GROUP 16 NON-METAL

Selenium is found in two forms. The first is a silvery-gray, metal-like solid composed of spiral chains of selenium atoms. The second is a red, amorphous powder composed of individual rings of eight selenium atoms (Se₈) stacked on top of each other.

Selenium is an essential trace element naturally present in many foods, such as wheat, meat, nuts (in particular, Brazil nuts), and fish. It plays an important role in enzymes involved in immune mechanisms, antioxidant function, thyroid hormone metabolism, and male fertility. Selenium deficiency has reportedly promoted the incidence of multiple sclerosis, cancer, arthritis, infertility, and high blood pressure. But you run the risk of selenium poisoning if you consume an amount above the tolerable upper intake level of 400 μg (micrograms) per day. Symptoms of selenium poisoning range from “garlic breath” and hair loss to fatigue and irritability to potential cirrhosis of the liver and death.

Selenium is very similar to sulfur (directly above it on the periodic table) in that its compounds are also foul-smelling. One example is the “garlic breath” associated with consuming excessive amounts of selenium. This condition is caused by the volatile and pungent methyl selenium molecules the body produces when it tries to purge excess selenium. The element also contributes to the “aroma” of skunk scent through the molecule butyl seleno-mercaptan, C₄H₉SeH: there’s more information about skunk scent in “Sulfur, S” on page 46.

Shine a light on selenium’s metal-like form and its electrical conductivity increases a thousandfold. Devices such as solar cells, photocopiers, and photographers’ light meters utilize this quirky trait.

Selenium sulfide (approximate formula SeS₂) consists of selenium and sulfur atoms bonded to each other in closed rings. It’s used as an antifungal agent in medical shampoos to treat flaky scalp and dandruff.

Selenium produces a brilliant ruby color, known as selenium ruby, when added to cadmium sulfide glass.