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solubility in organic solvents

in this q i know that LiI has higher polarization therefore higher covalent character due to I being larger but what has this got to do with being more soluble in organic solvents??
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Talk about the trend in radii, then the covalent character and how the bonding in LiI is easily overcome. Then, link this to the bonds water forms with it and how it requires less energy.
Original post by typicalvirgo
Talk about the trend in radii, then the covalent character and how the bonding in LiI is easily overcome. Then, link this to the bonds water forms with it and how it requires less energy.


it says organic solvents not water? i thought maybe the more covalent character the more it is able to dissolve in organic solvents... am ir right? but i dont understand why tho
Original post by pondsteps
it says organic solvents not water? i thought maybe the more covalent character the more it is able to dissolve in organic solvents... am ir right? but i dont understand why tho

Oops! Excuse my error, yes you're right! Since covalent bonds are weaker than ionic :-) you could then link it to vdw/dipole forces instead of electrostatic attractions :-)
(edited 7 years ago)
Original post by typicalvirgo
Oops! Excuse my error, yes you're right! Since covalent bonds are weaker than ionic :-) you could then link it to vdw/dipole forces instead of hydrogen bonding :-)


Oh, but why does having more covalent character effect the strengh of the dipole forces??? (Do stronger dipole forcee even mean more solubility??)
Original post by pondsteps
Oh, but why does having more covalent character effect the strengh of the dipole forces??? (Do stronger dipole forcee even mean more solubility??)


The rule of thumb is "like dissolves like"

i.e. covalent substances are more soluble in covalent solvents.

The greater the degree of covalency in the bonding the more likely it is to be soluble in a covalent solvent.

Substances that undergo hydrogen bonding tend to be soluble in protic solvents.

For something to dissolve the solution must be thermodynamically more stable than the individual components. Hence, the degree of attraction between solute and solvent is a major factor.
Original post by pondsteps
Oh, but why does having more covalent character effect the strengh of the dipole forces??? (Do stronger dipole forcee even mean more solubility??)

Sorry if it wasn't clear, but I meant you can mention how you would have slight vdw forces with LiI, since it has covalent character, but not with LiCl since it is more ionic and would hence form electrostatic attractions with the solvent. It could be a nice concluding sentence in your answer if you wanted to include it, to really emphasise the difference in character of the compounds :-) Whether it is dipole-dipole or vdw really depends on the solvent, so be careful with it :-)
Remember, we learn that only covalent substances experience intermolecular forces!
(edited 7 years ago)
Original post by typicalvirgo
Sorry if it wasn't clear, but I meant you can mention how you would have slight vdw forces with LiI, since it has covalent character, but not with LiCl since it is more ionic and would hence form electrostatic attractions with the solvent. It could be a nice concluding sentence in your answer if you wanted to include it, to really emphasise the difference in character of the compounds :-) Whether it is dipole-dipole or vdw really depends on the solvent, so be careful with it :-)
Remember, we learn that only covalent substances experience intermolecular forces!

your explanation was very clear, thanks a lot.. but when asked my teacher today he confused me soooo much :frown: he said if they have covalent character they still do have ionic character so theyre considered ions so you have to look at their lattice energy and enthalpy of hydration and that stuff.. isnt that just for non covalent solvents like water ?? ( i just wanna know if he is right or wrong cos he confused me )

one more thing.. does LiI form dipole dipole forces with the organic solvent too?
Original post by pondsteps
your explanation was very clear, thanks a lot.. but when asked my teacher today he confused me soooo much :frown: he said if they have covalent character they still do have ionic character so theyre considered ions so you have to look at their lattice energy and enthalpy of hydration and that stuff.. isnt that just for non covalent solvents like water ?? ( i just wanna know if he is right or wrong cos he confused me )

one more thing.. does LiI form dipole dipole forces with the organic solvent too?


In terms of lattice enthalpies, your teacher is kinda right, but he explained it oddly.

If you have two lattice enthalpies of MgO, with one being experimental and one being theoretical, and you get values that have a big difference between them, you know that the substance is not completely ionic, and that the experimental value considers covalent character. That's how you see if something has covalent character.

If you're comparing two substances, the more negative one has stronger ionic bonds because of the size of the ions and their charge resulting in a strong electrostatic attraction between oppositely charged ion. The one that is less negative can't be inferred to have covalent character until you compare the experimental and theoretical data.

Also, water is a polar covalent substance, so its not completely covalent. Remember the spectrum from covalency to ionic?

In terms of Lil, it has to form dipole-dipole attractions because in order for it to dissolve, it must form bonds with the water and we're talking about charges here, so its not a temporary dipole and can't be hydrogen bonding because I or Li are not electronegative enough.

Hope this helped :-)

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