Alternative periodic tables quantum numbers of the electron configuration, hence it has a four-dimensional base. In Theodor Benfey's periodic table (1964), the elements form a two-dimensional spiral, starting from hydrogen, and folding their way around two peninsulars, the transition metals, and lanthanides and actinides. A superactinide island is already slotted in. The Chemical Galaxy (2004) is organized in a similar way. Timothy Stowe's physicist's periodic table is three-dimensional with the three axes representing the principal quantum number, orbital quantum number, and orbital magnetic quantum number. Helium is again a group 2 element. Paul Giguère's 3-D periodic table consists of 4 connected billboards with
Periodic table the last member of the f-block for period 6". Later spectroscopic work found that the electron configuration of ytterbium was in fact [Xe]4f6s. This meant that ytterbium and lutetium—the latter with [Xe]4f5d6s—both had 14 f-electrons, "resulting in a d- rather than an f- differentiating electron" for lutetium and making it an "equally valid candidate" with [Xe]5d6s lanthanum, for the group 3 periodic table position below yttrium. Lanthanum has the advantage of incumbency since the 5d electron appears for the first time in its structure whereas it appears for the third time in lutetium, having also made a brief second appearance