The basicity of framework oxygen atoms of alkali and alkaline earth-exchanged zeolites has been studied using
reactivity descriptors based on a local hard±soft acid±base (HSAB) concept. We have calculated the `local softness' and
the `relative nucleophilicity' values of the framework oxygen atoms of zeolite clusters as the measure of basicity. The
local softness and relative nucleophilicity appear to be more reliable descriptors to predict the experimental basicity
trend, compared to the negative charge on the oxygen atom. Ó 2000 Elsevier Science B.V. All rights reserved.