Reactive nonmetals
Chlorine
A pungent green-yellow halogen used to disinfect water.
Atomic #17Mass35.45Blockp-blockPeriod3Group17
Cl17 · 35.45
3D Atom Explorer
Inside the Chlorine 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 Chlorine atom step by step.
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Electron configuration
[Ne] 3s2 3p5
A neutral Chlorine atom has 17 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 37 e⁻
Electrons fill inner shells before outer ones; the outermost (valence) shell drives the element's chemistry.
Properties
Physical & atomic properties
- State (room temp)
- Gas
- Melting point
- 172 K (-102 °C)
- Boiling point
- 239 K (-34 °C)
- Density
- 0.003214 g/cm³
- Electronegativity
- 3.16 Pauling
- Atomic radius
- 100 pm
- 1st ionization energy
- 1251 kJ/mol
- Category
- Reactive nonmetals
History
Discovery & naming
- Discovered
- 1774
- Discovered by
- Carl Wilhelm Scheele
- Origin of name
- Greek 'chloros', meaning pale green.
Notable uses
Water disinfection, PVC plastic, and bleaches.
Cosmic origin
Where Chlorine comes from
Stellar fusion and dying stars
A product of oxygen burning in massive stars, dispersed when they explode.
Simplified origin map — many elements form through more than one astrophysical pathway.
Summary
- Atomic number
- 17
- Atomic mass
- 35.45
- Category
- Reactive nonmetals
- Group · Period
- 17 · 3
- Block
- p-block
- Shells
- 2 · 8 · 7