Consider the following species:
Question:

Consider the following species:

$\mathrm{N}^{3-}, \mathrm{O}^{2-}, \mathrm{F}^{-}, \mathrm{Na}^{+}, \mathrm{Mg}^{2+}$ and $\mathrm{Al}^{3+}$

(a) What is common in them?

(b) Arrange them in the order of increasing ionic radii.

Solution:

(a) Each of the given species (ions) has the same number of electrons (10 electrons). Hence, the given species are isoelectronic.

(b) The ionic radii of isoelectronic species increases with a decrease in the magnitudes of nuclear charge.

The arrangement of the given species in order of their increasing nuclear charge is as follows:

$\mathrm{N}^{3-}<\mathrm{O}^{2-}<\mathrm{F}^{-}<\mathrm{Na}^{+}<\mathrm{Mg}^{2+}<\mathrm{Al}^{3+}$

Nuclear charge $=+7+8+9+11+12+13$

Therefore, the arrangement of the given species in order of their increasing ionic radii is as follows

$\mathrm{Al}^{3+}<\mathrm{Mg}^{2+}<\mathrm{Na}^{+}<\mathrm{F}^{-}<\mathrm{O}^{2-}<\mathrm{N}^{3-}$

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