Transition elements lanthanide series

As regards the transition elements, the first row in particular show some common characteristics which define a substantial part of their chemistry the elements of the lanthanide and actinide series show an even closer resemblance to each other. 

The three series of elements arising from the filling of the 3d, 4d and 5d shells, and situated in the periodic table following the alkaline earth metals, are commonly described as transition elements , though this term is sometimes also extended to include the lanthanide and actinide (or inner transition) elements. They exhibit a number of characteristic properties which together distinguish them from other groups of elements ... 

The total lanthanide contraction is of a similar magnitude to the expansion found in passing from the first to the second transition series, and which might therefore have been expected to occur also in passing from second to third. The interpolation of the lanthanides in fact almost exactly cancels this anticipated increase with the result, noted in preceding chapters, that in each group of transition elements the second and third members have very similar sizes and properties. 

The redox behaviour of Th, Pa and U is of the kind expected for d-transition elements which is why, prior to the 1940s, these elements were commonly placed respectively in groups 4, 5 and 6 of the periodic table. Behaviour obviously like that of the lanthanides is not evident until the second half of the series. However, even the early actinides resemble the lanthanides in showing close similarities with each other and gradual variations in properties, providing comparisons are restricted to those properties which do not entail a change in oxidation state. The smooth variation with atomic number found for stability constants, for instance, is like that of the lanthanides rather than the d-transition elements, as is the smooth variation in ionic radii noted in Fig. 31.4. This last factor is responsible for the close similarity in the structures of many actinide and lanthanide compounds especially noticeable in the 4-3 oxidation state for which... 

Krebs, Robert E. The history and use of our earth s chemical elements a reference guide. Westport (CT) Greenwood P, 1998. ix, 346p. ISBN 0-313-30123-9 A short history of chemistry — Atomic structure The periodic table of the chemical elements — Alkali metals and alkali earth metals - Transition elements metals to nonmetals — Metallics and metalloids - Metalloids and nonmetals — Halogens and noble gases - Lanthanide series (rare-earth elements) — Actinide, transuranic, and transactinide series... 

The 3rd group of the Periodic Table (the 1st column within the block of the transition elements) contains the metals scandium, yttrium, lanthanum, and actinium. Lanthanum (atomic number 57) may be considered the earliest member of the family of metals, called lanthanides (general symbol Ln), forming, inside the principal transition series, an inner transition series (up to atomic number 71). Scandium and yttrium together with the lanthanides are also called rare earth metals (general symbol R). 

The number of lanthanide ions that can be studied simultaneously in the same aqueous solution is dependent on several considerations. Firstly, the extraction constants Ke of the lanthanides change by approximately 104 on transition from La3+ to Lu3+. It is thus difficult to provide a constant TTA concentration across the lanthanide series because of the inaccuracy of the D values. Secondly, the gamma ray spectra emitted by the tracers from each phase must contain one or more characteristic peaks which can be easily counted for a desired element. We must choose several lanthanide mixtures. 

Period 5 (group 3 [IIIB] to group 12 [IIB]) is located in the second row of the transition elements and represents 10 of the transition metals to nonmetals found in the periodical table of chemical elements. This period is also known to include some of the so-called rare-earth elements. Most of the rare-earths are found in the lanthanide series, which follows barium (period 6, group 3). (Check the periodic table to locate the major rare-earth elements in the lanthanide series. These are addressed in a later section of the book.)... 

As the first element in the third series of the transition elements, hafnium s atomic number ( jHf) follows the lanthanide series of rare-earths. The lanthanide series is separated out of the normal position of sequenced atomic numbers and is placed below the third series on the periodic table ( La to 7,Li). This rearrangement of the table allowed the positioning of elements of the third series within groups more related to similar chemical and physical characteristics—for example, the triads of Ti, Zr, and Hf V, Nb, andTa and Cu, Ag, and Au. 

The lanthanide series is composed of metallic elements with similar physical properties, chemical characteristics, and unique structures. These elements are found in period 6, starting at group 3 of the periodic table. The lanthanide series may also be thought of as an extension of the transition elements, but the lanthanide elements are presented in a separate row of period 6 at the bottom of the periodic table. 

Symbol Ce atomic number 58 atomic weight 140.115 a rare-earth metal a lanthanide series inner-transition /-block element metaUic radius (alpha form) 1.8247A(CN=12) atomic volume 20.696 cm /mol electronic configuration [Xe]4fi5di6s2 common valence states -i-3 and +4 four stable isotopes Ce-140 and Ce-142 are the two major ones, their percent abundances 88.48% and 11.07%, respectively. Ce—138 (0.25%) and Ce—136(0.193%) are minor isotopes several artificial radioactive isotopes including Ce-144, a major fission product (ti 284.5 days), are known. 

