This pack of yellow atoms are used to represent, typically, sulfur (sulphur) atoms and is for extending your existing set or for replacing lost atoms. Each pack contains 10 balls with four holes in each ball at 109°. Each atom is 23 mm diameter.
Why would I need these? You could use them to represent tetrahedral sulfur in, say, sulfate.
The Molymod® system is the original, unique, dual-scale system of high quality low-cost molecular models. These enormously popular sets are ideal for students but are also used by scientists all over the world.