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Si
14
P
15
S
16
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32
As
33
Se
34
Sn
50
Sb
51
Te
52

 

Periodic table

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Arsen

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Arsenic

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Arsenic

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Arsen

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Arsenico

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Arsénico

 

As
As
Arsenum

PERIODIC TABLE OF THE ELEMENTS

ARSENIC

NITROGEN GROUP

 

Atomic number:33

Group numbers:15

Period:4

Electronic configuration:[Ar] 3d10 4s2 4p3

Formal oxidation number:-3 +3 +5

Electronegativities:2.18

Atomic radius / pm:124.5

Relative atomic mass:74.92160 ± 0.00002

 

Arsenic was discovered by Albertus Magnus (DE) in 1250. The origin of the name comes from the Greek word arsenikon meaning yellow orpiment. It is a steel-grey, brittle semi-metal that resists water, acids and alkalis. It tarnishes in air, burns in oxygen and is highly toxic by inhalation or ingestion. Arsenic is found in mispickel (arsenopyrite). Many of its compounds are deadly poison and used as weed killer and rat poison. Some compounds, called arsenides, are used in the manufacture of paints, wallpapers and ceramics. It is also used in semiconductors

PHYSICAL PROPERTIES

Density / g dm-3:5780 (alpha, 293 K)

 4700 (beta, 293 K)

Molar volume / cm3mol-1:12.96 (alpha, 293 K)

 15.94 (beta, 293 K)

Electrical resistivity / μΩcm:33.3 (20 °C)

THERMAL PROPERTIES

Thermal conductivity / W m-1K-1:50

Melting point / °C:817

Boiling point / °C:614

Heat of fusion / kJ mol-1:27.7

Heat of vaporization / kJ mol-1:31.9

Heat of atomization / kJ mol-1:301.42

IONIZATION ENERGIES

First ionization energy / kJ mol-1:944.46

Second ionization energy / kJ mol-1:1797.82

Third ionization energy / kJ mol-1:2735.48

ABUNDANCE OF ELEMENTS

in the atmosphere / ppm:-

in the Earth's crust / ppm:1

in the oceans / ppm:0.003

CRYSTALLOGRAPHIC DATA

rhombohedral

Crystal structure:

rhombohedral

Unit-cell dimensions / pm:

a=413.18, α=54°10'

Space group:

R3m

ISOTOPES

IsotopeRelative atomic massMass percent (%)
75As74.921596(2)100

REDUCTION POTENTIALS

Balanced half-reaction Eo / V
H3AsO4 + 3H+ + 2e- = AsO+ + 3H2O+0.55
H3AsO4 + 2H+ + 2e- = H3AsO3 + H2O+0.559
H3AsO4 + 2H+ + 2e- = H3AsO3 + H2O+0.577 (1 mol dm-3 HCl)
H3AsO4 + 2H+ + 2e- = H3AsO3 + H2O+0.577 (1 mol dm-3 HClO4)
H2AsO4- + 3H+ + 2e- = H3AsO3 + H2O+0.666
HAsO42- + 4H+ + 2e- = H3AsO3 + H2O+0.881
HAsO42- + 3H+ + 2e- = H2AsO3- + H2O+0.609
AsO43- + 3H2O + 2e- = H2AsO3- + 4OH-- 0.67
2H3AsO4 + 4H+ + 4e- = As2O3(s) + 5H2O+0.58
2H2AsO4- + 6H+ + 4e- = As2O3(s) + 5H2O+0.687
2HAsO42- + 8H+ + 4e- = As2O3(s) + 5H2O+0.901
2AsO43- + 10H+ + 4e- = As2O3(s) + 5H2O+1.27
AsO43- + 8H+ + 5e- = As(s) + 4H2O+0.648
As2O3(s) + 6H+ + 6e- = 2As(s) + 3H2O+0.234
AsO+ + 2H+ + 3e- = As(s) + H2O+0.254
H3AsO3 + 3H+ + 3e- = As(s) + 3H2O+0.248
H2AsO3- + 4H+ + 3e- = As(s) + 3H2O+0.429
H2AsO3- + H2O + 3e- = As(s) + 4OH-- 0.68
As(s) + 3H+ + 3e- = AsH3(g)- 0.608

 

32 Germanium <=
33 Arsenic
 => 34 Selenium