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Iodine

The element was discovered long back in 1811 by Barnard Courtois. Since it was the time of Anglo French war, the British army prevented the French army to get saltpetre for making gun powder and hence the urge to discover the alternate. The scientific formula for saltpetre is potassium nitrate and to prepare this compound the use of Iodine was necessary. Apart from historical facts, Iodine is one of the essential elements for human nutrition. It is calculated that more than almost 200 million people around the world have insufficient iodine intake and are found to be at risk of developing iodine deficient diseases. 

Various methods of quantifying the iodine level in soil, plants and various food items are carried out but the most common method of iodising salt is found to be slow but effective. The levels of iodine in these samples can be carried out by iodometric tests, where addition of oxidising agents like KMnO4 helps taking out iodine from their iodide forms.

 

Iodine Atom Structure

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Around 1969 the hyper valency for some specific molecules involving atoms exceeding the original octet valence was declared by Musher. This was done by utilising more lone pairs for the actual bonding. The hyper valent bonds of iodine were defined as a three center four electron bond using a valence bond model. 

The tri valent iodine molecules (IX3 or ArIX2 or λ3 –iodanes) usually take the T shape structure with linear form of X – I – X with a 3 center 4 electron and a highest occupied molecular orbital at hyper valent iodine ligand.

These hyper valent bonds are weaker than regular covalent bonds. The least electronegative amongst the three ligands is attached to iodine atom through a common covalent bond. The penta valent iodine molecules (IX5 or ArIX4 or λ5 –iodanes) have two of the hyper valent iodine bonds and make a square bi pyramidal structure.

For classification of hyper valent molecules, the nomenclature follows a specific pattern. It is known as N – I – L, or number of formal valence shell electrons about iodine atom, L is the number of ligands and I for Iodine atoms. 

So the overall Iodine structure that we get to see is T shaped IX3, the hyper valent bond with 3 center and 4 electrons (X – I – X) with both lower and higher molecular orbital order and finally the penta valent structure IX5

Iodine Properties

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Iodine is a non-metallic element which belongs to the halogen family of group 17 or VIIA of the periodic table. The existence in nature is basically monovalent anion in all kinds of brine and molecular compounds. 

Iodine can exist in several oxidation states like -1, 0, +1, +3, +5 and +7. The stable form of iodine is 127I. The chemical and physical properties of this element can vary with its elemental and molecular form of the said element. 

To understand this element better we can now look into the isolate this element by several methods. These isolation methods are taken from resources we come across in our everyday life. 

Ambient air: When we apply this method, a known volume of air is passed through a multistage filter and collect the particulate iodine. Hydrogen iodide (HI), molecular form of I2 vapour and hypoiodous acid or HOI, and the organic form of organo-iodine. 

For the particulate iodine fraction, the filters are extracted from sodium hydroxide or sodium sulphate solution containing the isotopic form of 129I as the internal standard. 

Once the filtration and acidification are over, silver nitrate is added to help precipitate the Iodine as silver iodide (AgI).

Water: 

In this method the sample is acidified with HCl and then taken for oxidation with H2O2 or even KMnO4 to help remove excess of oxidant. Then it is taken for titration with potassium iodate or KIO3 and then this is followed by spectrometry.

Drinking water:

In this method the use of high performance liquid chromatography technique along with ultra violet detection. The sample separation is carried out with analytical high performance liquid chromatography column. The iodate which is eluted is then reacted with acidified solution of bromine and then finally form tri bromide.  

Drinking water for total iodine:

After the addition of K2CO3 to this extracted sample, it is then centrifuged to help remove precipitated alkaline earth metals. The measurement of Iodine with the nitric acid addition along with NaCl, ammonium ferric sulphate and potassium sulfur cyanide and then finally taken for spectrometry. 

Sea water:

The iodine in this sample is precipitated with silver nitrate. Once the precipitation is over, the precipitate is dissolved in acetic acid and then saturated with bromine. Once the filtration is over the filtrate is then reduced in volume a finally reacted with starch solution and cadmium iodide. Once this is over it is taken for spectroscopic analysis.

Soil:

Once the sample is completely dried, the sieving is carried out and then finally extracted with 2N (2 normal solution) sodium hydroxide. The addition of arsenious acid is followed and then finally taken for spectrometry tests.

Vegetation:

The sample is prepared by microwave digestion using nitric acid or hydrogen peroxide. This is followed by treatment with sodium thiosulphate solution to help convert the iodate to iodide. 

Iodine Isotopes

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The different version of atoms of any particular element called isotopes can sometimes be very useful. In most of the cases though these are radioactive and that means they are either unstable or radiate of spontaneously. 

In nature, iodine atom has 74 neutrons in the nucleus. This is considered to be stable due to its abundancy in nature. This is stable mainly because of its non-spontaneous characteristics. Decays slowly and is available in all kinds of vegetables and fruits.

Iodine has a number of isotopes used for various purposes but most of these have short half-life (123I) and hence is used only for single photon emission computed tomography. 

Similarly the iodine 125 or 125I is produced by neutron bombardment of Xenon 124. The first product of Xe-125 then decays to give Iodine 125. 

The effect of this radiation on tissues helps in removing tumours and prostate cancer. The introduction of radioactive iodine to organic compounds is carried out by direct iodination with iodine or by halogen exchange. 

Interesting Facts about Iodine

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There are many known facts available everywhere about Iodine and its uses in our daily life but apart from these there exists some unknown facts as well about this element.

Iodine has some interesting facts about ferments and the accumulation of iodine. Iodine in small concentration can have an effect upon the activities of ferments. These ferments are capable of accumulating iodine. Iodine and tuberculosis organisms can accumulate and this limits of accumulation depends upon the level of tuberculosis process. 

Iodine application in pharmaceutical is well known but iodine is also used as the contrasting agent for any type of imaging methods, especially in computed tomography or CT scan. 

We all know that iodized salts help in goitre related diseases but very few know that the amount of iodine that is mixed in the producing units become almost close to nano level when we are ready to consume it. Iodine being very volatile can never remain isolated in edible salt. Whatever level of iodides that still remains in salt gets almost vaporised as soon we use it in hot pan. 

The reason that even this small amount on a daily basis has actually helped eradicate goitre problem is because the amount of iodine required for a healthy life is also very small and hence no major problem.

Deficiency of iodine can also cause goitre in animals. But then how do stray animals manage the level of iodine in their body? It is interesting to note that animals have these strange habit of licking specific rocks and other surfaces occasionally. Some animals manage to maintain the level by eating vegetables which are rich in iodine. 

After any nuclear holocaust the air becomes dense with toxic iodine levels. Ingesting or inhaling these iodine is highly carcinogenic. 

Iodine Uses

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  • Iodine is used as disinfectant for treating water for over 200 years.
  • The use of iodine as disinfectant is again a topic of sensitivity because thyroid is one of major condition humans and animals suffer 
  • Iodine is used in war scenario for cleansing and sterilizing cuts and wounds
  • Iodine in its isotopic form is used as remedy against cancer
  • Iodine is also used to help protect against microbes and pathogens 
  • The beta form of iodine is used as remedy for throat infection and gurgling 
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