Editing HSAB theory (section)

{{short description|Chemical theory about acids and bases}}
'''HSAB''' is an [[acronym]] for "hard and soft [[Lewis acids and bases|(Lewis) acids and bases]]".  HSAB is widely used in [[chemistry]] for explaining the stability of [[chemical compound|compounds]], [[reaction mechanism]]s and pathways. It assigns the terms 'hard' or 'soft', and 'acid' or 'base' to [[chemical species]]. 'Hard' applies to species which are small, have high charge states (the charge criterion applies mainly to acids, to a lesser extent to bases), and are weakly [[Polarizability|polarizable]]. 'Soft' applies to species which are big, have low charge states and are strongly polarizable.<ref>{{cite book|title=Modern Inorganic Chemistry| author=Jolly, W. L.| isbn=978-0-07-032760-3|year=1984|publisher=McGraw-Hill|location=New York}}</ref>

The theory is used in contexts where a qualitative, rather than quantitative, description would help in understanding the predominant factors which drive chemical properties and reactions. This is especially so in [[transition metal]] [[chemistry]], where numerous experiments have been done to determine the relative ordering of [[ligand]]s and transition metal ions in terms of their hardness and softness.

HSAB theory is also useful in predicting the products of [[Salt metathesis reaction|metathesis]] reactions. In 2005 it was shown that even the sensitivity and performance of explosive materials can be explained on basis of HSAB theory.<ref>[https://archive.today/20120530215438/http://www3.interscience.wiley.com/cgi-bin/abstract/109931709/ABSTRACT] E.-C. Koch, Acid-Base Interactions in Energetic Materials: I. The Hard and Soft Acids and Bases (HSAB) Principle-Insights to Reactivity and Sensitivity of Energetic Materials, ''Prop., Expl., Pyrotech. 30'' '''2005''', 5</ref>

[[Ralph Pearson]] introduced the HSAB principle in the early 1960s<ref>{{cite journal|title=Hard and Soft Acids and Bases|author=Pearson, Ralph G.|journal= [[J. Am. Chem. Soc.]] |year=1963| volume= 85 |issue=22|pages=3533–3539|doi=10.1021/ja00905a001}}</ref><ref>{{cite journal|doi=10.1021/ed045p581|title=Hard and soft acids and bases, HSAB, part 1: Fundamental principles|author= Pearson, Ralph G.|journal=[[J. Chem. Educ.]]| volume =1968|issue=45| pages= 581–586|year=1968|bibcode = 1968JChEd..45..581P }}</ref><ref>{{cite journal|doi=10.1021/ed045p643|title=Hard and soft acids and bases, HSAB, part II: Underlying theories|author= Pearson, Ralph G.|journal=[[J. Chem. Educ.]]| volume =1968|issue=45| pages= 643–648|year=1968|bibcode = 1968JChEd..45..643P }}</ref> as an attempt to unify [[inorganic chemistry|inorganic]] and [[organic chemistry|organic]] reaction chemistry.<ref>[https://archive.today/20120530215443/http://www3.interscience.wiley.com/cgi-bin/summary/112214582/SUMMARY] R. G. Pearson, Chemical Hardness – Applications From Molecules to Solids, Wiley-VCH, Weinheim, 1997, 198 pp</ref>