Iron is a Block D, Group 8, Period 4 element. The electronic configuration is [Ar] 3d⁶ 4s². In its elemental form iron's CAS number is 7439-89-6. The iron atom has a radius of 124.1.pm and it's Van der Waals radius is 200.pm. Iron is the most commonly used metal for commercial applications due to its hardness, historical availability and low cost. Once used on its own, it is now alloyed with nickel and other elements to produce steel and other high strength, non-corrosive structural metals. Iron as a metal and as its many compounds has numerous uses. It is a primary colorant in glass and ceramics. It is a catalyst. It is the basis for low grade magnets and because of its magnetic properties is used extensively in memory tape. Recent applications for Iron nanoparticles include in water treatment of carbon tetrachloride in contaminated groundwater, magnetic data storage and resonance imaging (MRI) and in certain alloy and catalyst applications. Iron can also be introduced into processes using iron foil, pellets, rod and wire by thin film Chemical Vapor Deposition (CVD) and Physical Vapor Deposition (PVD) processes including Thermal and Electron Beam (E-Beam) Evaporation, Low Temperature Organic Evaporation, Atomic Layer Deposition (ALD), Organometallic and Chemical Vapor Deposition (MOCVD) for specific applications such as fuel cells and solar energy. Iron 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. Iron was first discovered by Early Man.