Chlorine (Cl)
Chlorine is element 17, a halogen in period 3, group 17 of the periodic table. At room temperature it is a gas.
Electron configuration [Ne] 3s2 3p5
Electrons per shell 2, 8, 7
Chlorine data
| Atomic number | 17 |
|---|---|
| Symbol | Cl |
| Atomic mass | 35.453 u |
| Category | Halogen |
| Group | 17 |
| Period | 3 |
| Block | p |
| State at 25 °C | gas |
| Melting point | 172 K (-101.1 °C) |
| Boiling point | 239 K (-34.1 °C) |
| Density | 0.003214 g/cm³ (3.214 g/L) |
| Electronegativity (Pauling) | 3.16 |
| Atomic radius | 99 pm |
| 1st ionization energy | 1251 kJ/mol |
| Electron affinity | -349 kJ/mol |
| Oxidation states | -1, +1, +2, +3, +4, +5, +6, +7 |
| Common ion charge | − |
| Discovered | 1774 |
Orbital diagram
Each box is one orbital holding up to two electrons of opposite spin. Following Hund’s rule, electrons spread out singly across a subshell before pairing.
Work through chlorine’s configuration and its ions →
Where chlorine sits
Chlorine belongs to the halogens. Its Pauling electronegativity of 3.16 puts it among the strongest electron-pullers on the table; see the electronegativity chart and periodic trends for context. To use its mass in a calculation, try the molar mass calculator.
Chlorine FAQ
What is the electron configuration of chlorine?
Chlorine (Z = 17) has the configuration 1s2 2s2 2p6 3s2 3p5. In noble-gas shorthand that is [Ne] 3s2 3p5.
How many valence electrons does chlorine have?
7 (outer shell (n = 3)).
What is the atomic mass of chlorine?
The standard atomic weight of chlorine is 35.453 u, so one mole weighs 35.453 g.
Is chlorine a metal?
No. Chlorine is a halogen.
What is the charge of a chlorine ion?
Chlorine most commonly forms Cl−.