Atomic radius is the measure of the distance from the centre of the nucleus to the outer electron.
Shielding is the effect of the inner shells of electrons on weakening the attraction between the protons in the nucleus and the outer electron.
The atomic radius is a measure of the distance from the nucleus to the valence electron.
Shielding is the measure o the effect of inner sub shells of the S P D and F on their interference of the nuclear charge of the protons on the valence electron.
Ionic radius can be defined as the size of the radius of an ion from the nucleus to the valence electron. The ionic radius is difficult to measure due to the overlap of ions in a lattice structure.
Electron affinity is a measure of the energy released when an electron is added to an atom to create a negatively charged ion.