Chlorine (Cl) – element 17
Chlorine is a chemical element with the symbol Cl and atomic number 17. It is a reactive nonmetal in group 17 (halogens), period 3 of the periodic table (p-block), and is a gas at room temperature.
Chlorine (Cl) has atomic number 17, atomic mass 35.45 u and electron configuration [Ne] 3s2 3p5.
Chlorine facts
| Symbol | Cl |
|---|---|
| Atomic number | 17 |
| Atomic mass | 35.45 u (g/mol) |
| Category | reactive nonmetal |
| Group | group 17 (halogens) |
| Period | 3 |
| Block | p-block |
| Phase at 20 °C | Gas |
| Electron configuration | 1s2 2s2 2p6 3s2 3p5 |
| Noble-gas notation | [Ne] 3s2 3p5 |
| Electrons per shell | 2, 8, 7 |
| Valence electrons | 7 |
Bohr model and shells
Chlorine has 17 electrons in 3 shells: 2, 8, 7. Full configuration and noble-gas notation are in the table; work out any element or ion with the electron configuration calculator.
Physical and atomic properties
| Melting point | 171.6 K (-101.5 °C) |
|---|---|
| Boiling point | 239.11 K (-34.0 °C) |
| Density | 3.2 g/L |
| Electronegativity (Pauling) | 3.16 |
| Electron affinity | 348.575 kJ/mol |
| Ionization energies | 1251.2, 2298, 3822 kJ/mol (1st, 2nd, 3rd) |
| Discovered by | Carl Wilhelm Scheele |
Use the atomic mass in the molar mass calculator for any formula containing Cl.
Position in the periodic table
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Molecules with chlorine
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Frequently asked questions
What is the atomic mass of chlorine?
The atomic mass of chlorine is 35.45 u, so one mole of chlorine atoms weighs 35.45 g.
What is the electron configuration of chlorine?
Chlorine has 17 electrons: 1s² 2s² 2p⁶ 3s² 3p⁵, or [Ne] 3s² 3p⁵ in noble-gas notation. Electrons per shell: 2, 8, 7.
How many valence electrons does chlorine have?
Chlorine has 7 valence electrons (group 17).
Is chlorine a metal?
No. Chlorine is a nonmetal (reactive nonmetal).
Where is chlorine on the periodic table?
Chlorine is in group 17 (halogens), period 3, in the p-block.
Data: Periodic-Table-JSON (CC BY-SA 3.0); standard atomic weights from IUPAC (abridged). Values in brackets are the mass number of the longest-lived isotope.