Chemical Element: selenium

(Modern Latin: from Greek, selene, the moon; nonmetal)

Chemical-Element Information

Symbol: Se
Atomic number: 34
Year discovered: 1817

Discovered by: Jöns Jakob Berzelius (1779-1848), a Swedish chemist, who devised chemical symbols, determined atomic weights, contributed to the atomic theory, and discovered several new elements.


  • Jöns Jacob Berzelius reported that tellurium was present in sulfuric acid from a Swedish factory, but in the following year decided that the impurity was not tellurium but another closely related element that he subsequently identified as selenium.
  • Selenium is a chemical element that is closely allied in physical and chemical properties with sulfur.
  • In 1873, Willoughby Smith discovered that crystalline selenium developed a tremendous increase in electrical conductivity when exposed to light, regaining its resistance immediately when the light was shut off.
  • This property eventually was applied in motion-picture sound tracks, television, the telegraphic transmission of photographs, and many other devices depending on light-sensitive materials.
  • Some species of plants are not only tolerant of selenium, but actually require selenium for growth and development.
  • When used as food for animals or humans, the plants are toxic, causing either chronic or fatal poisoning.
  • Selenium poisoning in horses is accompanied by loss of hair from tail and mane and by abnormal hoof growth; extreme cases produce blind staggers or even death.
  • In humans, selenium may concentrate in the lungs, liver, kidney, or spleen.
  • Occupational dermatitis is a mild form of poisoning.
  • Few cases of death have been reported.
  • Recent studies indicate arsenic as a possible inhibitor for selenium poisoning.
  • It is known that soils which are leached by abundant ground water lose some selenium and that plants grown in areas of plentiful rainfall contain less selenium, even though the soil contains the element.
  • The Colorado river, for example, carries away selenium from certain irrigated areas in the western United States.
  • Bottom deposits and growths in the Gulf of California and the Gulf of Mexico contain notable amounts of selenium.

Name in other languages:

French: sélénium

German: Selen

Italian: selenio

Spanish: selenio


Information about other elements may be seen at this Chemical Elements List.

A special unit about words that include chemo-, chem- may be seen here.