“…In fact, whether the electrons reside in the 6s orbital or in a hybrid 6s-6p orbital is still an item of ongoing research and not yet firmly entered into textbooks. , The so-called inert-pair effect explains not only the liquidity of Hg, but also helps to rationalize the superior stability of Tl, Pb, and Bi ions in the lower-oxidation states of +1, + 2, and +3, respectively. ,, Apart from chemical stability, the stereochemical activity of the inert-pair, specifically of Pb 2+ ion, could adversely affect the functions of biological channels involving Mg 2+ , Ca 2+ , Fe 2+ , or Zn 2+ ions, commonly referred to as lead-poisoning or saturnism . Although the stereochemical implications of the inert-pair on the structure of Pb 2+ complexes were demonstrated crystallographically long ago, molecular level understanding of lead poisoning appeared only recently with computational modeling experiments using density functional theory. − …”