Reactive nonmetals
Iodine
A halogen essential to thyroid function and antiseptics.
Atomic #53Mass126.90Blockp-blockPeriod5Group17
I53 · 126.90
3D Atom Explorer
Inside the Iodine atom
Switch between Bohr and Quantum Cloud modes to compare a simple teaching model with a more realistic probability-based view, and follow the guided tour to explore the Iodine atom step by step.
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Electron configuration
[Kr] 4d10 5s2 5p5
A neutral Iodine atom has 53 electrons (equal to its proton count). Choosing a different isotope above changes only the neutron count.
Shell distribution
Shell 12 e⁻Shell 28 e⁻Shell 318 e⁻Shell 418 e⁻Shell 57 e⁻
Electrons fill inner shells before outer ones; the outermost (valence) shell drives the element's chemistry.
Properties
Physical & atomic properties
- State (room temp)
- Solid
- Melting point
- 387 K (114 °C)
- Boiling point
- 457 K (184 °C)
- Density
- 4.93 g/cm³
- Electronegativity
- 2.66 Pauling
- Atomic radius
- 140 pm
- 1st ionization energy
- 1008 kJ/mol
- Category
- Reactive nonmetals
History
Discovery & naming
- Discovered
- 1811
- Discovered by
- Bernard Courtois
- Origin of name
- Greek 'iodes', meaning violet.
Notable uses
Antiseptics, thyroid medicine, and iodized salt.
Cosmic origin
Where Iodine comes from
Neutron star mergers
Chiefly a product of rapid neutron capture rather than quiet stellar production.
Simplified origin map — many elements form through more than one astrophysical pathway.
Summary
- Atomic number
- 53
- Atomic mass
- 126.90
- Category
- Reactive nonmetals
- Group · Period
- 17 · 5
- Block
- p-block
- Shells
- 2 · 8 · 18 · 18 · 7