This kit contains 111 atoms parts and 140 links. Each colored ball has a certain number of holes that represents the valency of each atom, e.g. Hydrogen has one hole; Carbon atoms have 4 holes. Elements include: Carbon, Hydrogen, Nitrogen, Oxygen, Sulphur, Phosphorus, Halogen, and Metals. Use medium links for single covalent bonds; long links for double or triple bonds. Short white links replace medium links in compact models. Demonstrate molecular and structural formulae; and structural isomerism.