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Chlorine (Cl)

Chlorine is a chemical element of the periodic table with chemical symbol Cl and atomic number 17 with an atomic weight of 35.446 u and is classed as nonmetal and is part of group 17 (fluorine group). Chlorine is gas at room temperature.

Chlorine in the periodic table

Atomic number17
Group17 (Fluorine group)
AppearancePale yellow-green gas
Color Yellow
Number of protons17 p+
Number of neutrons18 n0
Number of electrons17 e-
From Wikipedia, the free encyclopediaChlorine is a chemical element with symbol Cl and atomic number 17. It also has a relative atomic mass of 35.5. Chlorine is in the halogen group (17) and is the second lightest halogen following fluorine.

Physical properties

Phase at STPGas
Density3.2 g/cm3
Atomic weight35.446 u

Thermal properties

Melting point171.6 K
-101.55 °C
-150.79 °F
Boiling point239.11 K
-34.04 °C
-29.272 °F
Heat of vaporization10.2 kJ/mol

Atomic properties

Electronegativity (Pauling Scale)3.16
Electron affinity348.575 kJ/mol
Oxidation states−1, +1, +2, +3, +4, +5, +6, +7
(a strongly acidic oxide)
Ionization energies
  1. 1251.2 kJ/mol
  2. 2298 kJ/mol
  3. 3822 kJ/mol
  4. 5158.6 kJ/mol
  5. 6542 kJ/mol
  6. 9362 kJ/mol
  7. 11018 kJ/mol
  8. 33604 kJ/mol
  9. 38600 kJ/mol
  10. 43961 kJ/mol
  11. 51068 kJ/mol
  12. 57119 kJ/mol
  13. 63363 kJ/mol
  14. 72341 kJ/mol
  15. 78095 kJ/mol
  16. 352994 kJ/mol
  17. 380760 kJ/mol

Electron configuration for chlorine

Electron configuration
Shorthand configuration
[Ne] 3s2 3p5
Electron configuration
Full configuration
1s2 2s2 2p6 3s2 3p5
Electron configuration chart
Electrons per shell2, 8, 7
Valence electrons 7
Valency electrons 1
Bohr model
ChlorineElectron shell for Chlorine, created by Injosoft ABCl
Figure: Shell diagram of Chlorine (Cl) atom.
Orbital Diagram

The history of Chlorine

Discovery and first isolationCarl Wilhelm Scheele (1774)
Named bySir Humphry Davy (1810)
Recognized as an element byHumphry Davy (1808)
Discovery of chlorine
Chlorine played an important role in the experiments conducted by medieval alchemists, which commonly involved the heating of chloride salts like ammonium chloride (sal ammoniac) and sodium chloride (common salt), producing various chemical substances containing chlorine such as hydrogen chloride, mercury(II) chloride (corrosive sublimate), and hydrochloric acid (in the form of aqua regia). However, the nature of free chlorine gas as a separate substance was only recognised around 1630 by Jan Baptist van Helmont. Carl Wilhelm Scheele wrote a description of chlorine gas in 1774, supposing it to be an oxide of a new element. In 1809, chemists suggested that the gas might be a pure element, and this was confirmed by Sir Humphry Davy in 1810, who named it after the Ancient Greek χλωρός (khlōrós, "pale green") because of its colour.


List of unique identifiers for Chlorine in various chemical registry databases
CAS Number7782-50-5
ChemSpider ID4514529
EC number231-959-5
PubChem CID Number24526