An iodide
ion is the ion I
−.
Compounds with
iodine
Iodine is a chemical element with the Symbol (chemistry), 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 , ...
in formal
oxidation state
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. ...
−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
Iodine deficiency is a lack of the mineral (nutrient), trace element iodine, an essential nutrient in the diet (nutrition), diet. It may result in metabolic problems such as goiter, sometimes as an endemic goiter as well as congenital iodine defi ...
affects two billion people and is the leading preventable cause of
intellectual disability
Intellectual disability (ID), also known as general learning disability in the United Kingdom and formerly mental retardation, Rosa's Law, Pub. L. 111-256124 Stat. 2643(2010). is a generalized neurodevelopmental disorder characterized by signif ...
.
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
The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride s ...
(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 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 iodinating agents, as required for the biosynthesis of myriad iodide-containing natural products. Iodide can function as an antioxidant reducing species that can destroy ozone and reactive oxygen species
In chemistry, reactive oxygen species (ROS) are highly reactive chemicals formed from diatomic oxygen (). Examples of ROS include peroxides, superoxide, hydroxyl radical, singlet oxygen, and alpha-oxygen.
The reduction of molecular oxygen ...
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 (chemistry), 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 , ...
can assume oxidation state
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. ...
s 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