The Physical Properties of Gold
Since gold exists only as one single isotope, it belongs to the group of 22 mononuclidic elements. Unlike that of all other elements, the nucleus of mononuclidic elements always contains the same number of protons and neutrons. Although a heavy metal, non-alloyed gold is, thanks to its high ductility, almost as soft as tin.
It can be hammered into gold leaf or rolled into gold foil with a minimum thickness of 2000 atomic layers. Such extremely thin foil was used for example in Ernest Rutherford's gold foil experiment studying scattering, where white light appeared greenish through the foil.