Aufbau on a Chessboard Allan K. Hovland St. Mary's College of Maryland, St. Mary's City, MD 20686 Writing ground state electron configurations for the elements is an exercise that few introductory, general, or inoreanic chemistrv students escaoe. Most texts introduce the students to some mnemonic device to assist them in constructina the anorooriate confiaurations. These methods are based upon thkauibau principle, which refers to the use of the order of the increasing energies of the sublevels to predict elrctnm configurati& ~ h c m n e m o n i cfirst in~roduced hv Yi'. and subsequently moditied, forms the hasis for most of the mnen~onirs;sed today. A variation on this mnemonic is shown in Figtlre I. Problems wirh this method were noted by Carpenter' who discussed the use of an alternate procedure, a vairation of which is shown in Figure 2. 1 have developed and been using another method that improves upon that described by Carpenter. I find that the chesshoard (or checkerboard) offers a convenient frame of reference for a mnemonic to use in writing the electron confiaurations of the elements. T o use this method one does tKe following:
2) Reading is done from left to right as is done for text.
3) The first number of each diagonal corresponds to the first princi-
pal quantum level containing the associated subshells. (The p subshells for which n must he 2 or greater begin on the second diagonal, etc.) While my experience has shown that students find this to he a most convenient method for determining electron configurations, the instructor should caution the students regarding special cases.
' Yi. P. J. Chem. Educ. 1947, 24, 567.
Carpenter, A. K. J. Chem. Educ. 1983, 60,562.
1) On the chessboard, the squares on the diagonal running from lower left to upper right are marked s and numbered from 1 to 8
starting in the lower left square. 2) Moving up t o the next diagonal of thr same color. the squares are
marked pnnd nurnhrred from 2 to:.again, Ileginning at the lefthand square. 3) The third and fourth diagonals are successively labeled with d's and f s with the numbering for the squares running from 3 to 6 and 4 to 5, respectively. Following these instructions, a diagram as shown in Figure 3 can be drawn. Using this mnemonic, electron configurations for a given element are produced by starting at the bottom left and reading left to right on the successive rows filling the subshells as they occur. This procedure has several pedagogical advantages over the above-mentioned methods.
Figure 2. Variation of mnemonic describsd by Carpenter
1) The chessboard provides a frame of reference familiar to most
students.
I ( Figure 1. Variation an Yi's mnemonic for determining electron configuration.
Figure 3. Mnemonic for determining electron configurations using a shessboard as a frame of reference.
Volume 63 Number 7
July 1986
607
