Trends within the Series

Much that has been noted concerning the trends within the alkali-metal family can be applied also to the alkaline earths. As the radius of the atom increases, removal of the outer electrons becomes easier both the ionization potentials for the free atoms and the E° values for the metals show this  

Be radius 0.9 A ionization potential 9.3 volts E° 1.7 volts Ba radius 2.0 A ionization potential 5.2 volts E° 2.9 volts 

As with the other families, the oxides and salts of the lighter and 

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The propensity of sulfur, selenium and tellurium to catenate is illustrated by the formation of an extensive series of polyanions for all three chalcogens. The structures of these polyanions exhibit interesting trends within the series in which the ability of tellurium and, to a lesser extent, selenium to adopt... 

In Ihis chapter the theories developed previously will be used 10 help correlate the important facts of the chemistry of groups 1—12 Much of the chemistry of these elements, in particular the transition metals, has already been included in the chapters on coordination chemistry (Chapters II, 12, and 13). More will be discussed in the chapters on organometaJlic chemistry (Chapter 15), clusters (Chapter 16), and the descriptive biological chemistry of the transition metals (Chapter 19). The present chapter will concentrate on the trends within the series (Sc to Zn, Y to Cd, Lu to Hg, La to Lu, and Ac to Lr), the differences between groups (Ti — Zr - Hf Cu — Ag - Au), and the stable oxidation stales of the various metals. 

This situation does not necessarily mean that all kinetic data that have been obtained by the Coats and Redfem and similar methods are incorrect. For example, the calculated activation energy frequently has about the same value regardless of whether the correct rate law has been identified or not. That happens because the rate of the reaction responds to a change in temperature according to the Arrhenius equation. The rate law used to fit the kinetic data does not alter the influence of temperature. Also, many kinetic studies on reactions in the solid state have dealt with series of reactions using similar compounds. As long as a consistent kinetic analysis procedure is used, the trends within the series will usually be vahd. Undoubtedly, however, many studies based on incomplete data analysis procedures have yielded incorrect kinetic parameters and certainly have yielded no reliable information on reaction mechanisms. 

Increa sing the bulkiness of the alkyl group from the esterifying alcohol in the ester also restricts the motion of backbone polymer chains past each other, as evidenced by an increase in the T within a series of isomers. In Table 1, note the increase in T of poly(isopropyl methacrylate) over the / -propyl ester and similar trends within the butyl series. The member of the butyl series with the bulkiest alcohol chain, poly(/-butyl methacrylate), has a T (107°C) almost identical to that of poly(methyl methacrylate) (Tg = 105° C), whereas the butyl isomer with the most flexible alcohol chain, poly( -butyl methaciylate), has a T of 20°C. Further increase in the rigidity and bulk of the side chain increases the T. An example is poly(isobomyl methacrylate)... 

Highlights of both studies are summarized and shown in Table 1. The primary difference between the two studies was the time at which the polymers were thermally treated. Both systems were heat treated at 500 °C in an inert atmosphere. Samples of the halo pendent system were further treated by heating between 425-450 °C for l-20h. As-spun monomethyl PBZT exhibited the highest measured compressive properties unfortunately, after heat treatment, the polymer lost 60% of its compressive strength. Within the series of fibers, there was no systematic trend of correlation between methyl pendent content and compressive strength. Gamma radiation of the as-spun fiber showed no... 

These data indicate that the most strongly adsorbed sulfur compound on the site responsible for denitrogenation is dibenzothiophene. The trend within the thiophene derivative series is in agreement with the theoretical calculations for electron density on sulfur presented in Figs. 28 and 29. Studies like this could be quite useful in determining whether the reason alkyldibenzothiophenes have low reactivities is related to limitations in... 

The major bonding interaction between the heterocarbonyl ligand and the metal in rf complexes is the back-bonding interaction (d — zr ce), whereas in 771 complexes the donation 771 (d — nE) dominates. Therefore, from the trends in orbital energies of the heterocarbonyl compounds (see Section II), one would expect that in mononuclear complexes rf coordination is increasingly favored within the series O, S, Se, Te. This expectation is conformed by the experimental results (see Section III,B). 

Energies calculated for the EH and CNDO models are approximations, and are more important for indicating trends within a series than for giving absolute numbers. They do suggest that the answer as to which is trapped first, the electron or the silver ion, could depend on the substrate site and the size and composition of the nucleus, Calculations by the semiclassical method likewise give only approximate values, and the amount of the approximation is unknown. 

All of the azines are weak bases, in which the natures and positions of substituents alter the ease and orientation of N-protonation. This review does not aim to provide a comprehensive survey of basic characteristics within the series, but merely highlights the reactivities of particular ring nitrogen atoms with proton acids, since these reactivities are frequently related to trends observed in N-alkylation, N-acylation, and N-oxidation. 

Table 14-1 summarizes some of the important trends within the halogen series. 

There appears to be no obvious relationship between the trend in these rate constants and trends in size, electronegativity, or electronic structure within the series. The question is a more subtle one and probably cannot be answered until we have more nearly exact knowledge about the species present in such solutions. 

In spite of all these problems it is suggested to compare trends of interatomic distances applying the same method on a series of molecules. For this, structural parameters of a carefully chosen molecule must be taken as a reference and only the changes of these parameters within the series should be considered. Applying this strategy, a comparison of differences provides essential information how well both methods describe the effects controlling the molecular structure. This is demonstrated below in Section V. 

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