iodine

Origin of Name

The name originates from the Greek word iodes, meaning “violet-colored,” which is the color of iodine’s vapor.

Occurrence

Iodine is the 64th most abundant element on Earth. It occurs widely over the Earth, butnever in the elemental form and never in high concentrations.
It occurs in seawater where some species of seaweed and kelp accumulate the elementin their cells. It is also recovered from deep brine wells found in Chile, Indonesia, Japan,and Michigan, Arkansas, and Oklahoma in the United States. The iodine is recovered fromcremated ashes of seaweed. The ashes are leached with water to remove the unwanted salts.Finally, manganese dioxide (MnO₂) is added to oxidize the iodine ions (I^1-) to produceelemental diatomic iodine (I₂). The following reaction takes place: 4I^1- + MnO₂ → MnI₂ +I₂ + 2O^2-.
Chilean saltpeter [potassium nitrate (KNO₃)] has a number of impurities, includingsodium and calcium iodate. Iodine is separated from the impurities and, after being treatedchemically, finally produces diatomic iodine. Today, iodine is mostly recovered from sodiumiodate (NaIO₃) and sodium periodate (NaIO₄) obtained from Chile and Bolivia.

History

Discovered by Courtois in 1811. Iodine, a halogen, occurs sparingly in the form of iodides in sea water from which it is assimilated by seaweeds, in Chilean saltpeter and nitrate-bearing earth, known as caliche in brines from old sea deposits, and in brackish waters from oil and salt wells. Ultrapure iodine can be obtained from the reaction of potassium iodide with copper sulfate. Several other methods of isolating the element are known. Iodine is a bluish-black, lustrous solid, volatilizing at ordinary temperatures into a blue-violet gas with an irritating odor; it forms compounds with many elements, but is less active than the other halogens, which displace it from iodides. Iodine exhibits some metallic-like properties. It dissolves readily in chloroform, carbon tetrachloride, or carbon disulfide to form beautiful purple solutions. It is only slightly soluble in water. Iodine compounds are important in organic chemistry and very useful in medicine. Forty-two isotopes and isomers are recognized. Only one stable isotope, ¹²⁷I, is found in nature. The artificial radioisotope ¹³¹I, with a half-life of 8 days, has been used in treating the thyroid gland. The most common compounds are the iodides of sodium and potassium (KI) and the iodates (KIO3). Lack of iodine is the cause of goiter. Iodides and thyroxin, which contains iodine, are used internally in medicine, and a solution of KI and iodine in alcohol is used for external wounds. Potassium iodide finds use in photography. The deep blue color with starch solution is characteristic of the free element. Care should be taken in handling and using iodine, as contact with the skin can cause lesions; iodine vapor is intensely irritating to the eyes and mucous membranes. Elemental iodine costs about 25 to 75￠/g depending on purity and quantity.

Characteristics

Iodine is the least reactive of the elements in the halogen group 17. Most people associateiodine with the dark-brown color of the tincture of iodine used as an antiseptic for minor skinabrasions and cuts. A tincture is a 50% solution of iodine in alcohol. Although it is still used,iodine is no longer the antibiotic of choice for small skin wounds. Since iodine is a poisonthat kills bacteria, iodine tablets are often used by campers and others to purify water that istaken from outdoor streams.

Uses

One of the most important uses of iodine is in the treatment of hypothyroidism, a conditionin which the thyroid gland is deficient in iodine. Iodine deficiency may lead to the formationof a goiter, wherein the gland that surrounds the windpipe in the neck becomes enlarged.There are other causes of goiter, including cancer of the thyroid gland. A deficiency of iodinecan also cause cretinism (infant hypothyroidism) in newborn babies, which can result inmental retardation unless the subject takes thyroid hormones for a lifetime. Green leafy foods,among other foods, contain iodine that when taken into the human body ends up in thethyroid gland. Some food grown in iodine-deficient soils do not contain adequate iodine forour diets. This is why iodine was added to table salt (about 0.01% potassium iodide) decadesago, specifically for people who live in regions with iodine-poor soils. The area around theGreat Lakes in the United States is one region with soil that is deficient in iodine. A healthydiet requires 90 to 150 micrograms of iodine each day that, in addition to being available iniodized salt, can be obtained from eating a balanced diet, including seafood.
The isotope iodine-131 is an artificial radioisotope of iodine used as a tracer in biomedicalresearch and as a treatment for thyroid disease. I-131 has a half-life of about eight days, whichmeans it will be eliminated from the body in several weeks.
In industry, iodine is used for dyes, antiseptics, germicides, X-ray contrast medium, foodand feed additives, pharmaceuticals, medical soaps, and photographic film emulsions and as alaboratory catalyst to either speed up or slow down chemical reactions.
Iodine is also used as a test for starch. When placed on starch (a potato for example), iodineturns the starch a dark blue color. Silver iodide is used in the manufacture of photographicfilm and paper. It is also used to “seed” clouds because of its ability to form a large numberof crystals that act as nuclei upon which moisture in the clouds condenses, forming raindropsthat may result in rain.

