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spiderflower

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## Homework Statement

Order each of the following sets of five atoms and ions according to decreasing size.

(i.e. "1" largest and "5" smallest)

N, Br-, Cs, P, Mg2+

## Homework Equations

When an atom loses electrons (becomes more +), its size decreases. Conversely, when an atom gains electrons (becomes more -), its size increases.

## The Attempt at a Solution

I know that Br- will be the largest, and Mg2+ will be the smallest. Then Cs will probably be the second largest considering its position on the periodic table. But for N and P I'm not entirely sure. So my best bet is: Br- > Cs > P > N > Mg2+

Or should I switch the P and N around?

One little problem... simply by adding one electron to Br will increase its size so much that it'll be larger than Cs? I find it a little unreasonable... but my teacher says that if there is a negatively charged ion, whatever the other ones, the anion will be the largest. How come?

Thank you very much in advance. :)