Facts About Iodine

Electron configuration and elemental properties of iodine.
Credit: Greg Robson/Creative Commons, Andrei Marincas | Shutterstock
Atomic Number: 53
Atomic Symbol: I
Atomic Weight: 126.90447
Melting Point: 236.7 F (113.7 C)
Boiling Point: 363.9 F (184.4 C)
Iodine is a bluish-black, lustrous solid.
Credit: Images of elements

Word origin: Iodine is named from the Greek term for violet, iodes, after the purple hue in its vapors.

Discovery: French chemist Bernard Courtois discovered iodine in 1811. Courtois was extracting sodium and potassium compounds from seaweed ash. Once these compounds were removed, he added sulfuric acid (H2SO4) to further process the ash. He accidentally added too much acid and a violet cloud formed. The gas condensed on metal objects in the room, creating solid iodine.

Properties of iodine

Iodine is a bluish-black, lustrous solid under standard conditions. Iodine is one of the halogens, a subset of the nonmetals, but is less reactive than most others in the group. [See Periodic Table of the Elements]

Iodine gas
Iodine can sublimate into a violet-pink gas.
Credit: Images of elements

Iodine can sublimate into a violet-pink gas. It is slightly soluble in water but dissolves easily in chloroform, carbon tetrachloride, or carbon disulfide to form bright purple solutions. It also exhibits some properties of metal.

Iodine vapor is irritating to the eyes and can cause lesions on the skin. Thirty isotopes of iodine are known, however, only one isotope is naturally occurring.

Sources of iodine

Iodine occurs naturally on Earth mainly as iodides found in oceans and brine pools. Seaweed or kelp is a main source of natural iodine. It also occurs in Chilean saltpeter, caliche or nitrate-bearing earth, brine, and in brackish waters from old oil and salt wells. Very pure iodine is obtained from a reaction of potassium iodide and copper sulfate.

Iodine ampules
Weak solutions of iodine are used to treat wounds.
Credit: Helga Chirk / Shutterstock

Uses of iodine

Iodine is an essential part of nutrition and medicine. Iodide compounds and thyroxine are used in medicine. A solution of potassium iodide (KI) and iodine in alcohol is used to treat external wounds. Iodine is also used to treat conjunctivitis, prevent goiters, for eye health and many other illnesses.

It is almost always added to table salt (iodized salt). Additionally, potassium iodide is used in photography and the free element is added to laundry starch solution.

(Source: Los Alamos National Laboratory)

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