Sodium ionic radius

Only body-centered cubic crystals, lattice constant 428.2 pm at 20°C, are reported for sodium (4). The atomic radius is 185 pm, the ionic radius 97 pm, and electronic configuration is lE2E2 3T (5). Physical properties of sodium are given ia Table 2. Greater detail and other properties are also available... 

A similar reasoning may explain the difference in reactivities of the lithium and sodium ion-pairs in THF. The larger ionic radius of the sodium than that of the lithium cation, favoring the formation of loose pairs, makes the sodium pair much more reactive than the lithium salt at lower temperatures. However, at higher temperatures the sodium salt becomes less reactive than the lithium salt as it looses its solvation more readily than the latter. 

The next question which arises is whether the surface charge of, say, excess sodium ions is in contact with the atoms of the adjacent phase (e.g. Au) or whether the excess Na is distributed some distance into the bulk of the electrolyte. There are two reasons why the excess charge may be distributed beyond the first atomic layer into the bulk. The first is that there may not be sufficient vacant sites within one ionic radius of the interface to accommodate all the excess charge, in which case some of the... 

Since the electron distribution function for an ion extends indefi-finitely, it is evident that no single characteristic size can be assigned to it. Instead, the apparent ionic radius will depend upon the physical property under discussion and will differ for different properties. We are interested in ionic radii such that the sum of two radii (with certain corrections when necessary) is equal to the equilibrium distance between the corresponding ions in contact in a crystal. It will be shown later that the equilibrium interionic distance for two ions is determined not only by the nature of the electron distributions for the ions, as shown in Figure 13-1, but also by the structure of the crystal and the ratio of radii of cation and anion. We take as our standard crystals those with the sodium chloride arrangement, with the ratio of radii of cation and anion about 0.75 and with the amount of ionic character of the bonds about the same as in the alkali halogenides, and calculate crystal radii of ions such that the sum of two radii gives the equilibrium interionic distance in a standard crystal. 

The ability of a metal alcoholate to accommodate an additional molecule of carbohydrate increases with increasing ionic radius " Li < Na < K < Cs. The difference in stoichiometry between lithium and sodium is much greater than that between either sodium and potassium, or potassium and cesium. The coordination number of an alkali metal is known to increase with increasing ionic radius. Brewer148 reported that the maximum number of donor groups oriented about an alkali metal cation is four for lithium, and as many as six for sodium, potassium, rubidium, or cesium. A greater surface area would allow accommodation of more than one carbohydrate moiety but, in addition, solvent molecules are more strongly attached to cations of smaller radius, and these may not be readily displaced by carbohydrate molecules. 

However, a careful study of the experimental data has led to some general trends. For instance, the nature of the final products depends heavily on the alkali cations used in the starting compounds sodium and lithium phenoxides reacting under similar experimental conditions yield the related salicylates as major products [18] (Scheme 5.1), whereas potassium, rubidium, and cesium phenoxides yield mixtures of 2-hydroxy-benzoic acid and 4-hydroxy-benzoic acid [1] (Scheme 5.2). As a rule of thumb, the yield of p-hydroxybenzoic acid generally increases with the increasing ionic radius of the alkali metal. Both, temperature and C02-pressure were also reported to be paramount in the selectivity of the carboxylation ... 

The simple pore was originally considered in the context of osmosis as an explanation of how water might move across a biological structure (e.g. an epithelium) in the absence of solute movement. This notion introduced by Brucke in the mid 19th century, (see Hille, 1984) was subsequently extended by Boyle and Conway (1941) to consider the selective ionic permeability of the resting cell membrane. Here the explanation for the high membrane permeability to potassium and to chloride, as compared to sodium, was simple. The hydrated ionic radius of sodium was greater than that of either the hydrated potassium or chloride ion, hence the pores postulated to be present in the membrane would act as a molecular sieve and permit the movement of potassium and of chloride but not of sodium. 

Barium reacts with metal oxides and hydroxides in soil and is subsequently adsorbed onto soil particulates (Hem 1959 Rai et al. 1984). Adsorption onto metal oxides in soils and sediments probably acts as a control over the concentration of barium in natural waters (Bodek et al. 1988). Under typical environmental conditions, barium displaces other adsorbed alkaline earth metals from MnO2, SiO2, and TiO2 (Rai et al. 1984). However, barium is displaced from Al203 by other alkaline earth metals (Rai et al. 1984). The ionic radius of the barium ion in its typical valence state (Ba+) makes isomorphous substitution possible only with strontium and generally not with the other members of the alkaline earth elements (Kirkpatrick 1978). Among the other elements that occur with barium in nature, substitution is common only with potassium but not with the smaller ions of sodium, iron, manganese, aluminum, and silicon (Kirkpatrick 1978). 

Alkali-earth metals (calcium, barium, and magnesium) complex with polysaccharides extensively (Reisenhofer et al., 1984). Calcium has a smaller atomic and ionic radius than does sodium and, because it has two valence electrons, it is endowed with greater polarizing and bonding ability than Na+. Ca and Ca2+ easily form insoluble complexes with oxygenated compounds. Polysaccharide salts of alkali-earth metals are generally insoluble. 

The definition of crystal radii from the location of the minimum of the experimental electron density between neighbouring ions appears to be physically satisfactory when the individual ions approximate to spherical shape and show little overlap, as is the case in sodium chloride. Where deviations from spherical symmetry become more significant and the zone of electron cloud overlap is appreciable, the concept of ionic radius becomes dubious. 

The idea of the existence of specific adsorption appeared as an explanation for the fact that electrocapillary curves at mercury electrodes are different for different electrolytes at the same concentration (Fig. 3.4a). For sodium and potassium halides in water the differences arise at potentials positive of fsz, which suggests an interaction with the anions. As the effect is larger the smaller the ionic radius of the anion, the idea of specific adsorption with partial or total loss of hydration arose. 

To obtain a picture of how loosely the valence electron in an alkali metal is held, consider two quantities connected with the most common of the alkali metals, sodium, the atomic radius arid the ionic radius. Now, one must be careful in speaking of the sizes of atoms or ions just as... 

The observation of very pronounced inhibition of the sodium dodecyl sulfate-catalyzed hydrolysis of methyl orthobenzoate by inorganic cations is also consistent with the proposed mechanism for the micelle catalyzed reaction (Romsted et al., 1967 Dunlap and Cordes, 1968). For alkali-metal cations, the inhibition was found to increase with increasing ion size, i.e. ionic radius, but for alkaline-earth cations the inhibitory effectiveness was observed to be relatively independent of the ion. For... 

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