Nuclear physicists discovered in 1989 that the atoms of some elements exist in microclusters. These are tiny groups of between two and several hundred atoms. Most of the transition group precious metals in the center of the periodic chart exhibit a monoatomic state. If you have more than a specific number of these atoms in a microcluster, the atoms will aggregate into a lattice structure with metallic properties. If you have fewer than that critical number of atoms, that microcluster will disaggregate into monatomic atoms with ceramic properties. Monatomic atoms are not held in position by electron sharing with their neighboring atoms as are atoms in a classical lattice structure. The critical number of atoms for rhodium is 9 and the critical number of atoms for gold is 2. The significance of this is that if you have two or more gold atoms in a microcluster, it will exhibit metallic characteristics. However, if you have 9 or fewer atoms in a microcluster of rhodium atoms, the microcluster will spontaneously disaggregate to become a group of monatomic rhodium atoms. You might wonder why there is one equilibrium state at a certain deformation level and a different equilibrium state at a different level of deformation. This is a question for nuclear scientists to ponder. It has been observed that the valence electrons of monatomic elements are unavailable for chemical reactions. This means that monatomic atoms are chemically inert and have many of the physical properties of ceramic materials. Because the valence electrons are unavailable, it is impossible to use standard analytical chemistry techniques to identify a monatomic element.
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