Chlorine (Cl)

Stable isotopes of chlorine available from ISOFLEX

Isotope Z(p) N(n) Atomic Mass Natural Abundance Enrichment Level Chemical Form
Cl-35 17 18 34.96885271 75.78% 99.00% Sodium Chloride
Cl-37 17 20 36.96590260 24.22% 98.00% Sodium Chloride

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Chlorine was discovered in 1774 by Carl William Scheele. Its name derives from the Greek word chloros, meaning “pale green.”

A greenish-yellow gas with a suffocating odor, chlorine combines directly with nearly all other elements. It becomes a pale yellow crystal at -101.5 ºC. It is moderately soluble in water. It has known oxidation states from -1 to +7. It occurs as a diatomic molecule Cl2, containing a single covalent bond in which the Cl-Cl bond distance is 1.99 Å.

Chlorine is a respiratory irritant that was used in war as early as 1915. Today, much of the chlorine supply is used in the manufacture of chlorinated cleaning compounds, pulp bleaching, disinfectants and textile processing. It is also used in the production of safe drinking water all over the world.

Properties of Chlorine

Name Chlorine
Symbol Cl
Atomic number 17
Atomic weight 35.452
Standard state Gas at 298 ºK
CAS Registry ID 7782-50-5
Group in periodic table 17
Group name Halogen
Period in periodic table
Block in periodic table p-block 
Color Greenish-yellow
Classification Nonmetallic
Melting point -101.5 ºC
Boiling point -34.04 ºC
Thermal conductivity 0.0089  W/(m·K)
Electrical resistivity 10-8 Ω·m 
Electronegativity 3.16
Heat of vaporization 10.2 (per mole Cl atoms) kJ·mol-1
Heat of fusion 3.2 (per mole Cl atoms) kJ·mol-1
Density 2.03 g/cm3
Electron configuration [Ne]3s23p5
Most common oxidation state 2


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