Iodine

Iodine

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This article has been reviewed by the following Topic Editor: Sidney Draggan

Background

Previous Element: Tellurium

Next Element: Xenon
53

I

126.91
Physical Properties
Color bluish-black
Phase at Room Temp. solid
Density (g/cm3) 4.94
Hardness (Mohs) ---
Melting Point (K) 386.7
Boiling Point (K) 458.4
Heat of Fusion (kJ/mol) 15.3
Heat of Vaporization (kJ/mol) 42
Heat of Atomization (kJ/mol) 107
Thermal Conductivity (J/m sec K) 0.45
Electrical Conductivity (1/mohm cm) 0
Source Brines, Chilean nitrate (misc)
Atomic Properties
Electron Configuration [Kr]4d105s25p5
Number of Isotopes 1
Electron Affinity (kJ/mol) 295.16
First Ionization Energy (kJ/mol) 1008.4
Second Ionization Energy (kJ/mol) 1845.8
Third Ionization Energy (kJ/mol) 3184
Electronegativity 2.66
Polarizability (Å3) 5
Atomic Weight 126.91
Atomic Volume (cm3/mol) 25.7
Ionic Radius2- (pm) ---
Ionic Radius1- (pm) 206
Atomic Radius (pm) 133
Ionic Radius1+ (pm) ---
Ionic Radius2+ (pm) ---
Ionic Radius3+ (pm) ---
Common Oxidation Numbers -1,+1,+3,+5,+7
Other Oxid. Numbers ---
Abundance
In Earth's Crust (mg/kg) 4.5×10-1
In Earth's Ocean (mg/L) 6×10-2
In Human Body (%) .00002%
Regulatory / Health
CAS Number 7553-56-2
OSHA Permissible Exposure Limit (PEL) 10.38mg/m3
Ceiling: 0.1 ppm
OSHA PEL Vacated 1989 Ceiling: 0.1 ppm
NIOSH Recommended Exposure Limit (REL) Ceiling: 0.1 ppm
IDLH: 2 ppm
Sources:
University of Wisconsin General Chemistry
Mineral Information Institute
Jefferson Accelerator Laboratory
EnvironmentalChemistry.com
 

Liquid iodine. (Source:<a href='http://www.cvmbs.colostate.edu/ilm/proinfo/calving/notes/postcalvingcare.htm' class='external text' title='http://www.cvmbs.colostate.edu/ilm/proinfo/calving/notes/postcalvingcare.htm' rel='nofollow'>Colorado State University</a>) Liquid iodine. (Source:Colorado State University)

Iodine is a shiny blue-black solid element. Its atomic number is 53 and it is grouped with other elements that, together, are called the halogens, although iodine is the least reactive of the elements in this group. The French scientist Bernard Courtois discovered it in 1811 when he treated seaweed ash with sulfuric acid.

When iodine is heated, it sublimates, that is, it goes from a solid to a vapor without going through the liquid phase.

Iodine is essential to many life forms, including humans, and is found in thyroid hormones. A lack of iodine in the body will result in a condition known as a goiter where the thyroid gland in the neck becomes enlarged. In order to assure an adequate amount of iodine in the diet, table salt is iodized. This approach has greatly reduced the incidence of goiter since so many people regularly use table salt.

Name

Iodine was named from the Greek word iodes which means violet in reference to its color.

Sources

Iodine is primarily retrieved from underground brines (water with many dissolved salts and ions) that are associated with natural gas and oil deposits. It is also retrieved as a by-product with nitrate deposits in caliche deposits. Chile’s production of iodine is from this source. Seawater contains 0.05 ppm (parts per million) iodine which means that there are approximately 76 billion pounds of iodine in the world’s oceans. Iodine was first discovered in seaweed. Dried seaweeds, particularly those of the Liminaria family, contain as much as 0.45% iodine. Seaweed was a major source of iodine before 1959. Seaweed is a significant source for iodine in the diets of many people around the world. Production from caliche is presently the most economical of the options listed here.

Chile is the world’s leading iodine producing nation. Japan is second. Russia also produces significant amounts of elemental iodine.

Uses

Iodine is used in a number of chemical and biological applications. Silver iodide is used in photography. Iodide is used as a disinfectant. Iodine compounds are used as a catalyst. It is used as a supplement in animal feeds. Potassium iodine is included in table salt as a simple way to assure adequate iodine in the human diet. It is also used to make inks and colorants.

Substitutes and Alternative Sources

For many of iodine’s uses, there is no adequate substitute. For example, other substances cannot replace its applications in pharmaceuticals, and human and animal nutrition. There are some chemical applications for iodine that can be accomplished using other chemicals. For example, bromine and chlorine can be used in place of iodine for ink and colorant purposes, and for disinfectant purposes.

Further Reading

Citation

Mineral Information Institute (Lead Author);Sidney Draggan (Topic Editor) "Iodine". In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth December 15, 2007; Last revised Date August 28, 2011; Retrieved May 26, 2012 <http://www.eoearth.org/article/Iodine>

The Author

Mineral Information Institute The Mineral Information Institute (MII) is a national 501 (c)(3) not-for-profit organization dedicated to educating youth about the science of minerals and other natural resources, and about their importance in our every day lives. Each year MII works with interested professional and scientific associations, and various government and education agencies, to help classroom teachers develop materials that are directly usable by teachers in a variety of subjects and a multitude of grade levels. Al ... (Full Bio)

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