Selenium
Definition and meaning of Selenium in chemistry.
Selenium is a nonmetal chemical element with the symbol Se and atomic number 34. It is a relatively rare element in the Earth's crust that notably exhibits both photovoltaic and photoconductive properties. Because of these characteristics, it has the unique ability to convert light directly into electricity and decrease its electrical resistance when illuminated.
In more detail
Selenium is located in group 16 of the periodic table, placing it directly below sulfur and above tellurium, where it shares many chemical characteristics with both. It exists in several distinct allotropic forms, with the most stable and common being a dense purplish-gray semiconductor network. In nature, it rarely occurs in its pure elemental state and is predominantly found intertwined with sulfide ores such as pyrite and chalcopyrite. Chemically, it reacts vigorously with highly reactive metals to form various selenides, and it interacts with oxygen to produce oxides like selenium dioxide. Although acute exposure to concentrated selenium compounds is highly toxic, trace amounts are an essential micronutrient for cellular function in humans and many other animals.
Key facts
| Field | General Chemistry |
|---|---|
| Symbol | Se |
| Atomic number | 34 |
| Atomic mass | 78.971 u |
| Category | Nonmetal |
| State at room temperature | Solid |
| Melting point | 221 degrees Celsius |
| Boiling point | 685 degrees Celsius |
| Discoverer | Jons Jakob Berzelius (1817) |
The primary commercial application of selenium is in the glass manufacturing industry, where it is used to remove green tints caused by iron impurities and to produce striking ruby red glasses and protective enamels.
Frequently asked questions
Is selenium dangerous to humans?
Yes, while trace amounts are an essential nutrient for thyroid function and antioxidant enzymes, acute or chronic exposure to high levels of selenium compounds is highly toxic.
How is selenium produced industrially?
It is primarily obtained as a byproduct of electrolytic copper refining, where it is extracted from the anode mud that accumulates during the purification process.