5f series

The known oxidation states of plutonium present a 5f -series, starting from f1 [Pu(VII)] up to f5 [Pu(III)]. But contrary to the 4f - and 5f series across the period table, where the properties can be described by some smooth varying parameters, changing of the oxidation states influences the electronic properties drastically. Due to the large range of available oxidation states plutonium represents a favorable element among the actinides to study these effects. 

Crystal Chemical Studies of the 5f Series of Elements. I. New Structure... 

The answer was by no means straightforward since the first elements (Th, Pa, U) to be studied displayed properties reminiscent of both a transition series and a lanthanide series. The tendency was to expect that the electrons would follow the same order of filling as for the elements from La to Lu, in which the 4f shell is filled, giving rise to the lanthanide series, before the filling of the 5d shell. Consequently, Seaborg proposed the name actinides for this 5f series, Ac being the homologous of Ln. 

From Table 1 the scheme for the actinide metals shown in Fig. 4 is arrived at. The valence band structure is evidently more complicated in detail than that of the d-transi-tion metals because there are now four different angular momentum states to deal with. However, the d bands are now broad conduction bands. This is not surprising since the broadening of d-bands is a systematic trend from the 3rd to the 5th transition metal series and has now passed a stage further. The reason for this is that the wave functions of each new d-series must be orthogonal to those of the earlier series. The necessary additional orthogonality mode extends the wave functions spatially and broadens the bands. Precisely the same phenomenon occurs between the 4f and 5f series. Thus d-electrons play the role of the major conduction electrons in the actinides and the relative population of the sp conduction bands is reduced. The narrow f-bands are pinned to the Fermi level... 

Zachariesen, W. H. (1954). Crystal chemical studies of the 5f series elements. XXIII. On the crystal chemistry of uranyl compounds and of related compounds of transuranic elements. Acta Cryst. 7, 795-9. 

As already mentioned in Section 4, the 5 s and 5 p core level spectra of the 5f-series and a number of the preceding elements should show pronounced effects of giant Coster-Kronig fluctuation and decay processes much in the same way as happens in the 4.S, 4 p spectra in the range 48 Z < 70. In the case of the 5 p spectrum, the gCK interaction process becomes... 

Uranium is the fourth element of the actinide (5f) series. In the actinide series the 5/electrons are more effectively shielded by the Is and Ip electrons relative to the 4/electrons (shielded by 6s, 6p) in the lanthanide (4f series. Thus, there is a greater spatial extension of 5/orbitals for actinides than 4f orbitals for lanthanides. This results in a small eneigy difference between 5/V.y2 and 5 fn 1 6(17 s2 electronic configurations, and a wider range of oxidation states is therefore accessible to the early members of the actinide series (U—Am). Uranium has four common oxidation states, III, IV, V, and VI. 

In the hexavalent state these elements are similar to uranium in the quadrivalent state however they have, like uranium and protactinium in this valency state, externally the inert gas configuration of the thorium ion in the trivalent state that of the trivalent actinium ion. The name 5f series may perhaps be the best in place of actinides, thorides or uranides. 

In the group of the Rare Earths the ionic radius decreases steadily (Table 3C) with the same external electron configuration (Lanthanide contraction). This happens because with increasing nuclear charge (= atomic number) the effective charge (p. 27) increases through the incomplete screening by the 4f electrons, so that the outermost shell is contracted. The same phenomenon also appears in the 5f series. 

It is, in particular, the ions of the series Ti-Zn, Zr-Cd, Hf-Hg and the ions of the 5f-series which mainly form complexes, the elements of the eighth group being specially prominent. Of no single element are more complexes known than of trivalent cobalt. With most ions, with the exception of fluorine, as well... 

The occurrence of a heavy-electron state in metals is most distinctly observed in compounds where one of the chemical constituents is an element of the rare-earth (4f) or actinide (5f) series. Within these series, it is the elements at the beginning or the end of the res-Sective row of the periodic system that are most likely involved in this effect (Ce, Yb, U, Np). 

Figure 7. Variation of Fg with atomic number Z in the 4i ana 5f series...

The transactinide elements are defined simply as those elements with atomic number greater than 103 (Lr), which completes the actinide series with the complete filling of the inner 5f shell. The schematic periodic table of 2004 given in Fig. 16.1 shows the lanthanide (4f) series, the actinide (5f) series, and the transactinides as a 6d transition series that begins with element 104 (rutherfordium, Rf). According to results of atomic relativistic calculations (Pershina and Fricke,... 

---