The periodic table/Selenium

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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:

Chile
USA
Canada

Top 3 countries for production:

Japan
Germany, Belgium

Oxidation States and Isotopes

Common oxidation states: 6, 4, -2

Isotopes

Isotope	Atomic mass	Abundance (%)	Half life	Mode of decay
⁷⁴Se	73.922	0.89	> 5.5 x 10¹⁸ years	EC-EC
⁷⁶Se	75.919	9.37
⁷⁷Se	76.92	7.63
⁷⁸Se	77.917	23.77
⁸⁰Se	79.917	49.61
⁸²Se	81.917	8.73	> 9.5 x 10¹⁹ years	β-β-

Pressure and Temperature Data

Molar heat capacity: 25.363 J mol^-1 K^-1