Tungsten is a Block D, Group 6, Period 6 element. The electronic configuration is [Xe] 4f¹⁴ 5d⁴ 6s². In its elemental form tungsten's CAS number is 7440-33-7. The tungsten atom has a radius of 137.pm and it's Van der Waals radius is 200.pm. Tungsten has the highest melting point of all the metallic elements and because of this has its first significant commercial application as the filament in incandescent light bulbs and fluorescent light bulbs. Tungsten 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. Later it was used in the first television tubes. The first imaging equipment involved X-ray bombardment of a tungsten target. Tungsten expands at nearly the same rate as borosilicate glass and is used to make metal to glass seals. It is the primary metal in heating elements for electric furnaces and in any components where high pressure/temperature environments are expected, such as aerospace and engine systems. Tungsten was first discovered by Fausto and Juan Jose de Elhuyar in 1783.