Hydrated Cation Radii gly-uga

Hydrated Cation Radii gly-uga - Railsback's Some...

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Unformatted text preview: Railsback's Some Fundamentals of Mineralogy and Geochemistry Variation in hydrated radius of ions Hydration of an ion depends on the electrostatic attraction of water molecules to that ion. Because attraction of water molecules around an ion depends on that ion's density of charge, smaller ions (and thus ions of greater ionic potential) attract more water molecules. The result is the inverse relationship between non-hydrated radius and hydrated radius shown below. 4.6 hydration Inner hydration sphere on rat i 0 i o Incr ni c p eas ot ing en tia l FAg+ K+ NH4+ Tl+ Rb+ 0.8 1.0 1.2 1.4 1.6 Ionic radius with no hydration (Å) 10 Å hyd with us adi of r ase c re Na+ 5 One must appreciate that published radii of hydrated ions are statistical statements about a population of ions, each of which may change in extent of hydration through very short time scales. Thus the values plotted at left are averages through time of the hydrated radius of many individuals and are unlikely to equal the radius of the ion plus some multiple of 1.4Å, the radius of O2-. 2x i n radiu s with hy se of 0.6 4x increa 0.4 dratio n on s with hydrati Li+ 3.2 0.2 Ba2+ Pb2+ in radiu with hydratio n Ca2+ 6x increase 3.4 Cd2+ Sr2+ 8x increase in 3.6 ni c Mg2+ hydration 3.8 Zn2+ io radius with 14X increase in radius with 4.0 Be2+ 10X increase in radius Radius of hydrated ion (Å) 4.2 Outer hydration sphere g sin al ea ti cr en In pot 4.4 Cation with radius = 0.5 Å Cl- Br- I- Cs+ 1.8 2.0 2.2 Source of data: Conway, 1981, Ionic Hydration in Chemistry and Biophysics, as in Dove & Nix, 1997, Geochimica et Cosmochimica Acta, v. 61, p. 3331. LBR 9/30/97 rev 10/2006 815 HydratedCationRadii 04 ...
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