Iodide

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Iodide
I-.svg Iodide ion.svg
Identifiers
CAS number 20461-54-5 YesY
PubChem 30165
ChemSpider 28015 YesY
KEGG C00708 YesY
ChEBI CHEBI:16382
ChEMBL CHEMBL185537 YesY
Beilstein Reference 3587184
Gmelin Reference 14912
Jmol-3D images Image 1
Properties
Molecular formula I
Molar mass 126.90447 g mol-1
Related compounds
Other anions Bromide

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]

Compound Formula Appearance Use or occurrence
Potassium iodide KI white crystals iodine component of iodized salt
Hydrogen iodide HI colourless solution 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
HI He
LiI BeI2 BI3 CI4 NI3 I2O4,
I2O5,
I4O9
IF,
IF3,
IF5,
IF7
Ne
NaI MgI2 AlI3 SiI4 PI3,
P2I4
S ICl,
ICl3
Ar
KI CaI2 Sc TiI4 VI3 CrI3 MnI2 FeI2 CoI2 NiI2 CuI ZnI2 Ga2I6 GeI2,
GeI4
AsI3 Se IBr Kr
RbI SrI2 Y ZrI4 Nb Mo Tc Ru Rh Pd AgI CdI2 InI3 SnI4,
SnI2
SbI3 TeI4 I Xe
CsI BaI2   Hf Ta W Re Os Ir Pt AuI Hg2I2,
HgI2
TlI PbI2 BiI3 Po AtI Rn
Fr Ra   Rf Db Sg Bh Hs Mt Ds Rg Cn Uut Fl Uup Lv Uus Uuo
La Ce Pr Nd Pm SmI2 Eu Gd TbI3 Dy Ho Er Tm Yb Lu
Ac ThI4 Pa UI3,
UI4
Np Pu Am Cm Bk Cf Es Fm Md No Lr

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
Name iodide hypoiodite iodite iodate periodate
Formula I IO IO2 IO3 IO4 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]