Iodine: Applications and Properties

Iodine is a chemical element of the group 7 of the Periodic Table that is also known as halogen group. It is the second halogen discovered after chlorine and is considered the heaviest of stable halogens. The chemical symbol for the element is I, its unique atomic number is 53. The formula for elemental iodine is I2 since its molecules are diatomic, the CAS № 7553-56-2.

Physical and Chemical Properties

Some properties of iodine resemble those, characterizing all the elements of the group, like bromine, fluorine, etc. However, it also has some individual patterns. At the standard room temperature and pressure, this chemical is solid dark-grey to purple-black color with metallic luster. When heated, forms a purple vapor. It belongs to the category of reactive nonmetals. Here are some more physical characteristics:

  • Melting point: 113.7°C;
  • Boiling point: 184.4°C;
  • Density: 4.933 g/cm3;
  • Atomic mass: 126.904;
  • Specific gravity: 4.93 at 20 °C.

This halogen is slightly soluble in water; however, in nonpolar solvents like hexane or carbon tetrachloride, its solubility is much higher. Its usual oxidation states in the compounds are iodate, iodide and different periodate anions.

Discovery History

Iodine was first discovered in 1811. The French chemist Bernard Courtois was making saltpeter, using seaweeds as the source of potassium. However, one day, while processing the ash, he added too much sulfuric acid, and a cloud of purple vapor erupted from the mass. This vapor condensed and formed dark crystals.

Bernard Courtois brought the samples of the new substance to Charles-Bernard Desormes, Nicolas Clément, Joseph Gay-Lussac and André-Marie Ampère. Desormes and Clément confirmed it was a new element, and Gay-Lussac named it “iodine”, from the Greek word translated as “violet”. However, Humphry Davy was the first one to describe the substance to the Royal Society of London and for almost 50 years was mistakenly considered as its discoverer.


Iodine has many uses of varying importance. Nearly half of it serves for the creation of different organoiodine compounds, all the rest are used to form inorganic iodine compounds, potassium iodide, or just remain as a pure element.

The commercial use of this halogen began in 1839, after the invention of daguerreotype technique. Nowadays, the applications of this element are much wider. It is used to prepare disinfectants for water treatment. Besides, it is a part of some topical medical disinfectants for cleaning wounds and sterilizing skins before surgical operations. Pure iodine and its compounds are included in many drugs and added in very small amounts even to table salt.

It takes part in the manufacture of polarizing filters for LCD displays and acts as an X-ray radiocontrast agent. Further, this halogen is extensively used in analytical chemistry, since many of its procedures are based on uptake or release of iodine.

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