eighth period

Elements of the postulated eighth period, or R energy level, include the undiscovered elements 119 and 120. If elements beyond 120 are discovered, it is probable that those with atomic numbers 121 through 135 will belong to this period, and possible that their chemical behavior will be similar to that displayed by the actinon series. Elements 136 through 150, also candidates for membership in the postulated eighth period, will possibly behave in ways similar to those of the known transactinon series.