Periodic Table


Atomic number: 17
Atomic weight: 35.4527
Symbol: Cl
Group number: 17
Electronic configuration: [Ne].3s2.3p5


Chlorine is a greenish yellow gas which combines directly with nearly all elements. Chlorine is a respiratory irritant. The gas irritates the mucous membranes and the liquid burns the skin. As little as 3.5 ppm can be detected as an odour, and 1000 ppm is likely to be fatal after a few deep breaths. It was used as a war gas in 1915. It is not found in a free state in nature, but is found commonly as NaCl (solid or seawater).

General information

Discoveror: Carl William Scheele
Date discovered: 1774
Discovered at: Sweden
Meaning of name: From the Greek word "chloros" meaning "pale green"

Physical data

Standard state: gas at 298 K
Colour: yellowish green
Density of solid at ambient temperature/kg m-3: no data
Molar volume/cm3: 17.39

Radii /pm

Atomic: 79
Covalent (single bond):
Pauling radius for the ion [Cl]-: 181

Valence shell orbital radius maxima (Rmax)
orbital s p d f
radius68.276.2no datano data


Both values are quoted on the Pauling scale.

Pauling: 3.16
Allred Rochow: 2.83

Crystal Structure

structure: orthorhombic

The following CrystalMaker image represents the solid state structure. For most elements, the most stable allotrope is illustrated. Try WebElements version 2 for interactive virtual reality and CHIME images.


Temperatures (/K)

melting point: 171.6
boiling point: 239.11

Enthalpies /kJ mol-1

fusion: 6.41
vaporization: 20.4

single bond enthalpies:
Cl-F Cl-Cl Cl-Br Cl-I Cl-Cl
142 240 216 208 242.580

Ionization enthalpies /kJ mol-1

Number Enthalpy


This section gives some data for naturally occurring isotopes.
Nominal mass Accurate mass % natural abundance
35Cl34.968852721 (69)75.77 (5)
37Cl36.96590262 (11)24.23 (5)

Further Information

Copyright 1997 Mark Winter
Department of Chemistry at the University of Sheffield, Sheffield S3 7HF, England.

The current version of this document is at http://www.shef.ac.uk/~chem/web-elements-I/Cl.html