Chemical Properties
Heavy, grayish-black plates or granules having a metallic luster; characteristic odor.
Readily sublimed having a violet vapor.Soluble in alcohol, carbon
disulfide, chloroform, ether, carbon tetrachloride,
glycerol, and alkaline iodide solutions; insoluble
Physical properties
Iodine in its pure state is a black solid that sublimates (changes from a solid to a gas withoutgoing through a liquid state) at room temperature. It produces a deep purple vapor that is irritatingto the eyes, nose, and throat. Iodine tends to form nonmetallic diatomic molecules (I2).It is the heaviest of the naturally occurring halogens. (Although astatine, the fifth element ingroup 17, is heavier than iodine, it is a synthetic element and does not occur in nature exceptas a very small trace.) Iodine is the least reactive of the five halogens.
Iodine’s melting point is 113.7°C, its boiling point is 184.4°C, and its density is 4.93g/cm3.
Isotopes
There are a total of 145 isotopes of iodine. Only one (I-127) is stable andaccounts for 100% of iodine’s natural abundance on Earth. All the other 146 isotopesare radioactive with half-lives ranging from a 150 nanoseconds to 1.57×10+7
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 (I1-) to produceelemental diatomic iodine (I2). The following reaction takes place: 4I1- + MnO2 → MnI2 +I2 + 2O2-.
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.
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.
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.
