Iodine

I
Atomic No. - 53

In areas where there is little iodine in the diet, it's deficiency gives rise to goitre, so called endemic goitre.

The History Says

At the time, in past, when France was at war and gunpowder was in great demand, saltpeter was isolated from seaweed washed up on the coasts of Normandy and Brittany. To isolate the potassium nitrate, seaweed was burned and the ash was washed with water. The waste left was destroyed by adding sulfuric acid. One day Courtois added too much sulfuric acid and cloud of purple vapor rose. He noted that the vapor crystallized on cold surfaces making dark crystals. Courtois suspected that this was a new element but lacked the money to pursue his observations.

The Present Scenario

Chile is the world’s leading iodine producing nation. Japan is second. Russia also produces significant amounts of elemental iodine.

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The word "Iodine" has been derived from the Greek word "Iodes," which mean "violet." It is a chemical element in the periodic table with the symbol of 'I' and having atomic number of 53.

It is a bluish-black, lustrous solid which sublimes at the standard temperatures into a blue-violet gas having an irritating odor. Iodine dissolves easily in chloroform, carbon tetrachloride, or carbon disulfide and forms purple solutions. It is only slightly soluble in water.

Iodine was first discovered by Barnard Courtois, the son of manufacturer of saltpeter, in 1811.

Physical Properties of Iodine

Phase	Solid
Density	4.933 g/cm3
Melting point	386.85 K (113.7 °C, 236.66 °F)
Boiling point	457.4 K (184.3 °C, 363.7 °F)
Heat of fusion	(I2) 15.52 kJ/mol
Heat of vaprization	(I2) 41.57 kJ/mol
Heat capacity	(25 °C) (I2) 54.44 J/(mol-K)

Atomic Properties of Iodine

Crystal structure	Orthorhombic
Oxidation states	±1, 5, 7 (strongly acidic oxide)
Electronegativity	2.66 (Pauling scale)
Ionization energies	1st: 1008.4 kJ/mol 2nd: 1845.9 kJ/mol 3rd: 3180 kJ/mol
Atomic radius	140 pm
Atomic radius (calc.)	115 pm
Covalent radius	133 pm
Van der Waals radius	198 pm

Applications of Iodine

Deficiency of iodine in diet gives rise to goitre, so called endemic goitre. To combat such thing, a small amount of iodine is added to table salt in the form of sodium iodide, potassium iodide, potassium iodate and it is known as iodized salt. Some other uses of Iodine are as follows:

• One of the halogens, it is an essential trace element; the thyroid hormones, thyroxine and triiodothyronine contain iodine.
• Tincture of iodine is an essential component of any emergency survival kit. It is used for both to disinfect wounds and to sanitize surface water for drinking.
• In the field of organic chemistry and in medicine, Iodine compounds are important.
• Iodides and thyroxine, containing iodine, are used in internal medicine. In combination with alcohol, it is used externally to disinfect wounds.
• Silver iodide is used in photography.
• In nuclear disaster area, potassium iodide (KI) tablets are given to people. It prevents the body from absorbing the radioactive iodine and caesium, chemically related to potassium; by flushing the body with an excess of a related less-harmful chemical. The body removes the toxic chemical along with the antidote.
• To stabilize the filaments in light bulbs, tungsten iodide is used.
• Nitrogen triodide is an explosive and is commonly used in college pranks. It is too unstable to be used commercially.
• Iodine-131 is used as a tracer in medicine.

Daily Dose of Iodine

The World Health Organization (WHO) recommends the following average intake of Iodine for different age group and status:

Age (years) or status	Intake (micrograms/day)
0 to 1	50
1 to 6	90
7 to 12	120
Greater than 12	150
Pregnancy	200
Lactation	200