Ten-electron compounds

It is important to rccogni/.e that there is no llexibility in the choice of Z. There are no corrections to the integral values, and even though, for example, lead may form compounds as a doubly charged ion (the ten-electron compounds mentioned earlier), the true bands in the metal resemble the free-elcctron bands for Z = 4, not for Z = 2. On the other hand, the values of ki- given in Table 15-1 do not really warrant the precision indicated there they depend upon pressure and temperature, and where real accuracy is required, they should be redetermined for the circumstances at hand, from Fq. (15-4). 

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