Periodic Table of Radii

Selecting different definitions of the radius


Selecting regions of the table

Jmol Command

Example, Selecting only Cu: reset;select all; spacefill 0;label off;select ????.Cu;label %n;spacefill temperature;rotate y 90

The radii of atoms and ions can be defined and measured in a variety of ways for different purposes.  An individual  atom in the gas phase can be assigned a radius based on the occupied orbitals and their wave functions, as has been presented by Clementi (E. Clementi, D. L. Raimondi, and W. P. Reinhardt J. Chem. Phys. 47, 1300-1307 (1967) "Atomic Screening Constants from SCF Functions. II. Atoms with 37 to 86 Electrons").  Experimentally derived radii are defined so that the sum of radii give the distance between atoms in compounds, typically as solids.  The radius thus depends on the strength of the interaction between the two atoms as well as the elements or ions involved.  If the interaction involves only van der Waals (induced dipole) interactions, then van der Waals radii are obtained ( A. Bondi, J. Phys. Chem., 1964, 68, 441." van der Waals Volumes and Radii").  These are typically the largest of the experimental radii.  For covalent interactions, the radius decreases with the bond order between the atoms.  Radii for covalently bonded neutral atoms have been critically compiled from thousands of experimental structures. (B. Cordero, V. Gómez, A. E. Platero-Prats, M. Revés, J. Echeverría, E. Cremades, F. Barragán and S. Alvarez Dalton Trans., 2008, 2832-2838 "Covalent radii revisited").  Where there is a choice, the radius in this table is for a singly bonded atom, e. g. sp3 hydbridized carbon.   For ionic interactions, the radius will depend on the charge, increasing with the number of electrons, thus larger for anions and smaller for cations.  It also varies with the coordination number of the ion and the spin state for transition metal ions.  For this table, a coordination numbere of 6 is used, and high spin ions are chosen, using the "effective ionic radius" of Shannon (R. D. Shannon, Acta Cryst., 1976, A32, 751-67. "Revised effective ioinic radii and systematic studies of interatomic distances in halides and chalcogenides").