Answer to Question #145546 in General Chemistry for Michelle Duong

Question

why is the radius of sodium ion smaller than radius of oxide ion

Answer 1

In other words, Na+ has bigger effective nuclear charge than O2− , which translates to a bigger net positive charge felt by the outermost electrons. This will compress the energy levels a bit and make the ionic radius smaller for the sodium cation. Therefore, the oxide anion will have the larger atomic radius.