Atomic Radius Size of atom – the volume that encompasses 90 % of the electron density. Atomic Radius – one half the distance between the two nuclei in two adjacent atoms. Determined by x-ray diffraction.

Ionic radius – radius of a cation or anion (x- ray)

Ionization energy – the minimum energy required to remove an electron from a gaseous atom in its ground state. (KJ/mol) First ionization is easier than subsequent electron removal.

Electron affinity – The attraction an atom has for additional electrons large electron affinity – negative ion is more stable