<Li> typical soft acids: Ag, Mo (0), Ni (0), Pt </Li> <Li> typical hard bases: ammonia and amines, water, carboxylates, fluoride and chloride </Li> <Li> typical soft bases: organophosphines, thioethers, carbon monoxide, iodide </Li> <P> For example, an amine will displace phosphine from the adduct with the acid BF . In the same way, bases could be classified . For example, bases donating a lone pair from an oxygen atom are harder than bases donating through a nitrogen atom . Although the classification was never quantified it proved to be very useful in predicting the strength of adduct formation, using the key concepts that hard acid--hard base and soft acid--soft base interactions are stronger than hard acid--soft base or soft acid--hard base interactions . Later investigation of the thermodynamics of the interaction suggested that hard--hard interactions are enthalpy favored, whereas soft--soft are entropy favored . </P>

Define the term lewis base and give two examples