Classical electrostatic attraction

We discuss below the physics of the classical electrostatic attraction AVe t and the steric or Pauli repulsion AEPauli. Thereafter, we turn to the stabilizing or bonding interactions, both electron-pair bond formation and donor-acceptor interactions, as well as stabilization coming from admixing of (higher) virtual orbitals on one fragment due to the potential field of the other fragment (polarization). Finally, in the last part of this section we discuss some aspects of the mutual influence between the various interactions. 

The middle term is now a classical electrostatic attraction potential energy expression. Unfortunately this equation for the energy cannot be used as it stands, since we don t know the kinetic and potential energy functionals in the energy terms (T[p0]) and (UeetPol)-... 

Electrons described by bonding waveftmctions, that is, those that occupy bonding orbitals are more energetically stable than those electrons described by atomic orbitals in the separated atoms. Owing to the fact that an electron in this region has an attractive interaction with the two positively charged nuclei, it might appear reasonable to attribute the stability of a chemical bond to a classical electrostatic attraction. However, as will be shown below, the term that describes stability of the molecule relative to the two separated nuclei is a purely quantum mechanical quantity. 

Ionic bonding where an element which has lost electrons to form positively charged species is ionically bonded to another element, which has gained electrons to form a negatively charged species. This is classical electrostatic attraction,... 

Note that the long-range classical electrostatic limit furnishes an excellent approximation for the electrical attraction of the end groups, since these are separated far outside the range of significant exchange interactions. 

The interaction energy is further split up into three physically meaningful components as discussed earlier (1) the classical electrostatic interaction A Vc stat between the unperturbed charge distributions of the prepared fragments which is usually attractive, (2) the Pauli repulsive orbital interactions AEpauii, and (3) the stabilizing orbital interaction AEoi (Eq. [38]) ... 

A dynamic model of the atom has to be adopted, as a static model would be unstable because the electrons would fall into the nucleus under the electrostatic attraction force. Niels Bohr (1885-1962) developed a dynamic model for the simplest of atoms, the hydrogen atom, using a blend of classical and quantum theory. In this context the term classical is usually taken as meaning prequantum theory. 

Thomlinson [12] was the first chromatographer to note that the classical electrostatic ion-pair concept did not hold for bulky lipophilic IPRs he also emphasized that in the region between the mobile and stationary phases, the dielectric constant of the medium is far lower than that of the aqueous phase. It is now clear that water-enforced pairing effects [13] include hydrophobic attraction between hydrophobic moieties of the pairing ions and dielectric saturation actually the water-enforced pairing effects were demonstrated to be more important than electrostatic attraction even in a water-methanol system [14],... 

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