This kit contains 106 atoms parts and 86 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 as in water H-O-H; long links for double (oxygen) or triple bonds. Pear-shaped lobes can be used to represent lone pairs of electrons present in water and ammonia or the p-lobes responsible for pi bonding in ethene and benzene.