What do you understand by isoelectronic species? Name a species that will be isoelectronic with each of the following atoms or ions.
(i)${{F}^{-}}$ (ii)Ar
(iii) Mg2+ (iv) Rb+
Isoelectronic species have the same number of electrons but different nuclear charges. In case of isoelectronic species as the nuclear charge increases, their size decreases.
(i)${{F}^{-}}$ has 10 electrons (9 +1).
(ii) Ar has 18 electrons.
(iii) ${{Mg}^{2+}}$ has 10 electrons (12-2) and (iv) Rb+ has 36 electrons (37-1).
${{N}^{3-}}$, ${{O}^{2-}}$, Ne, ${{Na}^{+}}$ and ${{Al}^{3+}}$ are some species which are isoelectronic with ${{F}^{-}}$ and ${{Mg}^{2+}}$.
${{P}^{3-}}$ , ${{S}^{2-}}$, Cl-, K+ and ${{Ca}^{2+}}$ are some species which are isoelectronic to Ar.‘
Similarly, Br-, Kr and ${{Sr}^{2+}}$ are isoelectronic with Rb+.