to some small degree of uncertainty in view of the possible presence of impurities (oxoiodides, lower iodides, etc.) in the samples used. It is harder to obtain really pure anhydrous iodides than chlorides in the lanthanide series (cf. Section II). As for the chlorides, solution enthalpies for the iodides become more negative going across the lanthanide... 

In view of the aforementioned difficulties, both of incompatibility of concentration units and of chemistry and accuracy, we have selected sets of data to illustrate trends in solubilities. Only one paper deals with a selection of trichlorides across the lanthanide series its results... 

Studies of the lanthanide series, usually taken to include yttrium, have been made, and complexes of the general formula [Md SOJfX examined for various R and X groups. 

Studies on the use of sulfoxides in the extraction of scandium (325, 440), yttrium (188), and the lanthanide series (456) have all been reported and seem to show considerable promise. 

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