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The Chemical Bond: When Atom Size Instead of Electronegativity Difference Determines Trend in Bond Strength
Author(s) -
Blokker Eva,
Sun Xiaobo,
Poater Jordi,
Schuur J. Martijn,
Hamlin Trevor A.,
Bickelhaupt F. Matthias
Publication year - 2021
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202103544
Subject(s) - electronegativity , chemical bond , chemistry , pauli exclusion principle , bond order , bond length , atom (system on chip) , bond strength , computational chemistry , bond dissociation energy , steric effects , molecule , dissociation (chemistry) , quantum mechanics , stereochemistry , physics , organic chemistry , adhesive , layer (electronics) , computer science , embedded system
Abstract We have quantum chemically analyzed element−element bonds of archetypal H n X−YH n molecules (X, Y=C, N, O, F, Si, P, S, Cl, Br, I), using density functional theory. One purpose is to obtain a set of consistent homolytic bond dissociation energies (BDE) for establishing accurate trends across the periodic table. The main objective is to elucidate the underlying physical factors behind these chemical bonding trends. On one hand, we confirm that, along a period (e. g., from C−C to C−F), bonds strengthen because the electronegativity difference across the bond increases. But, down a period, our findings constitute a paradigm shift. From C−F to C−I, for example, bonds do become weaker, however, not because of the decreasing electronegativity difference. Instead, we show that the effective atom size (via steric Pauli repulsion) is the causal factor behind bond weakening in this series, and behind the weakening in orbital interactions at the equilibrium distance. We discuss the actual bonding mechanism and the importance of analyzing this mechanism as a function of the bond distance.