Easily Constructed Model of Twin Octahedrons Having a Common Plane Shukichi Yamana Faculty
of General Education,
Kinki University, Kowakae, Higashi Osaka 577, Japan
Makoto Kawaguchi Faculty of Science and Engineering, Ritsumeikan University, Kita-ku, Kyoto 603, Japan
A model of twin octahedrons having a common plane which is useful for teaching stereochemistry (especially t h a t of complex anions) can b e m a d e easily b y using a sealed, e m p t y envelope. The s t e p s a r e illustrated i n t h e figure a n d given below. 1) The envelope is folded dawn the center lengthwise, and the middle point of the base AA 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 n m corner on the right-hand side of
side of the envelope at E and^, respectively. 4) A line which originates at C and is parallel with the line BF, is drawn to crass the left-hand side of the envelope at G. 5) A line which originates at C and is parallel with the line AD, is drawn to crass the right~handside of the envelope at H . 6) The extension of the IineHE is drawn so that it crosses the lefthand side of the envelope at I . 7) The extension of the line GE is drawn so that it crosses the rieht-hand side of the envelone at J .
10) The envelope is unfolded. 11) Cut off the upper part of the envelope along the line A'A'. 12) Separate the front and back of the lower part of the envelope from each other by cutting the base along the line AB. 13) The remaining portion is folded both backward and forward along the lines G'C', IH', G J , CH, C'H', G'J, I H , and GC. 14) The corresponding points on the hack of the points G , A, C , B ,
H,E,G',A',C',B',H',andE',aremarkedasG*,A*,C*,B*,H*, E*, G'*, A'*, C'*, B'*, H'*, and E", respectively. 15) Separate the center line of the front obverse and from that of the back reverse forcing the left- and right-hand sides of the envelope to approach and meet hack to back. 16) Six regular triangles, H'E'J, E ' E J , E H J , HE*J, E*E'*J, and E'*H'J, are marked as al, az, b ~e l,, cn, and br, respectively. 17) Oblique lines are drawn to shade the four isosceles triangles, C'H'C'*, HCC* (on the new front). C'G'C". and GCC* ion the new back). 18) While keeping the two points J and I touching each other back to back, the C and C* are forced to approach and meet to produce an octahedron, infolding the shaded triangles HCC* and GCC* inslde. Similarly, t h e other octahedron moiety can he made b y t h e following procedure.
tively
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19) While keeping the two points J and I touching each other back
Journal of Chemical Education
to hack, the C'and C'* are forced to approach andmeet, folding the shaded triangles C'H'C" and C'G'C'* inside. are forced together so that their 20) The two octahedrons faces bl and bn and the pairs of the two faces a i and a n and e l and cn are also in contact. Finally, it is put together with tape to ~ r o d u c ethe model mentioned in the title.
References Yamana, S,,J, CHEM,
yamana, s.,
46, 246 i1968,,
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