How does ion size relate to solubility?
Compounds with small ions tend to be less soluble than those with large ions.
The solubility of a compound is the result of a competition. The ions in the compound attract each other, and the water molecules attract the ions.
If the water molecules have a greater attraction to the ions than ions have for each other, then the compound will be soluble in water.
Compounds with small ions are less soluble than compounds with large ions. Small ions are closer to each other, so they have strong attractive forces. It is more difficult for the water to break them apart, so they are less soluble.
Consider the sodium halides NaF, NaCl, NaBr, and NaI. The sizes of the halide ions in picometres are
The solubilities of the sodium halides in grams per hundred millilitres are:
The solubility increases as the size of the halide ion increases.