<P> Pekka Pyykkö divides these superactinides into three series: a 5g series (elements 121 to 138), an 8p series (elements 139 to 140), and a 6f series (elements 141 to 155), although noting that there would be a great deal of overlapping between energy levels and that the 6f, 7d, or 8p orbitals could well also be occupied in the early superactinide atoms or ions . He also expects that they would behave more like "super lanthanides", in the sense that the 5g electrons would mostly be chemically inactive, similarly to how only one or two 4f electrons in each lanthanide are ever ionized in chemical compounds . He also predicted that the possible oxidation states of the superactinides might rise very high in the 6f series, to values such as + 12 in element 148 . </P> <P> As an example from the late superactinides, element 156 is expected to exhibit mainly the + 2 oxidation state . Its first ionization energy should be about 395.6 kJ / mol and its metallic radius should be about 170 picometers . It should be a very heavy metal with a density of around 26 g / cm . Its relative atomic mass should be around 445 u . </P> <P> The transition metals in period 8 are expected to be elements 157 to 165 (or perhaps with element 121 replacing 157, similarly to the dispute on whether lanthanum or lutetium is better placed as the first 5d transition metal). To these element 166 may be added to complete the 7d subshell, although like its lighter group 12 homologues it is questionable if it would show transition metal character . Although the 8s and 8p electrons are bound so strongly in these elements that they should not be able to take part in any chemical reactions, the 9s and 9p levels are expected to be readily available for hybridization . </P> <P> The noble metals of this series of transition metals are not expected to be as noble as their lighter homologues, due to the absence of an outer s shell for shielding and also because the 7d shell is strongly split into two subshells due to relativistic effects . This causes the first ionization energies of the 7d transition metals to be smaller than those of their lighter congeners . </P>

Elements that are not in the periodic table