Neon-structure ions

As before, we may expect the values of Ss calculated for Z large to be valid for actual ions with the helium and neon structures. For the other structures we introduce the empirical corrections based upon those used for the mole refraction screening constant, with the aid of the principle of the constancy of the ratios of corresponding screening defects, already used for the diamagnetism screening constant. In this way the values of SSo and ASs given in Table VIII are obtained. An equation similar to equation (29) is to be used to find individual values of Ss. 

Sodium sulfate, Na2S04 32 (1 + 1 -f 6 + 24) valence electrons. This contains sodium ions and sulfate ion. The bonds between sodium and the outside of the sulfate (that is, the oxygen) are ionic. The positive sodium atoms are represented without valence electrons, that is, with the neon structure. The sulfur-to-oxygen bonds within the sulfate ion are largely covalent. The sulfate ion must be arranged so that there are no oxygen-to-oxygen covalent bonds, otherwise the compound would have the... 

These radii give the observed cation-anion distance in crystals in which cation and anion have the structure of the same argonon, such as Na+F (both ions with the neon structure) and K" C1 (both with the argon structure). The observed distances, Na" —F = 231 pm and —Cl = 314 pm, are equal to the sums of the corresponding radii. In other crystals, in which the anions are almost in contact, the observed distance is larger than the radius sum. 

As pointed out in Chapter 2, elements close to a noble gas in the periodic table form ions that have the same number of electrons as the noble-gas atom. This means that these ions have noble-gas electron configurations. Thus the three elements preceding neon (N, O, and F) and the three elements following neon (Na, Mg, and Al) all form ions with the neon configuration, is22s22p6. The three nonmetal atoms achieve this structure by gaining electrons to form anions ... 

No extensive comparison with experiment to test the values in Table IV will be made. The close agreement between the purely theoretical and the experimental results in the case of helium and neon allows one to place confidence in the R values for ions with these structures and the same remark applies with less force in the case of the argon structure, where only a small empirical correction was introduced. It is interesting to note that the theoretical values 3-57 and 6-15 for the rubidium and the caesium ion agree very well with the experimental ones, 3-56 and 6-17 (Table III), which were not used at all in the evaluation of the empirical corrections for these structures. Finally, we may mention that our values agree in general with those of Fajans and WulfE.i obtained by them from the experimental R values for salt solutions by the application of only the simplest theoretical considerations. 

The molal diamagnetic susceptibilities of rare gas atoms and a number of monatomic ions obtained by the use of equation (34) are given in Table IV. The values for the hydrogen-like atoms and ions are accurate, since here the screening constant is zero. It was found necessary to take into consideration in all cases except the neon (and helium) structure not only the outermost electron shell but also the next inner shell, whose contribution is for argon 5 per cent., for krypton 12 per cent., and for xenon 20 per cent, of the total. 

Laser Raman spectroscopy, particularly with helium-neon lasers, is another powerful tool in the study of carbocations. Because Raman spectra give valuable information on symmetry, these spectra help to establish, in detail, structures of the ions and their configurations. 

Hirvonen and co-workers reported that high-energy neon ion bombardment resulted in amorphization of the crystal structure and increased film hardness. However, the friction remained low, and this suggests that the amorphous coating readily recrystallised with basal plane orientation under a sliding stress. 

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