Chlorine is the 17th element of the periodic table. These chlorine facts contain chemical and physical data along with general information and history.
Basic Chlorine Facts
Atomic Number: 17
Element Symbol: Cl
Element Family: Halogen
Atomic Mass: [35.446; 35.457]
IUPAC guidelines to reflect the physical and chemical history of the magnesium sample. If a single value of the atomic mass is needed, use 35.4527.
Electron Configuration: [Ne]3s23p5 (shorthand) or 1s22s22p63s23p5 (full)
Discovery: Carl Wilhelm Scheele in 1774
Scheele isolated chlorine from hydrochloric acid. He thought the yellow gas he collected was an oxide of another compound, not a new element. This belief continued until 1811 when Sir Humphry Davy showed there was no oxygen in chlorine gas. Chlorine was its own element.
Name Origin: Davy named the new element chlorine from the Greek word chloros meaning yellow-green.
Natural chlorine is comprised of two stable isotopes: 35Cl, and 37Cl. Twenty two radioactive isotopes exist ranging from 28Cl to 51Cl.
Chlorine-35 is a stable isotope containing 18 neutrons. 75.77% of natural chlorine is chlorine-35.
Chlorine-37 is a stable isotope containing 20 neutrons. 24.23% of natural chlorine is chlorine-37.
Chlorine-36 is a radioactive isotope containing 19 neutrons. It is formed when cosmic radiation interacts with atmospheric chlorine. Chlorine-36 decays by β- decay into 36Ar 98.1% of the time or 36S by electron capture 1.9% of the time. The half-life is 301,200 years and can be found naturally in trace quantities.
(gas) 0.002898 g/cm3
(liquid at boiling point) 1.5625 g/cm3
Melting Point: 171.6 K (−101.5 °C, −150.7 °F)
Boiling Point: 239.11 K (−34.04 °C, −29.27 °F)
Critical Point: 416.9 K at 7.991 MPa
State at 20ºC: Gas
Heat of Fusion: 6.406 kJ/mol for Cl2
Heat of Vaporization: 20.41 kJ/mol for Cl2
Molar Heat Capacity: 33.949 J/mol·K for Cl2
Atomic Radius: 1.75 Å
Covalent Radius: 1.02 Å
Van der Waals Radius: 1.75 Å
Electron Affinity: 348.575 kJ/mol
1st Ionization Energy: 1251.186 kJ/mol
2nd Ionization Energy: 2297.663 kJ/mol
3rd Ionization Energy: 3821.78 kJ/mol
4th Ionization Energy: 5158.608 kJ/mol
5th Ionization Energy: 6541.7 kJ/mol
6th Ionization Energy: 9361.97 kJ/mol
7th Ionization Energy: 11018.221 kJ/mol
8th Ionization Energy: 33603.91 kJ/mol
Oxidation States: +7, +5, +1, -1 (common), +6, +6, +2 (uncommon)
Fun Chlorine Facts
- Chlorine rarely occurs freely in nature. You are much more likely to find chlorine combined with other elements (such as table salt NaCl) or itself the form Cl2.
- Chlorine is the third most abundant element in the Earth’s oceans.
- Chlorine is the 21st most abundant element in the Earth’s crust.
- Chlorine is the ninth most abundant element in the human body.
- Chlorine gas is has a yellow-green color and a strong smell.
- The smell of chlorine is an irritant. Humans can detect the smell at concentrations as low as 3.5 parts per million.
- Chlorine was an early chemical weapon. It reacts with the mucous membranes and can burn the skin. Concentrations around 1000 parts per million are typically fatal after a few breaths. Chlorine gas is also denser than air and would settle in low lying areas such as trenches and foxholes.
- Leaking chlorine containers are hazardous. Leaks in containers are detected using ammonia. The ammonia reacts with the chlorine and forms a white mist near the leak.
- Chlorine appears often in organic chemistry reactions where it replaces hydrogen atoms in molecules.
- Chlorine is used in the manufacture of a multitude of products such as plastics, paper, medicine, insecticides, disinfectants, textiles, dyes and petroleum products. It is commercially extracted by electrolysis from brine solutions.
- Scheele’s name for chlorine was muriaticum. The old name for hydrochloric acid was muriatic acid.
Learn more about elements on the periodic table.