Lab-Aids®. An economical model set ideal for teacher-directed individual study in basic chemistry. A student may construct models of many different compounds from reusable, color-coded, plastic pieces representing atoms and covalent electron bonds (not to scale). Assembled models are sturdy and easily disassembled or changed. The following atom centers (6 to 9 mm diam) are provided: 30 hydrogen, 16 oxygen, 30 carbon, 7 sulfur, 5 nitrogen, and 18 halogen. Set also includes 85 bonding pieces and an instruction manual.