The Hard/Soft Acid/Base Rule: A Perspective from Conceptual Density‐Functional Theory

Pearson's hard/soft acid/base (HSAB) rule indicates that, all other things being equal, hard acids prefer reacting with hard bases and weak acids with weak bases . While venerable, ubiquitous, and indubitably useful, the HSAB rule is not a physical law, nor are the hardness/softness and acidity/basicity physical observables. The goal of this chapter is to discuss the attendant ambiguities in the applicability and reliability of the HSAB rule …