Iodine [I] (CAS-ID: 7553-56-2) locate me
An: 53 N: 74 Am: 126.90447 (3)
Group No: 17  Group Name: Halogen
Block: p-block  Period: 5
State: solid at 298 K
Colour: Violet-dark grey, lustrous Classification: Non-metallic
Boiling Point: 457.4K (184.3'C)
Melting Point: 386.85K (113.7'C)
Density: 4.933g/cm3
Shell Structure diagram | Atomic Radius diagram
Isotopes | More Info
Discovery Information
Who: Bernard Courtois
When: 1804
Where: France
Name Origin
Greek: iodes (violet).
Sources
Occurs on land and in the sea in sodium and potassium compounds. Although the element is actually quite rare, kelp and certain other plants have the ability to concentrate iodine, which helps introduce the element into the food chain as well as keeping its cost down.
Uses
Required in small amounts by humans. Once used as an antiseptic, but no longer due to its poisonous nature. Silver iodide (AgI) is used in photography. Tungsten iodide is used to stabilise the filaments in light bulbs. Iodine-131 is used as a tracer in medicine.
Potassium iodide (KI tablets, or "SSKI" = "Super-Saturated KI" liquid drops) can be given to people in a nuclear disaster area when fission has taken place, to flush out the radioactive iodine-131 fission product. The half-life of iodine-131 is only eight days, so the treatment would need to continue only a couple of weeks. In cases of leakage of certain nuclear materials without fission, or certain types of dirty bomb made with other than radioiodine, this precaution would be of no avail.
Tungsten iodide (WI) is used to stabilize the filaments in light bulbs.
Iodine-123 and iodine-125 are used in medicine as tracers for imaging and evaluating the function of the thyroid.
Iodine-131 is used in medicine for treatment of thyroid cancer and Grave's disease.
Notes
It is an essential trace element; the thyroid hormones, thyroxine and triiodothyronine contain iodine.
Direct contact with skin can cause lesions, so it should be handled with care. Iodine vapour is very irritating to the eye and to mucous membranes.
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