# Arraging atoms/ions based on atomic radius

1. Apr 5, 2004

### 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!

Last edited: Apr 5, 2004
2. Apr 12, 2004

### 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?