Question

As the atomic number increases the ionic radius___?

Answer 1

when the number of protons (atomic number) increases, and the number of electrons stays fixed, the radius decreases. For example, \(Mg^{2+}\) and \(Na^+\) both have 10 electrons, but Mg has one proton more than Na, so the radius of \(Mg^{2+}\) is smaller than that of \(Na^+\). This arises from coulombic attractions from a greater amount of protons towards the electrons.