Atomic radii of the elements (data page)

The atomic radius of a chemical element is the distance from the center of the nucleus to the outermost shell of an electron.

Since the boundary is not a well-defined physical entity, there are various non-equivalent definitions of atomic radius.

Depending on the definition, the term may apply only to isolated atoms, or also to atoms in condensed matter, covalently bound in molecules, or in ionized and excited states; and its value may be obtained through experimental measurements, or computed from theoretical models.

For instance, the radii generally decrease rightward along each period (row) of the table, from the alkali metals to the noble gases; and increase down each group (column).

Data is as quoted at http://www.webelements.com/ from these sources: Greenwood, Norman N.; Earnshaw, Alan (1997).