chem question

[issa]

there are 5 isoelectric ions. which one has the largest radius?
Ca2+,K+,Ar,Cl-,or S2-? and why?

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[Flipper405]

I believe S2- would have the largest radius because it has the least protons in the nucleus, so the attraction between the electrons and the protons would be the weakest. The electrons would not be held as tightly; therefore, the atomic radius would be larger.

The last section here seems to have some information about this topic:
http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch7/sizeframe.html