An iodide
ion is the ion I
−.
Compounds with
iodine
Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...
in formal
oxidation state −1 are called iodides. 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.
Structure and characteristics of inorganic iodides
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 compared to 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
Silver iodide is an inorganic compound with the formula Ag I. The compound is a bright yellow solid, but samples almost always contain impurities of metallic silver that give a gray coloration. The silver contamination arises because AgI is hig ...
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.
[
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 ⇌
]
Redox, including antioxidant properties
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 :
:2I− ⇌ I2 + ''E''° = 0.54 volts (versus SHE
She most commonly refers to:
*She (pronoun), the third person singular, feminine, nominative case pronoun in modern English.
She or S.H.E. may also refer to:
Literature and films
*'' She: A History of Adventure'', an 1887 novel by H. Rider Hagga ...
)
Because iodide is easily oxidized, some enzymes readily convert it into electrophilic
In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively charged, have an atom that carri ...
iodinating agents, as required for the biosynthesis
Biosynthesis is a multi-step, enzyme-catalyzed process where substrates are converted into more complex products in living organisms. In biosynthesis, simple compounds are modified, converted into other compounds, or joined to form macromolecules. ...
of myriad iodide-containing natural product
A natural product is a natural compound or substance produced by a living organism—that is, found in nature. In the broadest sense, natural products include any substance produced by life. Natural products can also be prepared by chemical syn ...
s. Iodide can function as an antioxidant reducing species that can destroy ozone and reactive oxygen species such as hydrogen peroxide:
:2 I− + peroxidase + H2O2 + tyrosine, histidine, lipid, etc. → iodo-compounds + H2O + 2 e− (antioxidants).
Representative iodides
Natural occurrence
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.
Other oxyanions
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...
can assume oxidation states of −1, +1, +3, +5, or +7. A number of neutral iodine oxides are also known.
References
External links
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{{Iodides
Anions
Dietary minerals
Dietary antioxidants
Leaving groups
