The chemical properties of the heaviest main-group elements (mercury through radon and their superheavy congeners) often show features not found in their lighter counterparts.Major changes include enhanced stability of lower oxidation states,decreased importance of the highest oxidation state,and greater ability to form cluster species.The term "inert pair effect",originally coined by Sidgwick (1) to describe these differences,has become inadequate and obsolescent.Relativistic effects play an important role in the chemistry of these elements and provide a much better framework for explaining and understanding their unusual properties.This article will emphasize unusual properties and their relation to relativistic effects,with emphasis on recent research.
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