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Improved scales for metal ion softness and toxicity
Author(s) -
Kinraide Thomas B.
Publication year - 2009
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1897/08-208.1
Subject(s) - metal , ion , ionization , metal ions in aqueous solution , scale (ratio) , chemistry , analytical chemistry (journal) , physics , environmental chemistry , organic chemistry , quantum mechanics
Ten scales relating to chemical hardness or softness of metal ions were compiled. These included eight published scales such as those of Pearson, Ahrland, Klopman, and Misono. Another scale consisted of the logs of the solubility products of metal sulfides, and yet another was a consensus scale constructed from —log K values for metal ion binding to seven soft ligands. These 10 scales were normalized and averaged. The resulting consensus scale for softness (σ Con ) appeared to be superior to any of the 10 scales used in its construction based on correlations among the scales. Other possible indicators of softness were examined, including the standard electrode potential ( E 0 ) and the bulk metal density (ρ Metal ), both of which were also superior to most of the 10 scales just mentioned. Vales for σ Con may be computed from E 0 , ρ Metal , and the first ionization potential ( I P ), R 2 = 0.867, for the equation σ Con = aE 0 I P + b ρ Metal . A consensus scale for toxicity ( T Con ) derived from studies with many different taxa correlated well ( R 2 = 0.807) with σ Con computed from the preceding equation, but incorporation of ion charge (Z) into the following equation, T Con = a σ Con + b σ Con Z + cZ , increased R 2 to 0.923. Substitution of other softness scales for σ Con into equations to predict T Con reduced the value of R 2 . Thus, σ Con appears to be a superior scale for metal ion softness and toxicity, the latter being an interactive function of both softness and charge.