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  Home > JCE Print > Journal of Chemical Education > Issues > 1999  > January  >
In the Laboratory
The Ionization Energy of Helium
M. J. Kaufman and C. G. Trowbridge
Department of Chemistry, Emory University, Atlanta, GA 30322-2210
Cover
January 1999
Vol. 76 No. 1
p. 88
Abstract
Partial analysis of the visible emission spectrum of helium illustrates how one-electron quantum theory can be applied to a two-electron system. Lines corresponding to 1snd ® 1s2p singlet transitions can be identified in the spectrum by their ratios agreeing with the Bohr equation. In the 1snd levels the nd electron is extremely well shielded by the 1s electron. Therefore, the identified transitions can be fit very well by the Bohr equation with Zeff close to unity. These levels can be extrapolated to the ionization limit and combined with the observed energy of the 1s3d ® 1s2p emission and the provided energy of the lowest allowed helium absorption to give an ionization energy in excellent agreement with the literature. This simple experiment illustrates a number of important principles of atomic structure and spectroscopy.
More Information
*  Citation
 Kaufman, Myron J.; Trowbridge, C. G. J. Chem. Educ. 1999 76 88.
*  Keywords
 Physical Chemistry; Quantum Chemistry; Helium; Laboratory Instruction
*  History
 Created:
Last Updated:		 June 15, 1999
June 22, 2005
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