 A fifth transition metal series in which 7d orbitals are filled then would contain elements 155–164, and the eighth period would possibly end there.It is also possible that element 157 is in fact the first 7d transition metal, another shift resulting from relativistic effects.Elements 165 and 166 were predicted to be alkali and alkaline earth metals, though they may also mix characteristics of groups 11 and 12 and instead be placed below roentgenium and copernicium, respectively.