Solubility

[Astha Sahoo 3I]

I hope this is the right category to post my question in. I was just hoping someone could explain the solubility trends in the periodic table and the solubility rules that we should know for this class? An example that's been debated a lot is why NaF is more soluble than NaI, but AgI is more soluble than AgF. What do we look at when determining solubility, and what are exceptions to these rules? If someone could explain this to me before my midterm tomorrow I would greatly appreciate it :)

[Jenny Chau 1I]

Hi, I'm not too sure on solubility trends myself but I think using the electronegativity trend could work. Question 2D.7 asks you to determine which compound would be more soluble using electronegativities. The higher the difference of the electronegativity between two atoms would mean it has lower covalent character (and I think you can also think of it as having more ionic character) because the more electronegative atom will attract electrons more than the other and that means it's more soluble (my guess is because covalent bonds are very strong so it will hold the molecule together so the less covalent it is, the more soluble). This is at least my understanding :)

[Ariel Guan 1H]

^^ what she said. I like to think of it as more ionic character (less covalent character) = more soluble. To figure that out, you look at the electronegativity difference; if the difference is higher, then it has a higher ionic character and is therefore more soluble. I think that molecules that can separate into ions are more soluble because the ions would interact with the partial pos. and neg. charges in H20, and covalent compounds can't really separate in that way while ionic compounds can. So I'm pretty sure AgF is more soluble than AgI because F is super electronegative, so the electronegativity difference between Ag and F is higher than the difference between Ag and I. It's probably also helpful to note that most silver halides are basically insoluble in water (meaning AgCl, AgBr, AgI) with AgF being the exception. And that's because as you go down group 17, polarizability increases, which means that there is higher covalent character. There are also specific solubility rules that you can find online if you're curious.

[Nina Tartibi 1F]

The more electronegativity difference a molecule has, the more soluble it is. To answer your question about NaF vs. NaI, Fluorine is the most electronegative element on the periodic table, and Iodine, although very electronegative, is not as strong as F, because it's below F on the table (electronegativity increases across a period and decreases down a group). That means that there is a stronger electronegativity difference between Na and F than there is Na and I, therefore NaF is more soluble.

[Sydney Jensen 3L]

The higher the electronegativity, the higher the ionic character is of the molecule, which correlates to the solubility of the molecule. The more ionic character, the more soluble the said molecule will be, and the ionic character is based on the electronegativity differences.