The Element Iodine
Atomic Number: 53
Atomic Weight: 126.90447
Melting Point: 386.85 K (113.7°C or 236.7°F)
Boiling Point: 457.55 K (184.4°C or 364.0°F)
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
What's in a name? From the Greek word for violet, iodes.
Say what? Iodine is pronounced as EYE-eh-dine or as EYE-eh-din.
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 (H2SO4) to further process the ash. He accidentally added too 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 (NaIO3) and sodium periodate (NaIO4) 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 body's rate of physical and mental development. A lack of iodine can also cause a goiter, a swelling of the thyroid gland. Iodine is added to salt (iodized 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 (KI) 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 Abundance: 4.5×10-1 milligrams per kilogram
Estimated Oceanic Abundance: 6×10-2 milligrams per liter
Number of Stable Isotopes: 1 (View all isotope data)
Ionization Energy: 10.451 eV
Oxidation States: +7, +5, +1, -1
3s2 3p6 3d10
4s2 4p6 4d10