Ionic Potential
Ionic Potential
Ionic Potential
Ionic potential mediate ionic potential like Al3+ have sufficient density of
One important way to characterize ions is by their charge to bond strongly to O2- but not such dense
ionic potential. Ionic potential is an ion's charge divided charge as to repel each other, and so they make stable
by its radius, and it is thus a measure of density of oxides and/or hydroxides and thus are insoluble. The
charge. Ionic potential gives a sense of how strongly or cations of intermediate ionic potential also enter into
weakly the ion will be electrostatically attracted to ions of solids at high temperatures.
opposite charge, and to what extent the ion will repel The diagrams here show the effect of these trends in
other ions of like charge. Ionic potential varies greatly for the melting temperatures and solubilites of oxides. The
cations, from 0.75 for K+ to 45 for N5+. Earth Scientist's Periodic Table of the Elements and
Ionic potential is very useful in understanding the Their Ions shows many more geoscience trends that
behavior of relatively hard cations (see below). Cations result from variation in ionic potential. In addition, this
of low ionic potential like Na+ are typically soluble and book's page on "A bit of the Earth Scientist's Periodic
enter into solids only at relatively low temperatures, Table of the Elements and Their Ions as a cross-section
because they make weak bonds to O2-. On the other of the Earth" shows the implications of these trends at
hand, cations of high ionic potential, like S6+, bond so even larger scale, the pages on Bowen's Reaction Series
well to O2- that they make oxocomplexes like SO42- shows how ionic potential affects igneous crystallization,
(sulfate) that are soluble. Repulsions between S6+ ions, the pages on solutions and aqueous speciation show
and between the S66+ ion and other highly charged how ionic potential controls the behavior of catons in
cations, make most sulfate minerals relatively soluble, solution, and the page on "The Special Siituation of
and S6+ thus is an incompatible or volatile ion in high- Silicon" shows the implications of ionic potential for one
temperature systems. In between, cations of inter- important element.
500
Melting + 2+ 4+ 5+
Na
+
Mg 2+
Al 3+ Si 4+
P 5+ S 6+ temperature Na9.9 Mg –2.4 Al 3+ Si –3.9
–8.1
P–1.37 S 6+
1193 3125 2345 1996 855 290 Periclase
of oxides of Corundum Quartz
hard cations
+
K
+
Ca2+ Sc 3+ Ti 4+ V 5+ Cr 6+ K14.0 Ca2+ Sc3+ Ti 4+ 5+
V –7.6 Cr 6+
3200 Lime 1.4 –9.7
2103 943 Rutile Shcherbinaite
10
00
Solubility + 2+
Rb
+
Sr 2+
Y 3+
Zr 4+
Nb 5+
Mo6+ Rb Sr4.3 Y 3+ Zr 4+ Nb5+ Mo6+
673 2938 3123 1785 1074
of oxide 28.9 Baddeleyite
Molybdite
minerals
of hard
Cs
+
Ba2+ La 3+ Hf 4+ Ta 5+ W 6+
cations 2+
Ba6.7 La 3+ Hf 4+ Ta 5+ W 6+
1500
1500
2500
200
2500
–9.7
4+
3000
300
Th 4+ Th Thorianite
0
3493
IonicPotential04