Iodine
Contents
Background
| Previous Element: Tellurium Next Element: Xenon |
| |
| 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: |
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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 (Halite) 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 (Iodine) 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
- Common Minerals and Their Uses, Mineral Information Institute.
- More than 170 Mineral Photographs, Mineral Information Institute.
