Consider the following species:
`N^(3-)`,`O^(2-)`,`F^(ө)`,`Na^(o+)`,`Mg^(2+)` and `Al^(3+)`
a. What is common in them?
b. Arrange them in the order of increasing ionic radii.

Explanation

(a) Each one of these contains 10 electrons and hence all are isoelectronic ions.
(b) The ionic radii of isoelectronic ions decrease with the increase in the magnitude of the nuclear charge. For example consider the isoelectronic ions `: N^(3-) , O^(2-) , F^(-) , Na^(+) , Mg^(2+)` and `A1^(3+)` . All these ions have 10 electrons but their nuclear charges increases in the order :
`N^(3-) (+7) ,O^(2-) (+8) , F^(-) (+9) ,Na^(+) (+11) , Mg^(2+) (+12) ` and `A1^(3+) (+13). ` Therefore , their ionic radii decrease in the order `: N^(3+) O^(2-) gt F^(-) gt Na^(+) gt Mg^(2+) A1^(3+)`