Molecular explanation of the Hofmeister Series
The molecular origin of the Hofmeister series is not well understood and still a very active area of research. For example, see the upcoming Faraday discussion conference. The syllabus for the conference says:


  Although it is now clear that the Hofmeister series is intimately connected with ion hydration in homogeneous and heterogeneous environments and with ion pairing, the molecular origin of these effects has been poorly understood. Biochemists and physical chemists have been typically using the term Hofmeister series to put a label on ion specific behaviour in various environments, rather than to reach a molecular level understanding and, consequently, an ability to predict a particular effect of a specific salt ion.


(So, this is not an answer, but rather too long for a comment…)