(From the French iode, ultimately from the Greek iodes, "violetlike") A nonmetallic chemical element, one of the halogens, consisting of grayish-black crystals that volatilize into a violet-colored vapor. It is used as an antiseptic, in pharmacology, in the manufacture of dyes, and in photography. Iodine is essential to the human diet; a lack of it cause problems with the thyroid gland. Insufficient iodine in the diet causes goiter, although this condition is now rare because table salt is dosed with iodide.

Iodine was discovered by Barnard Courtois in 1811 in Paris, France; it was isolated from treating seaweed ash with sulfuric acid while recovering sodium and potassium compounds.

Symbol: I
Atomic number: 53
Atomic weight: 126.90447
Density (at room temperature and pressure): 4.93 g/cm3
Melting point: 114°C
Boiling point: 184.4°C
Valence: -1, +1, +5, +7
Ground state electron configuration: [Kr]4d105s25p5

See also: iodine-131

Symbol: I
Atomic Number: 53
Atomic Weight: 126.9045
Boiling Point: 457.5 K
Melting Point: 386.7 K
Density at 300K: 4.93 g/cm3
Covalent radius: 1.33
Atomic radius: 1.32
Atomic volume: 25.70 cm3/mol
First ionization potental: 10.451 V
Specific heat capacity: 0.145 Jg-1K-1
Thermal conductivity: 0.449 Wm-1K-1
Electrical conductivity: 10-5Ω-1m-1
Heat of fusion: 7.76 kJ/mol
Heat of vaporization: 20.9 kJ/mol
Electronegativity: 2.66 (Pauling's)

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Iodine's primary importance to the human body is related to the thyroid gland, which uses it to produce thyroxine and triiodothyronine, (two hormones that control the metabolism). A diet deficient in iodine can lead to a swelling of the thyroid, known as a 'goiter'.

Taking iodine pills, (in the form of Potassium Iodide), was also recommended during times of nuclear fallout, such as after a nuclear power station accident or detonation of a nuclear bomb. There is a high concentration of several radioactive isotopes of iodine, (predominantly Iodine-131), in nuclear fallout material and the theory is that the taking of Potassium Iodide pills would saturate the thyroid gland with non-radioactive iodine to such an extent that the excess, including the radioactive material, would be expelled from the body through the kidneys.

I"o*dine (?; 104), n. [Gr. violetlike; a violet + form: cf. F. iode, iodine. The name was given from the violet color of its vapor. See Violet, Idyl.] Chem.

A nonmetallic element, of the halogen group, occurring always in combination, as in the iodides. When isolated it is in the form of dark gray metallic scales, resembling plumbago, soft but brittle, and emitting a chlorinelike odor. Symbol I. Atomic weight 126.5. If heated, iodine volatilizes in beautiful violet vapors.

Iodine was formerly obtained from the ashes of seaweed (kelp or varec), but is now also extracted from certain natural brines. In the free state, iodine, even in very minute quantities, colors starch blue. Iodine and its compounds are largely used in medicine (as in liniments, antisyphilitics, etc.), in photography, in the preparation of aniline dyes, and as an indicator in titration.

Iodine green, an artificial green dyestuff, consisting of an iodine derivative of rosaniline; -- called also night green. -- Iodine scarlet, a pigment of an intense scarlet color, consisting of mercuric iodide. -- Iodine yellow, a brilliant yellow pigment, consisting of plumbic iodide.


© Webster 1913.

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