Decreasing Atomic Radii.?

Question

How do you order these from largest to smallest atomic radii? How do you know which is larger?


Cl-
Al3+
Na+
F-
Mg2

Answer 1

What do you mean about "Mg2"? Do you mean "Mg(2+)"?
Cl-, F-, Na+, Mg(2+), Al(3+).
The reasons:
Chlorine is in the third period and fluorine is in the second period. Of course then Cl- would have a larger radius than F-.
Though all the positive ions Na+, Mg++, and Al(3+) are the elements in the third period, their electrons only fill the electronic orbits of the second electron shell due to lost of their valence electron/s. In fact, they have the same number of electrons as F- ion does. Now, the high the nuclear charge, the closer the electrons would be to the nuclei. Thus the order of the atomic radii must be ordered the above way.