Atomic radius is a measurement used in atoms involving the distance from the center or nucleus to the outermost parts of the electrons. In a single atom, the nucleus is typically situated at the center with the protons scattered in the middle. The negatively-charged ions called electrons typically surround all atomic components and form the so-called outer shell. The outside of this shell and the actual center or nucleus form the basis for measuring atomic radius.
Owing to the differences in structures of atoms, the measurement of atomic radius may involve different parts other than the nucleus and the outer shell of electrons. For atoms that are closely connected with each other for example, atomic radius may be measured be measured in a different way. When two atoms are attached, the distance between the 2 nucleus involved is measured and divided into two to come up with the atomic radius. The variations in the atomic structure and its placement basically dictate on how the atomic radius is measured. With this difference, one specific atom may come up with different values for atomic radius because of its structure and its placement along with other atoms and particles.
The value given for atomic radius is also considered approximates rather than absolute. This is simply due to the fact that not all atoms are spheres and not all are fixed in terms of structure and placement. Variations already exist if atoms are neatly aligned with each other versus those that are actually attached and connected to each other. Densely-packed atoms for example lie so close to each other which basically lowers the value for atomic radius based on the location of the nucleus. The assumption also involves the spherical shape of most atoms when measuring atomic radius. For non-spherical types and atoms with odd shapes and structures, further variation in value is expected and the approximate value for atomic radius is given.