Selenium Allotropes and Physical Properties

Selenium can exist in multiple allotropes that are essentially different molecular forms of an element with varying physical properties. For example, one allotrope of selenium can be seen as an amphorous (“without crystalline shape”) red powder.  Selenium also takes a crystalline hexagonal structure, forming a metallic gray allotrope which is known to be stable.  The most thermodynamically stable allotrope of selenium is trigonal selenium and also appears as a gray. Most selenium is recovered from the electrolytic copper refining process. This is usually in the form of the red allotrope.

Selenium is mostly noted for its important chemical properties, especially those dealing with electricity. Unlike sulfur, selenium is a semiconductor, meaning that it conducts some electricity, but not as well as conductors. Selenium is a photoconductor, which means it has the ability to change light energy into electrical energy. Not only is selenium able to convert light energy into electrical energy, but it also displays the property of photoconductivity.  Photoconductivity is the idea that the electrical conductivity of selenium increases due to the presence of light or in other words, it becomes a better photoconductor as light intensity increases.