The Element Iodine

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Atomic Number: 53

Atomic Weight: 126.90447

Melting Point: 386.85ºK (113.7ºC or 236.7ºF)

Boiling Point: 457.55ºK (184.4ºC or 364.0ºF)

Density: 4.93 grams per cubic centimeter

Phase At Room Temperature: Solid

Element Classification: Non-Metal

Period Number : 5

Group Number : 17

Group Name : Halogen

History and uses

Iodine was discovered by the French chemist Barnard Courtois in 1811. Courtois was extracting sodium and potassium compounds from seaweed ash. Once these compounds were removed, he added sulfuric acid to further process the ash. He accidentally added to much acid and a violet colored cloud erupted from the mass. The gas condensed on metal objects in the room, creating solid Iodine. Today Iodine is chiefly obtained from deposits of sodium iodate and sodium periodate in Chile and Bolivia.

Trace amounts of iodine are required by the human body. Iodine is part of thyroxin a hormone produced by the thyroid gland that controls the bodys rate of physical and mental developement. A lack of Iodine can also cause a golter a swelling of the thyroid gland. Iodine is added to salt to prevent these diseases.

Iodine is used as a test for starch and turns a deep blue when it comes in contact with it. Potassium iodide is used to make photographic film and when mixed with iodine in alcohol as an antiseptic for external wounds. A radioactive isotope of iodine, iodine-131, is used to treat some diseases of the thyroid gland.

Care should be taken in handling and using Iodine. It can burn the skin and damage the eyes and mucous membranes. Pure Iodine is poisonous if ingested.


Estimated crustal abundace : 4.5x10^-1 milligrams per kilogram

Estimated oceanic abundance : 6x10^-2 milligrams per liter

Number of stable isotopes : 1

Ionization energy : 10.451 eV

Oxidation States: +7 +5 +1 -1