53IIodine

Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists at standard conditions as a semi-lustrous, non-metallic solid that melts to form a deep violet liquid at 114 °C (237 °F), and boils to a violet gas at 184 °C (363 °F). 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 Ancient Greek Ιώδης '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. As the heaviest essential mineral nutrient, iodine is required for 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. 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.

It is on the World Health Organization's List of Essential Medicines.

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Atomic properties

Standard atomic weight126.904 ±3·10-5
Atomic mass126.904 u

Atomic radii

Radius (empirical)140 pm
Radius (calculated)115 pm
Covalent radius139 ±3 pm
Van der Waals radius198 pm

Atomic shell

Electron configurationKr 4d10 5s2 5p5
Ionization energy(1st) 10.45126 eV
(2nd) 19.13126 eV
(3rd) 29.57 eV
(4th) 40.357 eV
(5th) 51.52 eV
(6th) 74.4 eV
(7th) 87.61 eV
Shell model
Electrons
k-shell:2
l-shell:8
m-shell:18
n-shell:18
o-shell:7

Physical properties

Phasesolid
Density4.94 g·cm−3
Molar volume2.572·10-5 m3·mol−1

Temperatures

Melting point386.8 K
Boiling point457.4 K
Liquid range70.55 K
Triple point386.6 K @ 12.1 kPa
Critical point819 K @ 11.7 MPa
Transition temperature1.2 K

Enthalpies

Melting enthalpy7.76 kJ·mol-1
Enthalpy of vaporization20.9 kJ·mol-1
Binding energy107 kJ·mol-1

Heat and conductivity

Thermal conductivity0.449 W·m-1·K-1

Elastic properties

Bulk modulus7.7 GPa

Electrical properties

Resistance1·108 Ωm

Magnetism

Magnetismdiamagnetic
Magnetic susceptibility-8.871·10-5 cm3·mol−1 (298 K)

Chemical properties

Basicitystrongly acidic
Oxidation state±1, 3, 5, 7
Standard potential0.536 V (I2 + 2e- → 2I-)

Electronegativity

Pauling scale2.66
Sanderson scale2.78
Allred-Rochow scale2.21
Mulliken scale2.74
Allen scale2.359
Ghosh-Gupta scale5.591 eV
Nagle scale2.27
Pearson absolute negativity6.76 eV

Other properties

Natural occurrenceprimordial
Crystal structureOrthorhombic
Goldschmidt Classificationlithophile
Superconductorwith transition tempperature under special conditions
Price/kg35 USD

Natural abundances

satellite_alt
Universe
1 ppb ≈ 1·1010 M☉
sunny
destruction
Meteorite
260 ppb ≈ 260 mg
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Earth’s crust
490 ppb ≈ 13,500 Mt
water_drop
Oceans
60 ppb ≈ 82.2 Gt
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Flowing water
5 ppb ≈ 80 kt
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Human body
200 ppb ≈ 14 mg