4s, 3 4 What? A. Kurtz Carpenter Lower Columbia College, Longview, WA 98632 When electron configurations are taught, students encounter difficulty in remembering the filling order of the orbitals. Many texts, (and I suspect, many instructors), use the angle line, Uncle Wiggly path' shown here (Fig. 1) in their explanation. The Uncle Wiggly system works well if you have a typewriter which produces exact spacing of letters and lines, or if you have the skill to print perfectly by hand. Since most of us do not have either, another scheme is badly needed. Described herein is one such scheme. I have found this method to he foolproof in its preparation, even with handwriting as sloppy as mine! This method is not new. I t has appeared in texts2 and in a t least one slide-cassette" production. In none, however, has it really been descrihed, nor has the way to prepare it been adequately detailed. Because I feel the need for such a system is great and that such foolproof system should have wide exposure, it is descrihed here. Preparation 1) Draw a grid of 7 X 7 squares; 2) Label the diagonal with the known "s" orbitals as shown (Fig. 2);
Figure 1. The Uncle Wiggly path for the filling order of orbitals.
Figure 2. Label the diagonal with the known "s" orbitals.
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Journal of Chemical Education
3) Fill in each row with all possible orbitals allowed for that energy level as shown (Fig. 3); and 4) Read the orbital sequence by following the columns down, beginning a t the left. If all orbitals in each column are written before advancing to the next column, the proper filling order is determined.4 (See Fig. 4.) Acknowledgment Thanks is given for the suggestion hy Dave Robare during the WC4 gathering to write this article.
' Term used by Dr. Dave Robare. North Seanle Community College, described to me at a Washington Community College Chemistry (WC4) conference for instructors, Lake Wilderness, WA, January 29-31, 1981. Nebergall. W. H.. Holtzclaw, Jr. H. F., Robinson, W. R.. "College Chemistry with Qualitative Analysis," 6th ed., D. C. Heath and Co.. Lexington. MA. 1980, p. 83. Mitchell, John P., "Electron Configurations and Orbital Diagrams," Series 850 Atomic Structures. No. 851, Prentice Hall Media, Community Skills Corp., Engelwood Cliffs,NJ, 1973. This process does not account for exceptions to the filling order as the electrons are added, e.g., Cr, 4s' 3 8 .
Figure level.
3. Fill in
each row
with
all possible orbitals allowed for that energy
Figure 4. Find the orbital sequence by following the columns down beginning at the len.
