Explain, in terms of atomic structure, why the radius of an na atom is larger than the radius of an na+ ion.

The NA+ ion has less electrons and therefore, the positive charge on Na+ is greater, pulling the electrons closer to the nucleus. Therefore, if the electrons move closer to the nucleus the radius will decrease.
Not only this, but the Na ion also drops a valence level because it only has one electron on its outer valence level. Therefore, another solution is that if the valence level drops, the radius drops as well

Hope this helped!!:D