The periodic table/Selenium

Discovery
Selenium was discovered by Jöns Jacob Berzelius in Stockholm, Sweden, in 1817. The name is derived from 'selene', the Greek name for the Moon.

Quick Facts
Name: Selenium

Symbol: Se

Mass: 78.963

Atomic Number: 34

Electron Configuration: [Ar] 3d10 4s2 4p4

Classification: non-metal

CAS Number: 7782-49-2

Appearance: Either as a silvery semi-metal or as a red powder

Discovery in: 1817

Key Isotopes: 80Se

Allotropes: Red Se, Black Se, Grey Se

Density: 4.79 g/L

Crystal Structure: hexagonal

Melting Point: 220.8 °C

Boiling Point: 685 °C

Uses
Selenium has both a photovoltaic action (converts light to electricity) and a photoconductive action (electrical resistance decreases with increased illumination). Selenium is therefore useful in photocells and solar cells. It can also convert a.c. electricity to d.c. electricity, so is extensively used in rectifiers. It is used by the glass industry, and to make stainless steel. It is also used in photocopiers.

Selenium is an essential trace element for some species, including humans, and our bodies contain about 14 milligrams. However, it is toxic in excess. It is carcinogenic and teratogenic.

Atomic Data
Atomic radius: 1.900 Å

Covalent radius: 1.18 Å

Electronegativity: 2.550

Electron affinity: 194.997 kJ mol-1

Ionisation energies

First: 940.961 kJ mol-1

Second: 2044.523 kJ mol-1

Third: 2973.714 kJ mol-1

Fourth: 4143.559 kJ mol-1

Fifth: 6589.943 kJ mol-1

Sixth: 7882.846 kJ mol-1

Seventh: 14993.809 kJ mol-1

Supply Risk
Scarcity factor: 4.5 (low risk)

Crustal abundance: 0.13 ppm

Reserve base distribution: 23.3%

Production concentration: 34.8%

Top 3 countries for mining:
 * 1) Chile
 * 2) USA
 * 3) Canada

Top 3 countries for production:
 * 1) Japan
 * 2) Germany, Belgium

Oxidation States and Isotopes
Common oxidation states: 6, 4, -2

Isotopes

Pressure and Temperature Data
Molar heat capacity: 25.363 J mol-1 K-1