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Iodine
*** Shopping-Tip: Iodine
{{Elementbox_header | number=53 | symbol=I | name=iodine | left=
tellurium .html">xenon
_above=bromine|Br | below=
astatine At | color1=#ffff99 | color2=black }}
{{Elementbox_series |
halogens }}
{{Elementbox_groupperiodblock | group=17 | period=5 | block=p }}
{{Elementbox_appearance_img | I,53| violet-dark gray, lustrous }}
{{Elementbox_atomicmass_gpm |
1 E-25 kg 126.90447List of elements by atomic mass (3) }}
{{Elementbox_econfig | [
krypton Kr] 4d
10 5s
2 5p
5 }}
{{Elementbox_epershell | 2, 8, 18, 18, 7 }}
{{Elementbox_section_physicalprop | color1=#ffff99 | color2=black }}
{{Elementbox_phase |
solid }}
{{Elementbox_density_gpcm3nrt | 4.933 }}
{{Elementbox_meltingpoint | k=386.85 | c=113.7 | f=236.66 }}
{{Elementbox_boilingpoint | k=457.4 | c=184.3 | f=363.7 }}
{{Elementbox_heatfusion_kjpmol | (I
2) 15.52 }}
{{Elementbox_heatvaporiz_kjpmol | (I
2) 41.57 }}
{{Elementbox_heatcapacity_jpmolkat25 | (I
2) 54.44 }}
{{Elementbox_vaporpressure_katpa | 260 | 282 | 309 | 342 | 381 | 457 | comment=(rhombic) }}
{{Elementbox_section_atomicprop | color1=#ffff99 | color2=black }}
{{Elementbox_crystalstruct | orthorhombic }}
{{Elementbox_oxistates | ±1, 5, 7
(strongly
acidic oxide) }}
{{Elementbox_electroneg_pauling | 2.66 }}
{{Elementbox_ionizationenergies3 | 1008.4 | 1845.9 | 3180 }}
{{Elementbox_atomicradius_pm |
1 E-10 m 140 }}
{{Elementbox_atomicradiuscalc_pm |
1 E-10 m 115 }}
{{Elementbox_covalentradius_pm |
1 E-10 m 133 }}
{{Elementbox_vanderwaalsrad_pm |
1 E-10 m 198 }}
{{Elementbox_section_miscellaneous | color1=#ffff99 | color2=black }}
{{Elementbox_magnetic | nonmagnetic }}
{{Elementbox_eresist_ohmmat0 | 1.3×10
7 }}
{{Elementbox_thermalcond_wpmkat300k | 0.449 }}
{{Elementbox_bulkmodulus_gpa | 7.7 }}
{{Elementbox_cas_number | 7553-56-2 }}
{{Elementbox_isotopes_begin | isotopesof=iodine | color1=#ffff99 | color2=black }}
{{Elementbox_isotopes_stable | mn=127 | sym=I | na=100% | n=74 }}
{{Elementbox_isotopes_decay | mn=129 | sym=I
| na=
synthetic radioisotope syn | hl=1.57×10
7year y
| dm=
beta emission Beta- | de=0.194 | pn=129 | ps=
xenon Xe }}
{{Elementbox_isotopes_decay | mn=131 | sym=I
| na=
synthetic radioisotope syn | hl=8.02070
day d
| dm=
beta emission Beta- | de=0.971 | pn=131 | ps=
xenon Xe }}
{{Elementbox_isotopes_end}}
{{Elementbox_footer | color1=#ffff99 | color2=black }}
'''Iodine''' (from the Gr. ''Iodes'', meaning "violet"), is a
chemical element in the
periodic table that has the symbol '''I''' and
atomic number 53. It is required as a
trace element for most living
organisms. Chemically, iodine is the least reactive of the
halogens, and the most
electronegativity electropositive halogen. Iodine is primarily used in
medicine,
photography and in dyes.
As with all other halogens (members of Group VII in the Periodic Table), iodine is found as diatomic molecules, and hence, has the molecular formula of I
2.
Notable characteristics
Iodine is a dark-gray/purple-black solid that
sublimation (chemistry) sublimates at standard temperatures into a purple-pink gas that has an irritating odor. This halogen forms compounds with many elements, but is less active than the other members of its Group VII (halogens) and has some metallic-like properties. Iodine dissolves easily in
chloroform,
carbon tetrachloride, or carbon disulphide to form purple solutions (It is only slightly
solubility soluble in water, giving a yellow solution). The deep blue color with
starch is a characteristic only of the free element.
