Iodine

Iodine,  ₅₃I

General properties
Pronunciation	/ˈaɪ.ədaɪn, -dɪn, -diːn/ ​(EYE-ə-dyne, -din, -deen)
Appearance	lustrous metallic gray, violet as a gas
Standard atomic weight (Ar, standard)	7002126904470000000♠126.90447(3)
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 Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson Br ↑ I ↓ At tellurium ← iodine → xenon
Atomic number (Z)	53
Group	group 17 (halogens)
Period	period 5
Element category	diatomic nonmetal
Block	p-block
Electron configuration	[Kr] 4d10 5s2 5p5
Electrons per shell	2, 8, 18, 18, 7
Physical properties
Phase at STP	solid
Melting point	386.85 K ​(113.7 °C, ​236.66 °F)
Boiling point	457.4 K ​(184.3 °C, ​363.7 °F)
Density (near r.t.)	4.933 g/cm3
Triple point	386.65 K, ​12.1 kPa
Critical point	819 K, 11.7 MPa
Heat of fusion	(I2) 15.52 kJ/mol
Heat of vaporisation	(I2) 41.57 kJ/mol
Molar heat capacity	(I2) 54.44 J/(mol·K)
Vapour pressure (rhombic) P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 260 282 309 342 381 457
Atomic properties
Oxidation states	7, 6, 5, 4, 3, 1, −1 ​(a strongly acidic oxide)
Electronegativity	Pauling scale: 2.66
Ionisation energies	1st: 1008.4 kJ/mol 2nd: 1845.9 kJ/mol 3rd: 3180 kJ/mol
Atomic radius	empirical: 140 pm
Covalent radius	139±3 pm
Van der Waals radius	198 pm
Spectral lines
Miscellanea
Crystal structure	​orthorhombic
Thermal conductivity	0.449 W/(m·K)
Electrical resistivity	1.3×107 Ω·m (at 0 °C)
Magnetic ordering	diamagnetic
Magnetic susceptibility	−88.7·10−6 cm3/mol (298 K)
Bulk modulus	7.7 GPa
CAS Number	7553-56-2
History
Discovery and first isolation	Bernard Courtois (1811)
Main isotopes of iodine
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct 123I syn 13 h ε, γ 123Te 124I syn 4.176 d ε 124Te 125I syn 59.40 d ε 125Te 127I 100% stable 129I trace 1.57×107 y β− 129Xe 131I syn 8.02070 d β−, γ 131Xe 135I syn 6.57 h β− 135Xe
view talk edit | references | in Wikidata

Iodine is a chemical element with symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a lustrous, purple-black metallic solid at standard conditions that sublimes readily to form a violet gas. The elemental form was discovered by the French chemist Bernard Courtois in 1811. It was named two years later by Joseph-Louis Gay-Lussac from this property, 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 even less abundant than the so-called rare earths. It is the heaviest essential mineral nutrient. Iodine is essential in the synthesis of thyroid hormones.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.