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

 

Periodic table

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Selen

en  English

Selenium

fr  French

Sélénium

hr  Croatian

Selenij

it  Italian

Selenio

es  Spanish

Selenio

 

Se
Se
Selenum

PERIODIC TABLE OF THE ELEMENTS

SELENIUM

CHALCOGENS ELEMENT

 

Atomic number:34

Group numbers:16

Period:4

Electronic configuration:[Ar] 3d10 4s2 4p4

Formal oxidation number:-2 +4 +6

Electronegativities:2.55

Atomic radius / pm:116

Relative atomic mass:78.96 ± 0.03

 

Selenium was discovered by Jöns Jacob Berzelius (SE) in 1817. The origin of the name comes from the Greek word selene meaning moon. It is a soft metalloid similar to sulfur, unaffected by water and soluble in alkalis and nitric acid. The colour ranges from grey metallic to red glassy. Selenium burns in air and is toxic by inhalation or ingestion. Also it conducts electricity when struck by light. Selenium is obtained from lead, copper and nickel refining. 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.

PHYSICAL PROPERTIES

Density / g dm-3:4790 (grey, 293 K)

 3987 (m.p.)

Molar volume / cm3mol-1:16.48 (grey, 293 K)

 19.80 (m.p.)

Electrical resistivity / μΩcm:12 (20 °C)

THERMAL PROPERTIES

Thermal conductivity / W m-1K-1:2.04

Melting point / °C:221

Boiling point / °C:685

Heat of fusion / kJ mol-1:5.1

Heat of vaporization / kJ mol-1:90

Heat of atomization / kJ mol-1:226.4

IONIZATION ENERGIES

First ionization energy / kJ mol-1:940.97

Second ionization energy / kJ mol-1:2044.54

Third ionization energy / kJ mol-1:2973.74

ABUNDANCE OF ELEMENTS

in the atmosphere / ppm:-

in the Earth's crust / ppm:0.05

in the oceans / ppm:-

CRYSTALLOGRAPHIC DATA

hexagonal

Crystal structure:

hexagonal

Unit-cell dimensions / pm:

a=436.56, c=495.90

Space group:

P3121

ISOTOPES

IsotopeRelative atomic massMass percent (%)
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)

REDUCTION POTENTIALS

Balanced half-reaction Eo / V
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

 

33 Arsenic <=
34 Selenium
 => 35 Bromine