An atom does not have a well-defined boundary so the atomic radius is measured by measuring the distance between two adjacent nuclei and then dividing by 2.
Either the covalent radius or the van der Waals radius (orbitals do not overlap) can be measured. For metals the metallic radius is determined. The atomic radius decreases across a period and increases down a group.
Either the covalent radius or the van der Waals radius (orbitals do not overlap) can be measured. For metals the metallic radius is determined. The atomic radius decreases across a period and increases down a group.