1.4 Hard and Soft Acids and Bases

This section will include:

• Introduction
• Irving-Williams series
• Classes a and b
• Classification of acids and bases

Introduction

First, the distinction between Brønstead acids and bases and Lewis acids and bases should be made clear:

A Brønstead acid is a proton donor
A Brønstead base is a proton acceptor

A Lewis acid is an electron pair acceptor
A Lewis base is an electron pair donor

Consider a simple transition metal complex, ML_n. The central metal ion (a Lewis acid) accepts an electron pair from each of the ligands (Lewis bases).

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