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Ion-dipole effects vs. atomic radius

by Bipolarity
Tags: atomic, effects, iondipole, radius
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Bipolarity
#1
Feb14-12, 01:17 AM
P: 783
When dissolved in water, which of the following ions will form stronger ion-dipole bonds with the water molecules? Li+ or Na+?

Both have roughly the same charge... Na has greater radius, but I don't see why or how that has any bearing on the problem.
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Borek
#2
Feb14-12, 02:55 AM
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Radius changes distance between charges.
Bipolarity
#3
Feb14-12, 03:03 PM
P: 783
Quote Quote by Borek View Post
Radius changes distance between charges.
I'm sorry but could you please elaborate a little more on that?
Radius I guess does decrease the force between the metal ion and each water molecule (due to Coulomb's law), but it turns out that Li+ actually forms more bonds with water. Why is that?

Borek
#4
Feb14-12, 04:48 PM
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Ion-dipole effects vs. atomic radius

Smaller ion means dipoles are closer to the charge, so the Coulomb force is larger.
dizam
#5
Feb14-12, 05:52 PM
P: 22
I believe this has to do with the difference in electronegativity. Lithium has a higher electronegativity.
DrDu
#6
Feb15-12, 02:27 AM
Sci Advisor
P: 3,555
Solvation is often treated within a simple model, the Born model, which treats the atom as a charged sphere inside the medium assumed to be continuous and described by its dielectric constant. The model is still used a lot to describe the solvation of proteins even today.
Confer e.g.
http://pchemandyou.blogspot.com/2008...solvation.html


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