Q126CP - Chemistry: Molecular Nature Of Matter And Change

Question

From the following ions and their radii (in pm), choose a pair that gives the strongest ionic bonding and a pair that gives the weakest:

${\mathbf{Mg}}^{\mathbf{2}\mathbf{+}}\mathbf{72}\mathbf{;}\mathbf{ }{\mathbf{K}}^{\mathbf{+}}\mathbf{138}\mathbf{;}\mathbf{ }{\mathbf{Rb}}^{\mathbf{+}}\mathbf{152}\mathbf{;}\mathbf{ }{\mathbf{Ba}}^{\mathbf{2}\mathbf{+}}\mathbf{135}\mathbf{;}\mathbf{ }{\mathbf{Cl}}^{\mathbf{-}}\mathbf{181}\mathbf{;}\mathbf{ }{\mathbf{O}}^{\mathbf{2}\mathbf{-}}\mathbf{140}\mathbf{;}\mathbf{ }{\mathbf{l}}^{\mathbf{-}}\mathbf{220}$

Step-by-Step Solution

Answer

The strongest bond is between ${\mathbf{Mg}}^{\mathbf{2}}\mathbf{+}\mathbf{and}\mathbf{ }{\mathbf{O}}^{\mathbf{2}}$ The weakest bond is in between ${\mathbf{Rb}}^{\mathbf{+}}\mathbf{and}\mathbf{ }{\mathbf{l}}^{\mathbf{-}}$.

Step 1: Relation between ionic bond strength, charge product and radius of bond

The ionic bond strength is proportional to the charge of the product and inversely proportional to the bond radius.

Step 2: Finding the strongest and weakest bond

The bonds ${\mathbf{Mg}}^{\mathbf{2}}\mathbf{+}\mathbf{and}\mathbf{ }{\mathbf{O}}^{\mathbf{2}\mathbf{-}}$ can be considered as strongest due to their biggest product of the charges and lowest radius sum.

The bonds ${\mathbf{Rb}}^{\mathbf{+}}\mathbf{ }\mathbf{and}\mathbf{ }{\mathbf{l}}^{\mathbf{-}}$ can be considered as weakest due to their smallest charge product and biggest radius sum.