An Easily Constructed Octahedron Model
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A model of an octahedron, which is necessary for teaching stereochemistry (especially of inorganic compounds) can he made easily by using a sealed, empty envelope. The steps are illustrated in the figure and given below.
G
A
C
E
A
1) The envelope is folded down the center lengthwise, and the middle point of the base AB is marked as C. 2) The lower part of the envelope is folded up so that the corner B falls on the center line. The point on the line is marked as D and a line EDF, perpendicular to the center line a t D, is drawn. 3) The upper part of the envelope is cut off along the horizontal line, EDF. The remaining partion is folded both backward and forward along the lines AD, BD, CE, CF, and GH. The intersection of the two lines AD and CE, and that of the other two lines BD and CF, are marked as G and H , respectively. 4) Cut theenvelope along the lines CG and CH. Ned,separate the obverse and reverse of the envelope from each other by cutting the base AB along the lines CA and CB. 5) The corresponding points on the reverse, of the D, G, H,and C, are marked as D*, G*, H*, and C*, respectively. 6) Oblique Lines are drawn to shade eight equilateral triangles (AGC, CHB, EGD, and DHF on the obverse and AG*Ca, C*H*B, EG*D*, and D*H*Fonthe reverse). Hereafter, themarks C and C* are used only for denoting the tops of the two clear triangles GHC and G*H*C*, respectively. 7) The right- and left-hand sides of the envelope are forced to approach to make four Lines (GH, HH*, H*G*, and G*G), constitute a square. 8) The four points A, C, B, and C*, are forced to approach and meet, and finally are put together with pasting tape to produce a tetrahedral cone GHH*G*C, infolding all the soiled triangles inside. Similarlv. the uooer tetrahedral cone can be made by the following procedures. 9) ~hkenvelopkis cut along the lines DG, DH, D*G*, andD*H* 10) The tops D and D* of the two clear triangles DGH and D*G*H*, respectively, and the two pointa E and F are forced to approach and meet, and finally are put together with pasting tape to produce the upper half of the octahedron, inside of which all the shaded soiled triangles are enfolded.
References Yamana, S., J. CHEM. EDUC., 45,245 (1968). Yamana, S., and Kawaguchi, M., Ann. Rep. Res. Sci. Educ. Kyoto Uniu. Educ., 9,25 (1979). Shukirhi Yamana Kyoto Univewity of Education Fushimi-Ku. Kyolo,.lapsn 612
434 1 Journal of Chemical Education
Makoto Kawaguchi Department of Science a n d Engineering Ritsumeikan University Kita-Ku, Kyoto, J a p a n 603
