1735.45ClChlorine
Chlorine (Cl) — element 17halogen · group 17, period 3
Chlorine is a chemical element with the symbol Cl and atomic number 17. It is a halogen in group 17, period 3 of the periodic table (the p-block), with a standard atomic mass of 35.45 u. At room temperature (25 °C) chlorine is a gas.
💡 Known for: Disinfects drinking water and swimming pools, and combines with sodium to form table salt.
# Chlorine properties
| Symbol | Cl |
|---|---|
| Atomic number | 17 |
| Atomic mass | 35.45 u |
| Category | halogen |
| Group | 17 |
| Period | 3 |
| Block | p-block |
| Electron configuration | [Ne] 3s² 3p⁵ |
| Full configuration | 1s² 2s² 2p⁶ 3s² 3p⁵ |
| Electrons per shell | 2, 8, 7 |
| Protons / electrons | 17 / 17 |
| State at 25 °C | gas |
| Melting point | 171.6 K (-101.5 °C, -150.8 °F) |
| Boiling point | 239.11 K (-34 °C, -29.3 °F) |
| Density | 3.214 g/L |
| Electronegativity (Pauling) | 3.16 |
| First ionization energy | 12.968 eV |
| Atomic radius | 79 pm |
| Discovered | 1774 |
# Electron configuration of chlorine
The electron configuration of chlorine is [Ne] 3s² 3p⁵, written out in full as 1s² 2s² 2p⁶ 3s² 3p⁵. Its 17 electrons fill 3 shells as 2, 8, 7, so the outermost shell holds 7 electrons. As a group 17 element, chlorine has 7 valence electrons.
# Related elements
SSulfurprevious elementArArgonnext elementFFluorinegroup 17BrBrominegroup 17IIodinegroup 17AtAstatinegroup 17TsTennessinegroup 17
# Chlorine FAQ
What is the atomic number of chlorine?
The atomic number of chlorine is 17: every chlorine atom has 17 protons in its nucleus. Its symbol is Cl.
What is the atomic mass of chlorine?
The standard atomic mass of chlorine is 35.45 u.
What is the electron configuration of chlorine?
Chlorine's electron configuration is [Ne] 3s² 3p⁵ (1s² 2s² 2p⁶ 3s² 3p⁵), with 2, 8, 7 electrons per shell.
Is chlorine a metal?
No. Chlorine is a halogen, a nonmetal.
What is the melting point of chlorine?
Chlorine melts at 171.6 K (-101.5 °C, -150.8 °F) and boils at 239.11 K (-34 °C, -29.3 °F).
What is chlorine used for / known for?
Disinfects drinking water and swimming pools, and combines with sodium to form table salt.