Iodide

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Iodide
I-.svgIodide ion.svg
Identifiers
CAS number20461-54-5 YesY
PubChem30165
ChemSpider28015 YesY
KEGGC00708 YesY
ChEBICHEBI:16382
ChEMBLCHEMBL185537 YesY
Beilstein Reference3587184
Gmelin Reference14912
Jmol-3D imagesImage 1
Properties
Molecular formulaI
Molar mass126.90447 g mol-1
Related compounds
Other anionsBromide

Chloride
Fluoride

Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references
 
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"i-" redirects here. For the Internet-related prefix i-, see Wiktionary's entry i-.
Iodide
I-.svgIodide ion.svg
Identifiers
CAS number20461-54-5 YesY
PubChem30165
ChemSpider28015 YesY
KEGGC00708 YesY
ChEBICHEBI:16382
ChEMBLCHEMBL185537 YesY
Beilstein Reference3587184
Gmelin Reference14912
Jmol-3D imagesImage 1
Properties
Molecular formulaI
Molar mass126.90447 g mol-1
Related compounds
Other anionsBromide

Chloride
Fluoride

Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

An iodide ion is the ion I.[2] Compounds with iodine in formal oxidation state −1 are called iodides. This page is for the iodide ion and its salts, not organoiodine compounds. In everyday life, iodide is most commonly encountered as a component of iodized salt, which many governments mandate. Worldwide, iodine deficiency affects two billion people and is the leading preventable cause of intellectual disability.[3]

Structure and characteristics of inorganic iodides[edit]

Iodide is one of the largest monatomic anions. It is assigned a radius of around 206 picometers. 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 than are the smaller anions. One consequence of this is that sodium iodide is highly soluble in acetone, whereas sodium chloride is not. The low solubility of silver iodide and lead iodide reflects 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 of silver nitrate or lead(II) nitrate.[2]

Aqueous solutions of iodide salts dissolve iodine better than pure water. This effect is due to the formation of the triiodide ion, which is brown:

I + I2 I3

Redox, including antioxidant properties[edit]

Iodide salts are mild reducing agents and 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 a redox potential :

I 1/2 I2 + e (electrons) = - 0.54 Volt vs SHE

Because iodide is easily oxidized, some enzymes readily convert it into electrophilic iodinating agents, as required for the biosynthesis of myriad iodide-containing natural products. Iodide can function as an antioxidant reducing species that can destroy reactive oxygen species such as hydrogen peroxide:[4]

2 I + Peroxidase + H2O2 + tyrosine, histidine, lipid, etc. → iodo-Compounds + H2O + 2 e (antioxidants).

Representative iodides[edit]

CompoundFormulaAppearanceUse or occurrence
Potassium iodideKIwhite crystalsiodine component of iodized salt
Hydrogen iodideHIcolourless solutionstrong mineral acid
Silver iodideAgIyellow powder that darkens in lightphotoactive component of silver-based photographic film
Thyroxine
(3,5,3',5'-tetraiodothyronine)
C15H11I4NO4pale yellow solidhormone essential for human health
HIHe
LiIBeI2BI3CI4NI3I2O4,
I2O5,
I4O9
IF,
IF3,
IF5,
IF7
Ne
NaIMgI2AlI3SiI4PI3,
P2I4
SICl,
ICl3
Ar
KICaI2ScTiI4VI3CrI3MnI2FeI2CoI2NiI2CuIZnI2Ga2I6GeI2,
GeI4
AsI3SeIBrKr
RbISrI2YZrI4NbMoTcRuRhPdAgICdI2InI3SnI4,
SnI2
SbI3TeI4IXe
CsIBaI2 HfTaWReOsIrPtAuIHg2I2,
HgI2
TlIPbI2BiI3PoAtIRn
FrRa RfDbSgBhHsMtDsRgCnUutFlUupLvUusUuo
LaCePrNdPmSmI2EuGdTbI3DyHoErTmYbLu
AcThI4PaUI3,
UI4
NpPuAmCmBkCfEsFmMdNoLr

Other oxyanions[edit]

Iodine can assume oxidation states of −1, +1, +3, +5, or +7. A number of neutral iodine oxides are also known.

Iodine oxidation state−1+1+3+5+7
Nameiodidehypoioditeioditeiodateperiodate
FormulaIIOIO2IO3IO4 or IO65−

References[edit]

  1. ^ "Iodide - PubChem Public Chemical Database". The PubChem Project. USA: National Center for Biotechnology Information. 
  2. ^ a b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0080379419. 
  3. ^ McNeil, Donald G. Jr (2006-12-16). "In Raising the World’s I.Q., the Secret’s in the Salt". New York Times. Retrieved 2008-12-04. 
  4. ^ 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. PMC 2383960. PMID 18458346. 

External links[edit]