### Question 2.22

NCERT Class XI Chemistry

Which of the following are isoelectronic species i.e., those having the same number of electrons? Na+, K+, Mg2+, Ca2+, S2-, Ar.

### Solution in Detail

Calculate the electrons for each species:

Z = 11 for Na $\displaystyle \therefore $ Na+ has 11 - 1 = 10 electrons

Z = 19 for K $\displaystyle \therefore $ K+ has 19 - 1 = 18 electrons

Z = 12 for Mg $\displaystyle \therefore $ Mg2+ has 12 - 2 = 10 electrons

Z = 20 for Ca $\displaystyle \therefore $ Ca2+ has 20 - 2 = 18 electrons

Z = 16 for S $\displaystyle \therefore $ S2- has 16 + 2 = 18 electrons

Z = 18 for Ar $\displaystyle \therefore $ Ar 18 electrons

$\displaystyle \therefore $ (1) isolectronics are Na+, Mg2+

and (2) isolectronics are Ar, K+, Ca2+, S2-

### Video Explanation

(detailed solution given after this video)

Please watch this youtube video for a quick explanation of the solution:

### Concept for Advanced Students

Isoelectronic species have the same number of electrons

Isoelectronic species have about similar chemical properties

Isoelectronic molecules must have the same structure also

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