Question
Which one of the following sets of ions represents a collection of isoelectronic species?
A.
$${N^{3 - }},{O^{2 - }},{F^ - },{S^{2 - }}$$
B.
$$L{i^ + },N{a^ + },M{g^{2 + }},C{a^{2 + }}$$
C.
$${K^ + },C{l^ - },C{a^{2 + }},S{c^{3 + }}$$
D.
$$B{a^{2 + }},S{r^{2 + }},{K^ + },C{a^{2 + }}$$
Answer :
$${K^ + },C{l^ - },C{a^{2 + }},S{c^{3 + }}$$
Solution :
$$\left( {\text{A}} \right)\,\,{N^{3 - }} = 7 + 3 = 10{e^ - },$$ $${O^ - } \to 8 + 2 = 10{e^ - }$$
$${F^ - } = 9 + 1 = 10{e^ - },$$ $${S^{ - - }} \to 16 + 2 = 18{e^ - }$$ $${\text{(not}}\,\,{\text{iso}}\,\,{\text{electronic)}}$$
$$\left( {\text{B}} \right)\,\,L{i^ + } = 3 + 1 = 4{e^ - },$$ $$N{a^ + } = 11 - 1 = 10{e^ - },$$
$$M{g^{ + + }} = 12 - 2 = 10{e^ - }$$
$$C{a^{ + + }} = 20 - 2 = 18{e^ - }$$ $${\text{(not}}\,\,{\text{iso}}\,\,{\text{electronic)}}$$
$$\left( {\text{C}} \right)\,\,{K^ + } = 19 - 1 = 18{e^ - },$$ $$C{\ell ^ - } = 17 + 1 = 18{e^ - },$$
$$C{a^{ + + }} = 20 - 2 = 18e,$$ $$S{c^{3 + }} = 21 - 3 = 18{e^ - }$$ $${\text{(iso}}\,\,{\text{electronic)}}$$
$$\left( {\text{D}} \right)\,\,B{a^{ + + }}56 - 2 = 54e,$$ $$S{r^{ + + }}38 - 2 = 36{e^ - }$$
$${K^ + } = 9 - 1 = 18{e^ - },$$ $$C{a^{ + + }} = 20 - 2 = 18{e^ - }$$ $${\text{(not iso}}\,\,{\text{electronic)}}$$