This kit contains 52 atoms parts and 37 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, Boron, Nitrogen, Oxygen, Sulphur, Phosphorus, Halogen, and Metals Na, Ca, Mg, Be, Al, Si, and Cu. Atom parts represent any element having the structures sp3, tetrahedral, dsp3 trigonal bipyramid, d2sp3 octagonal. Use medium links for single covalent bonds as in water H-O-H; long links for double (oxygen) or triple bonds.