| Atomic Mass | 126.90447 |
|---|---|
| Electron Configuration | [Kr]5s24d105p5 |
| Oxidation States | +7, +5, +1, -1 |
| Year Discovered | 1811 |
| Atomic Mass | 126.90447 |
|---|---|
| Electron Configuration | [Kr]5s24d105p5 |
| Oxidation States | +7, +5, +1, -1 |
| Year Discovered | 1811 |
| Element Name | Iodine |
|---|---|
| Element Symbol | I |
| InChI | InChI=1S/I |
| InChIKey | ZCYVEMRRCGMTRW-UHFFFAOYSA-N |
| Atomic Weight |
126.904 47(3) 126.90447 126.9 126.90447(3) |
|---|---|
| Electron Configuration |
[Kr]5s24d105p5 |
| Atomic Radius |
Van der Waals Atomic Radius : 198 pm (Van der Waals) Empirical Atomic Radius : 140pm (Empirical) Covalent Atomic Radius : 139(3) pm (Covalent) |
| Oxidation States |
+7, +5, +1, -1 7, 6, 5, 4, 3, 1, -1 (a strongly acidic oxide) |
| Ground Level |
2P°3/2 |
| Ionization Energy |
10.451 eV 10.451236 ± 0.000025 eV |
| Electronegativity |
Pauling Scale Electronegativity : 2.66(Pauling Scale) Allen Scale Electronegativity : 2.359(Allen Scale) |
| Electron Affinity |
3.059eV 3.06eV |
| Atomic Spectra |
Lines Holdings Levels Holdings |
| Physical Description |
Solid |
| Element Classification |
Non-metal |
| Element Period Number |
5 |
| Element Group Number |
17 - Halogen |
| Density |
4.93 grams per cubic centimeter |
| Melting Point |
386.85 K (113.7°C or 236.7°F) 113.7°C |
| Boiling Point |
457.55 K (184.4°C or 364.0°F) 184.3°C |
| Estimated Crustal Abundance |
4.5×10-1 milligrams per kilogram |
| Estimated Oceanic Abundance |
6×10-2 milligrams per liter |
The name derives from the Greek iodes for "violet" because of its violet vapours. Iodine was discovered in seaweed by the French chemist Bernard Courtois in 1811, and named by the French chemist Louis-Joseph Gay-Lussac, when he proved it was an element in 1814.
Iodine was discovered by the French chemist Barnard Courtois in 1811. Courtois was extracting sodium and potassium compounds from seaweed ash. Once these compounds were removed, he added sulfuric acid (H2SO4) to further process the ash. He accidentally added too much acid and a violet colored cloud erupted from the mass. The gas condensed on metal objects in the room, creating solid iodine. Today, iodine is chiefly obtained from deposits of sodium iodate (NaIO3) and sodium periodate (NaIO4) in Chile and Bolivia. Trace amounts of iodine are required by the human body. Iodine is part of thyroxin, a hormone produced by the thyroid gland that controls the body's rate of physical and mental development. A lack of iodine can also cause a goiter, a swelling of the thyroid gland. Iodine is added to salt (iodized salt) to prevent these diseases.
From the Greek word iodes, violet. 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, Chilean saltpeter, nitrate-bearing earth (known as caliche), brines from old sea deposits, and in brackish waters from oil and salt wells.
| Year | Atomic Weight (uncertainty) [u] | Reference |
|---|---|---|
| 1985 | 126.904 47(3) | https://doi.org/10.1351/pac198658121677 |
| 1969 | 126.9045(1) | https://doi.org/10.1351/pac197021010091 |
| 1961 | 126.9044 | https://doi.org/10.1021/ja00881a001 |
| 1951 | 126.91 | https://doi.org/10.1039/JR9530000001 |
| 1933 | 126.92 | https://doi.org/10.1039/JR9330000354 |
| 1925 | 126.932 | https://doi.org/10.1039/CT9252700913 |
| 1909 | 126.92 | https://doi.org/10.1021/ja01931a001 |
| 1905 | 126.97 | https://doi.org/10.1021/ja01979a001 |
| 1902 | 126.85 | https://doi.org/10.1007/BF01370337 |
| Year | Isotope | Abundance (uncertainty) | Reference |
|---|
| 1975, 127I, 1, doi:10.1351/pac197647010075 |
Iodine 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.
Iodine is used as a test for starch and turns a deep blue when it comes in contact with it. Potassium iodide (KI) is used to make photographic film and, when mixed with iodine in alcohol, as an antiseptic for external wounds. A radioactive isotope of iodine, iodine-131, is used to treat some diseases of the thyroid gland.
Care should be taken in handling and using iodine. It can burn the skin and damage the eyes and mucous membranes. Pure iodine is poisonous if ingested.
