Chemical element · Atomic number 17
Chlorine
Chlorine in the periodic table: atomic number 17, electron configuration, atomic mass, physical data, oxidation states, media credit and visible sources.
Halogen
gaseous
35.45 u
Documented element sampleA securely sealed ampoule containing yellow-green chlorine gas.
Image credit: James St. John
Auto-oriented, limited to 1600 × 1200 pixels and re-encoded as WebP; the subject was not altered.
Atomic classification
Shell occupancy
Chlorine in the Bohr shell model
This shows the electron distribution of the neutral atom in a simplified shell model.
- K · n=1
- 2 electrons
- L · n=2
- 8 electrons
- M · n=3
- 7 electrons
- Electron configuration
- [Ne]3s2 3p5
- Electrons per shell
- 2 · 8 · 7
- Group
- 17
- Period
- 3
- Block
- P
- Element category
- Halogen
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Physical and chemical properties
- Atomic mass
- 35.45 u
- Standard state
- gaseous
- Density
- 0.003214 g/cm³
- Melting point
- 171.65 K
- Boiling point
- 239.11 K
- Electronegativity
- 3.16 (Pauling)
- First ionisation energy
- 12.968 eV
- Oxidation states
- +7, +5, +1, -1
- Discovery
- 1774
Safety and periodic classification
Safety
Safe handling cannot be inferred from Chlorine's position in the periodic table alone. Laboratory, classroom and disposal decisions must follow the documentation for the exact material and its safety data sheet.
Position and comparison
Chlorine is in period 3, group 17 and the P block. Its direct neighbours by atomic number are Sulfur and Argon. The recorded Pauling electronegativity is 3.16. Periodic trends are compared only through the separately sourced neighbouring values.
Sources and scope
PubChem attributes element data to sources including IUPAC, NIST and IAEA. Quanta stores the referenced snapshot locally and leaves unknown values unavailable.