Atomic radius or Atomic Radii is the total distance from the nucleus of an atom to the outermost orbital of its electron. We can define the atomic radius of a chemical element as:
The measure of the size of its atoms, usually the mean or typical distance from the center of the nucleus to the boundary of the surrounding shells of electrons.
Van-der-Waals radii are determined from the contact distances between unbonded atoms in touching molecules or atoms.
The metallic radius is the radius of an atom joined by the metallic bond. The metallic radius is half of the total distance between the nuclei of two adjacent atoms in a metallic cluster.