This pack of 10 red atoms are used typically to represent oxygen atoms and is for extending your existing set or for replacing lost atoms. Each pack contains 10 balls with four holes in each ball in a tetrahedral array. Each atom is 23 mm diameter.
Why would I need these? You could use them to represent a tetrahedral oxygen atom in the hydroxonium cation (H3O+) with three bonds to H and the fourth hole attached to an orbital lone pair shape (available separately), or a tetrahedral oxygen atom in an ether or alcohol with the third and fourth holes filled by orbital lone pair shapes (available separately).
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.