Iodine belongs to halogen group in the periodic table. Iodine is an essential mineral commonly found in sea food. Iodine plays an important role in proper functioning of thyroid hormone in the human body.
Discovery and History
Iodine Iodine sublimates into a beautiful violet vapor when heated: There's a torch under the plate in this photo. Iodine and iodine solutions were used as disinfectants before better antiseptic agents were found. Scroll down to see examples of Iodine. Iodine is a nonmetallic, nearly black solid at room temperature and has a glittering crystalline appearance. The molecular lattice contains discrete diatomic molecules, which are also present in the molten and the gaseous states. Above 700 °C (1,300 °F). Learn about the medical uses, claims, and side effects of iodine. Iodine Iodine sublimates into a beautiful violet vapor when heated: There's a torch under the plate in this photo. Iodine and iodine solutions were used as disinfectants before better antiseptic agents were found. Scroll down to see examples of Iodine.
During Napoleonic Wars, Bernard Courtois, a French chemist discovered Iodine in 1811, while he was extracting sodium and potassium compounds from seaweed ash. He noticed a cloud of violet gas when sulfuric acid was added to the ash and proposed that a distinct element is present in the ashes. Two years later Joseph Louis Gay-Lussac gave the name “iode” to this element, that is the Greek word for ‘’violet colored’’. Iodized table salt was sold first time in Michigan in 1924 .
Iodine is the 61st most abundant element on Earth. It is a rare element and does not exist in free -state. About 50mg per metric tons of iodine is present in the sea water . Iodine is the least abundant halogens and is present in only 0.46 ppm (parts per million) of earth crust rocks. The mineral Caliche (sedimentary rock), is the main source of iodine. Brine (high concentration of iodine in water) is also used for the extraction of iodine and Japan and USA have major deposits of brine. Iodine is also formed in oysters, seaweeds and cod liver. Human body contains iodine in the form of thyroxin produced by the thyroid glands. Iodine is chiefly obtained from sodium iodate (NaIO3) and sodium periodate (NaIO4). Chile and Japan are prime producer of iodine in the world.
Iodine is bluish black, shiny solid and has a pungent odor. It is non -metal but show some metallic properties. Iodine is hardly dissolved in water but gives a yellow color solution. Iodine belongs to group halogens, that are the salt formers. Iodine when dissolved in chloroform gives purple color solution. Melting point and boiling point of iodine are highest as compared to other halogens. Its melting point is 113.70C and boiling point is about 184.30C. Atomic number of iodine is 63 and easily attached with organic compounds. Iodine’s atomic weight is 126.90. The density of iodine is very low, about 4.94g/ml.
Iodine is reactive element among the halogens. It has lowest ionization energy and is easily oxidized. Iodine has various oxidation states, including +1 (iodides), +3, +5 (iodates) and +7 (periodate). and is more stable than bromine and chlorine. Iodine molecules act as Lewis acid with combined with many Lewis bases. Electron affinity of iodine is also similar to other halogen atoms. The simplest compound of iodine is hydrogen iodide. It is a colorless gas that reacts with oxygen to give water and iodine. Iodine does not react with oxygen or nitrogen. Iodine reacts with nonmetals and forms iodides, for example, silver and aluminum are converted into iodides. The iodide ion is a strong reducing agent and gives up electron easily. Iodide solutions are colorless but gives brownish tint due to oxidation. Iodine reacts with zinc and forms zinc iodide. This reaction is very exothermic and produce violet color vapors of iodine.
Significance and Uses
- Iodine in form of potassium iodide and alcohol is widely used as a disinfectant.
- Radioactive isotopes of iodine 131I is used to treat thyroid cancer.
- Iodine is used as catalyst in the preparation of acetic acid.
- Iodine is widely used in laboratories to test the presence of starch in solution.
- Iodine is used in iodoform test to detect the presence of methyl ketones.
- Iodine has antiviral and antimicrobial action.
- Erythrosine, an organo-iodine compound is important food coloring agent.
- Potassium iodide is used to make photographic films.
- Iodine is added in table salt for nutrition to prevent goiter in the thyroid gland.
- Tungsten iodide is used to stabilize filaments in light bulbs.
- Iodine is used in making of dyes and various pharmaceuticals products.
- Iodine- 129 is used in rainwater studies.
- Potassium iodide can be used for the treatment of people in a nuclear disaster area.
Iodine is an essential part of human diet because the body does not make iodine and it is needed to produce thyroid hormones that regulate the growth and metabolism of the body. Deficiency of iodine may cause enlargement of thyroid gland (goiter) hypothyroidism and intellectual disabilities in infants and children. Goiter disease is also present in animals like dog, cattle, goat and birds. People who consume iodine based food on daily bases can also face various health problems, such as disturbed heart beats and loss of weight. Pure iodine is dangerous and poisonous if ingested. In U.S, the recommended daily dose of iodine is 110 to 113µg for infants to 12 months, 90 µg for 1 to 18 years old, 220µg for pregnant women and 290µg for lactation. U.S Food and Drug recommends an intake of 150µg per day of iodine for both men and women.
