Seamless methacrylate (Lucite or Plexiglas) spheres of various opaque colors and diameters can be used to construct sturdy molecular mode1s.l The diameters and colors were as follows: 1 in. black (C) ; 3/a in. orange (H); '/* in. white (0); 7/s in. light blue (N); 3/4 in. pink (F); and l'/s in. crystal clear (S, CI). These sizes are not exactly proportional to the actual atomic diameters; however, since the spheres are available in in. gradations there is a close approximation. All sizes above 1 in. diameter are available only :IS clear spheres and must be painted an appropriate color. Construction of Models
To show orbital overlap, the spheres must be cut so that one or more circular plane faces are formed a t appropriate angles. Since actual orbital overlap for any given pair of elements may vary depending on chemical environment, type of bonding, etc., a constant average overlap was selected and represented by a face diameter on each sphere of 1.7 cm. This circle was scratched onto the surface of each sphere using sharp pointed dividers. Once the dividers were set a t the correct radius it was not necessary to change this setting. For elements having two or more valences, the location of the center points of the second, third, and fourth circular plane faces was determined by a trigonometric process., The direct distance, X, between the center points of two plane faces is given by: X
where +
=
=
180" - (90°
/
r--
2(R coa m)
+ '/z
