Discover the Largest Ion in an Isoelectronic Series: S2-, Cl-, K+, and Ca2+

[whozum]

15. The following ions comprise an isoelectronic series: S2, Cl, K+, and Ca2+
Which is the largest ion?

A. S2-
B. Cl-
C. K+
D. Ca2+
E. All should be the same size.

Don't even know what one is.

 

[so-crates]

What are your periodic trends for atomic size?

 

[whozum]

Atomic radius increases to the left and down.

 

[whozum]

Does the term "isoelectronic series" do anything for this problem?

 

[Borek]

It just means that all ions have exactly the same number of electrons, the only thing that changes is nucleus charge.

 

[GCT]

It quite self-explanatory, atoms with the same number of electrons. You should be able to figure out the electron number in a neutral atom of the element, and further deduce the electron number of a corresponding ion.

In reference to the size of each of these, you'll need to consider the relative proton number with the electron number, effective nuclear charge. Typically, a isoelectronic cation is smaller than the anion because you've got the same number of electrons for both with a smaller proton number for the latter.

 

[Gokul43201]

Not to blow any trumpets here but this essentially summarizes what has been said above by Borek and GenChemTutor, about comparing radii among isoelectronic ions.