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{{short description|Ratio of the electrical charge to the radius of an ion}}
{{Refimprove|date=August 2017}}
'''Ionic potential''' is the [[ratio]] of the [[electric charge|electrical charge]] (''z'') to the [[ionic radius|radius]] (''r'') of an [[ion]].<ref>{{Cite web| title = Ionic potential| url = http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/ionic-potential| access-date = 17 April 2017}}</ref>

<math display="block">\text{Ionic potential} = \frac{\text{electrical charge}}{\text{ionic radius}} = \frac{z}{r}</math>

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 [[ionic bond|bond]] formed by the ion with ions of opposite charge.<ref>{{Cite web| first=Bruce |last=Railsback| title = Ionic potential| url=http://railsback.org/Fundamentals/IonicPotential04P.pdf|access-date = 16 July 2020|url-status=}}</ref>

The ionic potential gives an indication of how strongly, or weakly, the ion will be electrostatically attracted by ions of opposite charge; and to what extent the ion will be repelled by ions of the same charge.

[[Victor Moritz Goldschmidt]], the father of modern [[geochemistry]] found that the behavior of an element in its environment could be predicted from its ionic potential and illustrated this with a diagram (plot of the bare [[ionic radius]] as a function of the ionic charge).<ref name="Kauffman1997">{{cite journal|last1=Kauffman|first1=George B.|title=Victor Moritz Goldschmidt (1888 – 1947): A tribute to the founder of modern geochemistry on the fiftieth anniversary of his death|journal=The Chemical Educator|volume=2|issue=5|year=1997|pages=1–26|issn=1430-4171|doi=10.1007/s00897970143a|s2cid=101664962}}</ref> For instance, the [[solubility]] of dissolved iron is highly dependent on its redox state. {{chem|Fe|2+}} with a lower ionic potential than {{chem|Fe|3+}} is much more soluble because it exerts a weaker interaction force with {{chem|OH|-}} ion present in water and exhibits a less pronounced trend to [[hydrolysis]] and [[Precipitation (chemistry)|precipitation]]. Under reducing conditions Fe(II) can be present at relatively high concentration in [[Anoxic waters|anoxic water]], similar to these encountered for other divalent species such as {{chem|Ca|2+}} and {{chem|Mg|2+}}. However, once anoxic ground water is pumped from a deep well and is discharged to the surface, it enters in contact with atmospheric oxygen. Then {{chem|Fe|2+}} is easily oxidized to {{chem|Fe|3+}} and this latter rapidly hydrolyzes and precipitates because of its lower solubility due to a higher z/r ratio.

Millot (1970) also illustrated the importance of the ionic potential of cations to explain the high, or the low, [[solubility]] of minerals and the expansive behaviour (swelling/shrinking) of [[clay minerals|clay materials]].<ref name="Millot1970">{{cite book|last1=Millot|first1=Georges|year=1970|title=Geology of clays: weathering – sedimentology – geochemistry|publisher=Springer Science & Business Media|doi=10.1007/978-3-662-41609-9|isbn=978-3-662-41611-2}}</ref>

The ionic potential of the different cations ({{chem|Na|+}}, {{chem|K|+}}, {{chem|Mg|2+}} and {{chem|Ca|2+}}) present in the interlayer of clay minerals also contribute to explain their swelling/shrinking properties.<ref name="DelvilleLaszlo1990">{{cite journal|last1=Delville|first1=Alfred|last2=Laszlo|first2=Pierre|title=The origin of the swelling of clays by water|journal=Langmuir|volume=6|issue=7|year=1990|pages=1289–1294|issn=0743-7463|doi=10.1021/la00097a017}}</ref> The more hydrated cations such as {{chem|Na|+}} and {{chem|Mg|2+}} are responsible for the swelling of [[smectite]] while the less hydrated {{chem|K|+}} and {{chem|Ca|2+}} cause the collapse of the interlayer. In [[illite]], the interlayer is totally collapsed because of the presence of the poorly hydrated {{chem|K|+}}.

Ionic potential is also a measure of the [[Polarizability|polarising power]] of a [[cation]].

Ionic potential could be used as a general criterion for the selection of efficient [[adsorption|adsorbents]] for [[Toxic heavy metal|toxic elements]].<ref name="LiYang2014">{{cite journal|last1=Li|first1=Ronghui|last2=Yang|first2=Weiyi|last3=Su|first3=Yu|last4=Li|first4=Qi|last5=Gao|first5=Shian|last6=Shang|first6=Jian Ku|title=Ionic potential: A general material criterion for the selection of highly efficient arsenic adsorbents|journal=Journal of Materials Science & Technology|volume=30|issue=10|year=2014|pages=949–953|issn=10050302|doi=10.1016/j.jmst.2014.08.010}}</ref>

==See also==

* [[Ionization energy]]
* [[Metal ions in aqueous solution]]
* [[Surface charge]]

==References==
<references />

{{DEFAULTSORT:Ionic Potential}}
[[Category:Binding energy]]
[[Category:Chemical properties]]
[[Category:Ions]]
[[Category:Physical chemistry]]
[[Category:Electrochemical potentials]]
[[Category:Atomic radius]]

{{Electrochem-stub}}

Ionic potential - Revision history

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