Relationship between the Atomic Structure and Electrochemistry. 1. Electric Force, Standard Reduction Potential E°, and Standard Reaction Gibbs Free Energy ΔG°.

Abstract

The relationship among the standard reaction Gibbs free energy ΔG°, the standard reduction potential E°, and the atomic structure parameters of radius, nuclear charge, and isoelectronic orbitals nl is accomplished through the attraction electric force Felec. In relationship with E°, it was necessary to define two new reference scales: E0° with a final state of E° in the element, which allowed to have a parabolic trend of ΔG° versus Felec, and E°,0 whose final state is the ion with a more negative charge (e.g., −1, –2, −3). The relationship with ΔG° is related to the concept of chemical stability, and the relationship with E°,0 is more related to the concept of electronegativity. In relationship with ΔG°, it was necessary to predict the values of possible new cations and noncommon cations in order to find a better trend of ΔG° versus Felec, whose stability is analyzed by Frost diagrams of the isoelectronic series. This dependence of ΔG° on Felec is split into two terms. The first term indicates the behavior of the minimum of ΔG° for each isoelectronic orbital nl, while the second term deals with the parabolic trend of this orbital. For the minima of the configuration np6, a hysteresis behavior of the minima of ΔG° is found: an exponential behavior from periods 1 and 2 and a sigmoidal behavior from periods 5 and 4 to interpolate period 3. It is also found that the proximity of unfilled np or (n + 1)s orbitals induces instability of the ion in configurations ns2/nd2/4f2 and nd10/nd8(n + 1)s2, respectively. On the contrary, the stability of the orbitals np6 does not depend on the neighboring empty (n + 1)s0 orbitals. Both phenomena can be explained by the stability of the configuration of noble gas np6 and the nd10(n + 1)s2 configuration. We have also found that it is possible to increase the reduction potential E°,0 (macroscopic electronegativity), although the electric force Felec decreases because the orbital overlap influences the electronegativity.