Hard and Soft Acids and Bases - University of North ：硬和软酸和碱-北大学

Hard and Soft Acids and Bases.We h__e already pointed out that the affinity that metal ions h__e for

Hard and Soft Acids and Bases. We h__e already pointed out that the affinity that metal ions h__e for ligands is controlled by size, charge and electronegativity. This can be refined further by noting that for some metal ions, their chemistry is dominated by size and charge, while for others it is dominated by their elctronegativity. These two categories of metal ions h__e been termed by Pearson as hard metal ions and soft metal ions. Their distribution in the periodic table is as follows: Figure 1. Table showing distribution of hard, soft, and intermediate Lewis Acids in the Periodic Table, largely after Pearson. Pearson’s Principle of Hard and Soft Acids and Bases (HSAB) can be stated as follows: Hard Acids prefer to bond with Hard Bases, and Soft Acids prefer to bond with Soft Bases.K This can be illustrated by the for__tion constants (log )for ahard metal ion, a 1 soft metal ion, and an intermediate metal ion, with the halide ions in Table 1: Table 1 .For__tion constants with halide ions for arepresentative hard, soft, and intermediate metal ion . ________________________________________________________________________ ---- K Log FClBrIclassification 1 ________________________________________________________________________ + Ag0.43.34.76.6 soft 2+ Pb1.30.91.11.3intermediate 3+ Fe6.01.40.5 -hard ________________________________________________________________________ 1