Periodic Table of the Elements
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Bottom FACULTY OF CHEMICAL TECHNOLOGY o PERIODIC TABLE OF THE ELEMENTS Bottom
  A B C D E F G H I J K L M N O P R S T U V X Z  
Periodic Table of the Elements Tableau périodique des éléments Periodni sustav elemenata Tavola periodica degli elementi Das Periodensystem der Elemente
Selenium Sélénium Selenij Selenio Selen

 
Atomic number: 34
Group numbers: 16
Period: 4
 
Discovery date: 1817
Se

Selenum
NEIGHBOURS
15
P
 16
S
 17
Cl
33
As
 34
Se
 35
Br
51
Sb
 52
Te
 53
I


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Selenium was discovered by Jöns Jakob Berzelius (Sweden) in 1817. The origin of the name comes from the Greek word selene meaning moon. It is soft metalloid similar to sulfur. Ranges from grey metallic to red glassy appearance. Unaffected by water. Soluble in alkalis and nitric acid. Burns in air. Toxic by inhalation or ingestion.
Bottom CHALCOGENS ELEMENT Top

Relative atomic mass: 78.96(3) Electronic configuration: [Ar] 3d10 4s2 4p4
Formal oxidation number: -2 +4 +6 Electronegativities: 2.55
Thermal conductivity: 2.04 W m-1 K-1 Electrical resistivity (20 °C): 12 μΩcm
Atomic radius: 116 pm Standard state (20 °C): solid
Density (g dm-3): 4790 (grey, 293 K)
3987 (m.p.)		 Molar volume (cm3 mol-1): 16.48 (grey, 293 K)
19.80 (m.p.)


Bottom THERMAL PROPERTIES Top

Melting point: 221 °C Heat of fusion: 5.1 kJ mol-1
Boiling point: 685 °C Heat of vaporization: 90 kJ mol-1
Critical temperature: 1484 °C Heat of atomization: 226.4 kJ mol-1


Bottom IONIZATION ENERGIES AND ABUNDANCE Top

1st ionization energy: 940.97 kJ mol-1 Abundance of element (air): - ppm
2nd ionization energy: 2044.54 kJ mol-1 Abundance of element (Earth's crust): 0.05 ppm
3rd ionization energy: 2973.74 kJ mol-1 Abundance of element (oceans): - ppm


Bottom ISOTOPES Top

Isotopes Relative atomic mass Abundance (%)
74Se73.922477(2)0.89(2)
76Se75.919214(2)9.36(11)
77Se76.919915(2)7.63(6)
78Se77.917310(2)23.78(9)
80Se79.916522(2)49.61(10)
82Se81.916700(2)8.73(6)


Bottom MINERALS AND USES Top

Selenium is obtained from lead, copper and nickel refining. Conducts electricity when struck by light. Light causes it to conduct electricity more easily. It is used in photoelectric cells, TV cameras, xerography machines and as a semiconductor in solar batteries and rectifiers. Also colours glass red. The price of 99.999 % pure amorphous selenium shot is 301.80 € for 1000 g.

Bottom REDUCTION POTENTIALS Top

Balanced half-reaction   Eo / V      Annotation
SeO42- + 2H+ + 2e- = SeO32- + H2O +0.880  
SeO42- + H2O + 2e- = SeO32- + 2OH- +0.05  
SeO42- + 3H+ + 2e- = HSeO3- + H2O +1.075  
SeO42- + 4H+ + 2e- = H2SeO3 + H2O +1.15  
HSeO4- + 3H+ + 2e- = H2SeO3 + H2O +1.090  
SeO32- + 6H+ + 4e- = Se(s) + 3H2O +0.875  
HSeO3- + 5H+ + 4e- = Se(s) + 3H2O +0.778  
H2SeO3 + 4H+ + 4e- = Se(s) + 3H2O +0.740  
SeO32- + 6H+ + 6e- = Se2- + 3H2O +0.276  
SeO32- + 7H+ + 6e- = HSe- + 3H2O +0.414  
HSeO3- + 6H+ + 6e- = HSe- + 3H2O +0.349  
HSeO3- + 7H+ + 6e- = H2Se(g) + 3H2O +0.386  
H2SeO3 + 6H+ + 6e- = H2Se(g) + 3H2O +0.360  
Se(s) + 2H+ + 2e- = H2Se(g) - 0.369  
Se(s) + 2e- = Se2- - 0.924  
Se(s) + H+ + 2e- = HSe- - 0.510  
Se(s) + 2H+ + 2e- = H2Se(g) - 0.399  

 

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