The values for the Pauli term for the hydrides is enough different to suggest that something different is going on, but I lack the chemical insight to comment further on that. Negative Ion Dissociation Energy (eV) Equilibrium Separation (nm)įor the alkali halides, the Pauli term is a few tenths of an eV. Some examples are shown below, with the Pauli term calculated from the other data as the value which would balance the energy. Since the ionization energies, electron affinities, and dissociation energies have been tabulated from experiment, and since the bond length is obtainable from independent experiments such as rotational spectroscopy, it is possible to estimate the energy of the Pauli repulsion by using the relationship above. The nature of the Pauli repulsion term for sodium chloride is shown in the energy diagram below. This requires energy and is experienced as a repulsion, preventing the ions from coming any closer to each other. No two electrons can occupy the same state, so as a new set of energy states is formed for the composite, two-nucleus system, the lower energy states are filled and some of the electrons are pushed into higher states. As they get closer, the increasing overlap of the wavefunctions causes some to be forced into higher energy states. When the ions are widely separated, the wavefunctions of their core electrons do not significantly overlap and they can have identical quantum numbers. This illustrates that the binding energy is overall simply proportional to A, since B/A is mostly constant. Binding energy is especially applicable to subatomic particles in atomic nuclei, to electrons bound to nuclei in atoms, and to atoms and ions bound together in crystals. The binding energy is usually plotted as B/A or binding energy per nucleon. It has a quantum mechanical character rooted in the Pauli exclusion principle, and is often called just the "exclusion principle repulsion". binding energy, amount of energy required to separate a particle from a system of particles or to disperse all the particles of the system. This repulsive force is more than just an electrostatic repulsion between the electron clouds of the two atoms. It is modeled above with two parameters C and a which can be adjusted to fit the data. Measured data about ionic diatomic molecules allow us to imply the energy of the Pauli repulsive force at the equilibrium separation. The energy balance of all these terms can be written in the form ![]() ![]() This repulsive force is typically called Pauli repulsion. Pauli Repulsion in Ionic Molecules Pauli Repulsion in Ionic MoleculesĪn ionic bond may be modeled in terms of the ionization energy to produce the positive ion, the electron affinity associated with the negative ion, the dissociation energy for the molecule, the coulomb potential between the ions, and the repulsive force which limits the closeness of approach of the ions.
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