Uses

Dyes (aniline dyes, phthalein dyes), alkylation and condensation catalyst, iodides, iodates, antiseptics and germicides, X-ray contrast media, food and feed additive, stabilizers, photographic film, water treatment, pharmaceuticals, medicinal soaps, unsat

Uses

Iodine is a halogen element extracted from chilean nitrate-bearing earth or from seaweed. it functions by its presence in the thyroid hormones. iodine deficiency is associated with goiter. sources are potassium and cuprous iodide and potassium and calcium iodate, of which the iodate form is preferred because of better stability. it is used as a food supplement.

Preparation

If extreme purification is unnecessary, commercial iodine or iodine regenerated from wastes can, according to a method described by Plotnikow, be sublimed, first over KI and then over BaO. It is then stored in ground glass containers placed in a desiccator over P2O5.

Definition

A dark-violet volatile solid element belonging to the halogens (group 17 of the periodic table). It occurs in seawater and is concentrated by various marine organisms in the form of iodides. Significant deposits also occur in the form of iodates. The element is conveniently prepared by the oxidation of iodides in acid solution (using MnO₂). Industrial methods similarly use oxidation of iodides or reduction of iodates to iodides by sulfur(IV) oxide (sulfur dioxide) followed by oxidation, depending on the source of the raw materials. Iodine and its compounds are used in chemical synthesis, photography, pharmaceuticals, and dyestuffs manufacture.
Iodine has the lowest electronegativity of the stable halogens and consequently is the least reactive. It combines only slowly with hydrogen to form hydroiodic acid, HI. Iodine also combines directly with many electropositive elements, but does so much more slowly than does bromine or chlorine. Because of the larger size of the iodine ion and the consequent low lattice energies, the iodides are generally more soluble than related bromides or chlorides. As with the other halides, iodides of Ag(I), Cu(I), Hg(I), and Pb(II) are insoluble unless complexing ions are present.
Iodine also forms a range of covalent iodides with the metalloids and non-metallic elements (this includes a vast range of organic iodides) but these are generally less thermodynamically stable and are more readily hydrolyzed than chlorine or bromine analogs.

Definition

Nonmetallic halogen element of atomic number 53; group VIIA of the periodic table; the least reactive of the halogens, aw 126.9045; valences = 1,3,5,7; no stable isotopes but many artificial radioactive isotopes.

Definition

Symbol I. A dark violet nonmetallic element belonging to group 17 of the periodic table; a.n. 53; r.a.m. 126.9045;r.d. 4.94; m.p. 113.5°C; b.p. 184.35°C.The element is insoluble in water but soluble in ethanol and other organic solvents. When heated it gives a violet vapour that sublimes. Iodine is required as a trace element by living organisms;in animals it is concentrated in the thyroid gland as a constituent of thyroid hormones. The element is present in sea water and was formerly extracted from seaweed. It is now obtained from oil-well brines (displacement by chlorine). There is one stable isotope, iodine-127, and fourteen radioactive isotopes. It is used in medicine as a mild antiseptic(dissolved in ethanol as tincture of iodine),and in the manufacture of iodine compounds. Chemically, it is less reactive than the other halogens and the most electropositive (metallic)halogen. In solution it can bedetermined by titration using thiosulphate solution:
I₂ + 25₂O₃^2-→ 2I^- + S_uO₆^2-.
The molecule forms an intense bluecomplex with starch, which is consequentlyused as an indicator. It was discovered in 1812 by Courtois.

Hazard

Toxic by ingestion and inhalation, strong irritant to eyes and skin. Questionable carcinogen.

Hazard

less than pure form, it can damage the skin, eyes, and mucous membranes. Both the elementalform and its compounds (gases, liquids, or solids) are toxic if inhaled or ingested. Even indiluted form (e.g., a tincture of iodine to treat minor skin wounds), it should be used withcare.
Although a poison in high concentrations, iodine is required as a trace element in our dietsto prevent thyroid problems and mental retardation in the very young.

Industrial uses

Iodine is a purplish-black, crystalline, poisonouselementary solid, chemical symbol I, bestknown for its use as a strong antiseptic in medicine,but also used in many chemical compoundsand war gases. In tablet form it is usedfor sterilizing drinking water, and has less odorand taste than chlorine for this purpose. It isalso used in cattle feeds. Although poisonousin quantity, iodine is essential to proper cellgrowth in the human body, and is found in everycell in a normal body, with larger concentrationin the thyroid gland.
A wide range of compounds are made forelectronic and chemical uses. Iodine is also achemical reagent, used for reducing vanadiumpentoxide and zirconium oxide into highpuritymetals.