Iodide

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An iodide ion is an iodine atom with a −1 charge. Compounds with iodine in formal oxidation state −1 are called iodides. This can include ionic compounds such as caesium iodide or covalent compounds such as carbon tetraiodide. This is the same naming scheme as is seen with chlorides 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 ions:

I⁻(aq) + I₂(s) → I₃⁻(aq)

The colour of the triiodide ion formed is brown.

[edit] Examples

Examples or common iodides include:

• hydrogen iodide (HI)
• sodium iodide (NaI)
• carbon tetraiodide (CI₄)
• silver iodide (AgI)
• nitrogen triiodide (NI₃)