Applications
In areas where there is little iodine in the diet—typically remote inland
areas and semi-arid equatorial climates where no marine foods are eaten—
iodine deficiency gives rise to
goiter, so called
endemic goiter. In some such areas, this is now combatted by the addition of small amounts of iodine to table salt in form of sodium iodide, potassium iodide, potassium iodate—this product is known as ''
iodized salt''. Iodine deficiency is the leading cause of preventable
mental retardation. Iodine deficency remains a serious problem that affects people around the globe.
Other uses:
*One of the
halogens, it is an essential
trace element; the
thyroid hormones, ''
thyroxine'' and ''
triiodothyronine'' contain iodine.
*
Tincture of iodine (3% elemental iodine in water/ethanol base) is an essential component of any emergency survival kit, used both to disinfect wounds and to sanitize surface water for drinking (3 drops per liter, let stand for 30 minutes)
*Iodine compounds are important in the field of
organic chemistry and are very useful in
medicine.
*Iodides and
thyroxine which contains iodine, are both used in internal medicine and, in combination with
ethanol alcohol (as tincture of iodine) are used externally to disinfect wounds.
*
Silver iodide is used in photography.
*
Potassium iodide (KI) tablets or liquid drops can be given to people in a nuclear disaster area when
Nuclear fission fission has taken place, to flush out the radioactive iodine-131 fission product. The half-life of iodine-131 is only eight days, so the treatment would need to continue only a couple of weeks. In cases of leakage of nuclear materials without fission, or a
dirty bomb, this precaution would be of no avail. KI might also serve to dilute the radioactive
caesium-137 produced by nuclear fission, because caesium is chemically related to potassium, but potassium chloride would serve as well. The latter is available in low-sodium table salt. The use of KI or NaI to dilute radioactive caesium is problematic, however, because the latter has a half-life of thirty years, requiring long-term dietary change if it is to be diluted with non-radioactive potassium.
*
Tungsten iodide is used to stabilize the filaments in
light bulbs.
*
Nitrogen triiodide is an explosive, too unstable to be used commercially, but is commonly used in college
pranks.
*
Iodine-131 is used as a tracer in medicine.
*Uncombined (elemental) iodine is mildly toxic to all living things.
History
Iodine (
Greek language Gr. ''iodes'' meaning violet) was discovered by
Barnard Courtois in
1811. He was the son of a manufacturer of
saltpeter (potassium nitrate, a vital part of gunpowder). At the time
France was at war and gunpowder was in great demand. Saltpeter was isolated from seaweed washed up on the coasts of
Normandy and
Brittany. To isolate the potassium nitrate, seaweed was burned and the ash then washed with water. The remaining waste was destroyed by adding
sulfuric acid. One day Courtois added too much sulfuric acid and a cloud of purple vapor rose. Courtois noted that the vapor crystallized on cold surfaces making dark crystals. Courtois suspected that this was a new element but lacked the money to pursue his observations.
However he gave samples to his friends,
Charles Bernard Desormes (
1777–
1862) and
Nicolas Clément (
1779-–
1841) to continue research. He also gave some of the substance to
Joseph Louis Gay-Lussac (
1778–
1850), a well-known chemist at that time, and to
André-Marie Ampère (
1775–
1836). On
November 29 1813 Dersormes and Clément made public Courtois’ discovery. They described the substance to a meeting of the Imperial Institute of France. On
December 6 Gay-Lussac announced that the new substance was either an element or a compound of oxygen. Ampère had given some of his sample to
Humphry Davy (1778–
1829). Davy did some experiments on the substance and noted its similarity to chlorine. Davy sent a letter dated
December 10 to the
Royal Society of London stating that he had identified a new element. A large argument erupted between Davy and Gay-Lussac over who identified iodine first but both scientists acknowledged Barnard Courtois as the first to isolate the
chemical element.
Occurrence
Iodine can be prepared in an ultrapure form through the reaction of
potassium iodide with
copper (II) sulfate. There are also several other methods of isolating this element. Although the element is actually quite rare,
kelp and certain other plants have the ability to concentrate iodine, which helps introduce the element into the food chain as well as keeping its cost down.
