The diamagnetic susceptibilities of salts forming ions with inert gas configurations

Abstract

In the preceding papers of this series, Part I (Hoare 1934) gave an account of the experimental method and results for sodium and potassium halides, Part II (Brindley and Hoare 1935) gave results for lithium, rubidium and caesium halides and a general discussion of this group of salts. The present paper deals with the halides of the alkaline earth metals. Although a few values have previously been obtained for these salts, this is the first time that a comprehensive systematic series of measurements has been made. When comparing the results for the halides of Mg, Ca, Sr and Ba with those for the alkaline halides, the effect of the positive ions being doubly charged must be considered. The positive and negative ions will be drawn closer together than if both ions were singly charged, but the change of interatomic distance on this account is not large owing to the intrinsic repulsion between adjacent ions varying as a high inverse power of their separation; the change will in fact be about 6-10% for the ions under consideration. The effects of the ionic charges on the electron distributions of the adjacent atoms have also to be considered; the positive ions will be subjected to approximately the same effects as the positive ions in the alkaline halides, but the negative ions will be subjected to larger effects owing to the positive ions being both doubly charged and at relatively smaller distances than in the alkaline halides. Whatever the effects of positive and negative ions on each other in crystal lattices may be, it seems unquestionable that these effects will be greater for the negative ions in the alkaline earth halides than in the alkaline halides, but will be of the same order for the positive ions in the two series of crystals.