Q10P - Chemistry: Molecular Nature Of Matter And Change

Question

Is ${\mathbf{S}}^{\mathbf{2}\mathbf{-}}$ larger or smaller than ${\mathbf{Cl}}^{\mathbf{-}}$ ? Is ${\mathbf{Mg}}^{\mathbf{2}\mathbf{+}}$ larger or smaller than ${\mathbf{Na}}^{\mathbf{+}}$? Explain.

Step-by-Step Solution

Answer

${\mathrm{S}}^{2-}$ is larger than  ${\mathrm{Cl}}^{-}$.

${\mathrm{Mg}}^{2+}$ is smaller than  ${\mathrm{Na}}^{+}$.

Isoelectronic ions

These are chemical species in which any two atoms or molecules or ions have the same number of valence electrons or the same electronic configuration.

Explanation

Among ${\mathrm{S}}^{2-}$ and ${\mathrm{Cl}}^{-}$ , both are isoelectronic ions. For isoelectronic anion, size increases as the charge on the ion increases. Hence, the charge on sulfur is more compared to chloride ions. Thus, ${\mathrm{S}}^{2-}$ is larger than  ${\mathrm{Cl}}^{-}$.

Among  and  , both are isoelectronic with 10 electrons and are isoelectronic cations. For isoelectronic cation as the charge of the cation increases, size decreases. Hence, the charge on magnesium is more compared to sodium. Thus,  is smaller than  .