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The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 19 (2014) pp 232-235

Are Slaters Rules the Best Approach for Calculating Effective Nuclear Charge for Undergraduates?

Preston Moore and Edward R. Birnbaum*

Department of Chemistry & Biochemistry, University of the Sciences in Philadelphia, 600 South 43rd Street, Philadelphia, PA 19104, e.birnba@usciences.edu
Received October 8, 2014. Accepted March 20, 2014.

Published: 11 July 2014

Abstract. The concept of effective nuclear charge (Zeff) is typically introduced to undergraduate students in freshman chemistry, and specific values calculated in a more advanced Inorganic Chemistry course using Slater’s Rules. These Zeff values are typically used to rationalize the periodicity observed in the first ionization energies (IE) measured for gaseous atoms across the Periodic Table, as well as for a variety of other observable properties of atoms and molecules, such as atomic electron affinity energies, atomic radii, acidity, etc. Although the periodic behavior of the Zeff calculated using Slater’s Rules roughly matches the periodicity of the gas phase ionization energies, the ionization energies calculated from the equation, IE = (Zeff /n*)2, fit very poorly for all the ns- and np-subshell elements. In this paper, much better fits are shown to be obtained using alternative approaches to the calculation of Zeff, and suggest that using Slater’s Rules greatly underestimates the shielding of s and p electrons within the same subshell.

Key Words: In the Classroom; general chemistry; inorganic chemistry; effective nuclear charge; atomic properties; ionization energy; slater’s rules; electron correlation; electron shielding; electron screening; electron-electron repulsion; periodicity

(*) Corresponding author. (E-mail: e.birnba@usciences.edu)

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