# The size of isoelectronic species

Question:

The size of isoelectronic species $-\mathrm{F}^{-}, \mathrm{Ne}$ and $\mathrm{Na}^{+}$is affected by

(a) Nuclear charge ()

(b) Valence principal quantum number (n)

(c) Electron-electron interaction in the outer orbitals

(d) None of the factors because their size is the same.

Solution:

The size of an isoelectronic species increases with a decrease in the nuclear charge (Z). For example, the order of the increasing nuclear charge of F, Ne, and Na+ is as follows:

$\mathrm{F}^{-}<\mathrm{Ne}<\mathrm{Na}^{+}$

Z     9     10     11

Therefore, the order of the increasing size of $\mathrm{F}^{-}, \mathrm{Ne}$ and $\mathrm{Na}^{+}$is as follows:

$\mathrm{Na}^{+}<\mathrm{Ne}<\mathrm{F}^{-}$