Aniodideionis the ion I−.[2]Compounds withiodinein formaloxidation state−1 are callediodides.In everyday life, iodide is most commonly encountered as a component ofiodized salt,which many governments mandate. Worldwide,iodine deficiencyaffects two billion people and is the leading preventable cause ofintellectual disability.[3]
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| Names | |||
|---|---|---|---|
| Systematic IUPAC name
Iodide[1] | |||
| Identifiers | |||
3D model (JSmol)
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| 3587184 | |||
| ChEBI | |||
| ChEMBL | |||
| ChemSpider | |||
| 14912 | |||
| KEGG | |||
PubChemCID
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| UNII | |||
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| Properties | |||
| I− | |||
| Molar mass | 126.90447g·mol−1 | ||
| Conjugate acid | Hydrogen iodide | ||
| Thermochemistry | |||
Std molar
entropy(S⦵298) |
169.26 J K−1mol−1 | ||
| Related compounds | |||
Otheranions
|
Fluoride | ||
Except where otherwise noted, data are given for materials in theirstandard state(at 25 °C [77 °F], 100 kPa).
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Structure and characteristics of inorganic iodides
editIodide is one of the largest monatomicanions.It is assigned a radius of around 206picometers.For comparison, the lighter halides are considerably smaller:bromide(196 pm),chloride(181 pm), and fluoride (133 pm). In part because of its size, iodide forms relatively weak bonds with most elements.
Most iodide salts are soluble in water, but often less so than the related chlorides and bromides. Iodide, being large, is less hydrophilic compared to the smaller anions. One consequence of this is that sodium iodide is highly soluble in acetone, whereas sodium chloride is not. The low solubility ofsilver iodideandlead iodidereflects the covalent character of these metal iodides. A test for the presence of iodide ions is the formation of yellow precipitates of these compounds upon treatment of a solution ofsilver nitrateorlead(II) nitrate.[2]
Aqueous solutions of iodide salts dissolve iodine better than pure water. This effect is due to the formation of thetriiodideion, which is brown:
- I−+ I2⇌I−
3
Redox, including antioxidant properties
editIodide salts are mildreducing agentsand many react with oxygen to give iodine. A reducing agent is a chemical term for an antioxidant. Its antioxidant properties can be expressed quantitatively as aredox potential:
- 2I−⇌ I2+E° = 0.54 volts (versusSHE)
Because iodide is easily oxidized, some enzymes readily convert it intoelectrophiliciodinating agents, as required for thebiosynthesisof myriad iodide-containingnatural products.Iodide can function as an antioxidantreducingspecies that can destroy ozone[4]andreactive oxygen speciessuch ashydrogen peroxide:[5]
- 2 I−+ peroxidase + H2O2+ tyrosine, histidine, lipid, etc. → iodo-compounds + H2O + 2 e−(antioxidants).
Representative iodides
edit| Compound | Formula | Appearance | Use or occurrence |
|---|---|---|---|
| Potassium iodide | KI | white crystals | iodine component of iodized salt |
| Hydrogen iodide | HI | colourless gas | strong mineral acid |
| Silver iodide | AgI | yellow powder that darkens in light | photoactive component of silver-based photographic film |
| Thyroxine (3,5,3′,5′-tetraiodothyronine) |
C15H11I4NO4 | pale yellow solid | hormone essential for human health |
Natural occurrence
editIodargyrite—natural, crystalline silver iodide—is the most common iodide mineral currently known. Iodide anions may sometimes also be found combined with mercury, copper and lead, but minerals with such compositions are even more scarce.[6]
Other oxoanions
editIodinecan assumeoxidation statesof −1, +1, +3, +5, or +7. A number of neutraliodine oxidesare also known.
| Iodine oxidation state | −1 | +1 | +3 | +5 | +7 |
|---|---|---|---|---|---|
| Name | iodide | hypoiodite | iodite | iodate | periodate |
| Formula | I− | IO− | IO− 2 |
IO− 3 |
IO− 4orIO5− 6 |
References
edit- ^"Iodide - PubChem Public Chemical Database".The PubChem Project.USA: National Center for Biotechnology Information.
- ^abGreenwood, Norman N.;Earnshaw, Alan (1997).Chemistry of the Elements(2nd ed.).Butterworth-Heinemann.ISBN978-0-08-037941-8.
- ^McNeil, Donald G. Jr (2006-12-16)."In Raising the World's I.Q., the Secret's in the Salt".New York Times.Retrieved2008-12-04.
- ^Pillar, Elizabeth A.; Guzman, Marcelo I.; Rodriguez, Jose M. (2013-10-01)."Conversion of Iodide to Hypoiodous Acid and Iodine in Aqueous Microdroplets Exposed to Ozone".Environmental Science & Technology.47(19): 10971–10979.Bibcode:2013EnST...4710971P.doi:10.1021/es401700h.ISSN0013-936X.PMID23987087.
- ^Küpper FC;Carpenter LJ;McFiggans GB; et al. (2008)."Iodide accumulation provides kelp with an inorganic antioxidant impacting atmospheric chemistry"(Free full text).Proceedings of the National Academy of Sciences of the United States of America.105(19): 6954–8.Bibcode:2008PNAS..105.6954K.doi:10.1073/pnas.0709959105.PMC2383960.PMID18458346.
- ^"Mineral/rock/commodity names containing 'iodide'".mindat.org.Retrieved2022-08-09.
External links
edit- "Seaweed use iodine as an antioxidant".Chemistry World blog.Archived fromthe originalon 2010-07-03.Retrieved2008-05-15.
- "Stressed seaweed contributes to cloudy coastal skies, study suggests".Retrieved2008-05-15.