elements in group 18 have complete outer electron shells on the periodic table of elements
atoms has electrons electron_shell is group. one_of_chemical_elements is helium. group_11_elements is coinage_metals. group_15_elements is pnictogens. rubidium_atom is atom. electron is particle. one_of_chemical_elements is rubidium. each_element_in_periodic_table has number_associated_with mercury_atom is atom.