# How Many Isotopes Does Argon Have

Argon is a colorless and odorless noble gas with the atomic number of 18 and the chemical symbol Ar. The name comes from a Greek word meaning “lazy” or “inactive,” which relates to the fact that argon has very low chemical reactivity. Argon is common in the atmosphere, from where it is obtained for commercial purposes. Almost all (99.60%) of this argon is the naturally occurring isotope ^{40}Ar, but there are many other isotopes of Argon. If you want to know how many there are, keep reading to find out.

**How many isotopes does argon have?**

Argon has a total of 24 known isotopes and 1 isomer. Three of these isotopes, ^{36}Ar, ^{38}Ar and ^{40}Ar, are stable. The most abundant isotope of argon on Earth is created when the radioactive isotope ^{40}K decays to ^{40}Ar. The rest are radioactive and most of these radioactive isotopes have a half life of less than a minute. However, ^{39}Ar, which is created by cosmic ray activity, has a half life of 269 years. ^{42}Ar has a half life of 32.9 years and ^{37}Ar has a half life of 35.04 days. The most unstable isotope is ^{30}Ar with a half life of less than 20 nanoseconds.

**Did you know?**

The relationship between ^{40}K and ^{40}Ar is used to determine the age of rocks. This process is known as potassium-argon dating. ^{39}Ar is used for ground water and ice core dating.

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