Selenium (Se) 


History/Background Info: Selenium was discovered in 1817 by Jöns Jakob Berzelius, who found the element associated with Tellurium (named for the Earth).
It was discovered as a byproduct of sulfuric acid production. The byproduct was found to be toxic to humans that were working in the chemical industry. However, Selenium is an important veterinary toxin.
Origin of name: The name Selenium is Greek, coming from the Greek word for moon, which is selene.
Name of Discoverer and How: The discoverer was Jöns Jacob Berzelius. He discovered the element when he noticed that something was contaminating the sulfuric acid that was produced at a nearby factory in Sweden.

When, Where, and How: Selenium  was discovered in Sweden in 1817 by Jöns Jacob Berzelius.  Jöns noticed that something was infecting the sulfuric acid being made at a factory in Sweden. Berzelius originally thought that the element was Tellurium, but eventually came to the conclusion that it was an element that had yet to be discovered.

Three uses: There are many different and unique uses for Selenium. One use is for items that react to light, such as cameras and copy machines. Selenium is useful for items that respond to light because Selenium's resistance to electricity is dependent on how much light is reflected on it. If there is more light, than the selenium will be a greater conductor of electricity.

A second use of Selenium is in solar cells.  

A third use of Selenium is component in dandruff control shampoo.

Natural or synthetic: Selenium is a naturally occurring element, but it is very rare.

Where can it be found:  It is found in a couple materials, two of which are crooksite and clausthalite.  In the past, it was gathered from the dust left over after processing copper ores, but recently electrolytic copper refineries provide us with the most Selenium.

Is it Radioactive: Selenium is not considered a radioactive element.

 Selenium Isotopes:

Nominal Mass

Accurate Mass

% Natural Abundance

Chemical Form

74 Se

73.9224746 (16)

0.89 (4)


76 Se

75.9192120 (16)

9.37 (29)


77 Se

76.9199125 (16)

7.63 (16)



77.9173076 (16)

23.77 (28)


80 Se

79.9165196 (19)

49.61 (41)


82 Se

81.9166978 (23)

8.73 (22)


Hazards/ Safety Issues:  Selenium is nontoxic in small amounts and is necessary for proper nutrition, however, Selenium compounds can be very toxic.  Some soils have large enough amounts of Selenium that can cause environmental damage.

Description of element: There are several attributes to Selenium.  Three of those attributes are a gray crystalline material called metallic selenium, a red crystalline material, and a red amorphous powder.  Selenium also has similar physical properties as Sulfur and Tellurium.

Properties of element:The properties of Selenium are photovoltaic and photoconductive properties.  Photovoltaic means that light is directly converted to electricity and photoconductive is when the more light there is, the less electrical resistance there is.

Table with Element Information:  

Name of Element


Element's Symbol


Atomic number (z)


Atomic mass (A)


Nuclear notation




Melting point


Boiling point



4.79 g/cm-3 at 20°C

Atomic Radius


First ionization energy

940,7 kJ/mol -1

Specific heat

0.32 J/gK

Electron configuration

[Ar] 4s2 3d10 4p4

Section of the Periodic Table

To the right of the periodic steps



Major oxidation states


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