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{{dablink|"i-" redirects here. For the [[Internet-related prefix]] i-, see Wiktionary's entry [[wikt:i-|i-]].}}
An '''iodide''' [[ion]] is an [[iodine|iodine atom]] with a &minus;1 [[electric charge|charge]]. Compounds with iodine in formal [[oxidation state]] &minus;1 are called '''iodides'''. This can include [[Ion|ionic]] compounds such as [[caesium iodide]] or [[covalent]] compounds such as [[carbon tetraiodide]].  This is the same naming scheme as is seen with [[chloride]]s and [[bromides]] The chemical test for an iodide compound is to acidify the aqueous compound by adding some drops of [[acid]], to dispel any carbonate ions present, then adding [[lead nitrate]], yielding a bright yellow [[precipitate]] of [[lead iodide]]. Most ionic iodides are soluble, with the exception of yellow [[silver iodide]] and yellow [[lead iodide]]. Iron(III) iodide does not exist because iron(III) ions oxidize iodide ions in aqueous solution. Aqueous solutions of iodide dissolve iodine better than pure water due to the formation of [[complex ion]]s:

:I<sup>−</sup>(aq) + I<sub>2</sub>(s) {{unicode|⇌}} I<sub>3</sub><sup>−</sup>(aq)

The colour of the [[triiodide]] ion formed is brown.

==Examples==
Examples or common iodides include:
* [[hydrogen iodide]] (HI)
* [[sodium iodide]] (NaI)
* [[potassium iodide]] (KI)
* [[carbon tetraiodide]] (CI<sub>4</sub>)
* [[silver iodide]] (AgI)
* [[nitrogen triiodide]] (NI<sub>3</sub>)

==Iodide as an antioxidant==

{{Mergefrom|Iodide as an antioxidant|date=April 2007}}

==Clinical Use==

Iodide (>6mg/day) can be used to treat patients with [[hyperthyroidism]] due to its ability to block the release of [[thyroid hormone]] (TH), known as the Wolff-Chaikoff Effect, from the [[thyroid gland]]. In fact, prior to [[1940]], iodides were the predominant antithyroid agents. In large doses, iodides inhibit [[proteolysis]] of [[thyroglobulin]]. This permits TH to be synthesized and stored in [[colloid]], but not released into the bloodstream. 

Of note, this treatment is seldom used today as a stand-alone therapy despite the rapid improvement of patients immediately following administration. The major disadvantage of iodide treatment lies in the fact that excessive stores of TH accumulate, slowing the onset of action of [[thioamides]] (TH synthesis blockers). Additionally, the functionality of iodides fade after the initial treatment period. An "escape from block" is also a concern, as extra stored TH may spike following discontinuation of treatment. 


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[[Category:Anions]]
[[Category:Iodides|*]]
[[Category:Leaving group]]

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