Figure 1. Chlorine, with atomic number 17 and atomic weight of 35.45.[1]

Chlorine is the 17th element on the periodic table of elements and is the second lightest halogen.[2] Some of its properties are listed below:[2]

Atomic weight 35.45
Density (at 0oC) 0.002898 g/cm3
Boiling point 239.11 K
Melting point 171.7 K

Chlorine is a halogen, existing as a gas at room temperature. In nature, it's found in minerals (primarily halite, otherwise known as salt) and other compounds.[2]

Chlorine Uses

Figure 2. Chlorine liquid at 7.4 bars of pressure in an ampoule and embedded in glass.[3]

Chlorine is primarily used as a disinfectant. It's used in water, ranging from drinking water to swimming pools. It's used in almost every product that requires disinfecting at some stage of its production. Chlorine is also a component of polyvinyl chloride (PVC) plastic which is used for things like window frames, car interiors, electrical wiring insulation, and water pipes. Other chlorine compounds are used in the manufacturing process for bullet-proof vests, parachutes, cockpit canopies, and so on.[4]

Chlorine is an element with many applications in chemistry. It's an oxidising agent and an excellent substitution element. In the past, chlorine was used to make chloroform and carbon tetrachloride (cleaning solvent). Chlorine gas is highly toxic and was used as a chemical weapon in the First World War.[2]


Chlorine has two isotopes found in nature:[2]

Symbol Natural Abundance
35Cl 75.75%
37Cl 24.24%


The video below is from the University of Nottingham's periodic videos project.[5] They have created a complete suite of short videos on every element on the periodic table of elements.

For Further Reading


  1. Made internally by a member of the Energy Education team
  2. 2.0 2.1 2.2 2.3 2.4 Royal Society of Chemistry Periodic Table, Chlorine [Online], Available:
  3. Wikimedia Commons, File:Chlorine liquid in an ampoule.jpg [Online], Available:
  4. Chemical Safety Facts, Chlorine [Online], Available:
  5. See more videos from the University of Nottingham on different elements here:

Authors and Editors

Ashley Sheardown, Jason Donev
Last updated: January 4, 2019
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