Question
Which of the following are isoelectronic species, i.e. those having the same number of electrons?
Na+, K+ , Mg2+, Ca2+, S2-, Ar.
Solution
Number of electrons present in different species are:
11Na+ = 11 - 1 = 10; 19K+ = 19 - 1 = 18;
12Mg2+ = 12 - 2 = 10
20Ca2+ = 20 - 2 = 18; 16S2- = 16 + 2 = 18
Ar = 18
11Na+ = 11 - 1 = 10; 19K+ = 19 - 1 = 18;
12Mg2+ = 12 - 2 = 10
20Ca2+ = 20 - 2 = 18; 16S2- = 16 + 2 = 18
Ar = 18
Hence isoelectronic species are
(i) Na+ and Mg2+
(having number of electrons = 10).
(ii) K+, Ca2+, S2- and Ar (having number of electrons = 18).