Cl
Chlorine
Element 17 · Halogen
Chlorine (Cl)
Chlorine is a toxic yellow-green halogen gas. Combined with sodium, it forms table salt; on its own it is a powerful disinfectant.
- Halogen
- Period 3
- Group 17
- p-block
- gas at room temperature
Key properties
- Atomic mass
- 35.45
- u
- Electron configuration
- [Ne] 3s2 3p5
- Melting point
- -101.5 °C
- 171.65 K
- Boiling point
- -34 °C
- 239.11 K
- Density
- 3.214 g/L
- Electronegativity
- 3.16
- Pauling
- Atomic radius
- 175 pm
- van der Waals
- 1st ionisation energy
- 12.968 eV
Compare with every element:Electronegativity chartAtomic radius chartIonisation energy chartDensity chart of the elementsMelting point chartElectron configuration chart
Did you know?
Notable facts about chlorine
- 01
Chlorinating drinking water is one of the biggest public-health advances in history.
- 02
Chlorine gas was used as a weapon in World War I.
- 03
Scheele thought it was a compound; Davy proved it was an element in 1810.
Applications
What is chlorine used for?
- Water purification
- PVC plastic
- Bleach and disinfectants
- Pharmaceuticals
History
Discovery & name origin
Discovered by
Year
Where
Sweden
Name origin
Greek chloros, “pale green” — named by Humphry Davy for the gas’s colour.
Atomic structure
Atomic properties
Atomic structure
Atomic properties
- Atomic number
- 17
- Atomic mass
- 35.45 u
- Group
- 17
- Period
- 3
- Block
- p-block
- Electron configuration
- [Ne] 3s2 3p5
- Full configuration
- 1s2 2s2 2p6 3s2 3p5
- Electrons per shell
- 2, 8, 7
- Electronegativity (Pauling)
- 3.16
- Electron affinity
- 3.617 eV
- Atomic radius (van der Waals)
- 175 pm
- Stable isotopes
- 2
Oxidation states
Highlighted: common oxidation states (+7, +5, +1, -1).
Successive ionisation energies
Energy to remove each electron in turn (kJ/mol). Big jumps show where a new, inner shell begins.
- 1st1,251.2
- 2nd2,298
- 3rd3,822
- 4th5,158.6
- 5th6,542
- 6th9,362
- 7th11,018
- 8th33,604
Physical
Physical properties & colour
Physical
Physical properties & colour
- State at 20 °C
- Gas
- Melting point
- 171.65 K · -101.5 °C · -150.7 °F
- Boiling point
- 239.11 K · -34 °C · -29.3 °F
- Density
- 3.214 g/L
- Molar heat capacity
- —
- Appearance
- Pale yellow-green gas
- CPK model colour
- Copied
The CPK colour is the convention used for this element’s atoms in molecular models.
FAQ
Chlorine questions
What is Cl on the periodic table?
Cl is the symbol for chlorine, element 17 on the periodic table. It sits in group 17, period 3, in the halogen category, and has an atomic mass of 35.45.
What is the atomic number of chlorine?
Chlorine has atomic number 17, so every chlorine atom has 17 protons in its nucleus. Its symbol is Cl and its atomic mass is 35.45.
Who discovered chlorine?
Chlorine was discovered by Carl Wilhelm Scheele in 1774 (Sweden). The name comes from Greek chloros, “pale green” — named by Humphry Davy for the gas’s colour.
What is chlorine used for?
Chlorine is used for: water purification; PVC plastic; bleach and disinfectants; pharmaceuticals.
Is chlorine a metal?
No. Chlorine is classed as a halogen.
What is the electron configuration of chlorine?
The electron configuration of chlorine is [Ne] 3s2 3p5. Its 17 electrons are arranged in shells as 2, 8, 7.