elements in group 18 have full / complete outer electron shells on the periodic table of elements
atoms has electrons electron_shell is group. one_of_chemical_elements is helium. mercury_ii_ion is mercury_atom. group_11_elements is coinage_metals. iron_ii_ion is iron_atom. one_of_chemical_elements is polonium. rubidium_atom is atom. electron is particle. mercury_atom is atom.