Iodine: properties of free atoms

Iodine atoms have 53 electrons and the shell structure is

The ground state electron configuration of ground state gaseous neutral iodine is  [Kr].4d10.5s2.5p5 and the term symbol is  2P3/2.

Atomic spectrum


A representation of the atomic spectrum of iodine.

Electronic configuration of neutral atomic iodine

Electronic configuration of iodine

The electronic configuration of iodine.

Kossel shell structure of iodine

The Kossel shell structure of iodine.

Ionisation Energies and electron affinity

The electron affinity of iodine is 295.2 kJ mol‑1. The ionisation energies of iodine are given below.

Ionisation energies of iodine
Ionisation energy number Enthalpy / kJ mol‑1

Effective Nuclear Charges

The following are "Clementi-Raimondi" effective nuclear charges, Zeff. Follow the hyperlinks for more details and for graphs in various formats.

Effective nuclear charges for iodine
2s39.07 2p48.85  
3s34.79 3p34.84 3d38.90  
4s25.30 4p24.03 4d20.93 4f(no data)
5s13.40 5p11.61 5d(no data)  
6s(no data) 6p(no data)  


These effective nuclear charges, Zeff, are adapted from the following references:

  1. E. Clementi and D.L.Raimondi, J. Chem. Phys. 1963, 38, 2686.
  2. E. Clementi, D.L.Raimondi, and W.P. Reinhardt, J. Chem. Phys. 1967, 47, 1300.

Electron binding energies

Electron binding energies for iodine. All values of electron binding energies are given in eV. The binding energies are quoted relative to the vacuum level for rare gases and H2, N2, O2, F2, and Cl2 molecules; relative to the Fermi level for metals; and relative to the top of the valence band for semiconductors.
Label Orbital eV [literature reference]
K 1s33169 [1]
L I2s5188 [1]
L II2p1/24852 [1]
L III2p3/24557 [1]
M I3s1072 [2]
M II3p1/2931 [2]
M III3p3/2875 [2]
M IV3d3/2630.8 [1]
M V3d5/2619.3 [1]
N I4s186 [2]
N II4p1/2123 [2]
N III4p3/2123 [2]
N IV4d3/250.6 [1]
N V4d5/248.9 [1]


I am grateful to Gwyn Williams (Jefferson Laboratory, Virginia, USA) who provided the electron binding energy data. The data are adapted from references 1-3. They are tabulated elsewhere on the WWW (reference 4) and in paper form (reference 5).


  1. J. A. Bearden and A. F. Burr, "Reevaluation of X-Ray Atomic Energy Levels," Rev. Mod. Phys., 1967, 39, 125.
  2. M. Cardona and L. Ley, Eds., Photoemission in Solids I: General Principles (Springer-Verlag, Berlin) with additional corrections, 1978.
  3. Gwyn Williams WWW table of values
  4. D.R. Lide, (Ed.) in Chemical Rubber Company handbook of chemistry and physics, CRC Press, Boca Raton, Florida, USA, 81st edition, 2000.
  5. J. C. Fuggle and N. Mårtensson, "Core-Level Binding Energies in Metals," J. Electron Spectrosc. Relat. Phenom., 1980, 21, 275.

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