Comparison between valence bond and communication theories of the chemical bond in H2

Abstract

In the communication theory of the chemical bond the molecular systems in atomic resolution are interpreted as information channels, in which ‘signals' of the electron allocations to constituent atoms are propagated from the molecular/promolecular input (source), determined by either the free atoms of the promolecule or the bonded atoms in the molecule, to the molecular output (receiver) of atoms in molecules. The transmission network of the system chemical bonds is determined by the molecular conditional two-electron probabilities in atomic resolution. The electron delocalization throughout the system is responsible for the effective ‘noise' affecting the transmission of such atom-assignment signals, which inhibits the amount of information passing through the molecular communication system. The conditional entropy and mutual information descriptors of such molecular communication channels, measuring the average noise and the amount of information flowing through the molecular channel, accordingly, provide the overall measures of the covalent and ionic bond components, respectively. The communication theory approach to the chemical bond in H2 is compared with the familiar valence bond (VB) description of Heitler and London. In the information-theoretic (IT) approach the non-bonding, purely covalent, and purely ionic combinations of the elementary VB structures are defined and their information channels are discussed. It is demonstrated, that the VB covalent and VB ionic components of the molecular ground state wavefunction are in fact both IT ionic. The purely IT covalent components of the molecular ground state are established and their communication channels are examined. The communication origins of the information ionicity and entropy covalency are identified and a distinction between the electron-sharing (covalent) and pair-sharing (coordination) bonds is briefly explored.