Question

Is Iodide anion, ${I^ - }$ isoelectronic with xenon?

Answer 1

Atoms or ions having the sum of electrons are called isoelectronic species. In simple words, different elements having the same number of electrons are isoelectronic species. Isoelectricity occurs when two more molecules have the same structure and electronic configuration but differ in the specific elements present at a specific point in the structure. For example, carbon mono-oxide and nitrogen are isoelectronic species because they contain two valence electrons i.e. an equal number of electrons.

Complete answer:
Isoelectronic species are different elements that have the same number of electrons. Since Iodide has an atomic number of 53 it has 53 electrons in total and has an electronic configuration $1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^2}3{d^{10}}4{p^6}5{s^2}4{d^{10}}5{p^5}$ but considering the anion, ${I^ - }$ the electron count will be 54 electrons.
Similarly, Xenon (Xe) has atomic number 54 and the electronic configuration of Xenon is $[Kr]4{d^{10}}5{s^2}5{p^6}$.
Since ${I^ - }$ and $Xe$ have the same number of electrons present, therefore ${I^ - }$ and $Xe$ are isoelectronic species.

Note:
Atomic number is equal to the total number of electrons or the total number of protons present in an atom. Atoms can achieve noble gas configuration either by losing or gaining electrons or by sharing electrons. Ionic bonds are formed by either gaining or losing electrons but covalent bonds are formed by sharing of electrons. Due to complete octets, noble gases are the most stable elements in the periodic table, i.e. noble gases have complete shells so they need not to react in order to gain stability, while all the other elements react to achieve their electronic configuration state.