Alkaline earth metals ionic potentials

Symbol Be atomic number 4 atomic weight 9.012 a Group IIA (Group 2) metal the lightest alkaline-earth metallic element atomic radius l.OOA ionic radius (Be2+) 0.30A electronic configuration Is22s2 ionization potential, Be 9.32eV, Be + 18.21 eV oxidation state +2... 

Symbol Mg atomic number 12 atomic weight 24.305 a Group II A (Group 2) alkaline-earth metal atomic radius 1.60A ionic radius (Mg2+) 0.72A atomic volume 14.0 cm /mol electron configuration [Ne]3s2 valence +2 ionization potential 7.646 and 15.035eV for Mg+ and Mg2+, respectively three natural isotopes Mg-24(78.99%), Mg-25(10.00%), Mg-26(11.01%). 

Redox potential pH Ionic activities Inert redox electrodes (Pt, Au, glassy carbon, etc.) pH-glass electrode pH-ISFET iridium oxide pH-sensor Electrodes of the first land and M" /M(Hg) electrodes) univalent cation-sensitive glass electrode (alkali metal ions, NHJ) solid membrane ion-selective electrodes (F, halide ions, heavy metal ions) polymer membrane electrodes (F, CN", alkali metal ions, alkaline earth metal ions)... 

The reactions of chlorobenzene and benzaldehyde with ammonia over metal Y zeolites have been studied by a pulse technique. For aniline formation from the reaction of chlorobenzene and ammonia, the transition metal forms of Y zeolites show good activity, but alkali and alkaline earth metal forms do not. For CuY, the main products are aniline and benzene. The order of catalytic activity of the metal ions isCu> Ni > Zn> Cr> Co > Cd > Mn > Mg, Ca, Na 0. This order has no relation to the order of electrostatic potential or ionic radius, but is closely related to the order of electronegativity or ammine complex formation constant of metal cations. For benzonitrile formation from benzaldehyde and ammonia, every cation form of Y zeolite shows high activity. 

Consequently, the pA ] (negative logarithm of K j) is 4.97. These pA values for a number of metals are plotted in Figure 1.4 as a function of the ionic potential. The straight line in this figure marks the relation between hydrolysis and ionic potential that would be expected if only electrostatic (i.e., ion-dipole) forces were operative. However, crystal field and covalent contributions to bonding increase the tendency for most transition and heavy metals to hydrolyze. The straight line most accurately predicts the hydrolysis behavior of the alkali and alkaline earth metals. 

Expressions for the force constant, i.r. absorption frequency, Debye temperature, cohesive energy, and atomization energy of alkali-metal halide crystals have been obtained. Gaussian and modified Gaussian interatomic functions were used as a basis the potential parameters were evaluated, using molecular force constants and interatomic distances. A linear dependence between spectroscopically determined values of crystal ionicity and crystal parameters (e.g. interatomic distances, atomic vibrations) has been observed. Such a correlation permits quantitative prediction of coefficients of thermal expansion and amplitude of thermal vibrations of the atoms. The temperature dependence (295—773 K) of the atomic vibrations for NaF, NaCl, KCl, and KBr has been determined, and molecular dynamics calculations have been performed on Lil and NaCl. Empirical values for free ion polarizabilities of alkali-metal, alkaline-earth-metal, and halide ions have been obtained from static crystal polarizabilities the results for the cations are in agreement with recent experimental and theoretical work. 

Some ceramics having large values of Eg are listed in Table 30.3. No entirely satisfactory relationship has been established between the ionic character of the bond and the atom size on Eg. In a homologous series of oxides, such as the oxides of the alkaline-earth metals. Eg increases with increasing ionic potential, < ), of the cation as shown in Figure 30.24. 

Cheng and co-workers recently reported Fc-cyclopeptides 12-15 (Scheme 5.4) and showed that they acted as redox-switchable cation receptors [26]. These Fc-cyclopeptides exhibited strong anodic shifts of their electrode potentials in the presence of alkaline earth metals and lanthanides. The extent of the anodic shift can be correlated with the charge density of the metal ion with a bias toward binding of lanthanides, alkaline earth metals, and the least sensitivity to alkaline metals [26]. Chowdhury et al, reported the syntheis and interaction of cychc Fc-Histidine conjagates 16 with metal ions (Scheme 5.5). Electrochemical measurements showed that the compound exhibited cathodic shifts in the order Na Li K+>Cs which in the order of their ionic sizes and suggest that the observed shift relates to the cavity of the compound [27]. 

In most organometallic compounds the M —C bond has, to a significant degree, covalent character. Definite ionic character of this bond is generally manifested only in compounds of the alkali and alkaline earth metals. The ionic or covalent contribution to the bond depends on ionization potential of the metal, the size of a resulting ion, the ratio of the ionic charge to its radius, and tr-donor, (j-acceptor, 7c-donor, and 7c-acceptor properties of ligands and their structure. 

With a few exceptions, the ionization potential of an atom increases within a given period with increase in atomic number. Because of this phenomenon, the alkali and alkaline earth metals form ionic compounds with electronegative ligands such as halogens, while the metalloids and nonmetals form compounds with considerable covalent character. Exceptions to the 8 rule are encountered most frequently in ionic compounds as well as in compounds of metalloids and nonmetals. In the latter case, compounds with more than eight valence electrons may be formed. These deviations are a function of properties of the central atom and the ligands. 

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