Sodium interatomic distance

The Alkali Halides.—In Table V are given the experimental interatomic distances for the alkali halides with the sodium chloride structure, together with the sum of the radii of Table II. 

The interatomic distances for such an intermediate were calculated,288 and, using the resulting data in conjunction with certain steric and oxidizing-potential considerations, it was successfully predicted that sodium bis-muthate and trivalent silver ion would also specifically oxidize 1,2-glycols. These reactions have since been studied.287 288... 

Estimation of Interatomic Distances. The notion of transferable interference radii — that, e.g., a hydrogen atom is approximately the same size whether it is attached to a phenyl ring (Fig. 1) or to a cyclohexane ring (Fig. 2) or that a sodium ion is approximately the same size whether it is surrounded by chloride ions in NaCl or by, say, bromide ions in NaBr — has found wide application in the estimation of distances between (i) adjacent atoms in adjacent molecules in molecular solids and (ii) adjacent atoms in ionic solids. Extension of these results to the estimation of interatomic distances within covalent molecules through use of the localized electron-domain model and one, new, two-parameter relation (but no new empirical radii) is illustrated in Fig. 28. 

In the alkali metals all the electrons may be accommodated within the limits of one zone. This may be shown by comparing the zone in a crystal with a particular atomic orbital. If the interatomic distances in the crystal lattice are assumed to increase, but with the retention of the original symmetry, the zones become narrower and are finally reduced to atomic dimensions. The first zone in a crystal of sodium corresponds to the s orbital and will contain N energy levels, i.e. it can accommodate 2N electrons. But for these there are only N electrons for which Nj2 levels are sufficient for their accommodation. Therefore one half of the levels of the first zone remain unoccupied. The differences in energy between the individual levels of the zone is not great and excitation of the electrons takes place easily in this fact lies the explanation of metallic properties. 

Fig. 4.9 Energies of free cations and of ionic compounds as a function of the oxidation state of the cation. Top Lines represent the ionization energy necessary to form the +1. +2, +3, and + 4 cations of sodium, magnesium, and aluminum. Note that although the ionization energy increases most sharply when a noble gas configuration is broken, isolated cations are always less stable in Itiifher oxidation states. Bottom Lines represent the sum of ionization energy and ionic bonding energy for hypothetical molecules MX, MXj, MXj, and MX in which the interatomic distance, r, has been arbitrarily set at 200 pm. Note that the most stable compounds (identified by arrows) arc NaX, MgXj, and AlXj. (All of the.se molecules will be stabilized additionally to a small extent by the electron affinity of X.)...

FIG. 7.2. Calculation of ionic radii from interatomic distances in crystals with the sodium chloride structure. 

It is clear that from the observed interionic distances we can deduce only the sum of two ionic radii, but that if any one radius is known then other radii may be found. Various independent methods are available for estimating the radii of certain ions, and the values so determined, taken in conjunction with data from the crystal structures not only of the alkali halides but also of many other compounds, lead to the semi-empirical ionic crystal radii shown in table 3.02 and in fig. 3.05. The interpretation of the radii given in this table is subject to a number of qualifications which will be discussed below. For the present, however, it is sufficient to treat the radii as constant and characteristic of the ions concerned. For the alkali halides with the sodium chloride structure it will be seen that the interatomic distances quoted in table 3.01 are given with fair accuracy as the sum of the corresponding radii from table 3.02. 

Fig. 5.16. Schematic representation of the spreading of the 3s and 3p energy levels of isolated sodium atoms as the atoms condense to form a crystal. The broken line represents the equilibrium interatomic distance in the solid.

In 2002, Roimebro et alP explored the perovskite-related stmcture of Na3AlH6. These studies determined the positions of the hydrogen atoms from neutron diffraction data of a deuterated sample. It was found that the best fit data was for the monoclinic space group Pliln (no. 14). The structure was a distorted face-centered cubic (FCC) structure of [AlDg] units with sodium in all of the octahedral and tetrahedral sites. The complex anions were found to be distorted [AlFIg] octahedra. Selected interatomic distances and bond angles are reported in Table 14.2. The Al-D distances were 1.746,1.758, and 1.770 A,... 

Hawthorne and coworkers. However, the interatomic distances of Cs to the carborane cages are such that it could be regarded as a cesium-carborane complex in which some degree of interaction exists between the metal and the 7C-electron density on the carborane cage. Since this cesium compound can also be prepared by an ion-exchange reaction directly from lithium, sodium or potassium salts of the C B -cage (see Figure 6b), further study of this and related compounds in solvent extraction of radioactive cesium metal ( Cs) from nuclear waste is envisioned. 

Figure 15. Interatomic distances in H-bonds (A, in parentheses), their energies (kcal/mol) of interactions, and estimated aromaticity descriptors for the /j-nitrosopheno-iate anion in two salts sodium and magnesium, respec-tiveiy. (Reprinted with permission from ref 47. Copyright 1998 Elsevier Science.)...

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