Molecule fragments also called moieties are the smallest building blocks handeded in the advanced mechanosynthesis of technology level III and II. When a simple resource molecule is picked up with an empty tooltip one always ends up with a few atoms on the tooltip. Some bonds need to be broken open to make it a reactive radical ready for deposition. It is generally not necessary to prepare the picked up molecule down until only one atom is left. That is in most cases one does not put down single atoms but small moieties (always bond molecules). Most often unused bonds are left hydrogen capped and and only one or two bonds are actively used - the one to the tooltip and the one to the workpiece. Hydrogen and oxygen with one and two bonds respectively are subject for single atomic deposition. The heavier elements of the same groups - the halogenes calcogenes - too.