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Why is the solubility among the silver halides (from AgF to AgI) decreasing(less soluble) as the size of the anion gets bigger? I thought that increasing the size of the components of a compound increases the compound's solubility(more soluble) because the bond holding it together gets weaker due to increased distance?
Silver Halides (except for AgF) have a very high lattice energy. We didn't cover this in class, but basically the energy of the bonds holding the structure of the silver halides together is too much to overcome, hence they are insoluble.
Per what I understand, the bigger the anion is, the more polarizable it is. This happens because larger anions have larger electron clouds that are easier to distort, giving them higher polarizability. This trait also means the larger anion will have more covalent character, because there is greater electrostatic attraction on the electron surrounding the anion, and it wants to share the electrons more with the cation. Increasing covalent character also leads to decreasing solubility, because covalent bonds mean there is higher dissociation energy (than ionic bonds), which makes it harder to break apart (i.e. in water)
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