Question

What do you understand by isoelectronic species? Name a species that is isoelectronic with each of the following atoms or ions.
(i) ${ F }^{ - }$ (ii) Ar (iii) $Mg^{ +2 }$ (iv) $Rb^{ + }$

Answer 1

Try to think about the meaning of the isoelectronic word if you don’t have an idea about that. In chemistry think about where we use iso word. Electronic means something related to electronic configuration.

Complete step by step answer: We know that atoms or ions having the same number of electrons and having the same electronic configuration are called isoelectronic species. Here are the means the same and electronic means electronic configuration. Two elements in the uncharged form do not have the same electronic configuration. Electronic configuration of one ion can be the same as that of another element or ion electronic configuration. Many elements try to attain an inert gas configuration because it is stable with fulfilled shells.
Now let us check the electronic configuration of each of the given species and find isoelectronic species to them.
(i) ${ F }^{ - }$
Fluorine has 9 electrons in uncharged form. It is one electron short of the fulfilled configuration so it tries to gain the electron and attain fulfilled configuration.
Electronic configuration of uncharged fluorine atoms is $1s^{ 2 }2s^{ 2 }2p^{ 5 }$.
Electronic configuration of negatively charged fluorine atoms is$1s^{ 2 }2s^{ 2 }2p^{ 6 }$.
Electronic species with 10 electrons in their uncharged or charged form having the same electronic configuration are isoelectronic. $O^{ -2 }$ , ${ Na }^{ + }$ are isoelectronic with ${ F }^{ - }$.
(ii) Ar
Argon has 18 electrons in its uncharged form. It has a stable configuration.
Electronic configuration of argon is $1s^{ 2 }2s^{ 2 }2p^{ 6 }3s^{ 2 }3p^{ 6 }$.
${ K }^{ + }$ , ${ Ca }^{ +2 }$ also have the same electronic configuration as that of Ar.
(iii) $Mg^{ +2 }$
Electronic configuration of Mg is $1s^{ 2 }2s^{ 2 }2p^{ 6 }3s^{ 2 }$.
Electronic configuration of $Mg^{ +2 }$ is $1s^{ 2 }2s^{ 2 }2p^{ 6 }$.
$O^{ -2 }$ ,${ Na }^{ + }$ are isoelectronic with Mg+2.
(iv) ${ Rb }^{ + }$
Electronic configuration of Rb is $1s^{ 2 }2s^{ 2 }2p^{ 6 }3s^{ 2 }3p^{ 6 }4s^{ 2 }3d^{ 10 }4p^{ 6 }5s^{ 1 }$.
Electronic configuration of ${ Rb }^{ + }$ is $1s^{ 2 }2s^{ 2 }2p^{ 6 }3s^{ 2 }3p^{ 6 }4s^{ 2 }3d^{ 10 }4p^{ 6 }$.
${ Rb }^{ + }$ has 36 electrons in its positively charged form. It is isoelectronic with ${ Br }^{ - }$, Kr.

Note: Inert gas configuration is a stable configuration so many elements try to attain that configuration by losing or gaining electrons. Some transition elements may have different electron configurations for the same number of electrons.