Lutetium is a Block F, Group 3, Period 6 element. The electronic configuration is [Xe]4f¹⁵5d¹6s². In its elemental form lutetium's CAS number is 7439-94-3. The lutetium atom has a radius of 171.8.pm and it's Van der Waals radius is unknown. Lutetium is the last member of the rare earth series. Lutetium is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra-high purity); metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder. Unlike most rare earths it lacks a magnetic moment. It also has the smallest metallic radius of any rare earth. It also has the smallest metallic radius of any rare earth. It is perhaps the least naturally abundant of the lanthanides. It is the ideal host for x-ray phosphors because it produces the densest known white material, lutetium tantalate (LuTaO4).Lutetium is the last member of the rare earth series. Lutetium is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra-high purity); metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder. Unlike most rare earths it lacks a magnetic moment. It also has the smallest metallic radius of any rare earth.