Silicon is a Block P, Group 14, Period 3 element. The number of electrons in each of Silicon's shells is 2, 8, 4 and its electronic configuration is [Ne] 3s² 3p². In its elemental form silicon's CAS number is 7440-21-3. The silicon atom has a radius of 117.6.pm and it's Van der Waals radius is 210.pm. Silicon is not toxic but can cause chronic respiratory problems if inhaled as a fine silica or silicate dust. Asbestos silicates are carcinogenic. Silicon is one of man's most useful elements. It makes up 25.7% of the earth's crust, by weight, and is the second most abundant element, being exceeded only by oxygen. The Czochralski process is commonly used to produce single crystals of silicon used for solid-state or semiconductor devices. Silica, as sand, is a principal ingredient of glass, one of the most inexpensive of materials with excellent mechanical, optical, thermal, and electrical properties. Silicon is available as metal and compounds with purities from 99% to 99.9999% (ACS grade to ultra-high purity); metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder. Ultra high purity silicon can be doped with boron, gallium, phosphorus , or arsenic to produce silicon for use in transistors, solar cells, rectifiers, and other solid-state devices which are used extensively in the electronics and space-age industries. Hydrogenated amorphous silicon has shown promise in producing economical cells for converting solar energy into electricity. Silcones are important products of silicon. They range from liquids to hard, glasslike solids with many useful properties. Silicon was first discovered by Jons Berzelius in 1823. The name Silicon originates from the Latin word "silex" which means flint or hard stone. See Silicon research below.