Covalent hydration location

Some of the scatter within the groups is undoubtedly due to differences in bond order and also to whether or not the nitrogens are located in the same ring. Nevertheless, some striking exceptions are apparent in which the pA values are much higher than expected. These include quinazoline, 1,3,5-, 1,3,7-, 1,3,8-, and 1,4,6-triazanaph-thalene, pteridine, and 1,4,5,8-tetraazanaphthalene. In all these cases, covalent hydration of the cation has been shown to occur, so the measured pA values are, in fact, equilibrium values involving both hydrated and anhydrous species. The hydrated species are, without... 

This general view on the EDL ignores the mechanism of surface charging and ion adsorption in the Stern layer. It cannot, therefore, reveal the fine details of real EDLs. For instance, ions may adsorb in the Stem layer with or without keeping their hydration shells and may accordingly be located on different planes parallel to the surface (inner and outer Helmholtz plane— IHP and OHP) co-ions may be covalently bound to the siuface and, thus, virtually increase the surface charge and last but not least, the structure of the EDL may be affected by surface morphology (Hunter 1988, Chap. 2). 

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