Atomic and Ionic Radius
In its neutral state, an atom has the same number of electrons and protons, so the attraction force between them are balanced. When electrons are taken away, the ionic radius decreases as there is less electron-electron repulsion and the pull that the positive nucleus has on the electrons is much greater.
That being said, negative ions are larger than their parent atoms because there is more electron-electron repulsion and there is a weaker pull between the nucleus and the electrons.