Iodine

Iodine,  ₅₃I

General properties
Appearance	lustrous metallic gray, violet as a gas
Staundart atomic wecht (Ar, staundart)	7002126904470000000♠126.90447(3)
Iodine in the periodic cairt
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 Airn Cobalt Nickel Capper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Siller (element) 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 Gowd Mercur (element) Thallium Leid (element) 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 Ununtrium Flerovium Ununpentium Livermorium Ununseptium Ununoctium Br ↑ I ↓ At tellurium ← iodine → xenon
Atomic nummer (Z)	53
Group	group 17 (halogens)
Period	period 5
Element category	diatomic nonmetal
Block	p-block
Electron confeeguration	[Kr] 4d10 5s2 5p5
Electrons per shell	2, 8, 18, 18, 7
Pheesical properties
Phase (at STP)	solit
Meltin pynt	386.85 K ​(113.7 °C, ​236.66 °F)
Bylin pynt	457.4 K ​(184.3 °C, ​363.7 °F)
Density (near r.t.)	4.933 g/cm3
Treeple pynt	386.65 K, ​12.1 kPa
Creetical pynt	819 K, 11.7 MPa
Heat o fusion	(I2) 15.52 kJ/mol
Heat o vapourisation	(I2) 41.57 kJ/mol
Molar heat capacity	(I2) 54.44 J/(mol·K)
Vapour pressur (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, 5, 3, 1, -1 (strongly acidic oxide)
Electronegativity	Pauling scale: 2.66
Atomic radius	empirical: 140 pm
Covalent radius	139±3 pm
Van der Waals radius	198 pm
Spectral lines o Iodine
Miscellanea
Creestal structur	​orthorhombic
Thermal conductivity	0.449 W/(m·K)
Electrical resistivity	1.3×107 Ω·m (at 0 °C)
Magnetic orderin	diamagnetic
Bouk modulus	7.7 GPa
CAS Nummer	7553-56-2
History
Diskivery	Bernard Courtois (1811)
First isolation	Bernard Courtois (1811)
Main isotopes o iodine
Iso­tope Abun­dance Hauf-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% - (SF) 129I trace 1.57×107 y β− 129Xe 131I syn 8.02070 d β−, γ 131Xe 135I syn 6.57 h β− 135Xe
Decay modes in parentheses are predictit, but hae nae yet been observed

Iodine is a chemical element wi seembol I an atomic nummer 53. The hiviest o the stable halogens, it exeests as a lustrous, purpie-black nan-metallic solit at staundart condeetions that sublimes readily tae form a violet gas. The elemental form wis diskivert bi the French chemist Bernard Courtois in 1811. It wis named twa years later bi Joseph Louis Gay-Lussac frae this property, efter the Greek ἰώδης "violet-coloured".

Iodine occurs in mony oxidation states, includin iodide (I⁻), iodate (IO⁻
₃), an the various periodate anions. It is the least abundant o the stable halogens, bein the saxty-first maist abundant element. It is even less abundant nor the sae-cried rare yirds. It is the hiviest essential mineral nutrient. Iodine is essential in the synthesis o thyroid hormones. Iodine deficiency affects aboot twa billion fowk an is the leadin preventable cause o intellectual disabilities.

The dominant producers o iodine the day are Chile an Japan. Iodine an its compoonds are primarily uised in nutreetion. Due tae its heich atomic nummer an ease o attachment tae organic compoonds, it haes an aw found favour as a nan-toxic radiocontrast material. Acause o the speceeficity o its uptak bi the human bouk, radioactive isotopes o iodine can an aw be uised tae treat thyroid cancer. Iodine is an aw uised as a catalyst in the industrial production o acetic acid an some polymers.