Answer:
The ionic radii increase as the atomic numbers increase.
Explanation:
As we go down a Group, we are adding one more electron shell to the ion.
Each successive shell is bigger than the one before it, so the ionic radius should increase with increasing atomic number.
Here is a table of the ionic radii of the X⁻ ions.
Element Z r/pm
F 9 133
Cl 17 181
Br 35 196
I 53 220
At 85 227
However, the relation between r and Z is not linear (see graph).
All we can say is the ionic radius increases as the atomic number increases.
