Transition elements second series

Transition Elements Second Series—Period 5, Groups 3 to 12... 

Fig. 2.23. MNN Auger series in the second series of transition elements [2.129].

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... 

Figure 4.93 illustrates some aspects of the break in the vertical trend of atomic orbital energies es and for early, middle, and late transition elements, showing the contrasting behavior of third-series versus first- and second-series elements. The... 

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.)... 

Ruthenium also belongs to the platinum group, which includes six elements with similar chemical characteristics. They are located in the middle of the second and third series of the transition elements (groups 8, 9, and 10). The platinum group consists of ruthenium, rhodium, palladium, osmium, iridium, and platinum. 

Indium has one odd characteristic in that in the form of a sheet, like the metal tin, it will emit a shrieking sound when bent rapidly. Indium has some of the characteristics of other metals near it in the periodic table and may be thought of as an extension of the second series of the transition elements. Although it is corrosion-resistant at room temperature, it will oxidi2e at higher temperatures. It is soluble in acids, but not in alkalis or hot water. 

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 ... 

This chapter consists of a description of the ions formed in aqueous solutions by the transition elements - the d-block elements - and a discussion of the variations of their redox properties across the Periodic Table from Group 3 to Group 12. There is particular emphasis on the first transition series from scandium to zinc in the fourth period, with summaries of the solution chemistry of the second (Y to Cd) and third (Lu to Hg) series. The d-block ions in solution are those restricted solely to aqua complexes of cations, e.g. [Fe(H20)f,]" +, and the various oxocalions and oxoanions formed, e.g. V02+ and MnCXj". Oxidation states that are not well characterized are omitted or referred to as such. 

Each d subshell consists of five orbitals and can accommodate 10 electrons, so each transition series consists of 10 elements. The first series extends from scandium through zinc and includes many familiar metals, such as chromium, iron, and copper. The second series runs from yttrium through cadmium, and the third series runs from lanthanum through mercury. In addition, there is a fourth transition series made up of actinium through the recently discovered and as yet unnamed element 112. 

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. 

FIGURE 20.3 Atomic radii (in pm) of the transition elements. The radii decrease with increasing atomic number and then increase again toward the end of each transition series. Note that the second- and third-series transition elements have nearly identical radii. 

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). 

The melting points for the second-series transition elements increase from 1522°C for yttrium to 2623°C for molybdenum and then decrease again to 321 °C for cadmium. Account for the trend using band theory. 

Transition metal difluorides are known mainly for first transition series elements, with palladium and silver difluorides from the second series, and no examples from the third. All these compounds have either the rutile structure, or, for chromium, copper, and silver, a distorted variant, which can be correlated with a Jahn-Teller distortion of the octahedral coordination of the ions. This rutile structure type is associated with smaller cations and, for comparison, although zinc difluoride has the same rutile structure, cadmium and mercury difluorides have the cubic fluorite structure with eight coordination of the cations (12). 

In contrast with the difluorides, the distribution of trifluorides extends to the third series of the transition metals, where iridium and gold trifluorides are fully characterized. In the second series, trifluorides are known for the elements from niobium to rhodium, with the exception of technetium, and in the first series, from titanium to cobalt. All the trifluorides have been characterized structurally, with earlier reports based on X-ray powder-diffraction data, since the compounds were not prepared in single-crystal form until more recently, when high-temperature, crystal-growth techniques became available. 

The second method for estimating the value of A is from plots of thermodynamic data for series of similar compounds of transition elements. This method is discussed further in chapter 7. 

This sequence is particularly well characterized for fluoride complexes of high-spin cations of the first-series transition elements (Allen and Warren, 1971). Moreover, between successive transition metal series, values of Ac increase by about thirty to fifty per cent. For example, in hydrated cations of the first and second transition series, Ac for [CftHjO) 3 and [Mo(H20)6]3+ are 17,400 cm-1 and 26,110 cm-1, respectively. 

Platinum is active as a catalyst because of its capacity to chemisorb atoms, that is, in some case its role as catalyst is to atomize gaseous molecules, such as H2,02, N2, and CO, giving atoms to other reactants and reaction intermediates (see Figure 2.5) [14,27], Nickel and palladium, which have the same position as platinum in the first and second series of transition elements and the same FCC structure, have catalytic properties very similar to those of platinum. 

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