Chlorine (Cl)

Halogens · Period 3 · Gas

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Element identity

Atomic number (Z): 17
Symbol: Cl
Atomic weight / isotope mass number: 35.45(1)
Category: Halogens
Physical state (reference): Gas
Period: 3
Group (reference): 17
Block: p

Physical properties

Appearance: Pale yellow-green gas
Density: 3.2×10⁻³ g·cm⁻³
Melting point: 171.6 K / −101.5 °C / −150.7 °F
Boiling point: 239.11 K / −34.04 °C / −29.27 °F
Sublimation point: Not available

Atomic and material properties

Electron configuration: [Ne] 3s² 3p⁵
Electrons per shell: K2 L8 M7
Oxidation states: 7, 6, 5, 4, 3, 2, 1, −1
Electronegativity (Pauling): 3.16
Atomic radius: 79 pm
Covalent radius: 102±4 pm
Molar ionization energies: 1st: 1251.2 kJ·mol⁻¹ 2nd: 2298 kJ·mol⁻¹ 3rd: 3822 kJ·mol⁻¹ 4th: 5158.6 kJ·mol⁻¹ 5th: 6542 kJ·mol⁻¹ 6th: 9362 kJ·mol⁻¹ 7th: 11,018 kJ·mol⁻¹ 8th: 33,604 kJ·mol⁻¹ 9th: 38,600 kJ·mol⁻¹ 10th: 43,961 kJ·mol⁻¹ 11th: 51,068 kJ·mol⁻¹ 12th: 57,119 kJ·mol⁻¹ 13th: 63,363 kJ·mol⁻¹ 14th: 72,341 kJ·mol⁻¹ 15th: 78,095 kJ·mol⁻¹ 16th: 352,994 kJ·mol⁻¹ 17th: 380,760 kJ·mol⁻¹
Thermal conductivity: 8.9×10⁻³ W·m⁻¹·K⁻¹
Molar heat capacity: Cl₂: 33.949 J·mol⁻¹·K⁻¹
Crystal structure: Orthorhombic
CAS number: 7782-50-5

Property source: Wikipedia — Chlorine, adapted from the Nuclides App snapshot. Quoted conditions and qualifiers are retained.

Sources and interpretation

Snapshot exported 24 October 2026 from the element assets used by Nuclides. Properties are a reference compilation, not a new evaluation. Missing values are shown as “Not available”. Density and phase depend on temperature, pressure and allotrope; retained conditions are part of the quoted property.

Atomic weight is dimensionless. Parentheses give uncertainty in the last quoted digits. A single integer in square brackets is an isotope mass number, not a standard atomic weight. The snapshot can differ from current evaluations; consult CIAAW standard atomic weights and the IUPAC periodic table for current values and conventions.

Element properties in the App snapshot are adapted from Wikipedia. Each element page links to its source article; text adaptations are available under CC BY-SA 4.0. No third-party images are included.

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