Walnut Models of Simple Molecules The orientation of occupied valence shell orbitals, due to their mutual repulsion, has a striking model in nature. The mechanical repulsion of walnuts growing with closely seated stems results in the orientation of the ellipsoidally shaped fruits in perfed agreement with the predictions of VSEPR theory.' Although not as flexible as the balloon mode1,2.3 the walnut model is offeredgenerously by nature. Possibly other nuts and fruits may exhibit similar behavior. The photo a t the top, left, illustrates the opposite orientation of two orbitals (like the bonding orbitals in BeC12) or alternatively, that of the two lohes of a single p orbital. The rest of the photographs are of 3,4, and 5 nuts, grown on the w e stem, and showing triangular, tetrahedral, and trigonal hipyramidal orientations, respectively. We found also groups of 6 nuts with octahedral orientation. The polar axis of the trigonal bipyramid in the lower right figure was marked by ink for ease of understanding. Thestem islocated in the equatorial position. Is this location just a matter of chance? It is more likely a proof for a less crowded equatorial plane, as predicted by the VSEPR theory. I t is also easy to understand how the triangular bipyramid can be rearranged to a square pyramid. The use of these models found in nature can be an efficient approach to helping students understand the geometry of molecules, as they look less strange to pupils than do artificial models, and they emphasize that the orientations are indeed "natural" ones. Gillespie, R. G., J. CHEM. EDUC., 47,19 (1970). Roberts,R. W.,and T r a ~ n h a mJ. , G., J. CHEM. EDUC., 53,233 (1976). Niac, G., J. CHEM. EDUC., 55,303 (1978). Gavril Niac lnstitutul Politehnic Cluj-Napoca, Romania
Cornel Florea Liceul "Terapia" Cluj-Napoca, Romania
Volume 57, Number 6, June 1980 1 429