Symbol La atomic number 57 atomic weight 138.91 a rare-earth transition metal, precursor to a series of 14 inner-transition elements known as the lanthanide series electron configuration [XejSdiGs oxidation state -i-3 atomic radius 1.879A ionic radius (LaS+) 1.061A electronegativity 1.17 two natural isotopes are La-139 (99.911%) and La-138 (0.089%). 

Symbol Lu atomic number 71 atomic weight 174.97 a lanthanide series element an /-block inner-transition metal electron configuration [Xe]4/i45di6s2 valence -1-3 atomic radius (coordination number 12) 1.7349A ionic radius (Lu3+) 0.85A two naturally-occurring isotopes Lu-176 (97.1%) and Lu-175(2.59%) Lu-172 is radioactive with a half-life of 4xl0i° years (beta-emission) several artificial isotopes known, that have mass numbers 155, 156, 167—174, 177—180. 

Symbol Tb atomic number 65 atomic weight 158.925 a lanthanide series element an inner-transition rare earth metal electron configuration fXe]4/96s2 valence states -i-3, +4 mean atomic radius 1.782A ionic radii, Tb3+... 

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. 

In Fig. 1, the valences of the transition 3d-, 4d-, 5d-series are also plotted. As for what regards the spread of valences, an interesting observation is that, at least for the hght actinides (if not for the whole series), there is more similarity between the actinides transition elements than the actinides and lanthanides. 

As seen in the first chapter, the study of the solid state properties of actinides and their compounds is advancing rapidly, since theoretical and experimental solid state physicists are increasingly interested in the pecuUar behaviour of 5f electrons, which cause solid state properties similar to those of d transition elements in the first half of the series and to those of 4f lanthanides in the second half ... 

The remaining exceptions concern the lanthanide series, where samarium at room temperature has a particular hexagonal structure and especially the lower actinides uranium, neptunium, and plutonium. Here the departure from simple symmetry is particularly pronounced. Comparing these three elements with other metals having partly filled inner shells (transition elements and lanthanides), U, Pu, Np have the lowest symmetry at room temperature, normal pressure. This particular crystallographic character is the reason why Pearson did not succeed to fit the alpha forms of U, Pu, and Np, as well as gamma-Pu into his comprehensive classification of metallic structures and treated them as idiosyncratic structures . Recent theoretical considerations reveal that the appearance of low symmetries in the actinide series is intimately linked to the behaviour of the 5f electrons. 

The exact position of the crossover depends however, on the type of compound that is formed from an actinide. It appears usually for the radioactive heavier actinides. In order to study it, therefore, compoimds of Pu, Am, Cm have to be investigated. Compounds of elements preceding them in the actinide series present properties due to the itineracy of the 5 f electrons, which are somewhat similar to the d-transition elements compounds (especially 3d). Heavier actinides are lanthanide-like although their properties may depart from a true lanthanide behaviour unfortunately, their rarity and the difficulty of their handling is such that very few photoemission results are available for them. 

Tucked into the periodic table between lanthanum (atomic number 57) and hafnium (atomic number 72) are the lanthanides. In this series of 14 metallic elements, the seven 4/orbitals are progressively filled, as shown in Figure 5.17 (page 185). Following actinium (atomic number 89) is a second series of 14 elements, the actinides, in which the 5f subshell is progressively filled. The lanthanides and actinides together comprise thef-block elements, or inner transition elements. 

The atomic radii of the second- and third-series transition elements from group 4B on are nearly identical, though we would expect an increase in size on adding an entire principal quantum shell of electrons. The small sizes of the third-series atoms are associated with what is called the lanthanide contraction, the general decrease in atomic radii of the /-block lanthanide elements between the second and third transition series (Figure 20.4). 

Crystal field theory is one of several chemical bonding models and one that is applicable solely to the transition metal and lanthanide elements. The theory, which utilizes thermodynamic data obtained from absorption bands in the visible and near-infrared regions of the electromagnetic spectrum, has met with widespread applications and successful interpretations of diverse physical and chemical properties of elements of the first transition series. These elements comprise scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel and copper. The position of the first transition series in the periodic table is shown in fig. 1.1. Transition elements constitute almost forty weight per cent, or eighteen atom per cent, of the Earth (Appendix 1) and occur in most minerals in the Crust, Mantle and Core. As a result, there are many aspects of transition metal geochemistry that are amenable to interpretation by crystal field theory. 

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