Iodine is found in the Earth's crust in very small amounts - 3*10-5% of the mass, and in addition, iodine is spray element. Reactive nonmetal refers to a halogen group. Because of its ubiquity, this element is literally everywhere. Fersman wrote about it this way: "...Everything is impregnated with iodine - the solid earth and rock... much more of it in the sea water a lot of iodine in the soil, flowing waters, even more in living organisms We use iodine... from the air... we introduce iodine in your body with food and water, we can not live without it..."

Simple iodine substance under normal conditions is crystal black and gray with a purple metallic luster, readily forms a purple pair that have a pungent smell

It is difficult to fully characterize the picturesque iodine.

Simple iodine substance under normal conditions is crystal black and gray with a purple metallic luster, readily forms a purple pair that have a pungent smell. Diatomic molecule of the substance - I2.

Iodine melts at a relatively low temperature of 113,5 degrees Celsius. And melt it is not so easy. For this purpose it is necessary that the iodine vapor pressure above the crystals is not less than one atmosphere. Due to the heat outdoors solid iodine sublimates immediately. And when the dark-gray crystals of iodine is heated in a sealed tube, it is clearly seen as a vessel filled with violet vapor, and then there is a hard, heavy and mobile liquid. This is a liquid iodine...

History of the discovery of iodine as follows. In 1811, when the French army dropped to his knees almost all of Europe, Emperor Napoleon Bonaparte hastily preparing for war with Russia. The new military campaign he needed gunpowder. Moreover, a lot of gunpowder. Get out of the sea nitrate was impossible, as the British fleet controlled all the coastal waters of France. Because of this, the French had to develop its production of potassium nitrate, the main component of which was potassium K2CO3. This was prepared by washing the ashes of seaweed.

Potash saltpeter receives pharmacist Courtois. Once again, closing his pharmacy at night, he decided to drive on the street his cat. Frightened cat jumped through the shelf and accidentally pushed the glass of concentrated sulfuric acid. The glass fell, crashed, got acid on the ash from seaweed. Surprised pharmacist immediately saw a cloud of smoke violet. It was unknown at the time of free iodine. So the cat helped in the discovery of this chemical element.

Iodine chemically quite active, albeit to a lesser extent than chlorine and bromine. Fairly well-known qualitative reactions to iodine is its interaction with starch, in which there is a blue coloration due to the formation of compounds. This reaction was discovered in 1814 by Jean-Jacques Colin and Henri-Francois Gautier de Klobri. With metals iodo vigorously with gentle heating reacted to form iodide. Since hydrogen iodine reacts only when heated and incompletely, forming hydrogen iodide. Iodine is a strong oxidant less than fluorine, chlorine and bromine. Hydrogen sulfide H2S, Na2S2O3 and other reducing restore it to the ion I-.