Selenium Selenium Selenium is a chemical element with symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, and also has similarities to arsenic. It rarely occurs in its elemental state or as pure ore compounds in the Earth's crust. Selenium (from Ancient Greek (selḗnē) "Moon") was discovered in 1817 by Jöns Jacob Berzelius, who noted the similarity of the new element to the previously discovered tellurium (named for the Earth). Selenium is found in , where it
Binary compounds of silicon practical applications), formed by annealing an amorphous Si-P alloy. The arsenic–silicon phase diagram measured at 40 Bar has two phases: SiAs and SiAs. The antimony–silicon system comprises a single eutectic close to the melting point of Sb. The bismuth system is a monotectic. In group 16 silicon dioxide is a very common compound that widely occurs as sand or quartz. SiO is tetrahedral with each silicon atom surrounded by 4 oxygen atoms. Numerous crystalline forms exist with the tetrahedra linked to form a polymeric chain. Examples are tridymite and cristobalite. A less common oxide is silicon monoxide that can be