Arraging atoms/ions based on atomic radius

[walker]

Arranging atoms/ions based on atomic radius

Hey, I'm in a bit of a bind here. I got a question that deals with atomic radius. The question asks to arrange the following atoms/ions in order from smallest to biggest:

Cl, S^{2-}, K, K^{+}, O

I know just by looking at the periodic table that O has the smallest radius and that K has the largest radius... I also know that since S^{2-} is larger than S and since S is larger than Cl that means S^{2-} is also larger than Cl.

K^{+} is smaller than K and larger than Cl since it has a greater energy level.

Here's my problem... I know that both K^{+} and S^{2-} fall somewhere between the Cl and K atoms... and by looking up the actual radius of the K^{+} and S^{2-} ions I know that the S^{2-} radius is larger than the K^{+} radius but how do i prove this?

Any help would be greatly appreaciated. Thanks!

 

[garytse86]

surely both K+ and S2- have the same number of electrons but different number of protons, since K+ has 3 more protons the overall attraction for electrons are stronger so smaller ionic radius?