About

Iodine is a lustrous, purple-black nonmetal that sublimes at standard temperatures into a violet gas with an irritating odor. It is an essential trace nutrient for humans, required by the thyroid gland to synthesize hormones that regulate metabolism. It is also used as a powerful disinfectant (tincture of iodine) and in polarizing filters for LCD screens.

Atomic Properties

Atomic Number53

Atomic Weight126.904 u

Neutrons (common)74

Electron Configuration[Kr] 4d¹⁰ 5s² 5p⁵

Full Configuration1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁵

Electrons per Shell2, 8, 18, 18, 7

Electronegativity2.66

Electron Affinity295.15 kJ/mol

Oxidation States+7, +5, +3, +1, -1

Covalent Radius139 pm

Van der Waals Radius198 pm

Ionic Radius220 pm

Periodic Table Position

Group17

Period5

BlockP

Chemical SeriesHalogens

Physical Properties

State at STPsolid

Appearancelustrous metallic gray solid, violet as a gas

Crystal Structureorthorhombic

Magnetic Orderingdiamagnetic

Thermal Properties

Melting Point386.85 K

Boiling Point457.4 K

Triple Point386.65 K

Thermal Conductivity0.449 W/(m·K)

Specific Heat0.214 J/(g·K)

Molar Heat54.44 J/(mol·K)

Heat of Fusion7.76 kJ/mol

Heat of Vaporization20.75 kJ/mol

Abundance

In Earth's Crust0.45 ppm

In Ocean0.06 ppm

In Solar System0 ppm

In Human Body0.2 ppm

In Universe0.001 ppm

Discovery

Discovered byBernard Courtois

Discovery Year1,811

Occurrenceprimordial

CAS Number7553-56-2

Electron Configuration

Energy

↿⇂

↿

Isotopes of Iodine

Symbol ▲	Mass (u) ▲	Abundance ▲	Half-life ▲	Decay Mode ▲
¹²⁷I	126.904470	100%	Stable	Stable
¹²⁹I	128.904980	Trace	16.14 My	Beta Minus Decay

Interactive Visualization

Explore the 3D Bohr model of Iodine in our interactive viewer.

View 3D Model of Iodine