Period 1 element lithium and fluorine (appearing twice), or left floating above the other elements and not assigned to any group in the periodic table. Helium is almost always placed above neon (which is in the p-block) in the periodic table as a noble gas, although it is occasionally placed above beryllium due to their similar electron configuration. Hydrogen (H) is the chemical element with atomic number 1. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H. With an atomic mass of 1.00794 amu, hydrogen is the lightest element. Hydrogen is
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