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|Shiny grayish-black flakes. It is a halogen.
|Required in small amounts by humans. Once used as an antiseptic,
no longer due to its poisonous nature.
History(Gr. iodes, violet) Discovered by Courtois in 1811, Iodine, a
Occurenceoccurs 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.
PropertiesIodine is a bluish-black, lustrous solid, volatizing 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.
UsesIodine compounds are important in organic chemistry and very useful in
Thirty isotopes are recognized. Only one stable isotope, 127I is found in
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 as a solution of KI and iodine in alcohol is used for external
Potassium iodide finds use in photography.
The deep blue color with starch solution is characteristic of the free
HandlingCare 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.
The maximum allowable concentration of iodine in air should not exceed 1
mg/m^3 (8-hour time-weighted average - 40-hour).