Ionic radius barium

The interpretation of the lattice vibrations for scheeUte type molybdates or tungstates with relatively light cations, Ca or Sr, has indicated that the lowest translational vibrations are produced by Mo—Mo or W—W motions respectively, while those at higher frequency are from cation-cation motions 98). This has not been found, however, in the case of the barium or lead compounds. The librational frequencies have been found to decrease hnearly with the ionic radius of the cation for AMO4 type compounds, where A = Ca, Sr, Ba, or Pb and M =Mo or W 98). 

The barium cation (ionic radius 1.43 A) has a good compatibility with [2.2.2]cryptands (cavity diameter ca. 2.8 A). This cryptand will solubilize even BaS04 in aqueous solution,486 and this phenomenon has been investigated with a view to removal of BaS04 scale deposited by the use of sea water as an injection fluid in oil-producing formations. The scale deposition can lead to blockage of wells.487... 

MacNevin and Ogle (87) investigated the effects of impurities on the photochromism of barium and calcium titanates as shown in Table V. Pure samples of barium and calcium titanate were not photochromic and doping with Ag+1, Cu+2, Sb+3, Sn+4, Zn+4, and Co+2 produced no enhancement of photochromism. However, increases in the concentrations of impurities such as Fe+3, Zn+2, Sb+5, and V+6 promote photochromic activity. MacNevin and Ogle concluded that the photochromism in these systems depends on the insertion into the lattice of an impurity ion having, (a) an ionic radius near that of Ti+4, and (b) an oxidation number other than 4 to make electron transfer possible. 

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. 

No significant modification of the crystal cell structure can be attributed to the substitution of barium (ionic radius 175 pm, coordination number XII) by K that has the same coordination number and a very close ionic radius (178 pm). 

Compare the hydration and hydrolysis of magnesium chloride with that of (a) sodium chloride, (b) barium chloride. Account for the differences in terms of ionic radius and charge. 

Barium compound hosts. More has been published on R-activated Ba compounds compared to Sr compoimds. The two host compounds do not vary much in their properties as R-activated phosphors. In fact many papers deal with both Ba and Sr phosphors. The high effective Z of the Ba compoimds turns these phosphors further away fixim tissue equivalence compared to the Sr compounds. There are some variations in the energy dependence and in the TL intensities of the two phosphors. The R ions substitute for the alkaline earths in the lattice. The considerable difference between the ionic radius of Ba (0.153 nm) and that of Sr (0.112 nm) may explain the changes in the GCs of the two compounds. As before, the review will deal separately with the various host compounds. 

For an example of fluorine-free polyether ligands used to successfully prevent oligomerization of barium complexes (particularly problematic for heavy Group 11 complexes due to the large ionic radius... 

One point of view is that the antiwetting action is due to the cation part, and tone may suppose that the antiwetting action would increase with the increasing ionic radius in the range aluminium, calcium, magnesium, barium. 

These are listed in Table 2.3 and shown in Figure 2.4. It will be seen that the atomic radii exhibit a smooth trend across the series with the exception of the elements europium and ytterbium. Otherwise the lanthanides have atomic radii intermediate between those of barium in Group 2A and hafnium in Group 4A, as expected if they are represented as Ln + (e )3. Because the screening ability of the f electrons is poor, the effective nuclear charge experienced by the outer electrons increases with increasing atomic number, so that the atomic radius would be expected to decrease, as is observed. Eu and Yb are exceptions to this because of the tendency of these elements to adopt the (+2) state, they have the structure [Ln +(e )2] with consequently greater radii, rather similar to barium. In contrast, the ionic radii of the Ln + ions exhibit a smooth decrease as the series is crossed. 

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