Selenium (Se)
"The Moonbeam, a hero whose power grows in the light, used in the 'electric eye' of photocopiers."
A memorable persona to anchor Se in your mind.
4.81
Grams per cm³
220.8
Celsius (°C)
190
Radius (pm)
Daily Life Link
Selenium is found in the blue-tinted glass on some buildings.
Discovery & History
Year Discovered
1817
Discovered By
Jöns Jacob Berzelius
Origin of Name
"The name is derived from ''selene'', the Greek name for the Moon."
Technical Properties
Atomic Mass
78.971 u
Standard State
solid
Boiling Point
685°C
Electron Configuration
[Ar] 3d104s24p4
1st Ionization Energy
9.752 eV
Electron Affinity
N/A
Oxidation States
"Selenium is a gray metalloid that conducts electricity when light shines on it."
Did You Know?
It has the unusual property of photoconductivity, meaning it conducts electricity better when light is shining on it. This property was used in early photocopiers.
It was named after Selene, the Greek goddess of the Moon, because it was always found in nature associated with tellurium (named after Tellus, the Roman goddess of the Earth).
While toxic in large amounts, selenium is an essential trace nutrient for humans and animals, acting as an important antioxidant.
Eating too much selenium can lead to a condition called selenosis, with symptoms that include garlic-scented breath and hair loss.