Chemical Causes of Metal Nobleness. Issue 5 (22nd January 2020)

• Record Type: Journal Article
• Authors: Kepp, Kasper P.
• Is Part Of: Chemphyschem. Volume 21:Issue 5(2020)
• Page Start: 360
• Page End: 369
• Publication Date: 2020-01-22
• Subjects: catalysis -- chemical reactivity -- gold -- noble metals -- platinum; Chemistry, Physical and theoretical -- Periodicals; 541.05
• DOI: 10.1002/cphc.202000013
• Languages: English
• ISSNs: 1439-4235

Abstract

Abstract: Humans have appreciated the "noble" metals for millennia, yet modern chemistry still struggles with different definitions. Herein, metal nobleness is analyzed using thermochemical cycles including the different bulk, gas, and solution states implied by these definitions. The analysis suggests that metal nobleness mainly reflects inability to fulfil the electron demands of electronegative oxygen. Accordingly, gold is the most noble metal in existence, not because of d‐band properties of the solid state, but because gold's electronegativity is closest to that of oxygen, producing weaker polar covalent bonding. The high electronegativity arises from the effective nuclear charge due to diffuse d‐states, enforced by relativistic effects. This explanation accounts for the activity series, corrosion tendency, and trends in oxygen chemisorption, which other models do not. While gold is the most noble metal, the ranking of Ag, Pt, and Pd depends on the thermochemistry as discussed in detail. Abstract : Who is the noblest ? Analysis of electronic and thermochemical properties indicates that metal nobleness is mainly caused by electronegativity due to occupation of diffuse d‐orbitals enforced by relativistic effects. Gold is outstanding in most aspects, explaining the consensus on its high nobleness, whereas thermochemical cycles show that the ranking of other metals are context‐dependent.