| |||
| Names | |||
|---|---|---|---|
| Systematic IUPAC name Iodide[1] | |||
| Identifiers | |||
3D model (JSmol) | |||
| 3587184 | |||
| ChEBI | |||
| ChEMBL | |||
| ChemSpider |
| ||
| 14912 | |||
| KEGG |
| ||
| UNII | |||
| |||
| |||
| Properties | |||
| I− | |||
| Molar mass | 126.90447 g·mol−1 | ||
| Conjugate acid | Hydrogen iodide | ||
| Thermochemistry | |||
Std molar entropy(S⦵298) | 169.26 J K−1 mol−1 | ||
| Related compounds | |||
Otheranions | Fluoride Chloride Bromide | ||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Aniodideion is I−.[2] Compounds withiodine in formaloxidation state −1 are callediodides. In everyday life, iodide is most commonly encountered as a component ofiodized salt, which many governments mandate. Worldwide,iodine deficiency affects two billion people and is the leading preventable cause ofintellectual disability.[3]
Iodide 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 thatsodium iodide is highly soluble in acetone, whereassodium chloride is not. The low solubility ofsilver iodide andlead 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 ofsilver nitrate orlead(II) nitrate.[2]
Aqueous solutions of iodide salts dissolve iodine better than pure water. This effect is due to the formation of thetriiodide ion, which is brown:
Iodide salts are mildreducing 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 aredox potential:
Because iodide is easily oxidized, some enzymes readily convert it intoelectrophilic iodinating agents, as required for thebiosynthesis of myriad iodide-containingnatural products. Iodide can function as an antioxidantreducing species that can destroy ozone[4] andreactive oxygen species such ashydrogen peroxide:[5]
| 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 |
Iodargyrite—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]
Iodine can assumeoxidation states of −1, +1, +3, +5, or +7. A number of neutraliodine oxides are also known.
| Iodine oxidation state | −1 | +1 | +3 | +5 | +7 |
|---|---|---|---|---|---|
| Name | iodide | hypoiodite | iodite | iodate | periodate |
| Formula | I− | IO− | IO− 2 | IO− 3 | IO− 4 orIO5− 6 |
