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chemical element with atomic number 53
Iodine, 53I
/ˈaɪədaɪn, -dɪn, -diːn/ ​(EYE-ə-dyn, -⁠din, -⁠deen)
lustrous metallic gray, violet as a gas
Standard atomic weight Ar, std(I)
126.90447(3)[1]
Iodine in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt
Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a lustrous, purple-black non-metallic solid at standard conditions that melts to form a deep violet liquid at 114 degrees Celsius, and boils to a violet gas at 184 degrees Celsius. However, it sublimes easily with gentle heat, resulting in a widespread misconception even taught in some science textbooks that it does not melt. The element was discovered by the French chemist Bernard Courtois in 1811, and was named two years later by Joseph Louis Gay-Lussac, after the Greek ἰώδης "violet-coloured".
Iodine occurs in many oxidation states, including iodide (I−), iodate (IO−
3), and the various periodate anions. It is the least abundant of the stable halogens, being the sixty-first most abundant element. It is the heaviest essential mineral nutrient. Iodine is essential in the synthesis of thyroid hormones.[4] Iodine deficiency affects about two billion people and is the leading preventable cause of intellectual disabilities.
The dominant producers of iodine today are Chile and Japan. Iodine and its compounds are primarily used in nutrition. Due to its high atomic number and ease of attachment to organic compounds, it has also found favour as a non-toxic radiocontrast material. Because of the specificity of its uptake by the human body, radioactive isotopes of iodine can also be used to treat thyroid cancer. Iodine is also used as a catalyst in the industrial production of acetic acid and some polymers.
2.1 Isotopes
3 Chemistry and compounds
3.1 Charge-transfer complexes
3.2 Hydrogen iodide
3.3 Other binary iodides
3.4 Iodine halides
3.5 Iodine oxides and oxoacids
3.6 Polyiodine compounds
3.7 Organoiodine compounds
4 Occurrence and production
5.2 Spectroscopy
5.3 Medicine
5.3.1 Elemental iodine
5.3.2 Other formulations
6 Biological role
6.1 Dietary intake
6.2 Deficiency
7 Precautions
7.1 Toxicity
7.1.1 Occupational exposure
7.1.2 Allergic reactions
7.2 US DEA List I status
History C ⟶ 575 ∘ C thermal gradient Ta 6 I 14 {\displaystyle {\ce {TaI5{}+Ta->[{\text{thermal gradient}}][{\ce {630^{\circ }C\ ->\
Most of the iodides of the pre-transition metals (groups 1, 2, and 3, along with the lanthanides and actinides in the +2 and +3 oxidation states) are mostly ionic, while nonmetals tend to form covalent molecular iodides, as do metals in high oxidation states from +3 and above. Ionic iodides MIn tend to have the lowest melting and boiling points among the halides MXn of the same element, because the electrostatic forces of attraction between the cations and anions are weakest for the large iodide anion. In contrast, covalent iodides tend to instead have the highest melting and boiling points among the halides of the same element, since iodine is the most polarisable of the halogens and, having the most electrons among them, can contribute the most to van der Waals forces. Naturally, exceptions abound in intermediate iodides where one trend gives way to the other. Similarly, solubilities in water of predominantly ionic iodides (e.g. potassium and calcium) are the greatest among ionic halides of that element, while those of covalent iodides (e.g. silver) are the lowest of that element. In particular, silver iodide is very insoluble in water and its formation is often used as a qualitative test for iodine.[44]
Iodine halides
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