Chlorine is a yellowy-green gas at room temperature with a very distinctive odor (commonly associated with household cleaning products that contain bleach). It is also a chemical element with the atomic number 17 and is represented by the chemical symbol Cl. There are over 2000 organic compounds that contain chloride and the best known of these is common salt (sodium chloride). This means that it is a very common element, and about 1.9% of seawater (in terms of mass) is chloride ions! Almost all of the naturally occurring chloride is made up of just two isotopes, but there are also many other isotopes of chloride that have been identified.
How many isotopes does chlorine have?
The two stable isotopes of chlorine are chlorine-35 (35Cl) and chlorine-37 (37Cl ). 35Cl makes up about 76% of all the naturally occurring chlorine found on Earth. 37Cl makes up most of the remaining 24%. However, there are trace amounts of the unstable (radioactive) isotope 36Cl, which is naturally produced in the atmosphere. It is also the longest lived radioactive isotope of chlorine with a half life of 301,000 years.
Aside from these 3 isotopes, there are 21 other unstable isotopes of chlorine. These range from 28Cl to 51Cl. All of these unstable isotopes have a half life of less than 1 hour and most have a half life of less than a second. The shortest lived isotopes of chlorine are 29Cl and 30Cl with half lives of just 20 and 30 nanoseconds! Most of the unstable isotopes below 35Cl decay to silicon and most of the unstable isotopes above 37Cl decay to Argon.
Did you know?
36Cl is an important isotope. It can be used in certain forms of geologic dating. Large amounts of this isotope were also produced by nuclear weapons testing in the 1950’s!