which of the folllowing species is not isoelctric with any of the others?

Question

a)V3+
b)Ca2+
c)Ar
d)CL-
e)S2-

Answer 1

This is much easier to answer if you look at a Periodic Table, say
http://en.wikipedia.org/wiki/Periodic_table

In order the elements are

Si, P, S, Cl, Ar, K, Ca, Sc, Ti, V

adding an electron will make the element isoelectronic with the element to the right, removing an electron will make it isoelectronic with the element to the left. So

Si, P, S, Cl, Ar, K, Ca, Sc, Ti, V

_________________________V3+
______________Ca2+
______________Cl-
______________S2-

Answer 2

Oh dear the formatting didn't work. I'll try again

Si, P, S, Cl, Ar, K, Ca, Sc, Ti, V

___________________V3+
_________Ca2+
_________Cl-
_________S2-

Answer 3

So four are isoelectronic.

Answer 4

So adding of removing the electrons gives all of them 18 elctrons like Argon except for V3+, correct? Thsi makes it the non-isoelctric species? It wasn't explained to me this way and this makes it much easier to see. Thanks!