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.
In everyday life, iodide occurs most often as a component of iodine-added salts prescribed by many governments. Iodine deficiency affects 2 billion people worldwide and is the most common preventable cause of intellectual disability.
Structure of Inorganic Iodides
Triiodide ion
I2 + I- ➡I3-
Three center, four electron bonding [I-I-I]-
Lewis Structure
I-
Chemical substance consisting of iodine combined with another element.
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 color, which is chemically represented as follows:
I− + I2 ⇌ I3−
Characteristics of Iodide
Iodine has a moderate vapour pressure at room temperature and in an open vessel slowly sublimes to a deep violet vapour that is irritating to the eyes, nose, and throat. This chapter tabulates the physical properties of iodine in solid, liquid, and gas phases. Iodine dissolves easily in most organic solvents such as hexane, benzene, carbon tetrachloride, and chloroform owing to its lack of polarity, but it is only slightly soluble in water. However, the solubility of elemental iodine in water can be increased by the addition of sodium or potassium iodide. Iodine accepts electrons from the solvent molecule into its lowest unoccupied molecular orbital (LUMO). This reduces the transition energy of the iodine atom from the highest occupied molecular orbital (HOMO) to LUMO, changing the characteristic purple to brown color.
Physical Properties of Iodide
The physical characteristics of iodine are those that can be observed without changing one substance to another. Physical characteristics are things that we can perceive, such as color, luster, freezing point, boiling point, melting point, density, hardness, and odor. The physical characteristics of iodine are as follows.
Chemical Properties of Iodide
Chemical properties can only be observed during a chemical reaction. Reactions to substances can be caused by changes due to burning, rusting, heating, explosions, discoloration, etc. The chemical properties of iodine are:
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 because chlorine is more reactive than iodine. The chemical equation for the same is given as follows.
2KI + Cl2 → 2KCl + I2
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− ⇌ \[\frac {1} {2}\] 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 functions 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.
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 goiter, a thyroid problem, which is caused by a lack of iodine and prevents 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 goiter and hypothyroidism.
FAQs on Iodide (I⁻)
1. What is an iodide ion?
An iodide ion is a single atom of iodine that has gained one electron. This gives it a negative charge, making it an anion (a negatively charged ion). Its formation allows iodine, which is a non-metal, to form stable ionic compounds with metals, such as potassium iodide (KI) or sodium iodide (NaI).
2. What is the chemical formula for the iodide ion?
The chemical formula for the iodide ion is I⁻. The 'I' is the symbol for the element iodine, and the superscript minus sign '⁻' indicates that it has a negative charge of one. It is important not to confuse the symbol 'I' with the letter 'L'.
3. How is iodide different from the element iodine?
Iodide (I⁻) and iodine (I₂) are two different forms of the same element, with key differences in their structure, charge, and function.
- State: Iodine (I₂) is the elemental form, a diatomic molecule where two iodine atoms are bonded together. Iodide (I⁻) is the ionic form (anion), which is a single atom carrying an extra electron.
- Charge: Elemental iodine (I₂) is neutral with no charge. The iodide ion (I⁻) has a negative charge of -1.
- Role: Humans typically consume iodine in the form of iodide, often from iodized salt. Elemental iodine is primarily used as a disinfectant and in chemical synthesis.
4. Where is iodide naturally found?
The primary natural source of iodide is the ocean. It is absorbed and concentrated by marine life, especially seaweed (like kelp) and sea fish. Iodide is also found in smaller amounts in soil and air, originating from the oceans. Commercially, it is often extracted from brine deposits associated with oil and gas fields.
5. What are some common uses of iodide compounds?
Iodide compounds have several important applications across different fields:
- Nutrition: Potassium iodide (KI) is added to table salt to create iodized salt, a crucial method for preventing iodine deficiency disorders like goitre.
- Medicine: Potassium iodide is used to protect the thyroid gland from radioactive iodine exposure during a nuclear emergency. Povidone-iodine is a widely used topical antiseptic.
- Chemical Synthesis: Iodide ions are effective catalysts and reagents in many organic chemistry reactions, such as the Finkelstein reaction.
- Weather Modification: Silver iodide (AgI) is used in cloud seeding to induce precipitation due to its structural similarity to ice.
6. Are all iodide salts soluble in water?
No, not all iodide salts are soluble in water. While most common iodides, such as potassium iodide (KI) and sodium iodide (NaI), are highly soluble, there are key exceptions mentioned in solubility rules. The iodides of silver (AgI), lead (PbI₂), and mercury(I) (Hg₂I₂) are notably insoluble in water and form distinct coloured precipitates when their respective ions are mixed in a solution.
7. Why is the iodide ion considered a good reducing agent?
The iodide ion (I⁻) is a good reducing agent because of its large atomic size and relatively low electronegativity compared to other halogens. Its outermost electron is far from the nucleus and is not held tightly. This makes it easy for the iodide ion to lose this electron (undergo oxidation) and donate it to another substance, thereby reducing that substance. This property is why iodide can react with and decolorize strong oxidizing agents.
8. How can you test for the presence of iodide ions in a solution?
A common laboratory test for identifying iodide ions (I⁻) in a solution involves using an oxidizing agent and a starch indicator. The typical procedure is:
- First, an oxidizing agent like chlorine water or acidified hydrogen peroxide is added to the sample solution. This oxidizes the colourless iodide ions (I⁻) into elemental iodine (I₂), which has a brownish colour in water.
- Next, a few drops of starch solution are added.
- If iodide ions were present, the newly formed iodine (I₂) reacts with the starch to produce a characteristic deep blue-black colour, confirming a positive test.
9. How do the properties of halide ions change down Group 17, and where does iodide fit in?
As you move down Group 17 (the halogens) from fluorine to iodine, there are predictable trends in the properties of their ions (halides). The iodide ion (I⁻) exemplifies the characteristics at the bottom of the group:
- Ionic Radius: The iodide ion has the largest ionic radius among the common halides (F⁻, Cl⁻, Br⁻, I⁻) because it has the most electron shells.
- Reducing Power: The ability of a halide ion to act as a reducing agent increases down the group. Therefore, the iodide ion (I⁻) is the strongest reducing agent among the stable halides.
- Oxidizing Power of the Element: Conversely, elemental iodine (I₂) is the weakest oxidizing agent among the halogens (F₂, Cl₂, Br₂, I₂).
10. Why is silver iodide (AgI) effective for cloud seeding?
Silver iodide (AgI) is effective for cloud seeding because its crystalline lattice structure is very similar to that of natural ice. When microscopic particles of AgI are introduced into clouds containing supercooled water droplets (water below 0°C but still liquid), they act as artificial ice nuclei. The water droplets freeze onto the AgI particles, forming ice crystals. These crystals grow larger and heavier until they fall as rain or snow, initiating precipitation.