Iodine compounds are important in organic chemistry and very useful in medicine. Iodides, and thyroxine which contains iodine, are used internally in medicine, and as 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.
Ultrapure iodine can be obtained from the reaction of potassium iodide with copper sulfate. Several other methods of isolating the element are known.
See more information at the Iodine compound page.
| CID | Name | Formula | SMILES | Molecular Weight |
|---|---|---|---|---|
| 30165 | iodide | I- | [I-] | 126.9045 |
| 167195 | iodine-131(1-) | I- | [131I-] | 130.906126 |
| 135300 | iodine-123(1-) | I- | [123I-] | 122.90559 |
| 5360629 | iodine | I | [I] | 126.9045 |
| 5460719 | iodine(1+) | I+ | [I+] | 126.9045 |
| 10176142 | iodine-125(1-) | I- | [125I-] | 124.90463 |
| 71587415 | iodine-130(1-) | I- | [130I-] | 129.90667 |
| 10290791 | iodine-124(1-) | I- | [124I-] | 123.90621 |
| 46830029 | iodine-135(1-) | I- | [135I-] | 134.91006 |
| 71587249 | iodine-129(1-) | I- | [129I-] | 128.90498 |
| 131873571 | iodine-125 | I | [125I] | 124.90463 |
| 9855482 | iodine-133(1-) | I- | [133I-] | 132.90783 |
| 9942141 | iodine-121(1-) | I- | [121I-] | 120.90741 |
| 76956536 | iodine-132(1-) | I- | [132I-] | 131.90799 |
| 76967037 | iodine-122(1-) | I- | [122I-] | 121.90759 |
| 76968265 | iodine-120(1-) | I- | [120I-] | 119.9101 |
| 76971819 | iodine-126(1-) | I- | [126I-] | 125.90562 |
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 mucus membranes. The maximum allowable concentration of iodine in air should not exceed 1 mg/m3 (8-hour time-weighted average - 40-hour).
| Stable Isotope Count | 1 |
|---|---|
| Summary | Thirty isotopes 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. |
131I (with a half-life of about 8 days) and 129I are both fission products; 129I is a long-lived fission product with a half-life of 1.7×107 years that can be helpful in the detection of the movement of radiation after a radioactive event, such as occurred at the Japanese reactors at Fukushima. In nuclear reactors and weapons tests, uranium and plutonium undergo fission processes in which one of the fission products is the long-lived isotope 129I. This isotope has been used as a groundwater tracer to determine evidence of nuclear fission, and it can also be tracked in rainwater as evidence of a fission event in the air (weapons explosion; Fig. IUPAC.53.1) [390], [391], [392].
![Fig. IUPAC.53.1: Global distribution of ¹²⁹I in water samples before the Fukushima disaster in Japan. Scale spans 1×10⁵ atoms ¹²⁹I/L to 1×10¹¹ atoms ¹²⁹I/L on a logarithmic (lg10) scale. (Image Source: Snyder, G., A. Aldahan, and G. Possnert, 2010) [392].](https://pubchem.ncbi.nlm.nih.gov/images/iupac/j_pac-2015-0703_fig_076.jpg)
Natural cosmogenic 129I enters groundwater and other terrestrial environments from the atmosphere and then decays to 129Xe. The isotope-amount ratio n(129I)/n(127I) can be used as a clock to estimate time since cosmogenic 129I entered the system. The amount of product 129Xe in such cases is too small to measure; however, excess quantities of 129Xe can be found in meteorites and other very old samples that contained extinct primordial 129I. Younger water bodies also can be differentiated from older water bodies by determining the amount of anthropogenic 129I released since the 1960s from sources such as nuclear bomb tests [393], [394].
125I, which has a half-life of about 59 days, is used encapsulated in radiotherapy to target and treat sites of cancerous tumors [395]. 120gI (with a half-life of 1.36 h), where the “g” indicates ground state, and 124I (with a half-life of 100 h) are radioactive isotopes that emit positrons and they are used in quantitative, diagnostic imaging of the body using positron emission tomography (PET) [383], [384], [385], [387], [388], [389]. 123I and 131I (with half-lives of 0.55 day and 8 days, respectively) are used with single-photon emission computed spectroscopy (SPECT) for basic three-dimensional imaging [386], [395]. Radioactive iodine isotopes are produced from radioactive tellurium isotope.
