Selenium

Category: non-metal Atomic number: 34 Colour: metallic grey Melting point: 221°C (430°F) Boiling point: 685°C (1,265°F) First identified: 1817

There are many elements that are both essential parts of the human diet and at the same time toxic if consumed in large doses. Selenium is one – it is crucial in the production of certain enzymes within the human body (we consume it in a wide variety of foodstuffs, including nuts and tuna). Recent clinical tests have suggested that the decline in selenium consumption (as a result of declining popularity of rich sources such as offal) is contributing to declining sperm counts in men; test subjects given a selenium supplement recorded considerably higher counts than a control group. However, if consumed in large doses, it can cause bad breath, hair loss, weakened nails, tiredness and confusion, and even fatal cirrhosis of the liver; though it is also (in the form of selenium sulphide) toxic to the scalp fungus that causes dandruff – and is used in safe doses in anti-dandruff shampoos.

Selenium was discovered by Jöns Jacob Berzelius in 1817. He investigated the chemical make-up of a reddish powder that was deposited in chambers in which sulphuric acid was being made. After initially mistaking it for tellurium (see here), he realized it must contain a new element, which he named after Selene, the goddess of the moon. (Berzelius discovered the hard way that selenium can cause bad breath, as he was affected by this himself after exposure to it!) Selenium can also take the form of a silvery, metallic substance, leading some chemists to define it as a metalloid.

Don’t Try This at Home

This traditional warning before a science demonstration is one that Jöns Jacob Berzelius preferred to ignore. Many of his ground-breaking experiments were actually carried out in the kitchen of his apartment, which was on the corner of Nybrogatan and Riddargatan in the city of Stockholm.

The main contemporary use of selenium is as an additive to glass: it can either remove a greenish tint or be used to colour the glass reddish bronze, depending on how it is added. In various compounds, it can also be used in photovoltaic cells, solar cells and photocopiers, to create pipes (allied with brass) and to make synthetic rubber tougher.