Lanthanide, oxidation numbers

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... 

Lanthanide elements, 411, 389 contraction, 413 electron configurations, 415 occurrence and preparation, 413 oxidation numbers, 414 properties, 412 Lanthanum... 

Transition metah—found in the groups located in the center of the periodic table, plus the lanthanide and actinide series. They are all solids, except mercury, and are the only elements whose shells other than their outer shells give up or share electrons in chemical reactions. Transition metals include the 38 elements from groups 3 through 12. They exhibit several oxidation states (oxidation numbers) and various levels of electronegativity, depending on their size and valence. 

In Fig. 1, we have plotted the oxidation numbers of the actinides and of the lanthanides. We see that for the lanthanides the valence 3 is the most stable valence throughout the series. There are exceptions Ce displays for instance tetravalency in many compounds Eu and Yb display divalency. These exceptions are understood e.g., Eu and Yb are at the half-filling and at the filling of the 4f shell, which are stable electronic configurations. There is a tendency for both to share just the two outer 5 s electrons in bonding, displaying therefore, divalency, and preserve these stable configurations. 

On the contrary, there is a spread of oxidation numbers for the light actinides (at least up to Cm), which, for Pu and Np, range from 3 to 7 After Cm, however, the trivalent oxidation state is always met, and this second half of the actinide series approaches more the behaviour of the lanthanides. 

Fig. 1. Oxidation numbers for - d-transition series , - f-transition series (lanthanides and actinides) (non-common or uncertain oxidation numbers have been put between brackets)...

Let us assume that the metallic valence is three for most lanthanides, and two for Eu and Yb. This is consistent with the chemistry of these elements, since (Fig. 1) three is their most common oxidation number. Trivalency has been explained in the proceeding chapter, by assuming the easy promotion of one 4 f electron to a 5 d level. The conduction quasi-free electrons are therefore of 5d and 6 s origin. We may say that the conduction band has a prevalent (s, d) character. 

When the itinerant state is formed, a volume collapse AV/V is always encountered, as predicted by the theory of the preceding sections. In one of the lanthanides, cerium, this volume collapse is particularly accentuated for its isostructural transition from the y to the a form, possibly associated with a change in metallic valence from three to four (both oxidation numbers are stable in cerium chemistry) (see Fig. 1 of Chap. A),... 

The properties of the elements of the sixth period are influenced by lanthanide contraction a gradual decrease of the atomic radius with increasing atomic number from La to Lu. The elements of groups 5 to 11 for the fifth and sixth periods have comparable stmctural parameters. For instance, Nb and Ta, as well as the pair Mo and W, have very similar ionic radii, when they have the same oxidation number. As a result, it is very difficult to separate Nb and Ta, and it is also not easy to separate Mo and W. Similarly, Ag and Au have nearly the same atomic radius, 144 pm. Recent studies of the coordination compounds of Ag(I) and Au(I) indicate that the covalent radius of Au is even shorter than that of Ag by about 8 pm. In elementary textbooks the phenomenon of lanthanide contraction is attributed to incomplete shielding of the nucleus by the diffuse 4f inner subshell. Recent theoretical calculations conclude that lanthanide contraction is the result of both the shielding effect of the 4f electrons and relativistic effects, with the latter making about 30% contribution. 

Hydrated salts are readily prepared by reaction of the lanthanide oxide or carbonate with the acid. Salts of non coordinating anions most often crystallise as salts [Ln(OH2)9]X3 (X e g. bromate, triflate, ethylsulphate, tosylate). The tricapped trigonal prismatic structure was first established by X-ray diffraction in 1939 for the [Nd(H20)9] + ion in [Nd(H20)9] (6103)3 this was an important structure historically, as it was the first clear indication that lanthanides conld have high coordination numbers. It has since been verified for many other salts (Figure 10). 

The maximum oxidation number of any atom in any of its compounds is equal to its periodic group number, with a few exceptions. The coinage metals have the following maximum oxidation numbers Cu, +2 Ag, +2 and Au, +3. Some of the noble gases (group 0) have positive oxidation numbers. Some lanthanide and actinide element oxidation numbers exceed 3, their nominal group number. 

The two rows beneath the main body of the periodic table are the lanthanides (atomic numbers 58 to 71) and the actinides (atomic numbers 90 to 103). These two series are called inner transition elements because their last electron occupies inner-level 4/orbitals in the sixth period and the 5/orbitals in the seventh period. As with the d-level transition elements, the energies of sublevels in the inner transition elements are so close that electrons can move back and forth between them. This results in variable oxidation numbers, but the most common oxidation number for all of these elements is 3+. 

The lanthanides and actinides, called the inner transition elements, occupy the/region of the periodic table. Their valence electrons are in s and /orbitals. Inner transition elements exhibit multiple oxidation numbers. 

The lanthanides and actinides react by losing the valence electrons in their s orbitals. Because these elements can also lose electrons from their d and /orbitals, they have multiple oxidation numbers. 

These functionalized clusters contain a maximum number of ferrocene units anchored to the molecular framework and may represent model compounds for the fixation of organometallic fragments on a lanthanide oxide surface (Baskar and Roesky, 2006). 

The 4f electrons play only a small role in bonding. These metals are highly electropositive with a +3 oxidation number being typical. Because of this, the 4f electrons are similar in terms of physical and chemical properties. Lanthanide chemistry changes gradually as you move across the series they are typically +3 oxidation state. 

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