17ClChlorine35.45 u
Chlorine (Cl)
Chlorine is a halogen with atomic number 17, in period 3 and group 17 of the periodic table. Its atomic mass is 35.45 u and its electron configuration is [Ne] 3s² 3p⁵. Gas at 25 °C.
Key facts
| Atomic number | 17 |
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| Atomic mass | 35.45 u |
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| Category | Halogen |
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| Period | 3 |
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| Group | 17 |
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| Block | p |
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| Electron configuration | [Ne] 3s² 3p⁵ |
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| Electrons per shell | 2, 8, 7 |
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| Electronegativity (Pauling) | 3.16 |
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| Oxidation states | −1, +1, +2, +3, +4, +5, +6, +7common in bold |
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| State at 25 °C | Gas |
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| Melting point | 171.6 K−101.55 °C |
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| Boiling point | 239.11 K−34.04 °C |
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| Density | 3.214 g/L |
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Atomic properties
| First ionization energy | 12.968 eV |
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| Electron affinity | 349 kJ/mol |
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| Atomic radius | 99 pm |
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| Covalent radius | 102 pm |
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| Van der Waals radius | 175 pm |
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| Common ions | Cl⁻ |
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| Protons, neutrons, electrons | 17, 18, 17 |
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Physical and thermal properties
| Molar volume | 17.39 cm³/mol |
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| Heat of fusion | 3.2 kJ/mol |
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| Heat of vaporization | 10.2 kJ/mol |
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| Specific heat | 478.2 J/(kg·K) |
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| Thermal conductivity | 0.0089 W/(m·K) |
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| Thermal expansion | --- |
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| Mohs hardness | --- |
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| Young’s modulus | --- |
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| Crystal structure | Base orthorhombic |
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| Magnetic type | Diamagnetic |
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Identification and history
| CAS number | 7782-50-5 |
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| Latin name | Chlorum |
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| Discovered by | Carl Wilhelm Scheele · 1774 |
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| Named by | --- |
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Natural isotopes
| Isotope | Mass (u) | Abundance |
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| 35Cl | 34.968853 | 75.8 % |
| 37Cl | 36.965903 | 24.2 % |
Data checked against PubChem (NIH), IUPAC, the NIST Atomic Spectra Database and the IAEA (NUBASE and AME), the same data you see in the app.
A dash (---) means there is no reliable published measurement. The app never makes one up.
See Chlorine in the app
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Periodic Table