Are Slater’s Rules the Best Approach for Calculating Effective Nuclear Charge for Undergraduates?

TCE

The Chemical Educator

ISSN: 1430-4171 (electronic version)

Table of Contents

Abstract Volume 19 (2014) pp 232-235

Are Slater’s 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 43^rd 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 (Z_eff) 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 Z_eff 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 Z_eff calculated using Slater’s Rules roughly matches the periodicity of the gas phase ionization energies, the ionization energies calculated from the equation, IE = (Z_eff /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 Z_eff, 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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