Atomic radii ranking

[jheidenr]

Ok, its pretty simple to rank atomic radii by saying that the radius of an atom increases as you move down a group and increases as you move from right to left along a period...but what about for ions? for example, which has a greater atomic radius, Ca2+ or Ar? or between Ca+ and K? Can anyone explain this to me? Thanks!

 

[BAJackson16]

the heavier atomic weight means that it will pull the same amount of electrons closer together, hence making it smaller.

i think this is right?

 

[mg777]

Atomic radii that have the same electronic equivalence can be ranked straightforward. the cation is always smaller than the neutral or anionic species, b/c theres less repulsive force, and thereforce allowing the atom to pull its consitituent electrons more toward its center center. so in the case of Ca2+ and Ar, Ca 2+ is smaller.

 

[jheidenr]

ok, its starting to make more sense now...so what about an anion, say Cl- compared to S?

 

[mg777]

well those 2 atoms there are a little bit different than youre first question. those two Cl- and S are not electronically equivalent. however, if youre comparing Cl to Cl-, Cl- will be larger bc it basically has more electrons making a larger repulsive force and thus spreading out the atom and its electrons more. to rephrase your question and make the atoms electronically equivalent and thus a more probable DAT style question, b/w S- and Cl; S- would be larger b/c of the previous reasoning.

as far your original 2 molecules, i would think Cl- is larger b/c of the negative charge,

 

[jheidenr]

Thanks mg777! that clears up a lot of confusion...I can tell by your intelligent posts and the video links in your signature that you're someone who definitely has their head on straight!