Element 17
Chlorine
Halogens
Chlorine (Cl) is in the p-block of the periodic table — group 17, period 3.
Chlorine is a chemical element with symbol Cl and atomic number 17.
Key data
- Atomic number
- 17
- Atomic mass
- 35.450 u
- Group / Period
- 17 / 3
- Block
- p-block
- Phase at STP
- Gas
- Density
- 3.2 g/cm³
- Melting point
- -101.5 °C
- Boiling point
- -34.0 °C
- Electron configuration
- [Ne] 3s2 3p5
Periodic table block
Chlorine is in the p-block (group 17, period 3). Elements land in the p-block when their highest-energy electrons fill a p subshell — this region holds most nonmetals, the metalloids, and the metals on the right of the table.
New to this? Periodic table blocks explained: s, p, d, and f
Common uses
- •Pool sanitizer
- •Bleach
- •PVC plastics
Discovery
Year: 1774
Discovered by: Carl Wilhelm Scheele
Frequently asked questions
What is the atomic number of Chlorine?
Chlorine has atomic number 17. Its symbol is Cl and its atomic mass is 35.45 u.
What category of element is Chlorine?
Chlorine is classified as halogens. It sits in group 17, period 3 of the periodic table.
What block of the periodic table is Chlorine in?
Chlorine is in the p-block (group 17, period 3). Its highest-energy electrons occupy the p subshell — you can see this in its electron configuration, [Ne] 3s2 3p5.
What is Chlorine used for?
Common uses of Chlorine include: Pool sanitizer, Bleach, PVC plastics.
When was Chlorine discovered?
Chlorine was discovered in 1774 by Carl Wilhelm Scheele.
Play the game
Test your knowledge in The Lab
20-round element ID, cryptic 3-clue guesser, and an interactive periodic table.
Open The Lab →