Chapter 7, Problem 59QP

Group the species that are isoelectronic: ${\text{Be}}^{\text{2+}}{\text{, F}}^{\text{-}}{\text{, Fe}}^{\text{2+}}{\text{, N}}^{\text{3-}}{\text{, He, S}}^{\text{2-}}{\text{, Co}}^{\text{3+}}\text{, Ar}$.

Interpretation Introduction

Interpretation:

Theisoelectronic species are to be identified from the given species.

Concept introduction:

The electronic configuration of a noble gas is $n{s}^{2}n{p}^6$.

The species that have identical electronic configurations but different nuclear charges are called isoelectronic species.

Answer to Problem 59QP

Solution: The ion-pairs are ${\text{Be}}^{2+}\text{and He}$, ${\text{F}}^{-}{\text{and N}}^{3-}$, ${\text{S}}^{2-}\text{and Ar}$, and ${\text{Fe}}^{2+}{\text{and Co}}^{3+}$.

Explanation of Solution

A neutral atom in its ground state cannot be isoelectric with any other element. However, ions may have the same electronic configurations with different atoms or ions.

The electronic configurations of the given elements are as follows:

${\text{Be}}^{2+}\text{and He}$

Electronic configuration for beryllium ion is as follows:

$\text{Be: }1s^{2}2s^2\to {\text{Be}}^{2+}\text{: }1s^2$

There are total two electrons in beryllium ion.

Electronic configuration for helium atom is as follows:

$\text{He: }1s^2$

There are total two electrons in helium atom.

The electronic configurations of ${\text{Be}}^{2+}\text{and He}$ are same. So, they are isoelectronic with each other.

${\text{F}}^{-}{\text{and N}}^{3-}$

Electronic configuration for fluorine ion is as follows:

$\text{F: }1s^{2}2s^{2}2p^5\to {\text{F}}^{-}\text{: }1s^{2}2s^{2}2p^6$

There are total 10electrons in fluorine ion.

Electronic configuration for nitrogen ion is as follows:

$\text{N: }1s^{2}2s^{2}2p^3\to {\text{N}}^{3-}\text{: }1s^{2}2s^{2}2p^6$

There are total 10electrons in nitrogen ion.

The electronic configurations of ${\text{F}}^{-}{\text{and N}}^{3-}$ are same. So, they are isoelectronic with each other.

${\text{S}}^{2-}\text{and Ar}$

Electronic configuration for sulphur ion is as follows:

$\text{S: }1s^{2}2s^{2}2p^{6}3s^{2}3p^4\to {\text{S}}^{2-}\text{: }1s^{2}2s^{2}2p^{6}3s^{2}3p^6$

There are total 18 electrons in sulphur ion.

Electronic configuration for argon atom is as follows:

$\text{Ar: }1s^{2}2s^{2}2p^{6}3s^{2}3p^6$

There are total 18electrons in argon atom.

The electronic configurations of ${\text{S}}^{2-}\text{and Ar}$ are same. So, they are isoelectronic with each other.

${\text{Fe}}^{2+}{\text{and Co}}^{3+}$

Electronic configuration for iron ion is as follows:

$\text{Fe: }\left[\text{Ar}\right]3d^{6}4s^2\to {\text{Fe}}^{2+}\text{: }\left[\text{Ar}\right]3d^6$

There are total24 electrons in iron ion.

Electronic configuration for cobalt ion is as follows:

$\text{Co: }\left[\text{Ar}\right]3d^{7}4s^2\to {\text{Co}}^{3+}\text{: }\left[\text{Ar}\right]3d^6$

There are total 24electrons in cobalt ion.

The electronic configurations of ${\text{Fe}}^{2+}{\text{and Co}}^{3+}$ are same. So, they are isoelectronic with each other.

Hence, the ion-pairs ${\text{Be}}^{2+}\text{and He}$, ${\text{F}}^{-}{\text{and N}}^{3-}$, ${\text{S}}^{2-}\text{and Ar}$, and ${\text{Fe}}^{2+}{\text{and Co}}^{3+}$ are isoelectronic with each other.

Conclusion

The ion-pairs ${\text{Be}}^{2+}\text{and He}$, ${\text{F}}^{-}{\text{and N}}^{3-}$, ${\text{S}}^{2-}\text{and Ar}$, and ${\text{Fe}}^{2+}{\text{and Co}}^{3+}$ are isoelectronic with each other.