Lanthanum is the first element and prototype of the lanthanide series. In the periodic table, it appears to the right of the alkaline earth metal barium and to the left of the lanthanide cerium. Its placement has been disputed, but most who study the matter along with a 2021 IUPAC provisional report consider lanthanum to be best placed as the first of the f-block elements. The 57 electrons of a lanthanum atom are arranged in the configuration 5d16s2, with three valence electrons outside the noble gas core. In chemical reactions, lanthanum almost always gives up these three valence electrons from the 5d and 6s subshells to form the +3 oxidation state, achieving the stable configuration of the preceding noble gas xenon. Some lanthanum(II) compounds are also known, but they are much less stable.