Representative and transition elements

Solid state chemistry of thio-, seleno- and telluro-halides of representative and transition elements. J. Fenner, A. Rabenau and G. Trageser, Adv. Inorg. Chem. Radiochem., 1980, 23, 329-425 (434). 

SOLID-STATE CHEMISTRY OF THIO-, SELENO-, AND TELLUROHALIDES OF REPRESENTATIVE AND TRANSITION ELEMENTS... 

Solid-State Chemistry of Thio-, Seleno-, and Tellurohalides of Representative and Transition Elements... 

Values are in Angstrom units and correspond to 6-co-ordination The representative and transition elements... 

Considering the influence of electronic configurations on crystal structures it may be asked, whether certain structure t5rpes are restricted to fluorine compounds of the transition elements. Apart from the structure types distorted by the Jahn-Teller effect such a limitation is not obvious at all. On the contrary quite a number of structure prototypes are represented by compounds of the main group elements. Bonding thus must be similar in both, main group and transition element fluorides, at least as for the factors that influence crystal structmes. 

Although Equation 14.9 is oversimplified, the main points are correctly indicated the measured intensity depends on both the concentration of the element being determined and on the overall composition of the sample. For example, the intensity of the Ag Ka line from various silver ores depends on both the total silver content and the matrix composition (Fig. 14.10). These samples represent matrices containing various amounts of lead, barium, and transition elements, plus minerals... 

In recent years, our laboratory has sought to apply Aese relationships in a qualitative to semi-quantitative way to transition metal electrode reactions characterize by large structural change. We also have sought to study compounds that are representative of transition elements in biological systems, smce mner-shell effects often have important consequences on reactivity in such systems. In Ae following sections we describe results for a number of metalloporphyrins [3] and for several complexes of Mo Aat model Ae behavior of Ais element m molybdenum-containmg enzymes [4]. 

All common monatomic anions have noble gas configurations. Most monatomic cations of the representative elements (A groups) have noble gas configurations. The d- and /-transition elements form many compounds that are essentially ionic in character. Most d- and/-transition metal cations do not have noble gas configurations. 

The X-ray crystal structures of many of these complexes have now been determined representative examples are. shown in Fig. 4.11 from which it is clear that, at least for the larger cations, coordinative saturation and bond rhrectionality are far less significant factors than in many transition element complexes. Further interest in these ligands stems from their use in biochemical modelling since they sometimes mimic the behaviour of naturally occurring, neutral, macrocydic antibiotics such as valinomycin, monactin, nonactin, nigericin... 

In the preceding chapters we have studied the chemistry of the elements across the top of the periodic table and down the two sides. Now we shall consider the elements in the middle. These are usually referred to as the transition elements because chemists once believed that some elements behaved in a way intermediate between the extremes represented by the left and right... 

The elements in Groups 3 through 11 are called the transition metals because they represent a transition from the highly reactive metals of the s block to the much less reactive metals of Group 12 and the p block (Fig. 16.1). Note that the transition metals do not extend all the way across the d block the Group 12 elements (zinc, cadmium, and mercury) are not normally considered to be transition elements. Because their d-orbitals are full, the Group 12 elements have properties that are more like those of main-group metals than those of transition metals. Just after... 

Figure 7-2. Effective ionic radii of high- and low-spin divalent and trivalent ions of the first row transition elements. The filled points represent high-spin ions.

Transition metals tend to have higher melting points than representative metals. Because they are metals, transition elements have relatively low ionization energies. Ions of transition metals often are colored in aqueous solution. Because they are metals and thus readily form cations, they have negative standard reduction potentials. Their compounds often have unpaired electrons because of the diversity of -electron configurations, and thus, they often are paramagnetic. Consequently, the correct answers are (c) and (e). 

For the representative elements, the valence electrons are all electrons in the outer s and p orbitals of an atom. A quick way of determining the number of valence electrons is to locate the element on the periodic table. There are eight columns of representative elements. The first column, headed by H and Li, has one valence electron, the second column has two, skip the transition elements, the next column, headed by B and Al, has three. This continues to the last (eighth) column where there are eight valence electrons. The only exception to this procedure is helium, which only has two valence electrons. 

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