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.
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 |
|
