1 Hard vs. soft 1.1 When are ionic bonds strong? Ionic bonds are strong when the electrons have really transferred from the cation to the anion. In NaF Δ χ is 3.1 and therefore an electron really can be thought to have transferred from the electropositive sodium atom to the electronegative ±uorine atom. So ionic bonds are strong when Δ χ is a large number. Furthermore, we know that the electric potential energy, V ∝ q c q a r , where q c , q a and r are respectively the cation charge, the anion charge, and the distance between the cation and anion. Thus cations with a 2+ charge are twice as strong as 1+ charges, while 4+ charges have a whopping four times greater potential energy. Large charges on either the cation or the anion lead to strong ionic bonds. At the same time small r leads to stronger ionic bonds; small cations and anions, as they have smaller r associated to them, have stronger ionic bonds. In the table below, we list some common cations and anions and list the observed strength of
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