Question

Rank the following items in order of decreasing radius: Na, Na+, and Na-. Rank from largest to smallest radius. To rank items as equivalent, overlap them. Na Na+ Na-

Answer 1

So, when you think about this, just think about the valence e- in the clouds. I am sure that your textbook states that anions are bigger than the regular atom, while cations are smaller that the regular atom. Therefore, you can rank this as (L-S) Na-, Na, Na+.
The way I look at this is, when you have a pos. charge, this means that you have less electrons, which in turn will be more attracted to the pos. charged nucleus (electron have negative charges that are attracted to pos. charges, right?). when you have an anion, there are more e- floating around. e- repel each other, and so, their tendency is to go as far away from each other as possible since the effect of the - charges is greater than that of the attraction to the nucleus.