Ncert Exercises & Solutions

3.12 Consider the following species :

N3–, O2–, F–, Na+, Mg2+ and Al3+

(a) What is common in them?

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

(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:

$N^{3 -} < O^{2} < F^{‐} < N a^{+} < M g^{2 +} < A l^{3 +}$

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:

$A l^{3 +} < M g^{2 +} < N a < F^{‐} < O^{2^{‐}} < N^{3 ‐}$