Iodine

iodo yodo

Iodine is the only halogen that is solid at room temperature. The element forms a purple gas when heated, and is named after the Greek word iodine, meaning "violet". It was first discovered in algae, and many plants and animals in the sea have high levels of iodine. Seafood, including crabs and fish, provide the element in our diet. The human body needs small amounts of iodine to produce an important substance called thyroxine, which helps us grow. Iodine is also used to make printing ink, red and brown food dyes and disinfectants.

Summary of properties (I)

Atomic weight126.90447(3)
Discoverer (year)Courtois, Bernard (1811)
Natural formnon-metal solid (orthorombic) (I2)
Electron configuration[Kr] 4d10 5s2 5p5
Melting point (ºC)114
Boiling point (ºC)184
Abundance in earth's crust (ppm)0.45
Isotope (abundance)127I (100)
Density g/cm36.24
Van der Waals radius (pm)198
Covalent radius (pm)136
Electronegativity (Pauling)2.66
Vaporization enthalpy (kJ/mol)41.57
Enthalpy of fusion (kJ/mol)15.52
Specific heat capacity (J/g·K) at 25ºC and 1 atm0.25
Thermal conductivity (W/cm·K) at 25ºC and 1 atm0.004
Oxidation state+7, +5, +1, -1
Electron affinity (eV)3.06
1st Ionization potential (eV)10.4513

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