Which of the following pairs would have a smaller size. Explain.
(a) `Na^(o+) or Mg^(2+)` , (b) `O^(2-) or F^(ɵ)`
(c ) `P or As`

Answer

(a) `Mg^(2+)` , (b) `F^(ɵ)` , (c ) `P`

Explanation

(a) `Mg^(2+)`
Both `Na^(o+)` and `Mg^(2+)` are isoelectronic species with `10 e^(-)'s` each.
Effective nuclear charge `(Z_("eff"))` of `Mg^(2+)` is greater than that of `Na^(o+)`. Hence ionic of `Mg^(2+)` is less than the ionic radii of `Na^(o+)` ion.
`F^(ɵ)`
Both `O^(2-)` and `F^(ɵ)` are isoelectronic species with `10 e^(-)'s` each. `Z_("eff")` of `F^(ɵ) gt Z_("eff")` of `O^(2-)`. Hence ionic radii of `F^(ɵ)` is less than that of `O^(2-)` ion.
(c ) `P`.
Both `P` and as belong to the same `15` group. `P` is in the `3rd` period and As is in the `4th` period. Hence, the atomic size of `P` is less than that of As.