Isotopes
There are 37
isotopes of iodine and only one, I-127, is stable. The artificial
radioisotope I-131 (a beta emitter), also known as
radioiodine which has a
half-life of 8.0207 days, has been used in treating
cancer and other pathologies of the
thyroid glands. The most common compounds of iodine are the iodides of
sodium and
potassium (
potassium iodide KI) and the iodates (KIO
3).
I-129 (
half-life 15.7 million years) is a product of
xenon Xe-129
spallation in the
Earth's atmosphere atmosphere and
uranium and
plutonium fission, both in subsurface rocks and nuclear reactors. Nuclear processes, in particular nuclear fuel reprocessing and atmospheric nuclear weapons tests have now swamped the natural signal for this isotope. I-129 was used in rainwater studies following the
Chernobyl accident. It also has been used as a ground-water tracer and as an indicator of nuclear waste dispersion into the natural environment. If humans are exposed to I-129, the thyroid gland will absorb it as if it were non-radioactive Iodine, leading to elevated chances of thyroid cancer. Taking large amounts of regular iodine will saturate the thyroid and prevent uptake. Iodine pills are sometimes distributed to persons living close to nuclear establishments, for use in case of accidents that could lead to releases of radioactive Iodine.
In many ways, I-129 is similar to
chlorine-36. It is a soluble halogen, fairly non-reactive, exists mainly as a non-sorbing
anion, and is produced by cosmogenic, thermonuclear, and in-situ reactions. In hydrologic studies, I-129 concentrations are usually reported as the ratio of I-129 to total I (which is virtually all I-127). As is the case with Cl-36/Cl, I-129/I ratios in nature are quite small, 10
-14 to 10
-10 (peak thermonuclear I-129/I during the 1960s and 1970s reached about 10
-7). I-129 differs from Cl-36 in that its half-life is longer (15.7 vs. 0.301 million years), it is highly biophilic, and occurs in multiple
ionic forms (commonly, I- and iodate) which have different chemical behaviors. This makes it fairly easy for I-129 to enter the biosphere as it becomes incorporated into vegetation, soil, milk, animal tissue, etc.
Excesses of Xe-129 in meteorites have been shown to result from decay of I-129. This was the first
extinct radionuclide to be identified as present in the early
solar system. Its decay is the basis of the I-Xe
radiometric dating scheme, which covers the first 50 million years of
solar system evolution.
Precautions
Direct contact with skin can cause lesions, so it should be handled with care. Iodine vapor is very irritating to the
eye and to mucous membranes. Concentration of iodine in the air should not exceed 1
milligram mg/
cubic metre m³ (eight-hour time-weighted average).
Compounds
*
Ammonium iodide (NH
4I)
*
Caesium iodide (CsI)
*
Copper(I) iodide (CuI)
*
Hydroiodic acid (HI)
*
Iodic acid (HIO
3)
*
Iodine cyanide (ICN)
*
Iodine heptafluoride (IF
7)
*
Iodine pentafluoride (IF
5)
*
Lead(II) iodide (PbI
2)
*
Lithium iodide (LiI)
*
Nitrogen triiodide (NI
3)
*
Potassium iodide (KI)
*
Sodium iodide (NaI)
''See also
:category:Iodine compounds iodine compounds''
References
-
Los Alamos National Laboratory - Iodine
External links
{{Commons|Iodine}}
{{wiktionary|iodine}}
-
WebElements.com - Iodine
-
ChemicalElements.com - Iodine
-
who.int - WHO Global Database on Iodine Deficiency
-
Network for Sustained Elimination of Iodine Deficiency
See also
*
Iodized salt
Category:Iodine
bg:Йод
ca:Iode
cs:Jód
da:Jod
de:Iod
et:Jood
es:Yodo
eo:Jodo
fa:ید
fr:Iode
ko:아�오딘
io:Iodo
is:Joð
it:Iodio
he:יוד
lv:Jods
lt:Jodas
hu:Jód
nl:Jodium
ja:ヨウç´
no:Jod
oc:Iòde
pl:Jod
pt:Iodo
ru:Иод
simple:Iodine
sl:Jod
sr:Јод
fi:Jodi
sv:Jod
th:ไà¸à¹‚à¸à¸”ีน
uk:Йод
zh:碘
Iodine I
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Category:Chemical element symbol templates {{PAGENAME}}
This category contains articles related to the chemical element
iodine.
Category:Chemical elements
Category:Halogens
Category:Antiseptics
Category:Staining dyes
*** Shopping-Tip: Iodine
