Selenium , including Technical Data, Safety Data and its high purity properties, research, applications and other useful facts are discussed below. Scientific facts such as the atomic structure,ionization energy, abundance on Earth, conductivity and thermal properties are included. 

Selenium exhibits both photovoltaic action, where light is converted directly into electricity, and photoconductive action, where the electrical resistance decreases with increased illumination. These properties make selenium useful in the production of photocells and exposure meters for photographic use, as well as solar cells. Below its melting point, selenium is a p-type semiconductor and has many uses in electronic and solid-state applications. Selenium is available as metal and compounds with purities from 99% to 99.9999% (ACS grade to ultra-high purity); metals in the form offoil, sputtering target, and rod, and compounds as submicron and nanopowder.

Selenium facts, including appearance, CAS #, and molecular formula and safety data, research and properties are available for many specific states, forms and shapes on the product pages listed to the left. Elemental or metallic forms include pellets, rod, wire and granules for evaporation source material purposes. Nanoparticles and nanopowders provide ultra high surface area which nanotechnology research and recent experiments demonstrate function to create new and unique properties and benefits. 

Abundance. The following table shows the abundance of selenium and each of its naturally occurringisotopes on Earth along with the atomic mass for each isotope. Isotope Atomic Mass % Abundance on Earth Se-74 73.922477 0.89 Se-76 75.919214 9.36 Se-77 76.919915 7.63 Se-78 77.917310 23.78 Se-80 79.916522 49.61 Se-82 81.916700 8.73 The following table shows the abundance of Selenium present in the human body and in the universe scaled to parts per billion (ppb) by weight and by atom:   Typical Human Body Universe by Weight no data 0.1 ppb by Atom no data 0.001 ppb Safety Data and Biological Role. The safety data for selenium metal, nanoparticles and its compounds can vary widely depending on the form. For potential hazard information, toxicity, and road, sea and air transportation limitations, such as DOT Hazard Class, DOT Number, EU Number, NFPA Health rating and RTECS Class, please see the specific material or compound referenced in the left margin. Selenium compounds, in small amounts, have an essential biological role. Selenium may help to protect against free radical oxidants and some heavy metals, it is also said to stimulate the metabolism. Sheep grown in areas with deficient amounts of Selenium in the soil can develop "white muscle disease".  Ionization Energy. The ionization energy for selenium (the least required energy to release a single electron from the atom in it‘s ground state in the gas phase) is stated in the following table: 1st Ionization Energy 940.97 kJ mol-1 2nd Ionization Energy 2044.54 kJ mol-1 3rd Ionization Energy 2973.74 kJ mol-1 Conductivity. As to selenium‘s electrical and thermal conductivity, the electrical conductivity measured as to electrical resistivity @ 20 ?C is 12 μΩcm and its electronegativities (or its ability to draw electrons relative to other elements) is 2.55. The thermal conductivity of selenium is 2.04 W m-1 K-1.  Thermal Properties. The melting point and boiling point for selenium are stated below. The following chart sets forth the heat of fusion, heat of vaporization and heat of atomization. Heat of Fusion 5.1 kJ mol-1 Heat of Vaporization 90 kJ mol-1 Heat of Atomization 226.4 kJ mol-1

Formula	Atomic Number	Molecular Weight	Electronegativity (Pauling)	Density	Melting Point	Boiling Point	Vanderwaals radius	Ionic radius	Energy of first ionization
Se	34	78.96 g.mol -1	2.4	4.79 g.cm-3 at 20 °C	217 °C	688 °C	190.pm	0.198 nm (-2) ; 0.042 (+6)	940.97 kJ.mol-1

Oxides are available in forms including powders and dense pellets for such uses as optical coating and thin film applications. Oxides tend to be insoluble. Fluorides are another insoluble form for uses in which oxygen is undesirable such as metallurgy, chemical and physical vapor deposition and in some optical coatings. Selenium is available in soluble forms including chlorides, nitrates and acetates. These compounds are also manufactured as solutions at specified stoichiometries. 

Selenium is a Block P, Group 16, Period 4 element. The number of electrons in each of Selenium‘s shells is 2, 8, 18, 6 and its electronic configuration is [Ar] 3d104s2 4p4. In its elemental form selenium‘s CAS number is 7782-49-2. The selenium atom has a radius of 116.pm and it‘s Van der Waals radius is 190.pm. 

All elemental metals, compounds and solutions may be synthesized in ultra high purity (e.g. 99.999%) for laboratory standards, advanced electronic, thin fillm deposition using sputtering targets and evaporation materials, metallurgy and optical materials and other high technology applications. Information is provided for stable (non-radioactive) isotopes. Organo-Metallic Selenium compounds are soluble in organic or non-aqueous solvents. See Analytical Services for information on available certified chemical and physical analysis techniques including MS-ICP, X-Ray Diffraction, PSD and Surface Area (BET) analysis.