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It's Elemental

The Element Chlorine

[Click for Isotope Data]


17 Cl Chlorine 35.4527

Atomic Number: 17

Atomic Weight: 35.4527

Melting Point: 171.65 K (-101.5°C or -150.7°F)

Boiling Point: 239.11 K (-34.04°C or -29.27°F)

Density: 0.003214 grams per cubic centimeter

Phase at Room Temperature: Gas

Element Classification: Non-metal

Period Number: 3

Group Number: 17

Group Name: Halogen

What's in a name? From the Greek word for greenish yellow, chloros.

Say what? Chlorine is pronounced as KLOR-een or as KLOR-in.

History and Uses:

Since it combines directly with nearly every element, chlorine is never found free in nature. Chlorine was first produced by Carl Wilhelm Scheele, a Swedish chemist, when he combined the mineral pyrolusite (MnO2) with hydrochloric acid (HCl) in 1774. Although Scheele thought the gas produced in his experiment contained oxygen, Sir Humphry Davy proved in 1810 that it was actually a distinct element. Today, most chlorine is produced through the electrolysis of aqueous sodium chloride (NaCl).

Chlorine is commonly used as an antiseptic and is used to make drinking water safe and to treat swimming pools. Large amounts of chlorine are used in many industrial processes, such as in the production of paper products, plastics, dyes, textiles, medicines, antiseptics, insecticides, solvents and paints.

Two of the most familiar chlorine compounds are sodium chloride (NaCl) and hydrogen chloride (HCl). Sodium chloride, commonly known as table salt, is used to season food and in some industrial processes. Hydrogen chloride, when mixed with water (H2O), forms hydrochloric acid, a strong and commercially important acid. Other chlorine compounds include: chloroform (CHCl3), carbon tetrachloride (CCl4), potassium chloride (KCl), lithium chloride (LiCl), magnesium chloride (MgCl2) and chlorine dioxide (ClO2).

Chlorine is a very dangerous material. Liquid chlorine burns the skin and gaseous chlorine irritates the mucus membranes. Concentrations of the gas as low as 3.5 parts per million can be detected by smell while concentrations of 1000 parts per million can be fatal after a few deep breaths.

Estimated Crustal Abundance: 1.45×102 milligrams per kilogram

Estimated Oceanic Abundance: 1.94×104 milligrams per liter

Number of Stable Isotopes: 2 (View all isotope data)

Ionization Energy: 12.968 eV

Oxidation States: +7, +5, +1, -1

Electron Shell Configuration:


2s2   2p6

3s2   3p5

Citation and linking information

For questions about this page, please contact Steve Gagnon.