Chlorine (Cl): Electron Configuration, Properties and Uses
Chlorine (Cl): Electron Configuration, Properties and Uses
Electron configuration [Ne] 3s2 3p5 · group 17 · period 3 · Ar 35.45
Chlorine data
- Atomic number
- 17
- Relative atomic mass
- 35.45
- Group
- 17
- Period
- 3
- Block
- p
- Category
- Halogen
- Electron configuration
- [Ne] 3s2 3p5
- Full configuration
- 1s2 2s2 2p6 3s2 3p5
- Electrons per shell
- 2, 8, 7 (K L M)
- Valence electrons
- 7
- Electronegativity (Pauling)
- 3.16
- First ionisation energy
- 12.968 eV
- Atomic radius (van der Waals)
- 175 pm
- State at room temperature
- Gas
- Melting point
- −101 °C
- Boiling point
- −34 °C
- Density
- 3.214 g/L (0 °C, 1 atm)
- Common oxidation states
- +7, +5, +1, −1
- Discovered
- 1774
Source: PubChem (NIH, accessed 13 Nov 2026); atomic mass: IUPAC standard atomic weight.
Electron shell diagram
K 2 · L 8 · M 7
Orbital diagram (outer electrons)
About chlorine
Chlorine, symbol Cl, is element number 17 in the periodic table. It is a halogen in group 17, period 3, p-block. The element was discovered in 1774. At room temperature chlorine is a gas that is heavier than air (3.214 g/L) and liquefies at −34 °C.
Chlorine electron configuration
The electron configuration of chlorine is 1s2 2s2 2p6 3s2 3p5, or in short [Ne] 3s2 3p5. Its electrons occupy 3 shells: K = 2, L = 8, M = 7. Chlorine has 7 valence electrons in the M shell (3s2 3p5), which is why it sits in group 17. In ionic compounds chlorine gains electrons to fill its outer shell: Cl− = [Ar] (like argon).
Filling order: 1s2(2) → 2s2(4) → 2p6(10) → 3s2(12) → 3p5(17)
Uses of chlorine
Well-known applications of chlorine include water disinfection, PVC plastic, bleach, hydrochloric acid and solvents. For research and analysis you can browse chloride compounds in the AMI Scientific catalogue.
Safety
Chlorine gas is toxic and irritates the airways. Never mix bleach with acids, which releases chlorine. Always read the safety data sheet (SDS) before working with a chemical.
Other elements in group 17
Frequently asked questions
What is the electron configuration of chlorine?
The electron configuration of chlorine (Cl, atomic number 17) is 1s2 2s2 2p6 3s2 3p5, or [Ne] 3s2 3p5 in short. By shell: 2, 8, 7.
How many valence electrons does chlorine have?
Chlorine has 7 valence electrons.
Which group and period is chlorine in?
Chlorine is in group 17, period 3, p-block.
What is the atomic mass of chlorine?
The relative atomic mass of chlorine is 35.45. Use it to calculate molar mass with the molar mass calculator.
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