Ion-dipole effects vs. atomic radius

In summary, when dissolved in water, both Li+ and Na+ have roughly the same charge but Li+ forms stronger ion-dipole bonds with water molecules. This is due to its smaller size, which means the dipoles are closer to the charge and the Coulomb force is larger. This can also be attributed to Li+ having a higher electronegativity compared to Na+. The solvation of these ions can be described by the Born model, which treats the atom as a charged sphere in a continuous medium with a dielectric constant. This model is still used to explain the solvation of proteins today.
  • #1
Bipolarity
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2
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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  • #2
Radius changes distance between charges.
 
  • #3
Borek said:
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?
 
  • #4
Smaller ion means dipoles are closer to the charge, so the Coulomb force is larger.
 
  • #5
I believe this has to do with the difference in electronegativity. Lithium has a higher electronegativity.
 
  • #6
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/2008/01/born-model-of-solvation.html
 

1. What are ion-dipole effects?

Ion-dipole effects refer to the attractive forces between an ion and a polar molecule. This occurs when the positive or negative charge of an ion interacts with the partial charges of a polar molecule, resulting in an overall attraction between the two particles.

2. How do ion-dipole effects compare to atomic radius?

Ion-dipole effects are stronger than the effects of atomic radius. This is because the charges on an ion and the partial charges on a polar molecule are much larger than the size difference between two atoms. Therefore, the attractive forces between an ion and a polar molecule are more significant than the size difference between two atoms.

3. Can ion-dipole effects occur between non-polar molecules?

No, ion-dipole effects can only occur between an ion and a polar molecule. Non-polar molecules do not have partial charges, so there is no way for an ion to interact with them through ion-dipole forces.

4. How does the strength of ion-dipole effects change with distance?

The strength of ion-dipole effects decreases with distance. This is because the attractive forces between an ion and a polar molecule are strongest when the particles are close together. As the distance between the particles increases, the strength of the forces decreases.

5. What are some real-world examples of ion-dipole effects and atomic radius?

Ion-dipole effects are important in many biological processes, such as the binding of ions to enzymes or proteins. Atomic radius plays a role in determining the properties of elements, such as their melting and boiling points. Additionally, the size of atoms can affect the strength of chemical bonds and the reactivity of elements.

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