Definition:Argon
Chemical Element
Argon is the chemical element that has $18$ protons in the nuclei of its atoms.
Its chemical symbol is $\text {Ar}$.
Isotopes
Ar-$36$
Argon-$36$ is the isotope of argon which has $18$ neutrons in addition to its $18$ protons.
Ar-$36$ is the second most common stable isotope of argon, making up $0.34 \%$ of the argon found on Earth.
Ar-$38$
Argon-$38$ is the isotope of argon which has $20$ neutrons in addition to its $18$ protons.
Ar-$38$ is the least common stable isotope of argon, making up $0.06 \%$ of the argon found on Earth.
Ar-$40$
Argon-$40$ is the isotope of argon which has $22$ neutrons in addition to its $18$ protons.
Ar-$40$ is the most common stable isotope of argon, making up $99.6 \%$ of the argon found on Earth.
Linguistic Note
The word argon was taken from the Greek ἀργόν, the neuter singular form of ἀργός meaning lazy, inactive or inert, in reference to its chemical inactivity.