 Pekka Pyykkö and Burkhard Fricke used computer modeling to calculate the positions of elements up to "Z" = 172, and found that several were displaced from the Madelung rule.As a result of uncertainty and variability in predictions of chemical and physical properties of elements beyond 120, there is currently no consensus on their placement in the extended periodic table.Elements in this region are likely to be highly unstable with respect to radioactive decay and undergo alpha decay or spontaneous fission with extremely short half-lives, though element 126 is hypothesized to be within an island of stability that is resistant to fission but not to alpha decay.