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Ionic potential is the ratio of the electrical charge (z) to the radius (r) of an ion. [1]= = As such, this ratio is a measure of the charge density at the surface of the ion; usually the denser the charge, the stronger the bond formed by the ion with ions of opposite charge.
For example, from Fe 2+ + 2 e − ⇌ Fe(s) (–0.44 V), the energy to form one neutral atom of Fe(s) from one Fe 2+ ion and two electrons is 2 × 0.44 eV = 0.88 eV, or 84 907 J/(mol e −). That value is also the standard formation energy (∆ G f °) for an Fe 2+ ion, since e − and Fe( s ) both have zero formation energy.
The charge of the resulting ions is a major factor in the strength of ionic bonding, e.g. a salt C + A − is held together by electrostatic forces roughly four times weaker than C 2+ A 2− according to Coulomb's law, where C and A represent a generic cation and anion respectively. The sizes of the ions and the particular packing of the ...
The electrostatic interaction model of ions in solids has thus been extended to a point multipole concept that also includes higher multipole moments like dipoles, quadrupoles etc. [8] [9] [10] These concepts require the determination of higher order Madelung constants or so-called electrostatic lattice constants.
The bond then results from electrostatic attraction between the positive and negatively charged ions. Ionic bonds may be seen as extreme examples of polarization in covalent bonds. Often, such bonds have no particular orientation in space, since they result from equal electrostatic attraction of each ion to all ions around them.
For example, if a glass of water has sodium ions (Na +) dissolved uniformly in it, and an electric field is applied across the water, then the sodium ions will tend to get pulled by the electric field towards one side. We say the ions have electric potential energy, and are moving to lower their potential
The electrostatic potential energy, E pair, between a pair of ions of equal and opposite charge is: = where z = magnitude of charge on one ion e = elementary charge, 1.6022 × 10 −19 C ε 0 = permittivity of free space 4 π ε 0 = 1.112 × 10 −10 C 2 /(J·m)
Practically, this allows trends to be predicted qualitatively based on visual representations of electrostatic potential maps for a series of arenes. Electrostatic attraction is not the only component of cation–π bonding. For example, 1,3,5-trifluorobenzene interacts with cations despite having a negligible quadrupole moment.