The extensive occurrence of C–H···Cl hydrogen bonds has been established through a systematic statistical analysis of the Cambridge Crystallographic Database; chloride anions are shown to be better hydrogen-bond accepor systems than neutral chloride-containing molecules, and a similar situation pertains for the other halides. As a result of this study, we propose that the conceptual van der Waals cut-off criterion be dropped for establishing the presence of weak intermolecular and intramolecular interactions, and be replaced by a distance/angle criterion determined by the empirical approach outlined here.

In hyperalkaline aqueous solutions the calcium(ii) concentration is at least 2.3 × 10⁻⁴ M due to the formation of Ca(OH)_2(aq).