Iodide (I⁻)

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What is Iodide?

Iodide is described as an anion having a valency of -1. The iodine compounds having an oxidation state of -1 are referred to as iodides. The chemical formula for iodide is given as I.

Iodine is an element that is a halogen. This compound tends to accept an electron and exists as an ion, which is negatively charged. Thus, the anion name iodide can be used interchangeably with iodine. The IUPAC name is given as Iodide.

Structure and Characteristics of Inorganic Iodides

Iodide is given as the largest monatomic anion, and it is assigned with a radius of around 206 picometers. Additionally, in comparison, the lighter halides are considerably much smaller: chloride (181 pm), fluoride (133 pm), bromide (196 pm). In contrast, because of its size, iodide produces relatively weak bonds with most of the elements.

Most of the iodide salts are soluble in water, but they are often less related to the related bromides and chlorides. Being large, iodide is very less hydrophilic compared to the smaller anions. A consequence of this is given as sodium iodide is highly soluble in acetone, but sodium chloride is not. The low solubility of lead iodide and silver iodide represents the covalent nature of these iodide metals. The iodide ion presence test is given as the formation of yellow precipitates of these compounds after the treatment of either lead(II) nitrate or silver nitrate solution.

Also, the iodide salt's aqueous solutions dissolve iodine better than pure water. This effect is because of the formation of the triiodide ion, which is brown in colour, which is chemically represented as follows:

I + I2 ⇌ I3

Redox, Including Antioxidant Properties

Iodide salts are defined as mild reducing agents, and several react with oxygen to form iodine. A reducing agent is described as a chemical term for an antioxidant. Its antioxidant properties are expressed as a redox potential quantitatively:

I− ⇌ ​1⁄2 I2 + e  E° = 0.54 volts.

Since the iodide is easily oxidized, a few enzymes readily transform it into electrophilic iodine agents as needed for the biosynthesis of myriad iodide-containing natural products. Also, iodide function as an antioxidant reducing species that can destroy the species of reactive oxygen like hydrogen peroxide, where the chemical equation is represented as follows:

2 I + peroxidase + H2O2 + histidine, tyrosine, lipid,..... → iodide-compounds + H2O + 2 e (which are antioxidants). Iodide structure I- can be given as follows.

Lewis Structure


Properties of Iodide

Let us look at the important properties of Iodide as tabulated below.



Molecular Weight or Molar Mass

126.904 g/mol


3.13 g/cm³, solid

Melting point

113.7 °C

Boiling Point

184.3 °C

Chemical Formula


Physical Properties of Iodide I


Irritating odour




It is a purple-pink gas, and the solid iodine is purple or dark grey in colour

Specific heat



128 g/100 ml (6 °C)

Chemical Properties of Iodide I

  • The iodide compound's sodium salt reacts with lead nitrate and produces a yellow precipitate of sodium nitrate and lead iodide. The chemical equation for the same is given as follows.

Pb(NO3)2(aq) + 2 NaI(aq) → 2 NaNO3(aq) + PbI2(s) (which is a yellow precipitate)

  • Potassium iodide salt combines with chlorine by producing iodine and potassium chloride. Here, chlorine replaces iodine due to the fact that chlorine is more reactive than iodine. The chemical equation for the same is given as follows.

2KI + Cl2 → 2KCl + I2

Uses of Iodide I

Let us look at the important uses of the iodide compound as listed below:

  • Iodide holds a disinfectant property. It is not readily affected because of the chlorine by organic content or water pH, but the cold water temperature markedly reduces iodide disinfectant activity.

  • Iodine preparations like povidone-iodine can be used to disinfect the skin before surgery. The allergic reactions to the iodine are more common and should be evaluated carefully since the resultant stain may mask the swelling and redness.

  • Potassium iodide can also be added as a nutrient to prevent goitre, a thyroid problem, which is caused by a lack of iodine and prevent a mental retardation form associated with the deficiency of iodine.

Valency of Iodide

Iodine valence is -1 because, in its last shell, it has 7 electrons and receives one electron from making it stable.

Health Hazard of Iodide

A few of the Health Hazard of iodide can be given as follows.

The major and primary effects of long-term oral exposure to the elevated amounts of inorganic iodide are given as paradoxically, hypothyroidism and hyperthyroidism. The excess intake of this iodide compound can inhibit the synthesis and release of thyroid hormone, resulting in goitre and hypothyroidism.

FAQ (Frequently Asked Questions)

Q1. What is Iodide Used for?

Ans. Potassium iodide (with the chemical formula, KI) is described as a chemical compound used to shield the thyroid gland from potential radioactive iodine damage (radioiodine). A few radiological emergencies can also emit large amounts of radioiodine into the air.

Q2. Where Can the Iodide be Found?

Ans. Iodine is a compound, which is naturally found in the ocean and is preserved in its tissues by particular water plants and sea fish. Iodine can also be present in the water, soil, and air naturally. The seas are treated as the primary and major sources of natural iodine.

Q3. Is Iodized and Iodide the Same Thing?

Ans. Iodide and iodine are the only same product's different expressions. Whereas iodides only reflect healthy ingestion of iodine form. And. Iodides also contain the drawback of requiring n additional body energy to sever the iodide bond to use the compound of iodine.  

Q4. What is Iodide Compound Good for?

Ans. Iodine compound lowers the thyroid hormone, and it can easily destroy microorganisms such as fungi, amoebas, bacteria, including others. A specific form of iodine, known as potassium iodide, can often be used to treat nuclear accident effects, but it does not help prevent them.