Selenium is the chemical element of atomic number 34. Its symbol is Se. It is a non-metal chemically related to sulfur and tellurium. The element is toxic to high doses but in 1957 Schwarz and Foltz established that it is an essential element in the diet, useful in the prevention of certain diseases. It exists in various allotropic forms, of which a gray-like and metal-like stable; In this form selenium has a lower electrical resistance when exposed to light, therefore it is used in photocells. In nature it is found in sulfur-containing minerals, such as pyrite.
#Se #Se34 #Selenium