This pack of 10 purple atoms are often used to represent phosphorus atoms and is for extending your existing set or for replacing lost atoms. Each pack contains 10 balls with three holes in each ball at 107° (pyramidal). Each atom is 23 mm diameter.
Why would I need these? You could use them to represent a pyramidal phosphorus atom in a compound such as an phosphine (phosphane) where you do not want an empty hole and do not wish to display a lone pair.
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.