IODINE

HALOGENS ELEMENT

Atomic number:	53
Group numbers:	17
Period:	5
Electronic configuration:	[Kr] 4d¹⁰ 5s² 5p⁵
Formal oxidation number:	-1 +1 +5 +7
Electronegativities:	2.66
Atomic radius / pm:	133.1
Relative atomic mass:	126.904 47(3)

Iodine was discovered by Bernard Courtois (FR) in 1811. The origin of the name comes from the Greek word iodes meaning violet. It is a shiny, black, non-metallic solid with characteristic odour. It sublimes easily and as a gas it is violet and intensely irritating to the eyes, nose and throat. Iodine occurs on land and in the sea in sodium and potassium compounds. It is required in small amounts by humans. Iodine was once used as an antiseptic, but no longer due to its poisonous nature. The price of 99.5 % pure crystalline iodine is 140.50 € for 1000 g.

PHYSICAL PROPERTIES
Density / g dm^-3:	4930	(293 K)
Molar volume / cm³mol^-1:	25.74	(293 K)
Electrical resistivity / µΩcm:	1.3E+15	(20 °C)

THERMAL PROPERTIES
Thermal conductivity / W m^-1K^-1:	0.449
Melting point / °C:	113.7
Boiling point / °C:	184.4
Heat of fusion / kJ mol^-1:	15.27
Heat of vaporization / kJ mol^-1:	41.67
Heat of atomization / kJ mol^-1:	107.24

IONIZATION ENERGIES
First ionization energy / kJ mol^-1:	1008.40
Second ionization energy / kJ mol^-1:	1845.90
Third ionization energy / kJ mol^-1:	3184.04

ABUNDANCE OF ELEMENT
in the atmosphere / ppm:	-
in the Earth's crust / ppm:	0.5
in the oceans / ppm:	0.05

CRYSTALLOGRAPHIC DATA
Crystal structure:	base-centered orthorhombic
Unit-cell dimensions / pm:	a=726.47, b=478.57, c=979.08
Space group:	Cmca

ISOTOPES
Isotope	Relative atomic mass	Mass percent (%)
¹²⁷I	126.904468(4)	100

REDUCTION POTENTIALS
Balanced half-reaction	E^o / V
I₂(s) + 2e^- → 2I^-	+0.535
I₂(aq) + 2e^- → 2I^-	+0.615
3I₂ + 2e^- → 2I₃^-	+0.789
I₃^- + 2e^- → 3I^-	+0.536
H₅IO₆ + H⁺ + 2e^- → IO₃^- + 3H₂O	+1.601
HIO₅^2- + 3H⁺ + 2e^- → IO₃^- + 2H₂O	+1.898
HIO₅^2- + 8H⁺ + 6e^- → HIO + 4H₂O	+1.389
2HIO₅^2- + 18H⁺ + 14e^- → I₂(s) + 10H₂O	+1.384
3HIO₅^2- + 27H⁺ + 22e^- → I₃^- + 15H₂O	+1.357
HIO₅^2- + 9H⁺ + 8e^- → I^- + 5H₂O	+1.288
HIO₄ + 2H⁺ + 2e^- → HIO₃ + H₂O	+1.626
IO₄^- + 2H⁺ + 2e^- → IO₃^- + H₂O	+1.653
HIO₄ + 6H⁺ + 6e^- → HIO + 3H₂O	+1.290
IO₄^- + 7H⁺ + 6e^- → HIO + 3H₂O	+1.235
2HIO₄ + 14H⁺ + 14e^- → I₂(s) + 8H₂O	+1.300
3HIO₄ + 21H⁺ + 22e^- → I₃^- + 12H₂O	+1.276
HIO₄ + 7H⁺ + 8e^- → I^- + 4H₂O	+1.215
IO₃^- + 6H⁺ + 4e^- → I⁺ + 3H₂O	+1.155
IO₃^- + 4H⁺ + 4e^- → IO^- + 2H₂O	+0.972
2IO₃^- + 12H⁺ + 10e^- → I₂(s) + 6H₂O	+1.196
2IO₃^- + 12H⁺ + 10e^- → I₂(aq) + 6H₂O	+1.178
IO₃^- + 2Cl^- + 6H⁺ + 4e^- → ICl₂^- + 3H₂O	+1.24
2HIO₃ + 10H⁺ + 10e^- → I₂(s) + 6H₂O	+1.169
3HIO₃ + 15H⁺ + 16e^- → I₃^- + 9H₂O	+1.145
HIO₃ + 5H⁺ + 6e^- → I^- + 3H₂O	+1.078
2HIO + 2H⁺ + 2e^- → I₂(s) + 2H₂O	+1.354
2IO^- + 4H⁺ + 2e^- → I₂(s) + 2H₂O	+2.005
3HIO + 3H⁺ + 4e^- → I₃^- + 3H₂O	+1.213
3IO^- + 6H⁺ + 4e^- → I₃^- + 3H₂O	+1.701
IO^- + 2H⁺ + 2e^- → I^- + H₂O	+1.313
HIO + H⁺ + 2e^- → I^- + H₂O	+0.987
2ICl₃(s) + 6e^- → I₂(s) + 6Cl^-	+1.28
2ICl(s) + 2e^- → I₂(s) + 2Cl^-	+1.22
2ICl + 2e^- → I₂(s) + 2Cl^-	+1.19
2ICl₂^- + 2e^- → I₂(s) + 4Cl^-	+1.056
2IBr(aq) + 2e^- → I₂(s) + 2Br^-	+1.02