Chlorine (Cl)
Halogen · p-block · period 3 · group 17
Dense, pale green-yellow, choking gas.
Chlorine (symbol Cl) is chemical element number 17, a halogen in group 17, period 3 of the periodic table. Its standard atomic weight is 35.45 and its electron configuration is [Ne] 3s2 3p5. At room temperature it is a gas. Used as a chemical weapon in the First World War.
Properties
| Atomic number | 17 |
|---|---|
| Atomic mass | 35.45 |
| Category | Halogen |
| Block | p-block |
| Group · Period | 17 · 3 |
| Electron configuration | [Ne] 3s2 3p5 |
| Electrons per shell | 2, 8, 7 |
| State at 25 °C | gas |
| Melting point | 171.6 K |
| Boiling point | 239.11 K |
| Density | 3.214 g/L |
| Electronegativity (Pauling) | 3.16 |
| Radioactive | No |
| Origin | primordial |
| Discovered | 1774 · Carl Wilhelm Scheele |
Key facts about Chlorine
- Used as a chemical weapon in the First World War.
- Tiny amounts kill the microbes that cause cholera and typhoid in drinking water.
- Half of common table salt, NaCl, by formula.
- Never mix bleach with acid or ammonia — it releases toxic chlorine gas.
What Chlorine is used for
Water and pool disinfection, bleach, PVC plastic, solvents, medicines.
Where it sits in the periodic table
Chlorine is in group 17, period 3, of the p-block. Its electron configuration [Ne] 3s2 3p5 means its outermost shell holds 7 electrons, which is what places it here and explains much of its chemistry. See Chlorine on the interactive table →
Chlorine — frequently asked questions
What is Chlorine used for?
Water and pool disinfection, bleach, PVC plastic, solvents, medicines.
Is Chlorine radioactive?
No. Chlorine has at least one stable isotope and is not radioactive.
What is the electron configuration of Chlorine?
Chlorine has the electron configuration [Ne] 3s2 3p5, which is 2, 8, 7 electrons per shell.
What group and period is Chlorine in?
Chlorine is in group 17, period 3, in the p-block. Its outer shell holds 7 electrons.
Who discovered Chlorine?
Chlorine was discovered in 1774 by Carl Wilhelm Scheele.