Isotopes of Iodine
Iodine has 34 isotopes with mass numbers ranging from 108 to 141. 127I is the only stable isotope of iodine . The longest-lived isotope is 129I has half-life of 15.7 million years . 125I has half-life of 59 days.
. Audi, G.; Bersillon, O.; Blachot, J.; Wapstra, A. H. (2003). “The NUBASE evaluation of nuclear and decay properties” (PDF). Nuclear Physics A. 729: 3–128.
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Iodine is a non-metallic, solid element that belongs to the halogen family. This element makes a bold statement with its dark, shiny, gray-blue-black color. This eye-catching element is sure to be interesting.
Cool Iodine Facts
- Iodine’s name originates from the Greek word “ioeides”, meaning violet.
- Like bismuth, iodine plays a crucial role in the drug industry. Halogen atoms are sometimes incorporated into lead drugs, which are the starting point of drug development. This results in having a lipophilic drug, meaning it is not very water-soluble and non-polar. Non-polar drugs are able to easily transport across lipid membranes and tissue. The addition of halogens improves this property.
- More iodine is found in the ocean than the Earth’s crust. Seaweed in particular contains high concentrations of the element.
- The only naturally occurring isotope of iodine is iodine-127. Unlike pure iodine, it exists by itself in nature. Other isotopes are man-made.
- Iodine-131 is an important radioactive isotope. It has a high half-life of eight days. It is put into medicine to regulate the thyroid gland, treat goiter, treat thyroid cancer, and locate tumors.
- Iodine-129 changes from radioactive form to nonradioactive over the span of millions of years. The other radioactive isotopes change to their non-radioactive form in just seconds to days.
- From 1994 to 2000, worldwide iodine production increased from 13,726 tons to 18,993 tons.
Iodine vs Other Halogens
The element iodine belongs to the halogen family, along with fluorine, chlorine, bromine, and astatine. All halogens are highly electronegative and very reactive. However, compared to its family members, iodine is relatively less reactive. Still, it has the greatest reducing strength and readily gains electrons from other atoms. Out of the halogen family, iodine is the least soluble in water, with a solubility value of 0.03 grams per 100 grams of water. However, it reacts oppositely towards aqueous solutions of iodide, where it is very soluble. More specifically, this element reacts well with solutions containing potassium iodide (KI + I2 → KI3). KI acts to decrease the vapor pressure and to dilute iodine to make it safer.
Iodine Supplement Benefits
Iodine in Nature
Out of the halogen family, iodine is the least abundant. In nature, pure iodine is never alone. Instead, it exists as compounds. In addition to the Earth’s crust, this element is in seawater. Furthermore, thyroxine, a secretion of the thyroid gland in humans, contains iodine.
Iodine sublimates: Fact or fiction?
What is sublimation? Usually, when a solid vaporizes, it first has to melt into a liquid. When a solid sublimates, it directly transforms into vapor, completely skipping the liquid phase. This is an endothermic transition and only occurs when the temperature and pressure are below the triple zero. For iodine, the triple point is 113.5˚C at 12.1 kPa. Many believe that under these conditions, solid iodine will sublimate into gas. However, this is wrong.
There is a large misconception about how iodine can not be a liquid, an idea that even some textbooks are guilty of teaching. At normal pressures and at a temperature range of about 113.6˚C to 184.4˚C (236.48˚F to 363.92˚F), iodine exists as a liquid. Two factors feed into this misconception: First, iodine is very volatile. This makes it easy to explain how solid iodine can just simply vaporize. Second, iodine’s liquid state can be difficult to see; The vapor cloud’s intense violet color completely overwhelms the liquid.
Iodine Element Metal Or Nonmetal
As shown in the diagram, there is a point where the liquid and vapor states exist at the same time. By carefully controlling the temperature, so that it sits just above the melting point, one can visibly see the process of iodine melting.
Here is a quick video that demonstrates the liquid state of iodine:
Iodine’s Applications in Today’s World
Small amounts of iodine minerals are necessary for the production of vital thyroid hormones. These hormones play an essential role in humans and take part in controlling the rate of the heart, digestion, muscle contraction, and cell metabolism. Therefore, it is an important element in the drug development industry. Moreover, iodine is sometimes added to table salt. This not only ensures the incorporation of iodine in people’s diet but helps to prevent goiter. This is a disease when the thyroid gland swells and produces either a deficit or a surplus of thyroid hormones.
Elemental iodine can serve as an antiseptic. As stated, iodine and potassium iodide (learn what else reacts with potassium iodide here) form the triiodide, KI3. Solutions containing potassium iodide in alcohol kill germs that exist on external wounds. Compounds such as iodoform (CHI3) are also antiseptics.
Many may be familiar with Lugol’s iodine solution. This aqueous solution is almost guaranteed to be in any biology lab. This purple solution helps scientists detect the presence of starch in a substance, as the solution will turn dark blue.