| Isotope | Atomic Mass (uncertainty) [u] | Abundance (uncertainty) |
|---|---|---|
| 127I | 126.904 47(3) | 1 |
| Isotope | Atomic Mass (uncertainty) [u] | Abundance (uncertainty) |
|---|---|---|
| 127I | 126.9044719(39) | 1 |
| Nuclide | Atomic Mass and Uncertainty [u] | Half Life and Uncertainty | Discovery Year | Decay Modes, Intensities and Uncertainties [%] |
|---|---|---|---|---|
| 106I | 105.953516 ± 0.000429 [Estimated] | Not-specified | α ? | |
| 107I | 106.946935 ± 0.000322 [Estimated] | 20 us [Estimated] | α ? | |
| 108I | 107.943348 ± 0.000109 [Estimated] | 26.4 ms ± 0.8 | 1991 | α≈99.50±2.1%; p=0.50±2.1%; β+ ?; β+p ? |
| 109I | 108.938086022 ± 0.000007223 | 92.8 us ± 0.8 | 1984 | p=99.986±0.4%; α=0.014±0.4% |
| 110I | 109.935085102 ± 0.000066494 | 664 ms ± 24 | 1977 | β+=83±0.4%; α=17±0.4%; β+p=11±0.3%; β+α=1.1±0.3% |
| 111I | 110.930269236 ± 0.000005103 | 2.5 s ± 0.2 | 1977 | β+≈100%; α≈0.088±0.9%; β+p ? |
| 112I | 111.928004548 ± 0.000011 | 3.34 s ± 0.08 | 1977 | β+≈100%; α≈0.0012%; β+p=0.88±1%; β+α=0.104±1.2% |
| 113I | 112.923650062 ± 0.0000086 | 6.6 s ± 0.2 | 1977 | β+=100%; α=3.310e-5%[Estimated]; β+α ? |
| 114I | 113.922018900 ± 0.0000215 | 2.01 s ± 0.15 | 1977 | β+=100%; β+p ?; α≈7.7e-9%[Estimated] |
| 114Im | 113.922018900 ± 0.0000215 | 6.2 s ± 0.5 | 1995 | β+= ?; IT= ? |
| 115I | 114.918048000 ± 0.000031 | 1.3 m ± 0.2 | 1969 | β+=100% |
| 116I | 115.916885513 ± 0.000080555 | 2.91 s ± 0.15 | 1976 | β+=100% |
| 116Im | 115.916885513 ± 0.000080555 | 3.27 us ± 0.16 | 1990 | IT=100% |
| 117I | 116.913645649 ± 0.000027437 | 2.22 m ± 0.04 | 1969 | β+=100%; e+≈77% |
| 118I | 117.913074000 ± 0.000021213 | 13.7 m ± 0.5 | 1957 | β+=100% |
| 118Im | 117.913074000 ± 0.000021213 | 8.5 m ± 0.5 | 1968 | β+≈100%; IT ? |
| 119I | 118.910060910 ± 0.000023302 | 19.1 m ± 0.4 | 1954 | β+=100%; e+=51±0.4%; ε=49±0.4% |
| 120I | 119.910093729 ± 0.000016212 | 81.67 m ± 0.18 | 1957 | β+=100% |
| 120Im | 119.910093729 ± 0.000016212 | 242 ns ± 5 | 1974 | IT=100% |
| 120In | 119.910093729 ± 0.000016212 | 53 m ± 4 | 1967 | β+=100% |
| 121I | 120.907411492 ± 0.00000507 | 2.12 h ± 0.01 | 1950 | β+=100% |
| 121Im | 120.907411492 ± 0.00000507 | 9.0 us ± 1.4 | 1982 | IT=100% |
| 122I | 121.907590094 ± 0.000005561 | 3.63 m ± 0.06 | 1950 | β+=100%; e+=78±0.2%; ε=22±0.2% |
| 122Im | 121.907590094 ± 0.000005561 | 193.3 ns ± 0.9 | 2004 | IT=100% |
| 122In | 121.907590094 ± 0.000005561 | 79.1 us ± 1.2 | 2004 | IT=100% |
| 122Ip | 121.907590094 ± 0.000005561 | 78.2 us ± 0.4 | 2004 | IT=100% |
| 122Iq | 121.907590094 ± 0.000005561 | 146.5 ns ± 1.2 | 2004 | IT=100% |
| 123I | 122.905589753 ± 0.000003956 | 13.2232 h ± 0.0015 | 1949 | β+=100% |
| 124I | 123.906210297 ± 0.000002467 | 4.1760 d ± 0.0003 | 1938 | β+=100% |
| 125I | 124.904630610 ± 0.000001452 | 59.392 d ± 0.008 | 1947 | ε=100% |
