The superactinides may be considered to range from elements 121 through 157, which can be classified as the 5g and 6f elements of the eighth period, together with the first 7d element. In the superactinide series, the 7d 3/2, 8p 1/2, 6f 5/2 and 5g 7/2 shells should all fill simultaneously. This creates very complicated situations, so much so that complete and accurate CCSD calculations have been done only for elements 121 and 122. The first superactinide, unbiunium (element 121), should be similar to lanthanum and actinium : its main oxidation state should be +3, although the closeness of the valence subshells' energy levels may permit higher oxidation states, just as in elements 119 and 120. Relativistic stabilization of the 8p subshell should result in a ground-state 8s 8p valence electron configuration for element 121, in contrast to the ds configurations of lanthanum and actinium; nevertheless, this anomalous configuration does not appear to affect its calculated chemistry, which remains similar to that of actinium. Its first ionization energy is predicted to be 429.4 kJ/mol, which would be lower than those of all known elements except for the alkali metals potassium, rubidium, caesium, and francium : this value is even lower than that of the period 8 alkali metal ununennium (463.1 kJ/mol). Similarly, the next superactinide, unbibium (element 122), may be similar to cerium and thorium, with a main oxidation state of +4, but would have a ground-state 7d 8s 8p or 8s 8p valence electron configuration, unlike thorium's 6d 7s configuration. Hence, its first ionization energy would be smaller than thorium's (Th: 6.3 eV ; element 122: 5.6 eV) because of the greater ease of ionizing unbibium's 8p 1/2 electron than thorium's 6d electron. The collapse of the 5g orbital itself is delayed until around element 125; the electron configurations of the 119-electron isoelectronic series are expected to be [Og]8s for elements 119 through 122, [Og]6f for elements 123 and 124, and [Og]5g for element 125 onwards.