History of Iodine
Bernard Courtois accidentally discovered iodine in 1811 while extracting potassium chloride from seaweed ash. After removing the compound, he added sulfuric acid to process the seaweed ash more. However, he added too much, producing a violet-colored vapor cloud. This gas condensed into crystals, which chemist Sir Humphry Davy later identified as solid iodine in 1813.
Iodine is a very reactive element. It reacts with water to form hypoiodite (OI–). The hypoiodite ion is unstable and difficult to produce, as it only occurs in solution. The element also reacts with hot nitric acid and hot alkali to form iodic acid and iodate, respectively. Iodic acid acts as an astringent and crystallizes when cooled; Iodate is what gets added to table salt. As reactive as iodine is, it is unaffected by the oxygen or nitrogen in the air.
Additionally, iodine sublimes easily, meaning its solid-state vaporizes when heated. Upon vaporization, a beautiful, dark violet cloud produces. While this cloud is alluring to look at, it is crucial to avoid inhalation, as it will cause irritation.
Iodine Clock Reactions
The iodine clock reaction is quite spectacular. In this phenomenon, two colorless solutions combine into another clear solution. Then, almost spontaneously it turns into a deep-blue color. It is very mysterious. In this reaction, a strong oxidizer reacts with a strong reducing agent. An example is potassium iodate (KIO3), a strong oxidizer reacting with sodium bisulfite (NaHSO3), a strong reducing agent. This forms iodine.
To go into more detail, we first start with a potassium iodate-starch solution. Sodium bisulfite’s anions act to reduce the potassium iodate in this solution. This produces iodide anions, I–, which react with the potassium iodate to form an iodine solution. This new solution then reacts with iodine and forms triiodide anions, I3–. The bisulfite anions will then act on the triiodide anions, which converts them back to the iodide anions. When this process is complete, the remaining triiodide anions react with the starch molecules, which instantaneously produces the fascinating deep-blue color.
Where does the name come from? Depending on the concentration of the starting materials, the clear solution will take more or less time to turn blue- hence the name, “clock” reaction. The higher the concentration is, the faster the reaction rate will be. Secondly, the reaction rate increases as the temperature increases. Lastly, adding a catalyst will speed up the reaction as well.
Nitrogen triiodide = DISASTER
When iodine reacts with ammonia, it produces a solid called nitrogen triiodide. This black powder is a very indecisive, inorganic compound. When nitrogen triiodide crystals are wet, they are stable. When dry, the crystals are dangerous- they are touch-sensitive and become explosive. While a small explosion lacks the power to cause much damage, a large explosion certainly will. Stay away from dry nitrogen triiodide!
Iodides, where iodine is in the negative one oxidation state, are often white but can have a variety of colors. Silver iodide is more of a dull light yellow, while lead iodide looks like beautiful yellow gold platelets, as you can see in the golden rain experiment. Mercury (II) iodide and Tin (IV) iodide are both a nice looking orangish-red.
Synthesis of Iodine
A method of obtaining iodine is by combining an iodine ion with a stronger oxidizing agent. For example, bromine is a stronger oxidizing agent than iodine. Preparing two iodine ions with aqueous Br2, form I2 and two bromine ions ( 2 I– + Br2 → I2 + 2 Br– )
Iodine Oxidation States
Elemental iodine is neutral and possesses an oxidation state of 0. However, when present in a compound, iodine can possess different oxidation states and is considered a strongly acidic oxide. In its compounds, the most common oxidation state is -1, which is seen in iodide, I–. It is also seen in states of +7, +5, +3, and +1.
An oxyanion is a polyatomic ion that contains oxygen. The four most common oxyanions of iodine are hypoiodite, IO–; iodite, IO2; iodate, IO3–; and periodate, IO4–. Respectively, they have the oxidation states of +1, +3, +5, and +7.
Hypoiodites are the conjugate base of hypoiodous acid, as it is produced from the deprotonation of hypoiodous acid. This monovalent anion is often utilized as a reagent for direct oxidation reactions.
Iodides are very unstable and are never isolated. They are mainly used as an intermediate when synthesizing iodate from iodide.
Iodates are the conjugate base of iodic acid. They are utilized for iodine clock reactions.
Periodates are the conjugate base of periodic acid, as they are products of periodic acid deprotonation. They are commonly used in oxidation reactions that split bonds between vicinal carbons and unsubstituted hydroxyl or amino groups.
Properties of Iodine
- Melting point: 386.9 K; 113.7°C; 236.7°F
- Boiling point: 457.6 K; 184.4°C; 363.9°F
- Density: 4.933 g/cm³
- Atomic weight: 126.904
- Atomic number: 53
- Electronegativity: 2.66
- Classification: Halogen
- Natural abundance in the Earth’s crust: 0.000049%
- Electron shell configuration: [Kr] 4d10 5s2 5p5
- Isotopes: Iodine-127 is the only stable isotope
- Found naturally in: Petroleum deposits and caliche ore deposits; Food; Seaweed
- Toxicity: Toxic, especially in large amounts
Where can I buy Iodine?
Buying iodine is difficult because it is a classified precursor for illegal drug manufacturing.