| 126I | 125.905624205 ± 0.000004055 | 12.93 d ± 0.05 | 1938 | β+=52.7±0.5%; β-=47.3±0.5% |
| 126Im | 125.905624205 ± 0.000004055 | 128 ns | 2012 | IT=100% |
| 127I | 126.904472592 ± 0.000003887 | Stable | 1920 | IS=100% |
| 128I | 127.905809355 ± 0.000003887 | 24.99 m ± 0.02 | 1934 | β-=93.1±0.8%; β+=6.9±0.8% |
| 128Im | 127.905809355 ± 0.000003887 | 845 ns ± 20 | 1982 | IT=100% |
| 128In | 127.905809355 ± 0.000003887 | 175 ns ± 15 | 1991 | IT=100% |
| 129I | 128.904983643 ± 0.000003385 | 16.14 My ± 0.12 | 1951 | β-=100% |
| 130I | 129.906670168 ± 0.000003385 | 12.36 h ± 0.01 | 1938 | β-=100% |
| 130Im | 129.906670168 ± 0.000003385 | 8.84 m ± 0.06 | 1966 | IT=84±0.2%; β-=16±0.2% |
| 130In | 129.906670168 ± 0.000003385 | 133 ns ± 7 | 1989 | IT=100% |
| 130Ip | 129.906670168 ± 0.000003385 | 315 ns ± 15 | 1989 | IT=100% |
| 130Iq | 129.906670168 ± 0.000003385 | 254 ns ± 4 | 1975 | IT=100% |
| 131I | 130.906126375 ± 0.000000649 | 8.0249 d ± 0.0006 | 1939 | β-=100% |
| 131Im | 130.906126375 ± 0.000000649 | 24 us ± 1 | 2009 | IT=100% |
| 132I | 131.907993511 ± 0.000004364 | 2.295 h ± 0.013 | 1948 | β-=100% |
| 132Im | 131.907993511 ± 0.000004364 | 1.387 h ± 0.015 | 1973 | IT=86±0.2%; β-=14±0.2% |
| 133I | 132.907828400 ± 0.000006335 | 20.83 h ± 0.08 | 1940 | β-=100% |
| 133Im | 132.907828400 ± 0.000006335 | 9 s ± 2 | 1970 | IT=100% |
| 133In | 132.907828400 ± 0.000006335 | ~170 ns | 1984 | IT=100% |
| 133Ip | 132.907828400 ± 0.000006335 | 469 ns ± 15 | 2009 | IT=100% |
| 134I | 133.909775660 ± 0.000005213 | 52.5 m ± 0.2 | 1948 | β-=100% |
| 134Im | 133.909775660 ± 0.000005213 | 3.52 m ± 0.04 | 1970 | IT=97.7±1%; β-=2.3±1% |
| 135I | 134.910059355 ± 0.000002211 | 6.58 h ± 0.03 | 1940 | β-=100% |
| 136I | 135.914604693 ± 0.000015231 | 83.4 s ± 0.4 | 1949 | β-=100% |
| 136Im | 135.914604693 ± 0.000015231 | 46.6 s ± 1.1 | 1959 | β-=100% |
| 137I | 136.918028178 ± 0.000009 | 24.13 s ± 0.12 | 1943 | β-=100%; β-n=7.51±1.1% |
| 138I | 137.922726392 ± 0.0000064 | 6.26 s ± 0.03 | 1949 | β-=100%; β-n=5.33±1.1% |
| 138Im | 137.922726392 ± 0.0000064 | 1.26 us ± 0.16 | 2007 | IT=100% |
| 139I | 138.926493400 ± 0.0000043 | 2.280 s ± 0.011 | 1949 | β-=100%; β-n=9.74±2.4% |
| 140I | 139.931715914 ± 0.000013 | 588 ms ± 10 | 1972 | β-=100%; β-n=7.60±2.8%; β-2n ? |
| 141I | 140.935666081 ± 0.000017 | 420 ms ± 7 | 1974 | β-=100%; β-n=21.2±3% |
| 142I | 141.941166595 ± 0.0000053 | 235 ms ± 11 | 1975 | β-=100%; β-n ?; β-2n ? |
| 143I | 142.945475 ± 0.000215 [Estimated] | 182 ms ± 8 | 1994 | β-=100%; β-n ?; β-2n ? |
| 144I | 143.951336 ± 0.000429 [Estimated] | 94 ms ± 8 | 1994 | β-=100%; β-n ?; β-2n ? |
| 145I | 144.955845 ± 0.000537 [Estimated] | 89.7 ms ± 9.3 | 2010 | β-=100%; β-n ?; β-2n ? |
| 146I | 145.961846 ± 0.000322 [Estimated] | 94 ms ± 26 | 2018 | β-=100%; β-n ?; β-2n ? |
| 147I | 146.966505 ± 0.000322 [Estimated] | 60 ms >550ns [Estimated] | 2018 | β- ?; β-n ?; β-2n ? |
