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Is there a relationship between polarizability and electronegativity, such that as electronegativity decreases, the polarizability of the anion increases? The book used the example about a large iodide anion being easily polarizable due to electron cloud being further from nucleus.
I don't think there is a clear relationship between polarizability and electronegativity since polarizability depends on the type of atoms involved in the bonding as well. Roughly, we could say that as the electronegativity increases, the pulling of electron by an atom increases and therefore it has a tendency to pull electrons towards itself in bonding. However, as we do not have any information about the other atom to which this atom is bonded and we do not know its electronegativity we cannot determine how polar the bond will be since if the other atom also had a similarly strong electronegativity, the molecule wouldn't be as polar as it would have been were the electronegativities had a larger difference. So electronegativity may affect polarizability but it also depends on the electronegativity of the other atom in the bond as well.
Polarizability, or polarizing power depends solely on the anion's electronegativity. I is bigger and less electronegative than the other halogens, so it has a greater polarizability. Polarizing power, on the other hand, is determined by the cation's charge and size. These are separate things.
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