This is part of the series of 30 exercises developed during the E3D+VET program. The aim of this Erasmus+ program is the immersion in 3D printing of VET centres (website: ). There are 2 kinds of models: molecules and connectors. - Molecules: They are flat cylinders, with the name of the molecule engraved or embossed on them. They also have some holes in order to connect them with other molecules, with the connectors. - Connectors: They are basically sticks, for connecting the molecules, representating bonds. There are single, double and triple bonds.